CAE (Caprine Arthritis Encephalitis) is a chronic, progressive viral disease in goats that primarily attacks the joints, brain, udder, and lungs. There is no cure and no vaccine. Once a goat is infected, it carries the virus for life, often spreading it silently through the herd before symptoms ever appear. CAE is one of the most significant health concerns in goat keeping, particularly in dairy herds, where infection rates in medium and large herds can exceed 75%.
What Causes CAE
CAE is caused by a lentivirus, a type of retrovirus in the same family as the virus that causes HIV in humans (though CAE cannot infect people). Lentiviruses are defined by their slow, persistent nature. They integrate into the host’s DNA and remain there permanently, gradually causing damage over months or years. The virus is closely related to Maedi-Visna virus in sheep, and together they’re classified as Small Ruminant Lentiviruses.
The “slow burn” character of lentiviruses is what makes CAE so tricky to manage. A goat can be infected for years without showing any outward signs, all while shedding virus to herdmates and offspring.
How CAE Spreads
The single biggest transmission route is colostrum and milk. When an infected doe kids and her newborn nurses, the virus passes directly to the kid through ingestion. Most kids that seroconvert (develop detectable antibodies) do so between 3 and 6 months of age, reflecting that initial exposure in their first days of life.
Horizontal transmission, meaning spread between adult animals, also plays a significant role. Prolonged close contact allows the virus to move through a herd over time. Shared milking equipment, particularly contaminated milking cups, can transfer the virus between does. There’s also growing evidence that respiratory transmission may be more important in goats than previously thought, similar to how the related virus spreads efficiently through the airways of sheep.
Intrauterine transmission, where kids are infected before birth, was long considered rare. However, newer studies using PCR testing have found viral DNA in a considerable proportion of kids taken from their mothers immediately after birth, suggesting in-utero infection happens more often than once believed.
The Four Clinical Forms
Arthritis
Joint disease is the most recognizable form of CAE in adult goats. The virus targets the carpal joints (the “knees” of the front legs) most often, causing progressive swelling, stiffness, and pain. Affected goats gradually lose mobility. The joints may become visibly enlarged and firm to the touch. This form develops slowly, typically worsening over months to years, and is the reason “arthritis” is in the disease’s name.
Encephalitis
The brain form of CAE primarily affects young kids, usually between 2 and 6 months old. Kids develop progressive weakness in the hind legs, loss of coordination, and eventually paralysis. This form can progress rapidly and is often fatal. It’s less common than the arthritic form but far more dramatic and distressing to witness.
Hard Udder (Indurative Mastitis)
Sometimes called “hard bag,” this form is especially common in does kidding for the first time. The udder becomes firm and swollen, appearing full, but produces little to no milk. The tissue of the udder is progressively replaced by fibrous, non-functional tissue. For dairy goat owners, this is a devastating presentation because the doe’s milking career is essentially over. Infected does also persistently produce virus-laden colostrum and milk, making them a continuous source of infection for future kids.
Pneumonia
CAE can cause a chronic interstitial pneumonia, a slow inflammation deep in the lung tissue. This form is less dramatic than the others and can be easy to overlook, but it contributes to gradual weight loss and poor condition. Affected goats may have a persistent mild cough or labored breathing that worsens over time.
Many infected goats never develop obvious clinical signs. They remain carriers, silently maintaining the virus in the herd. This is one of the core challenges of CAE: the disease is far more widespread than the visible symptoms suggest.
How Widespread CAE Is
CAE prevalence varies enormously depending on herd size and management. A 2025 study in Hungary illustrates the pattern well. Among very small herds of 20 goats or fewer, only about 5% of herds were infected. But in medium herds (51 to 100 animals) and large herds (over 100), herd-level prevalence jumped to roughly 75 to 78%. Once the virus gets into a larger herd, it spreads efficiently: within infected herds, about 58% of individual goats tested positive on average.
Dairy goats tend to have higher infection rates than meat goats, largely because of the close, prolonged contact during milking and shared colostrum practices common in dairy operations.
Testing and Diagnosis
The most common screening tool is a blood test that detects antibodies to the virus. The standard version, called AGID (agar gel immunodiffusion), is widely used but can miss infections, especially in animals that haven’t yet developed a strong immune response. More sensitive ELISA tests catch more cases but still rely on the goat’s immune system producing detectable antibodies, which can take weeks to months after infection.
PCR testing detects the virus’s actual genetic material in the blood rather than waiting for the immune response. This approach can identify infection 25 to 45 days earlier than antibody-based tests, a meaningful advantage when you’re trying to catch and remove positive animals before they spread the virus. In one study, PCR detected the virus in 25% of goats that tested negative on ELISA, likely animals in the early “window period” before seroconversion.
For the most reliable results, combining both approaches works best. Blood-based PCR testing for proviral DNA has shown 100% specificity in goats with clinical CAE, making it the strongest confirmation tool available.
Prevention and Herd Management
Because there is no treatment or vaccine, preventing CAE comes down to breaking the transmission cycle. The cornerstone strategy involves separating kids from infected does immediately at birth, before they nurse.
Kids should be fed heat-treated colostrum or colostrum from confirmed CAE-negative does. To inactivate the virus, colostrum can be heated to between 133 and 139 degrees Fahrenheit and held at that temperature for one hour. This destroys the virus while preserving enough of the beneficial antibodies the kid needs. Pasteurized goat milk or milk replacer can be used for ongoing feeding.
Beyond kid management, keeping a CAE-free herd requires regular testing of all animals, typically every 6 to 12 months, and prompt removal or strict isolation of any goat that tests positive. New animals brought into the herd should be tested before introduction and ideally quarantined and retested after 60 days to account for the seroconversion window.
Milking hygiene matters too. Cleaning and disinfecting milking equipment between animals helps prevent mechanical transmission. Because CAE is an enveloped virus, it’s relatively fragile outside the body compared to hardier non-enveloped viruses. Enveloped viruses generally survive on surfaces for only hours to a few days, and standard disinfectants containing chlorine or iodine are effective against them. This is one small advantage: thorough cleaning of equipment and housing does reduce environmental transmission risk.
Living With CAE in Your Herd
Death directly from CAE is uncommon in adult goats. The disease instead causes a slow decline in productivity and quality of life. Infected does produce less milk, arthritic goats lose condition and mobility, and the persistent immune response drains energy that would otherwise go toward growth and reproduction. The economic impact comes from reduced milk yield, premature culling, and the ongoing cost of testing and management protocols.
If you’re buying goats, asking about the herd’s CAE status and requesting test results is one of the most important steps you can take. Many reputable breeders participate in voluntary CAE prevention programs and can provide documentation of negative test results. Starting with CAE-negative animals and maintaining strict biosecurity is far easier than trying to eliminate the virus from an already-infected herd.