Goat diseases - Caprine retrovirus
F.J. Keenan, revised by R.O. Morton, Biosecurity,
DPI&F
Caprine retrovirus (CRV), formerly known as Caprine arthritis encephalitis (CAE) or 'Big Knee' is a serious disease for the goat industry.
This DPI&F Note describes the clinical signs and methods of spread of CRV, and outlines some control measures.
Why is Caprine retrovirus a problem?
CRV is a chronic progressive disease which adversely affects health, production and life expectancy in both milk and fibre goats. Production losses of 25% and more have been reported.
Export markets for live goats require CRV free certification. This disease also affects domestic markets with a premium paid for goats from CRV free herds.
How much of a problem is Caprine retrovirus?
CRV is a major problem for the dairy goat industry and a small but significant problem for the fibre goat industry.
Many goat owners are eradicating CRV from their herds and the Department of Primary Industries and Fisheries coordinates an official Caprine Retrovirus Control Scheme on behalf of the goat industry. (For details see the protocol for the Caprine Retrovirus Control Scheme)
Caprine retrovirus occurs worldwide but only naturally infects goats. The virus is very closely related to Maedi-visna which causes a very similar disease in sheep overseas.
Clinical signs of Caprine retrovirus
The signs in CRV infected goats are age dependent. In kids less than 6 months of age CRV causes encephalitis. In older goats the virus primarily affects joints although adult goats may sometimes develop a persistent pneumonia.
CRV has a long incubation period lasting from a few weeks to many months.
Infection usually lasts for life.
Encephalitis
In kids less than 6 months the virus affects the brain and spinal cord causing a rapid progressive paralysis of the limbs and usually death. Some affected kids also develop a moderately severe pneumonia.
Arthritis
CRV primarily affects the surface tissues of joints, causing arthritis.
Usually a painful enlargement in both front knees is seen. Symptoms often occur several weeks after first kidding but may be seen as early as a few months or as late as a few years of age.
Affected goats show intermittent lameness, a proppy gait, a rough coat and often develop a wasting condition.
Pneumonia
Some infected adult goats have pneumonia which becomes progressively worse and fails to respond to antibiotic treatment.
Affected goats often suffer severe respiratory distress and have a poor tolerance to exercise. The coat becomes rough, animals lose weight and some animals develop varying degrees of arthritis.
Methods of spread
The main method of spread of CRV is from doe to kid through the milk. This is important when undertaking control strategies.
The virus does not appear to readily cross the placenta and most kids are infected after birth. Semen does not appear to be a method of spread.
Some transmission of infection occurs by direct contact; however the exact mechanism is unknown. Spread between dry goats is uncommon; spread between lactating and kidding goats is much more common.
Only limited spread of CRV occurs under extensive grazing conditions. This accounts for the low prevalence of CRV in fibre and feral goats.
Control of Caprine retrovirus
Control or eradication of CRV from an infected herd is possible but requires diligence and persistence. Control programmes must take into account the method of spread, the incubation period of the disease and the time required before infected animals show a positive blood test.
Strategies include:
1. Blood test to identify infected goats and remove them from the herd. If this is not possible then establish a separate 'infected' herd. The infected herd must be kept separate using either solid walls or double fencing.
2. Snatch birthing - remove the kids from does before they have any chance to suckle. To prevent suckling some owners cover the udders of does due to kid. Some goat producers have had their best success if kids are also washed immediately after snatching to remove any blood or mucus.
3. Rear kids on cow's colostrum and cow's milk or artificial replacements. It helps to rear kids in isolation from the rest of the herd until the virus is eradicated.
4. Segregate your herd from any herd which is not CRV free. This includes taking reasonable precautions when:
- attending shows, sales and goat clubs
- sending does to an outside buck
- swapping or buying kids (even a healthy day-old kid may be infected)
- feeding kids with milk from sources not certified CRV free
- using second hand equipment
Remember if you are undertaking a CRV control programme it is unlikely to be a short-term programme - it may take several years for success. Setbacks do occur and you should design your control programme to at least minimise the effect of any setback.
Currently there are no legal restrictions on the sale or movement of CRV infected stock in Queensland. Consequently, entry of goats to a herd from other than a CRV free source is at the owner's risk.
This DPI&F Note is also published on the DPI&F's PrimeNotes CD-ROM.
Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. The Department of Primary Industries and Fisheries Queensland has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter.
Last updated 10 June 2005
