African Swine Fever

This highly contagious disease with a high mortality is caused by an iridovirus. It is a totally different virus from that causing CSF. Clinically it is impossible to differentiate the two diseases. It is found mainly in Africa but there have been outbreaks in Southern European countries. It occurs in Central Asia. It also occurs in the Caribbean and South America. It is a notifiable disease in the UK. It affects domestic pigs and wild boar. It does not cause clinical signs but occurs in bush pigs (Potamochoerus porcus) and wart-hogs (Phacochoerus aethiopicus). Both these species of pig are carriers and spread the disease to domestic pigs. The disease can be spread by pig lice and soft ticks. The virus will survive for long periods of time in meat products. The severity of the clinical signs is extremely variable but in the majority of outbreaks they are acute after an incubation period of 5–7 days. Affected pigs will have a high rectal temperature and be hyperaemic. They will be anorexic, depressed and recumbent. They often vomit and show respiratory distress. There may be epistaxis and bloody diarrhoea. Death will follow in 48 h. The severe disease may result in neurological signs. If the less severe signs occur there is a lower viraemia and pigs will recover. There may be some transient joint inflammation. The first manifestation may be abortions. Diagnosis in live pigs is made by PCR and a variety of methods have been described. Virus isolation and diagnosis can also be carried out by replication of virus in primary macrophages and detection of infected cells by the characteristic haemadsorption of red blood cells around infected cells (Coggins, 1968). Diagnosis can be made by serum ELISA but this has a reduced sensitivity compared with PCR. At post-mortem the spleen, tonsils and gastro-hepatic lymph nodes should be submitted for virus isolation. This can be verified on PCR. There are pete-chiae in the kidneys, lymph nodes and heart.

Strict import controls on pigs, pig products and pig by-products should prevent the spread of this disease. However, illegal imports, accidentally or intentionally, continue to cause this disease to spread. The ban on swill feeding reduces the risk of exposure of pigs to illegally imported infected meat products. However, accidental exposure, particularly in farms with outdoor pigs and pet pigs, remains a risk. The infection of wild boar from exposure to infected meat is also possible, which could increase the risk of spread to domestic pigs if they come in contact with wild boar. Wild boar constitute a risk of trans-boundary spread in areas where wild boar are common.

There is no treatment or vaccine available. However the prospects for vaccine development are good.

This rapidly fatal disease in cattle is not nearly so acute in pigs, although of course it is still a zoonosis and is notifiable in the UK and throughout the world. It is extremely rare in the UK and most other temperate countries; however it is seen more often in tropical countries. The disease is caused by Bacillus anthracis. While the organism is in the pig it may multiply and is sensitive to penicillin. If the blood or other body fluids are allowed to leak out of the pig into the fresh air, the bacteria will form spores which are very resistant to boiling and most disinfectants. These spores can survive in the soil for decades. It is therefore vital that infected pigs are either burnt or buried in quicklime. Pigs can develop three forms: the enteric form, the septicaemic form and the skin form. Pigs can become infected with the enteric form in various ways: ingesting the spores in the soil when rooting, from biting flies and most importantly from eating contaminated foodstuffs. Pigs can develop the septicaemic form as a result of the enteric form. The organism normally gets into the circulation via the tonsils. Pigs can also become infected with the skin form through contamination of wounds. The septicaemic form is rare in pigs. The most common manifestation is swelling of the throat with difficulty in breathing. Pigs will have a raised rectal temperature and will be depressed and anorexic. Mortality is under 20%. However, recovery will be slow and often areas of skin become necrotic and slough off. Diagnosis can be carried out by seeing the organism with its tell-tale capsule in smears taken from subcutaneous oedema of the throat and stained with MacFadean’s stain. Smears should be taken on to blood slides and air-dried. These should then be fixed by heat from a naked flame. Old methylene blue should be applied to the slide when cool and left for 30 s. It should be washed off with running water. Once the slide is dry it can be examined under oil emersion. The rectangular bacteria in chains will take up the stain and the capsule will be clearly seen as a translucent covering.

It must be remembered that anthrax is a zoonotic disease and therefore the wisdom of treating pigs with anthrax is in question. Certainly the meat from infected pigs should not be used for human consumption.

There is a vaccine available in certain countries but it is not licensed for use in the UK or elsewhere in the EU.

Classical Swine Fever

Clostridium novyi Infection

This bacterium used to be called Clostridium oedematiens. It is type B Clostridium novyi which normally affects pigs. It is possible that type A will also cause a similar condition. It occurs worldwide. It causes sudden death in adult pigs and large fat pigs because it produces a powerful toxin. It replicates only in an anaerobic situation. This occurs in the liver of a pig affected with chronic pneumonia or severe enteritis. On post-mortem the liver is full of gas and looks like foam rubber. Diagnosis can be confirmed on FAT or PCR on the liver tissue. Post-mortem changes occur extremely rapidly, so trying to confirm the diagnosis by seeing the organism on smears is unreliable.

There is no treatment as the animals will be found dead. However, controlling the pre-disposing conditions such as the pneumonia or enteritis with antibiotics might be helpful. There is no licensed vaccine for pigs in the UK. Sheep vaccine can be used on the cascade system and seems to be effective.

Foot and Mouth Disease

FMD is a highly contagious disease which occurs as an acute disease in pigs. It is caused by an aphthovirus. It is notifiable throughout the world. It is not found in the UK and mainland Europe except occasionally there may be incursions from the East. It is not found in the USA, Australia or New Zealand. It is found in Asia, Africa and South America.

There are seven different serotypes. ‘A’, ‘O’ and ‘C’ are classically described as European serotypes. They are the only serotypes which have been found in Europe. They are also found in Asia and Africa. The Asia serotype is restricted to Asia. The three South African serotypes, ‘SAT 1’, ‘SAT 2’ and ‘SAT 3’, are found in Africa and on occasions have been found in Asia.

The virus is extremely contagious and can infect pigs by inhalation, ingestion and by skin wounds. The most important for an initial infection is when pigs eat an infected piece of meat. However, when an outbreak has become established then the respiratory route becomes extremely important. There is a massive outpouring of virus in exhaled air. With housed pigs kept in modern pig houses with good ventilation, there is a ‘plume’ effect. This can spread the virus over wide areas.

Clinical signs are seen in all ages of pig. They are very marked and unlikely to be missed by observant practitioners. There will be a sudden onset of severe lameness in the whole herd. Piglets and growing pigs will actually squeal if made to move. All ages will have hunched backs and be reluctant to move. They should have their feet washed with water, ideally from a hose, to clean off any debris and then the small raised areas will be seen. These rapidly turn into vesicles approximately 1 cm in diameter. Vesicles will be seen on the tongue and the snout, which make the pig produce excessive saliva. Disinfectants should not be used to clean the feet as they will lessen the chances of virus isolation.

Leptospirosis

This can be considered to be a multisystemic disease as it can cause meningitis, jaundice and fever in young pigs. However its main manifestation occurs in the reproductive system of sows which leads to abortions and stillbirths.

Malignant Catarrhal Fever

Malignant catarrhal fever (MCF), a cattle disease which is caused by ovine herpes virus type 2 (Ov-HV2), has been recorded in pigs. The main clinical signs are: corneal opacity, ocular discharge and respiratory distress. Diagnosis is made by PCR. The disease is contracted from sheep.

PDNS is normally a disease of large fattening pigs. It often occurs at the same time as PMWS. There is no direct link between the two diseases. Some authorities suggest that there is a link between PDNS and Pasteurella multocida. The syndrome is likely to be a hypersensitivity reaction to either a virus or a bacterium. Affected animals have confusing clinical signs. The pigs are normally pyrexic. The most obvious other sign is the marked, purplish, widespread skin coloration. This is mainly on the hindquarters. There is no treatment and euthanasia is advised. On postmortem there is general lymphadenopathy with the kidneys swollen and petichiated. There is also pneumonia.

Porcine Reproductive and Respiratory Syndrome

PRRS is a disease which affects all ages of pig when there is no immunity in the herd. This situation is now rare as not only is the virus widespread but also there are many good vaccines available. Sows will show respiratory distress but not marked pyrexia. Only a few animals will show the classical sign of blue ears. Abortions will occur and as time goes on there will be a larger percentage of stillbirths and returns to service. There will be a sharp rise in the number of weak piglets born. These will have conjunctivitis. Many will not survive. The number of deaths in the weaner pens will rise. The pigs will have pneumonia. Post-mortems will not be very helpful as there will be a rise in the number of other conditions usually seen in the herd. Frozen tonsil samples will reveal the virus. Antibiotics will not be effective in controlling the disease. Vaccination is the key.

Post-weaning Multisystemic Wasting Syndrome