Introduction/Causative Agent: Chlamydia psittaci is a gram-negative organism that causes abortions in sheep and goats. This disease is sometimes called chlamydiosis. Some strains of C. psittaci are also associated with other diseases such as keratoconjunctivitis (pinkeye), arthritis, and pneumonia. In 1950, Scottish scientists were the first to describe abortions due to C. psittaci. In Scotland the disease is known as "enzootic abortion of ewes." It was reported in the United states in 1958 and in Canada in 1976.
Clinical Signs: The most common symptom noted in sheep and goats is abortion. These abortions can affect as much as 30% of a sheep flock and even a higher percentage of a goat herd. The typical abortions occur in the last month of gestation. Occasionally, the disease can cause stillbirths and the birth of weak lambs or kids. Some females may have a fever and display a small amount of bloody vaginal discharge a few days before she aborts.
Chlamydia psittaci causes some severe changes to the placenta. Some of these changes may include a change of the placental membranes from the normal clear and shiny appearance to a more opaque and reddened appearance. The membranes can often take on a thick and leathery appearance, with a layer of yellow discharge. The normally pliable cotyledons (which attach the placenta to the caruncles on the inside of the uterus) can be thick and stiff.
Disease Transmission: The major sources of infection from one animal to the next are aborted fetuses, placentas, vaginal discharges, and infected feces. These tissues and substances will often contaminate feed and water sources consumed by non-infected animals. In most cases, the infected female will abort, mount an appropriate immune response to the Chlamydia psittaci organism, and clear the infection. However, it is important to note that some animals may become infected and not abort. These females can still spread the disease through vaginal secretions and their feces when they are stressed. Studies also indicate that some females may also become carriers for the disease. This means that she may spread the C. psittaci organism to other animals throughout her life.
Although transmission from male to female at breeding is possible, contaminating contact with an aborted fetus, placenta, vaginal discharge, and infected feces is the most common method of transmission. There is also evidence that ticks and insects may also play a role in the transmission of this disease.
Diagnosis: Evidence of abortions in the flock or herd is often an indication of a possible Chlamydia problem. However, diseases such as vibriosis and Q fever can also cause signs similar to Chlamydia abortions. When a Chlamydia abortion problem is suspected, the following samples should be collected and sent to a diagnostic laboratory:
Treatment: There are many different medications that can be used to treat Chlamydia psittaci infections. One of the most common is chlortetracycline (250 mg/head/day for 3 weeks) fed in the diet during an outbreak. Lower levels of chlortetracycline (80 mg/head/day) or tetracycline (400-500 mg/head/day) during the last 4-6 weeks of pregnancy is reported to prevent abortion. In milking herds, injections of long-acting oxytetracycline (20 mg/kg) are sometimes given during the last 6-8 weeks of gestation, followed by a final dose 3 weeks after giving birth. These injections are often given about 2 weeks apart depending on labor and cost issues.
Prevention: There is a killed vaccine approved for use in sheep that seems to be fairly effective. However, the vaccine causes some significant stiffness and soreness when used in goats. Because some combination vaccines have the potential to cause injury to the unborn fetus, the vaccines should be given a few weeks before the breeding season.
Attention should also be given to good management and sanitation procedures. This would include isolating any ewe or doe that aborts from the rest of the flock or herd, sterilizing pens and birthing facilities and equipment, and making certain that feed and water are not contaminated. It is also essential that any aborted fetus or placenta is properly buried or burned.
Public Health Concerns: Because Chlamydia psittaci is transmissible to humans (zoonotic), anyone who has contact with aborted animals or fetal membranes should wear rubber gloves and masks. Women who are pregnant are especially at risk and should avoid contact with a flock or herd during the lambing or kidding season. If infected, pregnant women can miscarry or experience a flu-like illness.