Although vaccines are available against many infectious diseases of small ruminants, they labor under the difficulty that individual animals may be of low value, and consequently, the cost of vaccines must also be very low to make economic sense. This severely limits vaccine choices for these species. Additionally, many small ruminant operations are traditionally managed and function at a low technological level. Nevertheless, small ruminants are the most significant livestock species in many countries, especially in less developed or arid regions. Conversely, some sheep and goat products such as wool and mohair are of significant value, and the highly efficient sheep producing systems in countries such as Australia and New Zealand are important contributors to their economies. Therefore it is not surprising that these countries are the sources of some of the most innovative and effective small ruminant vaccines. As in other food animals, the veterinarian should be aware of the potential of injected vaccines to induce injection site lesions including blemishes in show animals. Reaction sites that require trimming at slaughter may result in a significant financial penalty. In general, subcutaneous injection in the caudolateral neck region is preferred, with an injection behind the elbow over the ribs as a possible alternative. Do not administer vaccines over the loin or hindquarters where the valuable meat cuts are located. As always, animals must be properly restrained to minimize struggling and to ensure proper delivery of the full dose of vaccine. The use of excessively long needles over 0.5 inches long should be avoided and they should be changed often. Remember, the needle used to withdraw vaccine from the bottle should not be used for injection. The most important vaccines given routinely to sheep and lambs in North America are those used to protect against Clostridial diseases. Specifically, the preferred vaccine is CD-T toxoid. This protects against enterotoxemia caused by Clostridium perfringens types C and D and also tetanus caused by Clostridium tetani. These Clostridial organisms can grow rapidly in an animal and secrete a complex mixture of toxins and enzymes. Seven toxinotypes (A–E) have been identified. Cl. perfringens type C causes a hemorrhagic enteritis (“bloody scours”) in suckling lambs during the first few weeks of life. It may be triggered by changes in feed or receiving too much milk. Vaccination of the ewe in late pregnancy, four weeks before lambing, offers protection. Cl. perfringens type D causes enterotoxemia (overeating disease) and pulpy kidney disease. It usually affects lambs over one month of age and is often precipitated by a change of feed. This results in abrupt changes in the intestinal microbiota and clostridial proliferation. This leads to sudden death in weaned lambs on a high carbohydrate diet. Like type C, the type D Cl. perfringens vaccine should be administered to pregnant ewes in late pregnancy to ensure adequate levels of antibodies in colostrum and protection of lambs for four to six weeks. Polyvalent clostridial vaccines contain a complex mixture of toxoids and bacterins from up to eight different species. They are normally administered in two doses and elicit responses that are protective for at least a year. Studies however suggest that antibody levels peak about 36 days after vaccination and are maintained up to 90 days before declining rapidly. They may be undetectable by 6 months. Factors other than antibodies must be responsible for the prolonged immunity seen in practice. As might be expected, large individual variations in response occur between animals. Additionally, some antigenic competition occurs in these complex mixtures. Cl. tetani and Clostridium novyi type B are immunodominant and induce the highest antibody levels whereas Clostridium septicum the lowest. Clostridial vaccines are available in 3-, 7-, and 8-way combinations, each containing a mixture of toxoids and bacterins. In addition to Cl. perfringens types -B, -C and -D, they may contain Clostridium sordellii, Cl. septicum, Cl. novyi, Clostridium haemolyticum, and Cl. tetani (Table 17.1). The 7- and 8-way vaccines are combination vaccines used to protect against other clostridial diseases such as malignant edema, “big head”, and blackleg caused by wound infections. These should only be used if these other clostridia are known to be present in a flock. Table 17.1 ■ Feeder lambs should be vaccinated at time of purchase, and 2–4 weeks later. Withdrawal time 21 days. Dichelobacter nodosus Corynebacterium pseudotuberculosis Withdrawal time 21 days. Do not use in known infected animals because a severe reaction may result. Withdrawal time 21 days. Annual revaccination. Withdrawal time 60 days. Do not use within 24 hours of dipping or spraying. Withdrawal time 21 days. Withdrawal time 21 days. Withdrawal time 21 days. This table is an example of a consensus vaccination program. 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. Be sure to follow the manufacturer’s recommendations on the label. Tetanus is a potential risk at docking and castration time. If their ewes were vaccinated when pregnant then revaccination of lambs is unnecessary. Vaccination at the time of docking or castration of lambs may not be protective because it takes about 7 to 10 days for antitoxic immunity to develop. Tetanus antitoxin should be used to provide immediate protection in such cases. Maternal antibodies will probably protect lambs and kids for about two months depending on their titer. Footrot is a common, complex, and important disease in the sheep industry. It is a painful and debilitating infection of the interdigital skin and is the most important cause of lameness in sheep. Footrot is primarily caused by a complex mixture of bacteria of which the most important is an anaerobic gram-negative bacterium, Dichelobacter nodosus. Infection by D. nodosus is preceded and accompanied by maceration and colonization of the interdigital skin by Fusobacterium necrophorum. Footrot causes significant losses because animals must be treated and/or culled. Based on the antigenicity of their fimbriae there are 10 major serogroups of D. nodosus (A-I and M), and within these serogroups there are additional serotypes. (Other classification systems have identified as many as 21 serotypes). Immunity is serogroup specific and multiple different serogroups may be found within a single sheep flock. Sheep and goats can be immunized against footrot using vaccines against D. nodosus containing either whole cell antigens or fimbrial antigens. Whole cell vaccines are rarely protective against heterologous subgroups. The fimbriae provide the major antigenic determinants (also called epitopes) and as such are the major protective antigens. These fimbriae are composed of repeating protein subunits called pilins. Pilin monomers, although antigenic are not protective. Denatured fimbriae are not protective either. However, fimbriae containing pilin polymers are as effective as whole cell vaccines. These fimbrial antigens may be derived by physicochemical methods or produced in recombinant organisms. Ideally footrot vaccines should contain antigens representing all the serogroups. A multivalent recombinant fimbrial vaccine containing ten serogroups (A, B1, B2, and C to M) is currently used in Australia and other countries. It is not ideal, and protection lasts for less than 10 weeks. Specific monovalent or bivalent vaccines, in contrast, can provide protection for up to 16 weeks or longer against homologous challenge. The reduced immunogenicity of multivalent vaccines appears to be caused by competition between their antigens. Attempts to produce a universal footrot vaccine have been unsuccessful. Autogenous, outbreak-specific footrot vaccines have also been used successfully. In flocks infected with just one or two serogroups, serogroup-specific fimbrial or whole cell vaccines may be effective and permit eradication of the disease. If flocks are infected by more than one serogroup then sequential vaccination cycles using monovalent vaccines given at three-monthly intervals over several years may also prove effective. Footrot is a seasonal disease because it results from animals standing in water and mud for prolonged periods. The vaccine should be given four months before the start of the “wet” season. Because duration of immunity is so short, sheep may require boosting every three to six months. Vaccination for footrot is simply another tool that should be used in conjunction with other procedures, such as regular foot trimming and foot soaking in disinfectant baths in an effort to eliminate the infection. This disease of sheep is caused by Corynebacterium pseudotuberculosis. It causes abscess formation in lymph nodes. If the organism becomes systemic it can cause a chronic wasting disease. C. pseudotuberculosis also causes an acute disease of buffalo called edematous skin disease. Caseous lymphadenitis results from wound infections and may be associated with poor hygiene during shearing. It is a robust organism and can persist in the environment for up to a year. A formalin-inactivated bacterin using biovar 1 is used in healthy sheep and goats over three months of age. Adverse reactions have occurred in goats given the sheep vaccine. Once the prevalence of infection is reduced to a low level then infected animals should be culled rather than vaccinated. Campylobacter fetus is one of the most common causes of abortion, late fetal loss in ewes, and the birth of dead or weak lambs. It is rarely a problem in goats. It may be prevented by vaccination given shortly before breeding. Two inactivated vaccines are available in the United States. They contain both C. fetus and Campylobacter jejuni. A third vaccine is available in Australia and New Zealand. This may contain multiple C. fetus strains (DL42, 6/1, 134) in addition to C. jejuni. Immunity develops in about 21 days. Do not use the vaccine licensed for cattle in sheep. Bronchopneumonia caused by Pasteurella multocida, Bibersteinia trehalosi, and Mannheimia haemolytica is common in sheep and goats of all ages. It may be especially important in young lambs that have received insufficient colostrum. These organisms are normal inhabitants of the sheep nasopharynx. In times of stress caused by shipping, weather extremes, or overcrowding they can invade the lungs and cause pneumonia. Several types of vaccine are available to control these infections. These include whole cell bacterins, leukotoxin-toxoids, and cell surface iron binding proteins. The whole cell bacterins rely on outer membrane protein antigens specific for each serotype. M. haemolytica has 12 serotypes of which A2 is the most prevalent. Unfortunately, A2 is poorly immunogenic in sheep. As expected, these bacterins work reasonably well against homologous serotypes, but are less effective in protecting against unrelated serotypes. Leukotoxins are critical virulence factors for M. haemolytica because they kill white blood cells. Addition of a leukotoxoid to these vaccines thus increases their efficacy. Like the outer membrane proteins, however, there is a great diversity in leukotoxin types. M. haemolytica needs iron for growth. It expresses iron-binding proteins (siderophores) on its surface. Antibodies against these siderophores will effectively reduce its growth. Like the outer membrane proteins and leukotoxoids these proteins differ between different bacterial strains. However, when used in a vaccine against the appropriate strain they can be very effective. The prevalence of respiratory disease in lambs increases beginning around three weeks of age. Maternal antibodies to these organisms appear to interfere minimally with vaccination of lambs so they can be vaccinated as early as 10 days of age. They should then be boosted three to four weeks later. A third booster may be needed around 12 to 14 weeks of age. If sheep are intensively housed and at high risk of respiratory disease then they may be revaccinated semiannually or annually. The gram-negative intracellular bacterium, Chlamydia abortus, causes enzootic abortion in sheep and goats worldwide. Infected animals shed large amounts of the agent in the diseased placenta and uterine fluids. Killed vaccines are widely available. A temperature-sensitive mutant (strain 1B) has been generated by inducing mutations in a wild type strain (AB7) using the mutagen, N-methyl-N’-nitro-N-nitrosoguanidine. This organism has a reduced growth rate at 39.5°C. It is used in some European countries. Unfortunately, strain 1B has been implicated in cases of vaccine breakdown. Genomic sequencing has indicated that its genomic sequence is identical to its parent strain. As a result, it is not attenuated and can cause serious disease outbreaks. Vaccine-identical strains have been isolated from cases of disease. Contagious ecthyma (orf, soremouth, or scabby mouth) is a skin disease of sheep and goats. The virus infects wounds around the mouth (often caused by abrasions or thorns such as from prickly pear cactus). As a result of these large painful lesions, the lamb or kid is unable to suckle. The infection may then spread to the ewe and cause mastitis. Soremouth vaccine is unique because it contains virulent virus obtained from the scabs of affected animals. Lambs should be vaccinated when around one month of age. A booster may be administered two to three months later. The vaccine is brushed on to scarified, woolless skin at a time and place chosen by the sheep producer. It is commonly administered by a scratch to the inner thigh or foreleg of a lamb. The vaccine may be available in a container with the needle attached and a dye to ensure a successful take. Otherwise the vaccine may simply be brushed over the scratches. Ewes are vaccinated inside the ear or under the tail. The site should be checked 7 to 10 days after vaccination to ensure vaccine “take.” If positive, the scratch will be raised and inflamed (Fig. 17.1). It produces an uncomfortable lesion, but after 12 to 14 days the scab falls off, the lesions heal, and the young animal is immune. They should be revaccinated annually. Ewes and does should be vaccinated well ahead of lambing. Animals should not be vaccinated immediately before a show. Vaccinated animals should be segregated from unprotected animals until the scabs have fallen off.
Sheep and goat vaccines
Vaccine administration
Antibacterial vaccines
Clostridial diseases
Disease/Vaccine
Vaccine Timing
Comments
Bacterial Diseases
Clostridial diseases—C, D, and T (CORE)
Vaccinate at 6–8 weeks, and revaccinate 3–4 weeks later. If ewes were not vaccinated for Cl. perfringens, their lambs may be vaccinated at 2–3 days of age and revaccinated 2–3 weeks later.
If not previously vaccinated, ewes must be vaccinated twice at 6–4 weeks before lambing, with the last dose 4 weeks before lambing. If previously vaccinated a single dose is sufficient. Revaccinate annually.
Footrot
Vaccinate before the anticipated problem. Revaccinate between 6 weeks and 6 months later,
Revaccinate every 6 months. Withdrawal time 60 days.
Caseous lymphadenitis
Vaccinate sheep and goats over 3 months of age. Revaccinate 4 weeks later on the opposite side of the animal.
May be combined with clostridia. Annual revaccination.
Campylobacter fetus-jejuni bacterin
Vaccinate before breeding and revaccinate in 60–90 days.
Annual revaccination.
Bacterial pneumonia (M. haemolytica and P. multocida)
Vaccinate breeding ewes and revaccinate 2–4 weeks apart. Revaccinate again 2–4 weeks before lambing. Lambs vaccinated under 3 months should be revaccinated at 4–6 months.
Revaccinate ewes annually before breeding or during pregnancy according to the label recommendations. May be combined with clostridia. Withdrawal time 21 days.
Chlamydia
Vaccinate 60 days before breeding and revaccinate 30 days later.
Administered with Campylobacter bacterins.
Anthrax
In known problem areas vaccinate twice at a 2–3 week interval.
Withdrawal time 42 days. Annual revaccination.
Viral Diseases
Soremouth
Vaccinate lambs at 1 month. Revaccinate 2–3 months later. Range lambs entering a feedlot should be vaccinated at least 10 days previously.
Use this vaccine well ahead of lambing or showing.
Bluetongue
Vaccinate lambs over 3 months of age and revaccinate 3 weeks before the breeding season or after lambing.
Do not vaccinate pregnant animals. Vaccine is strain specific so select it carefully.
Rabies
Vaccinate lambs over 3 months of age.
Revaccinate annually or 3 yearly depending on the vaccine.
Footrot
Caseous lymphadenitis
Campylobacter fetus
Bacterial pneumonia
Ovine enzootic abortion
Antiviral vaccines
Soremouth
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