9 Diseases of the Respiratory and Circulatory Systems Respiratory disease is extremely prevalent in commercial growing and fattening pigs. It accounts for a considerable amount of deaths and perhaps more importantly of lower growth rates. The importance of respiratory disease is not so high in outdoor pigs and is of little importance in pet pigs. The predominant signs are dyspnoea, tachycardia, pyrexia and coughing (Fig. 9.1). There are other signs which are not seen in all respiratory diseases, e.g. blueing of the ears and twisting of the snout. Signs of respiratory disease will lead to other problems, e.g. violent coughing will lead to rectal prolapse and twisting of the snout will lead to a nasal discharge. Diagnosis on history and clinical signs may be possible but confirmation is likely to require post-mortems coupled with virus and bacterial examination. Respiratory health status of a herd can be made by lung examination of slaughtered pigs at the abattoir or by group blood sampling. The mode of infection is from pig to pig, i.e. mixing of pigs. This can be at an on-farm level or by incoming pigs. In small herds there is always a danger from pigs going to shows or the borrowing of a boar. Some respiratory disease may be airborne and carried on the wind. Prevention is best achieved by keeping a closed herd and by carrying out strict biosecurity. Veterinary surgeons should be mindful of not risking the introduction of disease by their routine visit. Ideally they should be ‘pig free’ for 3 days before a visit to a high health status herd. Vaccination is extremely useful. Good ventilation and temperature control are vital. Antibiotics should be used responsibly. A study in Belgium (Del Pozo Sacristan et al., 2012) demonstrated that chlortetracycline was able to decrease the prevalence of pneumonia lesions when administered in the feed during two alternate weeks starting at the onset of clinical respiratory disease. Performance losses and clinical signs in a herd infected with Mycoplasma hyopneumoniae were numerically, but not significantly, reduced. The causes of respiratory disease are, in the main, viruses, bacteria and endoparasites. Inclusion body rhinitis (IBR) is a very rare respiratory disease which is lethal to young piglets but signs, except transitory sneezing, are rarely seen in adults. It is also called porcine cytomegalovirus infection (PCMV). As the name suggests, it is caused by a cytomegalovirus. The virus is found worldwide with up to 90% of herds in the UK affected. However, clinical signs are rarely seen. The virus may be spread across the placenta causing early embryonic death. There is sow-to-sow transfer and also boar-to-sow transfer. In naive herds baby pigs under 2 weeks of age will show respiratory signs. These include rhinitis, sneezing and respiratory distress. Up to a quarter of the litter may die. If weaner pigs are infected they will be ill with anorexia, pyrexia, coughing and have a nasal discharge. Virus may be isolated from the nasal discharge, which is often purulent and may sometimes contain blood. Postmortem will reveal a serious rhinitis, but there is no damage to the turbinates or twisting of the snout. The diagnosis can be confirmed by an ELISA or PCR. There is no vaccine available but once a herd has experience an outbreak the clinical signs seem to disappear. Abortion rates are low. Clinicians might advise antibiotics for the secondary infections in the face of an outbreak to lessen the mortality in the baby pigs. Fig. 9.1. A pig in respiratory distress. This is a very serious syndrome caused by an arterivirus. It is also called porcine epidemic abortion and respiratory syndrome (PEARS). It is known to pig keepers in the UK as ‘blue ear’. As the name implies, PRRS will cause reproductive problems in sows and respiratory signs in fattening pigs. It is found throughout the world except it is not seen in Australia or New Zealand. The main spread of the infection is by pig-to-pig contact using the respiratory route. It can also be spread venereally and by AI. The adult pigs do not normally show a fever but laboured breathing and inappetence for 2–4 days. The infection will spread through a whole herd of adults in 10 days. There will be early embryonic deaths, abortions and stillbirths. Skin changes occur more commonly in growing pigs, showing the classic blue ear appearance. Baby pigs often show oedema of the eyelids and conjunctivitis. Mortality may not be high in well-managed herds. The post-mortem picture may well be confusing as often there are other respiratory pathogens involved. ELISA and PCR will confirm the diagnosis. Serology retrospectively may be helpful after an abortion storm particularly if rising titres can be demonstrated. Being a viral disease there must be secondary bacterial infection, but treatment with a variety of antibiotics is rarely helpful. NSAIDs certainly have a place for treatment. Injectable preparations may be given to individual bad cases. Treatment with oral paracetamol or aspirin in the early stages is worthwhile. There are several commercial vaccines available, which are very effective. Post-weaning multisystemic wasting syndrome (PMWS) is extremely important in commercial pigs. It is caused by a circavirus. It is obviously important in backyard pet pigs obtained from commercial stock. There is a vaccine available. Ideally backyard fattening pigs should be vaccinated before movement. Naturally, good hygiene practices should be paramount, as well as avoiding stress. Once the pigs are showing signs antibiotic treatment is rarely worthwhile and so euthanasia should be carried out. PMWS, as the name suggests, is a multisystemic disease (see Chapter 13). These viruses are specific to pigs. They are influenza A viruses. The common strains are H1N1, H1N2 and H3N2. They causes coughing and dyspnoea. These viruses are found in Europe, Asia and North America. They are not found in Australia or New Zealand. The virus enters the upper respiratory tract and multiplies in the bronchial epithelium. There is a viraemia. Often the disease is made considerably worse by other infections, e.g. viruses like PRRS, bacteria like Pasteurella multocida and parasites like ascarids. The virus may damage fetuses in utero, causing abortions and stillbirths. The fever is very severe for the first 24 h with rectal temperatures up to 42°C and many pigs in an outbreak will be prostrate. Coughing may be severe enough to cause vomiting. The conjunctiva will be very inflamed causing excess lacrimation. There may be a bilateral nasal discharge (Fig. 9.2). The disease may blow through in 2 weeks with the majority of the pigs recovering. The few that remain prostrate should be destroyed. In the individual pig warmth will aid recovery which is often quite rapid without treatment. Recovery may be accelerated by injectable or oral NSAIDs including oral aspirin. Adult pigs as well as growing pigs are affected. On post-mortem severe necrotizing pneumonia will be seen. The virus antigen may be found by reverse transcriptase PCR (RT-PCR). It must be remembered that other pathogens are also likely to be present. The virus may be spread by birds, particularly turkeys. The virus will survive in meat. It should be stressed that meat scraps must not be fed to pigs. There is no licensed vaccine available in the UK but there are vaccines available in the rest of the world. Fig. 9.2. A bilateral nasal discharge. This is a highly contagious respiratory disease, caused by Actinobacillus pleuropneumoniae. The disease causes problems worldwide. The bacterium is relatively delicate but will survive outside the body at ambient temperatures in damp conditions. It will also survive in cold fresh water. Transmission is by aerosol or nose-to-nose contact. It is an acute disease with a mortality of 30% in non-immune pigs. There is a fibrinous pleurisy, which may be heard on auscultation. There is a very high rectal temperature. If there is cyanosis death will follow in a few hours. There are often other pathogens involved. If it is not fatal, pigs will show chronic respiratory signs for weeks and will not gain weight, particularly if other respiratory pathogens are involved. Chronically infected pigs should be destroyed on humane grounds. On post-mortem in acute cases there is a blood-stained fibrinous pleurisy. These lesions become greyish as the disease has developed. Histopathology will show infarcts and alveolar haemorrhages in a bronchopneumonia. Diagnosis can be confirmed on culture. There are several different serotypes which can be separated by ELISA tests. Certain serotypes are more common in different areas, e.g. serotype 2 is the most common serotype found in the UK. Serotypes 8, 3, 6 and 7 are also relatively common. Antibiotic treatment is rarely effective, as the antibiotics do not reach the affected areas. The organism is actually sensitive to most antibiotics commonly used in pig practice. High doses given for a minimum of 3 days coupled with injectable NSAIDs may help clinical cases. All in-contact pigs must be treated with high doses of the same antibiotic by mouth. There are commercially available vaccines. Practitioners should be advised to check the serotypes covered by the vaccine against the serotypes which are affecting the pigs. This shows as sneezing in young piglets. It is rarely fatal, but it is progressive and causes atrophy of the turbinate bones with distortion of the nasal septum, resulting in shortening and twisting of the upper jaw. It is caused by a toxigenic strain of P. multocida. Deaths occur if there is an additional Mycoplasma infection. It is found throughout the world but the incidence is not high. The disease also may be linked with Bordetella bronchisepitca infection (see below). P. multocida is a Gram-negative coccobacillus. Isolation of this organism is not diagnostic per se as it is only certain strains which are toxigenic. The organism is spread by close contact, with the sneezing aiding the spread. Pigs under 2 months of age are affected. The first signs are tear staining and nose bleeds. The twisting of the snout occurs only later in the disease process. The main economical effect of the disease is the poor growth rates. To try to establish the effect of the disease in an infected herd, the snouts of pigs are graded at the abattoir. There are normally five grades of the condition recorded as abnormal. Grade 1 is a slight deviation. Grade 2 is a slight atrophy. Grade 3 is a severe atrophy. Grade 4 is a loss of a turbinate. Grade 5 is a loss of all of the turbinates. When an outbreak is suspected the diagnosis is made mainly on clinical grounds. Practitioners should examine the baby pigs carefully to rule out other causes of damage to the face of the pig. Some of these are congenital, e.g. cleft lip (cheiloschisis), absence of a lower jaw (agnathia) and wrynose (craniofacial asymmetry). Baby pigs will develop septic conditions in this area due to poor technique used when clipping canine teeth. A definitive diagnosis can be made from nasal swabs using an ELISA. PCR tests are also available.
Respiratory Diseases
Introduction
Respiratory Diseases Caused by Viruses
Inclusion body rhinitis
Porcine reproductive and respiratory syndrome
Post-weaning multisystemic wasting syndrome
Swine influenza
Respiratory Diseases Caused by Bacteria
Actinobacillosis
Atrophic rhinitis
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