Chickens are the most common bird in the world, with about 23 billion living at any given time. These birds are primarily grown for industrial meat production. Their survival depends on human management, and, as a result, they are most intensively vaccinated livestock species. In intensive management systems, each bird may undergo an average of 12 to 20 vaccination procedures within its short life span. Immunization of poultry, although necessary for economic production and insurance, is no substitute for proper hygiene and appropriate biosecurity. Lack of hygiene and other stressors may result in less than satisfactory vaccine performance. Clearly, the role of vaccines is to protect birds against specific infectious diseases. In layers they are also needed to ensure that maternal immunity is passed to the chicks and to prevent vertical transmission of infections. Given the large size of many poultry operations and the small unit cost of individual birds, vaccines must be very inexpensive. For example, in early 2018, a vial of 10,000 doses of Newcastle-bronchitis vaccine cost US$23.99, 1000 doses of Marek’s disease vaccine cost US$29.99, and 1000 doses of Fowlpox vaccine cost US$6.99. Vaccines are commodities in the poultry industry and an unavoidable part of doing business. The most convenient time to vaccinate chicks is before they leave the hatchery (Tables 19.1, 19.2, and 19.3). As in many intensive animal industries, the cost of labor is critical. Vaccination procedures are therefore directed toward effectively vaccinating the largest number of birds in the shortest time, by the fewest workers, without causing any loss in productivity. The methods employed will also depend, in part, on the way in which the birds are housed and the nature of their watering systems. TABLE 19.1 ■ Withdrawal time 21 or 42 days. Withdrawal time 42 days. TABLE 19.2 ■ Withdrawal time 21 or 42 days. Withdrawal time 42 days. Withdrawal time 21 days. Withdrawal time 21 or 42 days. Withdrawal time 21 or 42 days. 1 day chicks may receive live vaccine. These tables are examples of consensus vaccination programs. Individual programs are variable and will reflect animal health, local environmental and housing conditions, severity of challenge, and disease prevalence, in addition to professional judgment. It is essential that the instructions on the individual vaccine label be followed. Withdrawal times are for meat unless otherwise stated. When a range is stated it means that some products have a longer withdrawal time than others. Check the label directions for the specific withdrawal time for each vaccine. TABLE 19.3 ■ Do not vaccinate during egg production. Withdrawal time 21 days. Do not vaccinate during egg production. These tables are examples of consensus vaccination programs. Individual programs are variable and will reflect animal health, local environmental and housing conditions, severity of challenge and disease prevalence in addition to professional judgment. It is essential that the instructions on the individual vaccine label be followed. Withdrawal times are for meat unless otherwise stated. When a range is stated it means that some products have a longer withdrawal time than others. Check the label directions for the specific withdrawal time for each vaccine. As with all vaccines, proper storage is essential. They should be stored carefully according to the manufacturer’s instructions and under no circumstances should they be allowed to get hot. Ideally the refrigerator should have an alarm installed in case of failure. They should be allowed to warm to room temperature and reconstituted with the appropriate diluent immediately before beginning the vaccination procedure. Automatic syringes must be carefully sterilized, properly calibrated, and checked for accuracy before use. Needles should be changed regularly (at least after every 1000 chicks). The reconstituted vaccine should be used completely within 45 minutes. Embryonic chickens have a functioning immune system by 16 to 18 days incubation. Vaccination of embryonic chicks in ovo is therefore a highly effective method of vaccinating large numbers of birds in a very short time. Automatic egg injection machines have been widely adopted. Injection through the eggshell is performed at 18.5 days when eggs are routinely transferred to hatching trays to avoid turning in the setter compartment of the incubator. The window for in ovo vaccination is considered to be 17.5 to 19.2 days when the chick is in the ideal position for vaccination. The chick should be in the hatching position with its head under the right wing and no visible intestines in the yolk sac stalk. Once internal pipping starts and pulmonary respiration begins it is too late to vaccinate. Automatic systems can inoculate up to 60,000 eggs per hour and eliminate the need for posthatching vaccination (Fig. 19.1). The machines can deliver precise amounts of vaccine without causing significant trauma to the developing chick. The machines work by gently lowering an injection head onto the top of the egg. A small diameter hollow punch makes an opening and the needle then descends through this hole to a controlled depth—1 inch. A specified volume of vaccine is injected, the needle withdrawn and cleaned in a sterilization wash. Correct placement of the vaccine is critical. Vaccine deposited in the air sac confers no protection; vaccine in the allantoic fluid protects about a quarter of the birds; vaccine delivered to the amniotic fluid or the body of the embryo results in over 90% protection. Success also depends on timing. If given slightly earlier (around 17 days) the vaccine will mainly enter the amniotic fluid and be swallowed by the embryo. If given slightly later (around 19 days), the needle will likely enter the embryo—ideally the right breast. When properly done this does not result in significant damage. It is also important that the eggs be correctly aligned in the injector. For example, the embryo should develop with its head toward the large end of the egg so that it can emerge through the air sac. If the egg is upside down it results in embryonic malpositions and decreased hatchability. In ovo vaccination requires specialized equipment, great accuracy, and a very high degree of hygiene because once opened to the environment by a needle puncture, eggs are susceptible to bacterial or fungal invasion. With appropriate hygienic precautions, however, the method is highly satisfactory. It is predominantly used for Marek’s disease vaccines containing the CVI 988/Rispens strain of virus. It may also be used for control of infectious bursal disease in addition to fowlpox, and avian influenza. More than half the broilers in the United States are vaccinated against Marek’s disease using this system. Studies have shown that compared with vaccination at hatching, in ovo vaccination significantly reduces condemnations and early mortality. Basic precautions must be taken to achieve the best results, especially good hatchery sanitation and proper disinfection of the hatching eggs. One special problem is aspergillosis. This fungus is often present in moldy litter and can give rise to “brooder pneumonia” in hatchlings. To minimize this risk, airflow patterns must be carefully regulated to ensure that it flows from clean to dirty areas. Moisture management, disinfection, and careful sanitation are all essential. The equipment must also be carefully and precisely maintained. Vaccines must be reconstituted in a clean room, preferably well away from any sources of feather dander. Vaccine vials are stored in liquid nitrogen. They must be thawed in a water bath; once thawed they are injected slowly into the diluent bag before use. All these steps must be performed aseptically. Generally, the diluent also contains a dye to confirm vaccination. It is important to ensure that the vaccine and diluent are thoroughly mixed. The work area should be sanitized before and after any procedure Day-old chicks may be vaccinated with a subcutaneous injection of 0.2 to 0.5ml vaccine into the skin behind the neck or intramuscular injection into the thigh. Automatic vaccination machines (poultry service processors) are primarily designed for neck injection. Some robots can take day-old hatchlings, debeak them, and then inject them with one or two measured doses of vaccine subcutaneously in the neck region (Figs. 19.2 and 19.3). The vaccine dose is adjustable and delivered at low pressure, thus minimizing tissue damage. Needles are automatically sterilized between each chick using a disinfectant spray. The newest robots can vaccinate up to 3500 chicks/hour (20,000–30,000/day)! A colored dye may be mixed with the vaccine to permit quality assurance and the chicks are monitored for hemorrhage or vaccine leakage. This can identify any chicks accidentally missed. The presence of blood may indicate a blunt needle or that the machine needs to be readjusted. When injecting the vaccine by hand, the neck skin should be lifted up and the vaccine injected subcutaneously along the mid-line with the needle pointing away from the head. Other possible injection sites include the inguinal fold, the breast muscle, the biceps, or the tail head and the gastrocnemius muscle. It should always be borne in mind however that muscle lesions should be avoided in birds destined for human consumption. Spray vaccination is a very effective method of immunizing large numbers of birds. It works especially well against respiratory diseases such as Newcastle disease and influenza. The type of sprayer used determines the vaccine droplet size. This in turn determines how far down the chicken’s respiratory tract the droplets will penetrate. Large droplets will be trapped in the nasal cavity, smaller droplets will reach the pharynx and trachea, while the smallest will reach the lungs and air sacs. These small droplets are deposited at the bifurcations of the primary to secondary bronchi. Here they are taken up and processed by antigen presenting cells. Spray vaccination can be performed with the birds enclosed in a spray cabinet or by spraying birds within an entire house. Droplets less than 50 μm are classified as aerosols, droplets 50 to 100 μm are considered fine spray, and 100 to 300 μm droplets are considered coarse spray. When using a spray cabinet, a measured amount of vaccine can be delivered to each batch of chicks. Each manufacturer will have recommendations for the volume of vaccine used per box. The sprayer should aim to generate “coarse” droplets. However, remember that droplet size depends not only on nozzle size, but also on the spray pressure. Higher pressure generates smaller droplets. The distilled water used should be cool but not cold. The delivery of the vaccine can be visualized either by means of a dye or simply by the amount of moisture present on the plumage. Factors such as air pressure and spray pattern and the volume delivered must be carefully monitored. In a hot dry environment, droplet size will shrink as the water evaporates. The distance between the nozzle and the bird also affects droplet size. Avoid trying to reach distant birds by raising the nozzle. When spraying an entire house, backpack sprayers are used. The vaccine is usually reconstituted in distilled water. The sprayers must not have been used for other purposes such as pesticide spraying. The droplet size should be 80 to 120 μm for young chicks. This size will be affected by the degree to which the backpack sprayer is pumped up. A team of sprayers dressed in appropriate protective clothing plus gloves, masks, and goggles, should walk slowly through the house spraying at least 1 gallon of vaccine per 100 feet. Each vaccinator should spray one side of the house and the nozzle should be directed about 3 feet above the heads of the birds. The objective of the process is to deliver droplets to the eyes, nares, and the respiratory tract. Vaccine deposited on litter and equipment is wasted. Fans and heater should be turned off. Curtains should be closed in open houses. Birds should be settled before spraying begins, perhaps by dimming the lights. In hatcheries, live attenuated vaccines against infectious bronchitis virus (IBV) and Newcastle disease virus (NDV) are administered as a coarse spray on day of hatch. Coarse spraying, by generating droplets greater than 100 μm, prevents the vaccine virus from penetrating deep into the respiratory tract. This in turn, prevents vaccine virus from causing lesions there. The large droplets land in the eyes and nares and are confined to the upper respiratory tract. These droplets do not damage the virus particles so that they replicate to a higher titer and induce a stronger protective response. Despite precautions, vaccine spraying is often suboptimal and many birds may be missed. Once vaccination is completed, equipment must be cleansed thoroughly with hot water and the fans and heaters turned on again. Gel diluents have been introduced to enhance coccidiosis vaccination. The vaccine is mixed with a thick gel diluent and then applied to chicks through a gel application bar. The gel remains on the feathers until preened off by the bird. It works well for coccidia where oocysts must be ingested. It may also work for infectious bronchitis and other viral diseases. Another common method for the mass administration of vaccines to large numbers of poultry is through their drinking water. To ensure that poultry drink the water, it should be withdrawn for 1 to 4 hours before vaccine administration depending upon the ambient temperature to ensure that they are somewhat thirsty. All birds should have access to the vaccine water at the same time to ensure that vaccine uptake is evenly distributed across the flock. It is important to determine daily water consumption beforehand to estimate the appropriate vaccine dose. The amount of water to be used for vaccination should be about one-third of average daily consumption. There are, however, standard guidelines based on the temperature including the birds’ age and type. The drinking water should not contain any chlorine or disinfectants. Likewise, sanitizer use should be discontinued 48 hours before vaccination. Lines should be flushed with a product that can remove litter, feed, and feces, in addition to detergents, minerals, and biofilms. The pH of the water supply should be between 7 and 6.5. Filters and oxygenators should be removed or disconnected. Waterers should be scrubbed with chlorine free water. Commercial products are available that may be added to the water to neutralize chlorine and other oxidants and optimize pH. Ideally the vaccine should be administered early in the morning and all birds should have easy access to it. Keep the waterers out of direct sunlight. Skim milk powder may be added as a stabilizer and also dye. The vaccine solution is placed in the drinkers or water tanks according to the manufacturer’s recommendations, and the water system is primed. Unvaccinated water should be drawn off and discarded. Birds should drink all the vaccine solution in 1 to 2 hours. If water has been cut off for too long, some thirsty birds may drink it so fast that the others may not get a sufficient dose. The water should remain free of chlorine medications or disinfectants for at least 24 hours after vaccination. Unfortunately, field conditions are often such that not all birds receive the vaccine. Perhaps as few as 60% may be vaccinated successfully with drinking water. Some commercial poultry vaccines are approved for administration by eye drops. The vaccines should be reconstituted with appropriate diluent and an eyedropper cap used. Allow one full drop to fall into the open eye of the bird and hold it until it swallows. Birds will usually get 0.03 ml of vaccine into the eye or nasal cavity where it is rapidly absorbed. Some vaccines may be administered into the plucked wing web using a two-pronged needle that has been dipped in the vaccine solution. It is given in the underside of the wing avoiding vulnerable structures such as veins, bone, or nerves. Antibacterial vaccines are especially significant in the poultry industry where the short production cycle precludes the use of antibiotics. Although viral diseases are of greater overall significance, antibacterial vaccines are also essential. Fowl cholera is caused by Pasteurella multocida, an acute fatal septicemia in chickens and turkeys. P. multocida vaccines include bacterins adjuvanted with aluminum hydroxide or oil emulsions, or they may contain attenuated live organisms. Multivalent Pasteurella vaccines usually contain the commonest serotypes 1, 3, and 4. The inactivated vaccines are usually given by injection. The attenuated live vaccines (M9 or PM-1 strains) may be given by the wing web or in drinking water. Protection develops in about two weeks. These diseases are caused by several pathogenic Mycoplasmas. The most important are Mycoplasma gallisepticum (MG) and Mycoplasma synoviae (MS). MG causes chronic respiratory disease, whereas MS causes respiratory disease or synovitis. It is generally best to maintain mycoplasma-free flocks, but inactivated, attenuated live and fowlpox-vectored vaccines are available for use in countries where vaccination is permitted. The use of these vaccines is prohibited in some states. Vaccines should only be used in flocks with birds of all ages and where infection is considered inevitable. Bacterins consist of suspensions of MG in an oil emulsion. These can protect against respiratory disease or egg production losses but will not prevent infection with field strains of MG. Live MG vaccines contain the mild F strain, or the safer avirulent ts-11 or 6/85 strains. The F strain is administered by the intranasal or eye drop method; the ts-11 strain is given in eye drops; the 6/85 strain is given by fine spray. A fowlpox recombinant MG vaccine is also available. It is administered in the wing web. The use of the attenuated vaccines has been characterized as controlled exposure by giving a mild infection at an age when little damage occurs. Pullets are generally vaccinated between 12 to 16 weeks of age. One dose is sufficient to make the birds permanent carriers. A live MS vaccine containing the MS-H strain is administered by eye drop. This is an acute respiratory disease of chickens caused by Avibacterium paragallinarum. It is characterized by nasal discharge, sneezing, conjunctivitis, diarrhea, and facial swelling. Affected hens show a significant drop in egg production. Coryza may be complicated by the simultaneous presence of many other bacteria in addition to infectious bronchitis virus. There are three serovars of A. paragallinarum (A, B, and C). These are not cross-protective so it is essential that any vaccines contain the appropriate serovar for that population of birds. Commercial bacterins are available in the United States and other countries. These generally contain all three serovars. Some vaccines produced by large manufacturers are marketed internationally and contain the most prevalent bacterial strains. However, there are concerns that these may not provide protection against more localized variants. Colibacillosis is caused by avian pathogenic Escherichia coli. This commonly starts as a respiratory infection and eventually leads to colisepticemia, sickness, deaths, and carcass condemnation. Colibacillosis is a leading cause of economic loss in the poultry industry. Vaccination is an obvious solution to this problem and many different inactivated and live vaccines have been developed. However, at the present time there is only a live attenuated vaccine available in the United States. The vaccine contains an aroA-deleted mutant designed for coarse spray or drinking water administration. Salmonellae present the poultry farmer with two potential problems. One is the fact that they may kill large numbers of birds. The other is that they may cause human food poisoning caused by the contamination of eggs and poultry meat with Salmonella enterica serotype Enteritidis. This is of major concern to the poultry industry for both legal and financial reasons. In Europe, for example, 10% to 15% of poultry meat at the retail level may be Salmonella positive. Young chickens may be infected by both vertical and horizontal transfer and they probably acquire the infection soon after hatching. Once established in the intestine, the Salmonellae can prevent colonization by other serovars. It is well established that cell-mediated immunity is essential for the control of Salmonellosis. If birds are vaccinated against one of the host-specific serovars such as Salmonella gallinarum, it induces a strong specific immunity. However, vaccination against the nonhost specific serovars is much less effective. The host-specific infections normally cause a septicemic disease involving macrophage colonization and minimal enteric infection. In contrast the nonspecific serovars tend to colonize the intestinal tract. These are the serovars that cause human food poisoning. Thus the greatest number of available vaccines are directed against serovar Enteritidis. These are all administered subcutaneously around 10 to 14 weeks of age and given in two doses 4 to 6 weeks apart. Many are combined with Newcastle and bronchitis vaccines. Some salmonella vaccines also contain other serovars such as Typhimurium, Kentucky, and Heidelberg. Spray and drinking water vaccines are also available for use in chickens and turkeys. Marek’s disease virus (MDV) is a member of the genus Mardivirus, an alphaherpesvirus. It causes a lymphoproliferative and neuropathic disease that affects the nerves, viscera, muscle, and skin of chickens. It is also immunosuppressive. As with other herpesviruses, chickens may become persistently infected without showing any clinical signs. There are three species of MDV: Gallid herpes virus 2 (serotype 1), Gallid herpesvirus 3 (serotype 2), and Meleagrid herpesvirus 1 (serotype 3, also called herpesvirus of turkeys, HVT). Serotype 1 includes all the virulent poultry strains and some attenuated vaccine strains. Marek’s disease is primarily controlled by vaccination either in ovo at day 18, or by subcutaneous injection at day of hatch. The need for vaccination against MDV has a significant economic impact on the poultry industry. Bivalent vaccines containing serotypes 1 and 3 or trivalent vaccines containing serotypes 1, 2, and 3 are used. These vaccines contain live virus and although they prevent tumor production they do not generate sterilizing immunity. Vaccinated chickens still get infected and can shed virulent field virus. It is suggested that this has resulted in the increased virulence of field strains of the virus. Several different modified live virus vaccines are available to control Marek’s disease. Turkey herpesvirus (HVT or MDV-3) is an avirulent virus that can effectively protect chickens against MDV. Strain FC126 of HVT is the most widely used MDV vaccine and commonly given to broilers as a monovalent vaccine and as a polyvalent vaccine in breeders and layers. Serotypes 1 and 2, and HVT are highly cell-associated and must be stored frozen in liquid nitrogen. Thus they must be carefully stored and thawed before use. This includes the use of safety glasses and gloves when removing the vaccine vials from the liquid nitrogen tank. The thawed vaccine is diluted appropriately and mixed well before use. Cell-free vaccines are available in some countries. These are less immunogenic but easier to store. HVT has an excellent safety record and like other herpesviruses is persistent. Immunity to HTV is not inhibited by maternal antibodies if given on the day of hatch or in ovo. It can also be used as a vector virus for recombinant vaccines against infectious laryngotracheitis, Newcastle disease, infectious bronchitis, avian influenza, and bursal disease. These recombinants are very effective in protecting against systemic disease, but immunity to mucosal infections such as NDV is inconsistent. MDV-2 strain is another naturally occurring avirulent strain of MDV used in vaccines. It only provides limited protection but it may be used in combination with other strains. There are situations in which HVT alone and MDV-2 alone cannot protect against very virulent strains. However, a combination vaccine containing both HVT and MDV-2 may show a synergistic effect. Attenuated MDV-1 vaccines have also been generated by serial cell culture passage. Strain CVI988 or Rispens is considered the most efficacious current vaccine (Dr B.H. Rispens was the first to isolate strain CVI 988 in 1972). It was attenuated by serial passage in chicken kidney cells. This vaccine has some residual virulence in susceptible chickens and can spread between birds. It is predominantly used for in ovo vaccination. Higher passage variants are less virulent but also less immunogenic. CVI988 is the vaccine strain of choice against very virulent strains of MDV. Newcastle Disease is a serious respiratory disease caused by virulent strains of avian paramyxovirus serotype 1 of the genus Avulavirus. All strains of the virus (NDV) are contained in a single serotype, but they are divided into two classes, class I and class II. Class II is then divided into 16 genotypes. Class 1 viruses are primarily found in wild birds because NDV can infect many different avian species. The incubation period of NDV lasts from three to six days. Clinical signs are nonspecific, namely depression, ruffled feathers, anorexia, hypothermia, and death. Some birds may develop neurologic disease with torticollis, ataxia, and paralysis. Viscerotropic velogenic ND is the most severe form of the disease resulting in the development of diphtheritic and necrotic, or hemorrhagic lesions along the gastrointestinal tract. Class II NDVs vary greatly in their virulence for chickens. They are classified as velogenic—rapidly lethal; mesogenic—intermediate; and lentogenic—relatively low virulence, based on their lethality for chick embryos. For example, class II, genotype II strains are so lentogenic that some, such as Hitchner B1 and LaSota, can be used in modified live vaccines. Because all the strains of NDV belong to a single serotype, proper vaccination should protect against all of them. Immunity is mainly derived from neutralizing antibodies against their hemagglutinin (H) and the fusion (F) glycoproteins. However, cell-mediated immune responses also reduce viral shedding, presumably by killing virus-infected cells. Sterilizing immunity is not achieved with current NDV vaccines. Vaccines prevent clinical disease and mortality, and they may reduce virus shedding and increase the dose of virus needed to infect a bird. Flock immunity is another positive outcome of vaccination although it is estimated that this will only have an impact when greater than 85% of the flock have hemagglutination inhibition titers greater than 8 after two doses of vaccine. Inactivated vaccines are given by the intramuscular or subcutaneous routes. They are often given to layers or breeders to provide persistent high antibody levels that can be transferred to their chicks. They are usually inactivated with formaldehyde or beta-propiolactone and adjuvanted by emulsification in mineral or vegetable oil. Because birds have to be handled individually, these vaccines are more expensive than the MLV vaccines. Permissible withdrawal times between vaccination and slaughter must also be taken into consideration because of the persistence of vaccine antigen. This may be 21 or 42 days depending upon the vaccine. Modified live lentogenic or mesogenic strains are used in MLV-NDV vaccines. The live vaccines are usually grown in embryonated chicken eggs or in tissue culture. Lentogenic strains used in these vaccines include B1, C2, LaSota, V4, NDW I2, and mesogenic strains used include Roakin, Mukteswar, and Komarov. The mesogenic vaccines cause mild disease so they are generally used in countries where Newcastle disease is endemic. In countries largely free of ND only lentogenic strains are permitted. These live vaccines are given in drinking water, by coarse sprayer, or by intranasal or intraocular administration. A lentogenic strain is also available for in ovo use. Some mesogenic strains may be given by wing web inoculation. The severity of vaccine reactions depends on the strain of the virus employed. For example, of the two major vaccine strains of Newcastle disease, the LaSota strain is a good immunogen but may provoke mild adverse reactions. In contrast, the B1 strain is considerably milder but is less immunogenic, especially if given in drinking water. Where disease risks are high, live LaSota vaccine can be given in the drinking water or as a spray at 5 to 6 weeks, followed by another dose at 10 weeks, and an inactivated vaccine at point of lay. It is also important to bleed and test samples of bird sera after vaccination to ensure that they develop protective antibodies. Recombinant vectored NDV vaccines using turkey herpesvirus or fowlpox vectors incorporating the hemagglutinin gene or the F gene, or both, are also available. Some of these may be appropriate for in ovo vaccination. NDV itself may also be used as a vector for other vaccines such as those against IBD or avian influenza. As with other poultry vaccines, maternal antibodies can interfere with early vaccination procedures. The significance of this varies between farms and between birds and two strategies have been employed to overcome this. One is to delay vaccination until two to four weeks when most birds can develop immunity. Alternatively, the birds are vaccinated at one day by coarse spraying or eye drop vaccination. This will infect the chicks until maternal immunity has gone and they can then respond to the infection themselves. However, these vaccines may cause respiratory problems in very young chicks. Reactions in spray-vaccinated birds may be significantly more severe than those receiving eye-nose drops, however, their antibody response is slightly but significantly greater. Although NDV vaccines can prevent clinical disease and mortality, a major impediment to prevent outbreaks is uneven vaccine application when using these mass administration techniques. It has proved difficult to attenuate live NDV strains sufficiently for in ovo use without affecting hatchability. Recombinant NDV vaccines expressing the fusion (F) gene may solve this problem. Layers may be vaccinated at frequent intervals to ensure adequate immunity. For example, they may be primed with an inactivated vaccine and then repeatedly boosted with more immunogenic live vaccines. Also called Gumboro disease, the causal agent of IBD is an avibirnavirus. It infects multiple bird species, but causes clinical disease only in chickens less than 10 weeks of age. The virus destroys B cells within the Bursa of Fabricius resulting in bursal atrophy and subsequent suppression of the antibody responses. This immunodeficiency will result in a poor response to other vaccines and overwhelming secondary infections. There are two serotypes of IBDV but severe bursal disease is only associated with serotype 1. All commercial vaccines are directed against this serotype. There are no reports of clinical disease caused by serotype 2. As with all RNA viruses, IBDV is rapidly evolving and as a result there is much variation in antigenicity and virulence, features that complicate vaccine development. Many different types of IBD vaccine are available, both monovalent and in combinations. These include live attenuated vaccines, inactivated oil-adjuvanted vaccines, live recombinant vaccines, or even immune-complex vaccines. Because this disease affects very young chicks it is important to exploit maternal immunity by vaccinating hens. The inactivated vaccines are water-in-oil adjuvanted products. They are mainly used to induce long-term immunity in breeding stock. They are safe to use in young valuable birds with maternal antibodies. They are best used in birds at 16 to 20 weeks that have been primed by live vaccines at 8 weeks of age. The viral structural protein 2 (VP2) is the major protective antigen in IBVD. This antigen can be expressed in different vector systems such as E. coli, yeast, fowlpox virus, baculovirus, and in plants. Commercially available VP2 recombinant vaccines include those from E. coli, the yeast Pischia pastoris, and baculovirus systems. They are not highly immunogenic and have to be boosted repeatedly. Given that these birds develop antibodies against only VP2, these have the potential to be DIVA vaccines. Modified live vaccines have been attenuated by serial passage in tissue culture or eggs. Depending on their degree of attenuation, live attenuated IBDV vaccines may be classified as mild, intermediate, or invasive based on their ability to replicate and cause bursal lesions. This also reflects their ability to overcome maternal immunity. Mild vaccines are used to prime broiler breeders before boosting with an inactivated vaccine. If chicks have maternally-derived antibodies, then vaccination should be delayed until this has waned. The mild vaccines show poor efficacy in the presence of maternal antibodies or against very virulent strains of IBDV. The intermediate or hot strains are more immunogenic but may induce bursal lesions. The vaccine is usually given in a spray or in drinking water. Immune-complex vaccines are made by mixing a live intermediate IBD virus with IBDV-specific hyperimmune chicken serum (IBDV-Icx vaccine, Cevac, Transmune). The advantage of this vaccine is that it can be used for in ovo vaccination. It can also be administered subcutaneously to one-day-old chicks. Studies on the fate of the immune-complex-bound virus indicate that it does reach the bursa, but five days later than uncomplexed virus. As a result, it causes much less bursal and splenic damage. It is likely that the immune-complexed virus localizes in areas within the spleen and bursa where it is more effectively processed and presented by follicular dendritic cells. Immune-complexes are much more immunogenic than vaccine antigen given alone. This is supported by the observation that chicks receiving the immune-complex vaccine develop many new germinal centers in their spleen. This vaccine is not available in the United States. Recombinant vectored vaccines use the herpesvirus of turkeys to express the VP2 antigen of IBDV. As a result, they can be used in a DIVA strategy because they only induce antibodies against VP2 in contrast to whole virus vaccines that induce antibodies against all IBDV proteins. They are designed so that they can be injected either into 18-day eggs or into 1-day-old hatchlings, where they are not inhibited by maternal antibodies. Infectious bronchitis is an economically significant respiratory disease of chickens that also causes nephritis, decreased egg production, poor growth, and high morbidity. It is caused by a gammacorona virus, avian infectious bronchitis virus (IBV). The combination of high morbidity, and loss of performance, together with secondary bacterial infections can lead to unsustainable losses. As a result, almost all commercial poultry are vaccinated against this virus. However, the ability to control or prevent infectious bronchitis outbreaks is rendered very difficult by the continuous emergence of new IBV genotypes, serotypes, and variants as a result of mutation and recombination. Over 50 serotypes and hundreds of variants have been identified and more continue to emerge. These variants arise as a result of sequence changes in a hypervariable region of the viral spike (S) glycoprotein. There is also a lack of cross-protection among these genotypes. Thus as variants appear and disappear, they necessitate the continual development of new vaccines. Both inactivated and live attenuated IBV vaccines are available. Currently most of these vaccines contain the Massachusetts strain either alone or in combination with the Arkansas, Connecticut, Georgia, Huyben (Holland), or Delaware strains. They are usually given in combination with Newcastle disease vaccines. Inactivated vaccines may be used alone or in combination with modified live virus (MLV) vaccines in layer/breeder flocks to induce maternal immunity and thus protect chicks from an early age. As we have seen with other diseases, the inactivated vaccines induce a relatively weak immune response without cell-mediated immunity, and thus require multiple doses and the use of adjuvants. These in turn increase handling costs and may cause significant injection site lesions. Modified live IBV vaccines containing three common serotypes are administered in the drinking water, or by coarse spray, and given at day one or within the first week. Some short-lived broilers receive only this single dose. For longer-lived broilers, a second dose is generally given two to three weeks later. Long-lived broiler breeders and layers receive multiple vaccine doses at two, four, and six weeks. Revaccination after that depends upon the local threat assessment. There is great diversity among the MLV strains employed depending on geographic location. For example, in North America the major vaccine strains are M41 (Massachusetts), Arkansas, and Connecticut. In Europe strains 4/91 and D274 predominate. These may be ineffective in other countries or locations. The Chinese QX strain has caused outbreaks in Africa, the Middle East, Europe, and Asia. These modified live vaccines induce a potent protective response but reversion to virulence, recombination, or mutation are ever-present risks. There are currently no licensed recombinant vaccines available. An economically important respiratory disease caused by gallid herpesvirus 1, ILT affects chickens, peafowl, pheasants, and partridges. The principle lesion is tracheitis and the disease can vary in severity from lethal asphyxiation to very mild or subclinical infection. As with other herpesviruses, infected birds may become healthy carriers. The disease is usually prevented by the use of either live attenuated vaccines or recombinant vectored vaccines. Modified live vaccine viruses have been attenuated either by prolonged passage in tissue culture or by passage in embryonated chicken eggs. The MLV vaccine may then be administered by spray, eye drops, or in the drinking water. Residual virulence may be an issue with some of these vaccines especially when delivered by spray vaccination. Reversion to virulence may also be an issue. Some recent ILT outbreaks have been attributed to egg adapted vaccines that have regained virulence. The chicken embryo passaged vaccine is the most widely used ILT vaccine. It induces rapid immunity and is easily administered through drinking water. In general, long-lived birds are routinely vaccinated against ILT, but short-lived birds such as broilers are only vaccinated if an outbreak is threatened As a result of residual virulence in modified live vaccines, efforts have been made to generate safer vaccines by developing viral vectored vaccines. These recombinant ILT vaccines contain either herpesvirus of turkeys (Marek’s serotype 3), or fowlpox virus expressing one or more of the ILT glycoproteins. The fowlpox-vectored vaccine expresses the glycoprotein B and UL32 genes. It may be given in ovo or by wing web puncture to one-day-old commercial layers. There are two HVT vectored vaccines, one expressing glycoproteins I and D, the other expressing glycoprotein B. They induce protective immunity against both ILT and Marek’s disease. They are not transmitted between birds and do not revert to virulence. They are also administered by subcutaneous vaccination to one-day-old chicks or in ovo. They are not as protective as the attenuated vaccines and are less able to prevent shedding. Avian reoviruses belong to the genus Orthoreoviruses in the Reoviridae family. They cause arthritis/tenosynovitis, proventriculitis, a runting-stunting syndrome, and “blue-wing disease” in broilers. Because these diseases affect very young birds, reovirus vaccines are often administered to breeding hens to stimulate maternal immunity and protect the newly hatched chicks. Both inactivated and modified live vaccines are available. The inactivated oil-emulsion adjuvanted vaccines may contain multiple strains and different pathotypes. They are used in replacement and breeder hens and are often used in combination with NDV, Marek’s or bronchitis vaccines. Live vaccines may contain the avirulent 2177 or 1133 strains. Some are given subcutaneously to one-day-old chicks. Others are given in drinking water to birds between 10 and 17 weeks of age. Over the past six years there has been a gradual increase in the number of disease outbreaks in vaccinated flocks. This is a result of changes in the circulating strains of the viruses, and so new, updated vaccines are needed. According to the US Department of Agriculture (USDA), the outbreak of highly pathogenic avian influenza (HPAI) that occurred in 2015 was the worst animal disease outbreak in US history. More than 200 premises were affected in 15 states and more that 48 million birds were depopulated. These recent outbreaks have made mass slaughter prohibitively expensive. Consideration is therefore being given to use vaccination to block or slow the spread of the disease when this disease recurs. In most countries where the disease is not endemic, vaccination against HPAI is actively discouraged or banned because it interferes with the detection of infected flocks. Vaccination alone is not a solution to the problem of HPAI, or H5/H7, low pathogenic avian influenza (LPAI) viruses because it raises the possibility that these strains could become endemic in avian populations. Additionally, although vaccines may prevent sickness and death, they will not prevent infection or viral shedding. In the United States, the USDA has established the National Veterinary Stockpile in case a decision has to be made regarding avian influenza vaccination. The stockpiled vaccines are primarily inactivated vaccines but a DNA-plasmid vaccine has also been conditionally licensed. If a decision to vaccinate is made, domestic distribution and use will be supervised and controlled by USDA veterinary services as part of an official USDA program. Vaccination may be used in control programs for both HPAI and LPAI. The recent emergence of pandemic influenza A strains such as H7N9 and H5N1, reveals the tremendous challenges to our current influenza control strategies. Better vaccines that provide protection against a wide spectrum of influenza viruses and long-lasting immunity are urgently needed. Over 95% of all avian influenza virus (AIV) vaccines used in poultry are inactivated, adjuvanted products given by injection. Vaccines containing mineral or vegetable oil based adjuvants generally induce the highest antibody titers. These vaccines are prepared from infectious allantoic fluid that is inactivated with beta-propiolactone or formaldehyde. Inactivated influenza A vaccines have been used in turkeys in the United States against LPAI and non-H5/H7 influenza A viruses. A vaccine against H1 and H3 swine influenza viruses has also been used in breeder turkeys. Vaccines against H9N2, H7N3, H5N2, H5N1, have been used extensively in Asia in response to specific disease outbreaks. Advances in molecular biology have allowed Marek’s disease (HVT) vectored vaccines, expressing the influenza virus hemagglutinin (HA), to be sold commercially. As a group, these vectored vaccines can stimulate both cellular and humoral immunity and are effective at preventing clinical disease and reducing virus shedding. All the licensed recombinant vaccines, because they only express the HA, may be used to differentiate vaccinated from infected birds. The vectored vaccines also work well with a prime-boost strategy where the vectored vaccine is given first and birds are revaccinated with a killed adjuvanted vaccine two or three weeks later. The use of a killed vaccine with a homologous hemagglutinin and a heterologous neuraminidase may allow the serologic differentiation of vaccinated and infected birds. A recombinant fowlpox influenza vaccine (TROVAC-AIV H5) expressing the hemagglutinin of avian influenza H5 has been licensed for use in Mexico, Guatemala, and El Salvador where it is widely employed. It can be administered to one-day-old chicks and serologic tests can readily distinguish vaccinated from naturally infected birds. Fowlpox is caused by an Avipoxvirus, a large, complex DNA virus. They are transmitted through aerosols or by biting insects. It is a slowly spreading infection characterized by proliferative skin lesions (dry pox) on unfeathered skin, or by diphtheritic lesions in the mucosa of the mouth, esophagus, larynx, or trachea (wet pox). The latter can result in asphyxiation of young chicks. In general mortality is low but may reach 50% in stressed flocks. Modified live fowlpox or pigeon poxvirus vaccines attenuated in cell culture or embryonated eggs are available. They may be given as monovalent vaccines or in combinations. Most are administered into the wing web after maternal immunity has waned. Some are administered subcutaneously to one-day-old chicks and there is also an in ovo recombinant vectored vaccine available that expresses ILT antigens. They may be used in situations where the disease is endemic because the infection spreads relatively slowly and may be administered in the face of an outbreak. They have also been used in pigeons, turkeys, and quail, in addition to chickens. The cause of epidemic tremor, avian encephalomyelitis virus is a picornavirus that affects the central nervous system. In young chickens it induces paralysis, ataxia, and muscular dystrophy. In older chickens, infection is usually subclinical but causes a decline in egg production and hatchability. Several modified live vaccines are available. Some may be combined with fowlpox. Most are administered by wing web vaccination using a double needle applicator. Breeder chickens are vaccinated at 10 to 16 weeks of age, at least 4 weeks before start of lay. The site of inoculation should be examined for “take” at 7 to 10 days postvaccination. A positive take is indicated by a swelling or scab at the site of inoculation. If given to laying flocks this vaccine can cause a serious drop in egg production. Egg drop syndrome (EDS) is caused by an adenovirus infection in laying hens. It is characterized by production of soft-shelled and shell-less eggs and also a 10% to 40% drop in egg production. An inactivated vaccine containing EDS’76 virus strain BC14 in a water-in-oil emulsion may be available. It should be administered intramuscularly to layers and breeders no later than 4 weeks before the expected onset of lay. Infection with Eimeria coccidia induces a strong, species-specific protective immunity. As a result, several live coccidial vaccines are used in commercial poultry. These vaccines typically contain live sporulated oocysts from multiple Eimeria species and strains. Some consist of virulent, drug-sensitive organisms administered repeatedly in very low doses of oocysts (trickle infection). Some of these organisms have been attenuated by repeated passage through eggs, but this only works well for Eimeria tenella. Other Eimeria species have been selected for precocity. Precocious strains mature very rapidly (30 hours faster than the parent strain), and, as a result, have less time to replicate, produce fewer oocysts, are less virulent because they cause less tissue damage, yet are highly immunogenic. This precociousness is a stable trait and the parasites do not regain virulence. All of these vaccines provide solid immunity to coccidia when applied carefully under good conditions. Nevertheless, the dose of coccidia vaccine must be carefully controlled, and the vaccines must be harvested from the feces of infected birds. Vaccinated birds shed oocysts that are transmitted to other birds. Because of regional strain variation, vaccination may not be effective in protecting against field strains in all locations. A transmission blocking subunit vaccine has been developed that contains two purified glycoproteins (Gam56 and Gam82) from the wall-forming bodies of macrogametocytes of Eimeria maxima. It is believed that the antibodies produced inhibit oocyst wall formation. This vaccine (CoxAbic, Netanya, Israel) is administered by injection with an oil-in-water adjuvant. It is given to breeder hens twice before the breeding season to provide maternal immunity to their chicks. Conventional live coccidiosis vaccines are delivered to day-old chicks either at the hatchery or on the farm by coarse spray, gel, or feed vaccination. The vaccine containers should be shaken gently at intervals to ensure that the oocysts do not settle but stay in suspension. Spray application of these vaccines involves the use of a large droplet size and the vaccine is dyed to stimulate preening and consumption of the vaccine by the birds. Likewise, the sprayed chicks should be placed in well-lit areas to encourage them to preen. Administration on feed involves spraying the feed with the diluted vaccine to moisten it. Newly hatched birds emerge from the sterile environment of the egg, and like mammals, require temporary immunological assistance. Serum immunoglobulins are actively transported from the hen’s serum to the yolk while the egg is still in the ovary (Fig. 19.4). During egg production about 30% of the hen’s immunoglobulin (Ig)Y will transfer from her plasma to the yolk. IgY in the fluid phase of egg yolk is therefore found at levels equal to or greater than those in hen serum. As the fertilized ovum passes down the oviduct, IgM and IgA from oviduct secretions are acquired with the albumin. As the chick embryo develops in ovo, it absorbs the yolk IgY, which then appears in its circulation. At the same time, the IgM and IgA from the albumin diffuse into the amniotic fluid and are swallowed by the embryo. Thus when a chick hatches, it possesses IgY in its serum, and IgM and IgA in its intestine. The newly hatched chick does not absorb all its yolk sac antibodies until about 24 hours after hatching. These maternal antibodies effectively prevent successful vaccination until they disappear between 10 and 20 days after hatching. Newly hatched chicks begin to make their own IgA at day three in the bursa, and day seven in the gut and lung. Interestingly, maternal IgA persists for at least seven days because it appears to be retained by the intestinal mucus. The presence of maternal antibodies may neutralize live vaccine strains and day of age vaccination is not therefore ideal. That is why in ovo vaccination is employed.
Poultry vaccines
Vaccine administration
Disease/Vaccine
Vaccination Schedule
Comments
Antiviral
Marek’s disease
Modified live viruses administered either in ovo or day 1.
Withdrawal time 21 days.
Newcastle disease
Given in ovo or at day one or days 9–14, either in the drinking water or by coarse sprayers.
Usually the B1 or LaSota strain.
Infectious bronchitis
Day 1 or 14–21 days administered in drinking water or by coarse spray. With Newcastle disease vaccine.
Use Massachusetts strain.
Infectious bursal disease
Given in ovo or on day 1 and boost at 8–12 days.
Withdrawal time 21 or 42 days.
Disease/Vaccine
Vaccination Schedule
Comments
Antibacterial
Fowl cholera
Vaccinate all chickens in the flock at 10–12 weeks. Revaccinate at 18–20 weeks.
Leave at least a 6 week gap between vaccine doses.
Mycoplasmosis
Only where permitted. Vaccinate at 12–16 weeks of age. Two doses are administered.
Infectious coryza
Vaccinate at 5–9 weeks of age. Revaccinate in 4 weeks.
No later than 3–4 weeks before onset of lay.
Colibacillosis
Given in drinking water or coarse spray. Vaccinate at 1 day of age and repeat in 3 weeks. Long lived birds may be revaccinated at 12–14 weeks of age.
Do not use antibiotics when using these vaccines.
Salmonellosis
Salmonella enteritidis. Vaccinate at 12–16 weeks and 4 weeks later. May revaccinate during molt. Other vaccines may be given by coarse spray or in the drinking water to 1 day of age chicks. A second dose should be administered 2 weeks later.
Withdrawal time 42 days.
Antiviral
Newcastle disease
Vaccinate with bronchitis at 9–14 days. Revaccinate at 4, 6, and 8–10 weeks. Alternatively, vaccinate with a MLV and then revaccinate at 4 and 16–20 weeks. Every 3–4 months thereafter revaccinate by water or aerosol.
Use B1 or LaSota strains.
Infectious bronchitis
Vaccinate at 9–14 days combined with NDV. Revaccinate at 4 and 8 weeks in water or coarse spray. Repeat every 3–4 months.
Withdrawal time 21 or 42 days.
Infectious bursal disease
Vaccinate at 10–20 days and revaccinate at 8–10 weeks and 16–18 weeks.
Usually administered by intramuscular injection, spray, or in the drinking water. Intermediate or invasive vaccines are used to vaccinate broilers and commercial layer replacements. They are sometimes delivered to 1-day chicks as a coarse spray to protect chicks lacking maternal antibodies. Second and third applications may be administered if there is a high risk of virulent disease.
Tenosynovitis (Reovirus)
Spray vaccines can be given to 1-day chicks or in drinking water to birds over 12 weeks of age. Boost at 6–8 weeks, 10–12 weeks, and 16–18 weeks.
Withdrawal time 21 or 42 days.
Encephalomyelitis
Vaccinate at 10–12 weeks In the wing web.
Withdrawal time 21 days.
Fowlpox
Vaccinate 10–12 weeks In the wing web. In ovo and 1 day of age vaccines are available.
Do not vaccinate during lay. Examine the injection site at 7–10 days to ensure “take”. Withdrawal time 21 days.
Chicken infectious anemia
Vaccinate birds over 12 weeks in the wing web. Do not vaccinate laying breeders.
Examine the injection site at 7–10 days to ensure “take.” Withdrawal time 21 days.
Laryngotracheitis
Vaccinate in ovo or birds 5–8 weeks by eye drop, spray, or drinking water. Revaccinate at 16–20 weeks.
Withdrawal time 21 days.
Disease/Vaccine
Vaccination Schedule
Comments
Antibacterial
Mycoplasma gallisepticum
Vaccinate at 10–14 weeks by spray or 18 weeks parenterally.
Antiviral
Newcastle disease
Vaccinate together with infectious bronchitis by water or coarse spray. At 14–21 days, 5 weeks, and every 5–6 weeks thereafter. B1 can be administered by eye drop or spray at 1 day. B1 or LaSota at 18–21 days, drinking water, LaSota at 10 weeks, and an inactivated adjuvanted vaccine at point of lay.
Withdrawal time 21 or 42 days.
Infectious bronchitis
Vaccinate on day 1, and then revaccinate at 14–21 days, 5 weeks, 8–10, 12–14, and 16–18 weeks. Revaccinate layers and breeders at 13–18 weeks of age.
Withdrawal time 21 or 42 days.
Infectious bursal disease
Vaccinate at 10–17 days. Revaccinate at 7 weeks and 6 months
Withdrawal time 21 or 42 days.
Encephalomyelitis
Vaccinate birds over 8 weeks but at least 4–6 weeks before start of lay.
Withdrawal time 21 days.
Fowlpox
Vaccinate at 10–12 weeks in the wing web. They should be over 8 weeks, but at least 4 weeks before start of lay.
Examine the wing site to ensure that the vaccine has taken.
Laryngotracheitis
Vaccinate at 8–12 weeks by eye drop. Revaccinate at 4 months.
Withdrawal time 21 days.
In ovo vaccination
Subcutaneous neck injection
Spray vaccination
Gel vaccination
Drinking water vaccines
Eye-drop/intranasal vaccination
Wing-web vaccination
Antibacterial vaccines
Pasteurellosis
Mycoplasmosis
Infectious coryza
Colibacillosis
Salmonellosis
Antiviral vaccines
Marek’s disease
Newcastle disease
Infectious bursal disease
Infectious bronchitis
Infectious laryngotracheitis
Avian reoviruses
Avian influenza
Fowlpox
Avian encephalomyelitis
Egg drop syndrome
Antiparasite vaccines
Coccidiosis
Maternal immunity
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Poultry vaccines
Vaccination Programs for Broilers
Vaccination Programs for Layers
