Introduction/Clinical Signs:
Caprine arthritis encephalitis (CAE) is a viral infection in goats throughout the world, which may lead to arthritis of the joints and, on rare occasions, inflammation of the brain (encephalitis). This virus can also cause problems with the respiratory system, causing pneumonia in adult goats. It may also cause mastitis (often called "hard udder" or "hard bag") and weight loss. Most infections occur in goat kids less then 6 months of age, yet many goats that become infected with CAE virus show no clinical signs.The most common sign associated with a CAE infection is joint problems. These problems can occur in almost any joint, but are found most often in the knee (carpus). One or multiple joints can be involved at any one time. The first signs that are noticed are often subtle. The goat may not walk normally, have difficulty getting up, and may have decreased feeding activity. Some goats may have swollen joints, with or without pain. These swellings feel cool and are not painful to the animal when touched. As the problem progresses, the goat becomes mildly to severely lame because of arthritis. The animal may lose weight and look unthrifty. When the changes in the joint become severe, the joint may become immovable (ankylosed) and held in a flexed position. When this occurs in the knee, the goat may actually have to walk on its knees. Unlike other infectious causes of arthritis, these goats do not have a fever.
The viruses that cause CAE and ovine progressive pneumonia (OPP) are very similar, and the neurological forms of both diseases look almost identical. Information about the neurologic form of CAE can be found on F618.
Disease Transmission:
The CAE virus is closely associated with white blood cells; therefore, any body secretions that contain white blood cells (colostrum, blood) are potential sources of virus to other goats in the herd. The CAE virus is primarily transmitted to kids via colostrum in the first few feedings after birth. Transmission can occur if a susceptible animal is exposed to contaminated milk, water, or feed; and when contaminated needles or equipment (tubes, drenching guns, tattooing equipment) are used. Transmission between adult goats is considered to be rare, except during lactation. In these situations, the virus is spread from one animal to the next in the milking parlor. Currently, CAE infections in sheep are not known to occur outside of laboratory situations.Diagnosis:
Serological (blood) testing (ELISA, AGID, or PCR) is the best way to identify infected animals. A positive test means the goat has been infected with the CAE virus and has made antibodies against the virus. These goats are potential shedders of the virus, especially if lactating. Newborns that have received virus-free colostrum that contains CAE antibodies may also test positive for several months because of passive transfer of maternal antibodies. Because of this, it is recommended to retest these animals a second time when they are 4-6 months old. Realize that antibody rich colostrum does not provide the newborn any protection from the CAE virus.A negative result means that a goat is either not infected or is producing amounts of antibody too low to be detected. Because of situations where infected animals test negative (false negatives), all animals should be retested on a regular basis.
Some experts also recommend testing all sheep present on the farm. This is because there is some evidence that sheep can be infected with CAE under the right conditions. Many times the serological tests, however, cannot tell the difference between animals infected with OPP and ones that are infected with CAE. Therefore, additional testing and observations are sometimes necessary before a diagnosis of OPP or CAE can be confirmed.
Treatment: There is no known treatment for CAE. The only thing that can be done is to keep the animal as comfortable as possible. This may include anti-inflammatory agents (phenylbutazone or aspirin), rest, and easy access to feed and water.
Prevention: Yearly testing is suggested for herds that are primarily virus-free. Testing before kidding is recommended. Any new animals brought into the herd should be quarantined and tested before introduction. Animals that test negative, but are in herds where positive animals are present, should be tested more often than once a year. This is important when adjusting the milking order so that all negative animals are milked first.
Special attention should be given to raising CAE-free kids. This means pasteurizing colostrum and removing the kids from their dams immediately after birth to be raised away from their mothers. The removal of kids from their mothers must take place before the mother has time to lick and clean the newborn and before the newborn nurses. Colostrum from any doe may be heated to between 133-138° F (56 to 59° C) and held at that temperature for one hour to inactivate the virus. An accurate thermometer is important. It is recommended to use a water bath or double boiler to regulate the temperature more closely. A large batch may be heat treated and frozen in smaller sized portions for later use (about 250 mLs pint per kid). If heated higher than 140° F, the usefulness of the colostrum will be greatly reduced due to denaturing of proteins, including antibodies. After colostrum is fed, heat treated goat milk should be fed. The following procedure can be used to heat treat milk (not colostrum): Using a double boiler system, bring the desired amount of milk to 165° F and keep it there for 15 seconds. Let the milk cool, and then feed it to the kid. See B520 for additional suggestions on heating colostrum and milk.
Raw Milk and the CAE Virus: There is no evidence that the CAE virus can infect humans; however, there are some serious human pathogens which have been shown to be transmitted through raw milk.