One Practioner's Approach to Caprine Arthritis Encephalitis

Joan S. Bowen, DVM

Over the past fifteen years numerous articles, editorials and breeder's opinions concerning caprine arthritis encephalitis have appeared in dairy goat publications. Many goat owners and veterinarians are confused by conflicting information and are uncertain how best to develop a good disease prevention program.

Early papers stated that 80% of all United States origin goats were infected with CAEV, but these statistics were based on a highly biased group of animals exhibiting clinical symptoms (1,2). Subsequent studies sampling all animals in numerous herds report infection rates averaging 31% (3,4). There appears to be no difference in prevalence between sexes or among breeds. Some authors report that fiber breeds of goats such as Angora and Cashmere are resistant, but their low CAEV test rate probably reflects lack of exposure and not disease resistance. The prevalence of CAEV increases with age in herds with positive testing animals.

An owner cannot determine whether or not his herd is infected based on the presence or absence of clinical symptoms of CAE. No one knows exactly what percentage of CAEV-infected goats develop clinical disease, but in my practice it is less than 10% of CAEV-positive goats. The level of stress in the herd and the quality of management have a tremendous impact on whether or not goats develop clinical disease. Well-fed goats in good housing that are not crowded rarely show clinical disease. Currently, four syndromes are attributed to CAEV infection. Chronic progressive arthritis, chronic progressive pneumonia and weight loss associated with chronic disease are the most common symptoms of CAE. The least common expression of CAE is an ascending paralysis in otherwise healthy, afebrile kids. An unusual form of udder edema that is non-responsive to traditional diuretic therapy may be associated with CAEV.

Whether or not an owner needs to use a CAEV prevention program depends on whether or not the herd has the CAE virus, the nature of the owner's goals and what the owner does with the goats. The best place for an owner to start is by serologic testing of every animal in the herd to see if the virus is present in the herd. All animals should be tested because recently-infected goats and diseased goats whose immune systems are compromised may test negative even though they have virus. It may take as long as six months after infection for an animal to develop antibodies. Finally, no test is 100% accurate, and testing the whole herd reveals whether or not the herd has CAEV and allows a more accurate interpretation of individual test results.

Some breeders have advocated selecting for CAEV-positive animals with the mistaken view that they will be resistant to CAE. Unfortunately, the antibodies produced by infected goats are not protective antibodies, and do not help the goat fight off the virus. Instead, animals producing antibodies are permanently infected with CAEV. Whole herd testing can be expensive, but monetary losses from poor milk production and performance, ill health, early culling and lost stock sales in a CAEV-infected herd are usually far greater.

The goals and uses of the goats will determine whether or not it is economically beneficial for an owner to have a CAEV negative herd. If the owner is only raising his own herd replacements or slaughtering all kids at an early age for meat, it may not be profitable to use a CAEV prevention program. However, if the owner plans to sell animals, ship goats across state lines or attend any shows that require a health certificate, then that owner should use a CAEV prevention program with the long term goal of achieving a CAEV negative herd.

It is unethical and in many states illegal to sell an animal that is known to carry an infectious, contagious or communicable disease, and CAE is infectious, contagious and communicable. All states require a health certificate for goats to travel across state lines, and many shows and fairs also require health certificates. On all United States origin health certificates, the examining veterinarian must sign a statement that says to the best of his knowledge, the animals listed on the certificate are free of infectious, contagious or communicable disease. No veterinarian can legally write a health certificate for a goat that tests positive for CAEV as the goat is considered infected regardless of whether or not it shows symptoms of clinical disease. At this time there are no officially recognized federal or state regulatory programs developed for the eradication of CAEV from individual herds.

Once the status of CAEV in the herd has been determined, the owner can proceed with a prevention program. All CAEV-positive animals should be culled or separated from all contact with CAEV-negative animals, as long term direct contact is the primary means of transmission in adult goats. Negative animals with previous exposure to positive animals should be tested at 6 month intervals so that animals that test positive can be identified and removed. Due to the presence of CAEV in white blood cells and the possibility of transmission through direct contact, negative animals should not share pen space, housing, water devices or feeders with positive animals. There is no evidence at this time to implicate CAEV transmission during short term direct contact as would exist at goat shows or hand-breeding goats. Kids should be removed from the doe at birth and placed in separate, clean housing. It is possible for a doe shedding virus to infect her kids while licking them clean. Some dairymen tape the teats of CAEV-positive does to prevent kids from nursing the doe if the doe kids unattended. A potential complication in this scheme is prenatal transmission of virus; to date there is no evidence that this occurs.

High levels of CAEV are present in the colostrum and milk from CAEV-infected does, so kids should be fed colostrum that has been heated to 135 degrees F for one hour, followed by pasteurized milk or commercial milk replacer. Because serologic tests may not accurately identify which goats are infected with virus, colostrum and milk from both negative and positive testing does should be treated. The few trials that have tested commercial colostrum replacers in kids have had unsatisfactory results, so commercial colostrum substitutes are not recommended for use in goats at this time. Due to the difficulty of heat-treating goat colostrum, some herds have used cow colostrum, but this practice should be discouraged. Colostrum from the adult goat herd has protective antibodies against those diseases that occur in the herd and to which the young will be exposed. Most goat owners vaccinate their pregnant does for enterotoxemia and tetanus and newborn kids need colostral antibodies to these two diseases to protect them until they are old enough to vaccinate. On the other hand, few, if any, cattlemen vaccinate their cows for enterotoxemia and tetanus. Cow colostrum may also serve as a source of mycoplasma, Staphylococcal mastitis, or Johne's disease.

Occasionally, an owner may choose to retain CAEV-positive animals for economic reasons. Otherwise healthy animals can be very productive and could serve as a source of genetic material through embryo transfer and artificial insemination for developing a CAEV-negative herd. Because CAE is chronic and progressive, animals exhibiting clinical disease should be eliminated. Non- steroidal anti-inflammatory agents such as aspirin, phenylbutazone or flunexin, may make a diseased animal more comfortable, but there is no effective treatment available for CAE at this time.

If a herd owner is going to go to the effort and time consuming process of eliminating CAEV from their herd, they should be very careful to follow the prevention program diligently every day. It only takes a small amount of virus-contaminated milk or colostrum to infect a kid. Purchases from other herds must be carefully considered and minimized. At the present time, the length of time required for a positive adult to infect a negative adult through direct contact is not known, but once infected, the goat is infected for life. There is no data available at this time from which recommendations could be made concerning how many negative tests or how many years use of a CAE prevention program would be necessary before a herd owner could discontinue use of the prevention program and not risk reinfection with CAEV.

Sheep may harbor a related virus that causes ovine progressive pneumonia. Research trials have proven that goats exposed to and infected with OPP will develop clinical symptoms of CAE, while sheep exposed to CAE will develop OPP. If the goat producer has both sheep and goat housed together, then both species should be tested and raised on a prevention program.