Yes, Caprine Arthritis Encephalitis (CAE) is contagious. The virus spreads primarily through infected milk and colostrum from doe to kid, but it can also pass between adult goats through prolonged close contact. Once a goat is infected, the virus persists for life, making prevention and herd management critical.
How CAE Spreads From Doe to Kid
The single biggest transmission route is milk. When a kid nurses from an infected doe, virus-carrying white blood cells in the colostrum and milk are absorbed intact through the kid’s gut lining. This makes the first hours and days of life the highest-risk window. Pooled colostrum or milk is especially dangerous because one or two infected does can spread the virus to every kid in the group.
In utero transmission and infection during birth are possible but uncommon. Research on cesarean-derived kids found that only 2 out of 32 showed signs of possible prenatal infection, and even those cases couldn’t fully rule out post-birth exposure. For practical purposes, the milk is the problem.
How CAE Spreads Between Adults
Adult-to-adult transmission is slower and less efficient, but it does happen. Any body fluid containing white blood cells carries the virus: milk, blood, saliva, tears, and respiratory secretions. In close confinement, goats sharing feeders, water sources, or breathing the same air in a barn can pass the virus through these fluids.
The conditions matter. In one study, casual short-term contact between infected bucks and uninfected does during breeding did not result in transmission. Airborne spread was not demonstrated either. But when uninfected does were milked alongside infected does in a dairy setting, a high percentage became infected in less than 10 months. Under non-dairy conditions with weaned goats, it took over 12 months of continuous direct contact before horizontal transmission could be detected. So the risk scales with how closely and how long goats are housed together, and shared milking equipment appears to be a significant factor.
Can CAE Spread to Sheep or Other Animals?
CAE virus belongs to a family of small ruminant lentiviruses closely related to Maedi-Visna in sheep. The host specificity isn’t absolute. Mixing sheep and goats, or feeding milk from one species to the other, can transfer viruses between them. The virus sometimes adapts to and persists in the new host species.
Cattle are not a practical concern. Newborn calves have been experimentally infected with CAEV, but the infection caused no symptoms and the virus disappeared within four months. No other animal species are considered hosts.
Why Infected Goats Can Never Clear the Virus
CAE is caused by a lentivirus, the same family as HIV. Once inside the body, it inserts its genetic material into the DNA of the goat’s own immune cells. Researchers have found viral material in macrophages (a type of white blood cell) throughout the body: in the lungs, liver, spleen, lymph nodes, brain, spinal cord, joints, mammary gland, intestinal lining, kidneys, and thyroid. The virus essentially hides inside the immune system itself, which is why no goat ever clears the infection. There is no cure, and no commercial vaccine is available.
What CAE Looks Like in Goats
Many infected goats show no symptoms for months or even years, which is part of what makes the virus so easy to spread unknowingly. When clinical signs do appear, they depend on the goat’s age.
Kids under six months can develop the encephalitis form: weakness in the hind legs, uncoordinated movement, and progressive paralysis. This presentation is less common but more dramatic.
Adults typically show the arthritis form. You may notice swollen joints (especially the knees), stiffness, reluctance to stand or walk, or a goat walking on its knees. Other signs include weight loss, a firm or swollen udder that produces little milk (sometimes called “hard udder”), and coughing or labored breathing from lung involvement.
Testing Your Herd
Because so many infected goats look perfectly healthy, blood testing is the only reliable way to know your herd’s status. The two main tests are AGID (agar gel immunodiffusion) and ELISA. Both detect antibodies the goat’s immune system produces against the virus, not the virus itself. This means a recently infected goat may test negative before its immune response develops. Most veterinarians recommend testing at least once a year and retesting new animals before introducing them to the herd.
A single negative test doesn’t guarantee a goat is free of the virus. It can take weeks to months after infection for antibodies to reach detectable levels. If you’ve recently purchased a goat or had a known exposure, testing again after 60 to 90 days gives a more reliable picture.
Preventing Transmission in Your Herd
Prevention centers on breaking the milk-to-kid chain. The most effective approach is removing kids from infected does immediately at birth, before they nurse. Kids should then be fed heat-treated colostrum: heated in a water bath to 56°C (133°F) for one hour. This temperature inactivates the virus without destroying the essential antibodies in the colostrum. After the first feedings, switch to pasteurized goat milk, pasteurized cow milk, or milk replacer.
For adult goats, reducing close confinement lowers risk. Avoid shared feeders and water troughs between known positive and negative animals. In dairy operations, milking negative does first and sanitizing equipment between groups helps prevent the kind of transmission seen in milking parlors. Keeping positive and negative goats in separate housing is the most reliable barrier, though not always practical for small operations.
When bringing new goats into your herd, quarantine and test them before allowing any contact with your existing animals. Buying from herds with a documented testing history reduces the chance of introducing the virus in the first place.