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Department of Agriculture New South Wales


Goat health - CAEV (big knee)

Agfact A7.9.1, second edition 1986

Robyn Wells, Veterinary Officer

Division of Animal Health

Seven Hills


Caprine arthritis encephalitis virus (CAEV) infection is a newly recognised but widespread disease of dairy goats. `Big knee' is the common name given to the disease because the virus can cause swelling and arthritis in the carpal (knee) joints.

The virus has a long dormant period in goats before signs of disease are observed. Not all infected goats develop clinical signs but they can still transmit the virus. The most common method of transmission is in the colostrum and milk. Transfer is therefore mainly from an infected doe to her kid. Dairy goats of all breeds are affected. Fibre goats and sheep can also become infected if fed on infected goats' milk or colostrum.

There is no evidence at present of human infection.

THE DISEASE

Goats infected with CAEV may show signs of:

  • encephalitis (inflammation of the brain) in kids which causes progressive nervous disorders.

  • arthritis (inflammation of the joints, hence 'big knee').

The CAE virus has also been implicated as a factor in goats showing signs of ill thrift, pneumonia and decreased milk production.

SIGNS OF DISEASE

The encephalitic form of the disease is rare and is seen only in kids 1 to 4 months of age. Initially the kids have a defective gait. This develops into a marked hind limb paralysis which leads to the death of the kid.

The common big knee or arthritic form of the disease initially starts as an enlargement of the tendon sheath and joint capsules. This is observed as a swelling around the knee joints although it can and does affect other joints. This form of arthritis is never painful, or hot to the touch.,


However, as the virus causes more damage to the joints, they swell further and become painful, leading to lameness. The synovial (joint) membrane becomes thickened, the synovial fluid becomes discoloured and cloudy, and the smooth surfaces of the joint are destroyed.

Swollen joints first appear in goats from 10 months to 3 years of age. Affected goats go lame, displaying a proppy gait. Severely affected animals lie down a lot and walk on their knees to avoid bringing together the joint surfaces. Rough hair coat and chronic wasting are indications of the disease. Fever is absent. Chronic wasting may result in death.

TRANSMISSION

As the virus is excreted in the colostrum and milk of infected does, kids become infected at their first suckle. This is the main method of transmission of the virus. Other methods of spread are poorly understood and thought to be of less importance. One such method includes prolonged direct contact.

DIAGNOSIS

Diagnosis is based on clinical signs, a blood test, or both. The blood test is available from the Department of Agriculture. The blood sample should be collected by your veterinary practitioner and is accompanied by a special form, available from your local veterinary office.

The blood test is used only as an indicator in adult goats to determine if the herd can be classed as positive or negative for the CAE virus. A negative result from an adult goat does not necessarily mean that the goat is free from the disease, especially where there have been no control measures taken to eliminate it. During the early period of infection, goats do not have antibodies to the virus present in the bloodstream and therefore do not react positively to the test.

This is because the test detects the antibody produced by the goat against the virus and not the presence of the virus itself.

TREATMENT

There is no known treatment for this infection in goats.

CONTROL

When goats positive to the CAEV blood test are found in a herd, the whole herd must be classified as 'at risk' or `suspect'. The fastest method of eradication of CAEV is to separate all kids from the does at birth before they suckle. It is imperative that they are not fed goats' colostrum or milk. The kids can be fed instead on artificial milk replacer or cows' colostrum and milk.

Goats' colostrum can be used if it is pasteurised at 54°C for 30 minutes. Goats' milk can be pasteurised to destroy the virus if kept at a temperature of 73°C for 15 seconds or at 62°C for 30 minutes. It is most important that these temperatures and times be adhered to or the virus will survive and the whole CAEV eradication program thus becomes worthless. It is therefore better to use cows' milk or milk replacers which are known not to contain virus.

Because not all the methods of transfer of the CAE virus are understood, separation of kids from infected adults is recommended for a distance of at least 2 metres. This is thought to eliminate the possibility of transfer by direct contact (horizontal transfer) of the virus.

If these guidelines are adhered to, CAEV infection can eventually be eradicated from goats.

CONCLUSIONS

To control and eradicate CAEV from your goats:

  • determine if your adult goat herd can be classified as positive or negative for CAEV using a blood test

  • if there are positive goats, the whole herd will be classified as positive

  • isolate kids at birth before they suckle, and feed them on
    cows' colostrum and milk or artificial milk replacers

  • keep kids that have been deprived of colostrum and goats' milk separate from the herd by at least 2 metres. Arrange a blood test to confirm their negative status

  • cull your old infected herd as young CAEV-free stock become available to replace them.

FURTHER INFORMATION

For further information, contact your veterinary practitioner, veterinary inspector or the Department of Agriculture.


© 1986 N.S.W. Dept. Ag.