Article Index "Chlamydia" Article Index

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By: N.C. Palmer, Vet Lab Services, Guelph
Reprinted December, 1990
Original Document
About the Author

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Chlamydiae, previously known as psittacosis-lymphogranuloma-venereum, Miyagawanella, and Bedsonia, are bacteria which differ from most other bacteria in that they can multiply only in living cells. There are two species, Chiamydia trachomatis, which infects humans, and Chiamydia psittaci which infects other animals. Each species has many strains and one of these strains causes abortion in sheep and goats. Strains of C. psittaci are also associated with other diseases such as keratoconjunctivitis (pinkeye), arthritis and pneumonia but the different diseases rarely occur together in the same flock.

Abortion due to chlamydiae was first described in 1950 from Scotland where it is known as "enzootic abortion of ewes". It was reported in the U.S. in 1958 and in Alberta in 1976. The first Ontario cases were diagnosed in 1977 and many infected sheep flocks have now been identified. The disease also occurs in goats in Ontario. Information about chlamydia infections in sheep probably is applicable to goats.

Signs of the Disease
The disease is characterized by abortion, usually towards the end of pregnancy, stillbirths and the birth of weak lambs or kids. The placenta is often severely damaged and may be retained in the uterus after abortion has occurred. The placental membranes instead of being clear and shiny, are opaque, reddened and thick, and often have a leathery appearance and a layer of yellow exudate. The cotyledons, which attach the placenta to the caruncles on the inside of the uterus, are thick and rigid instead of being pliable. Sometimes the fetus has a potbelly due to the collection of fluid in the abdomen and enlargement of the liver. In a newly infected flock, 30% of ewes may abort. In newly infected goat herds, the incidence may be even higher. When infection is established on a farm, rates of 5-10% are common as new animals are introduced to the infected environment.

Transmission of the Disease
Although transmission from ram to ewe at breeding is possible, the major sources of infection of clean animals are aborted fetuses, placentas, vaginal discharges, and infected feces. Chiamydiae are quite hardy and can remain viable for several days especially in cold weather. Animals pick up the infection by inhaling or consuming infected material such as food, water and dust particles. The newly infected animal will show no signs but when she becomes pregnant the chlamydiae may multiply in the placenta and cause the disease. Two important features of the disease should be noted: (1) an animal may be infected but may not abort, in fact she may have a normal lamb, but she may still spread the infection when stressed at lambing or at some other time; (2) although a ewe usually only aborts once in her lifetime she may remain a carrier capable of spreading the disease. The bacteria are carried in the intestine and in some lymphoid tissues.

Chlamydia abortion may be diagnosed in several ways. Signs in the flock are often enough to raise suspicion but are not reliable because they are often very similar to those of "vibrionic" and coxiella (Q Fever) abortion. Three types of laboratory tests are used in diagnosis. The first involves examination of the fetus, its stomach content, and especially the placenta under the microscope. Even a fragment of placenta may be useful. The second involves the growth of the bacteria in incubating hens eggs. The best material to use for this test is also placenta. Third, a blood test is available. Two clotted blood samples are needed, one taken at the time of abortion and the other taken two to three weeks later. A positive result is indicated by a "rising antibody titre" i.e. an increase in the level of blood antibody from the first to the second sample. The blood test must be used along with one of the other tests and several ewes (aborting and nonaborting) should be tested.

Control and Treatment
Unfortunately there is no practical way of identifying an infected or carrier animal. Newly-infected animals have a low, short-lasting antibody titre even though they may show a high titre if they abort later. However, even this high titre only lasts a few months.

Control measures are, therefore, based on accurate diagnosis and good hygiene such as isolation of aborting ewes and cleanup of infected pens. Quaternary ammonium compounds are satisfactory disinfectants. It is well recognized that crowding at lambing time increases the risk of abortion in the same or subsequent lambing season.

Chlamydiae are susceptible to chlortetracycline. It is said to prevent abortion when administered at the rate of 80 mg/head/day during pregnancy. In the face of an outbreak 250 mg/head/day for 3 weeks has been recommended, and appears to be effective.

A vaccine1 is available and generally is considered to be effective in sheep2. In Britain it is used in flocks with recurrent chlamydia abortion. Chlamydia does not appear to cause abortions in consecutive years in Ontario flocks, but there is limited information on this subject. If abortions do occur in consecutive years, a new diagnosis must be made since Coxiella, "vibrio", Toxoplasma, or some other agent could be responsible.

1 "Ovine Enzootic Abortion" vaccine, Wellcome: Burroughs Wellcome Inc., CP 500, Lachine, Que’. H8S 4B1

2 The information regarding the vaccine is included for the convenience of livestock owners and their veterinarians. Inclusion of this information is not an endorsement of the product by the Veterinary Laboratory Services Branch.

About the author: This Factsheet was authored by: N.C. Palmer, Veterinary Laboratory Services Branch, Guelph For more information contact: Your local Ontario Ministry of Agriculture, Food and Rural Affairs office.

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