Brucellosis is an infectious disease caused by bacteria of the genus Brucella. Various Brucella species affect sheep, goats, cattle, pigs, dogs, and other animals. In infected ruminants, brucellosis commonly causes abortion during the second half of gestation. Sheep are less susceptible than cattle, and brucellosis is not considred a common cause of abortion in sheep. Ovine brucellosis mainly affects rams, causing lesions in their reproductive organs.
Cache Valley Virus
Cache Valley Virus is an occasional cause of abortion outbreaks in sheep. It is spread by mosquitoes to pregnant ewes. If a ewe is infected at less than 28 days of gestation, the embryos usually die and are reabsorbed. If a ewe is infected after 45 days of pregnancy, there are usually no adverse effects.
If infection occurs between 28 and 45 days of gestation, the fetuses usually develop the “A-H syndrome,” resulting in various congenital abnormalies affecting the central nervous system. Ewes that are infected usually show no signs of disease and develop a good immunity that lasts for several years. Cache Valley virus is similar to Akabane Disease except that it only affects sheep.
Chlamydia
(enzootic abortion, EAE)
In the U.S., Chlamydia is the most common cause of abortion in ewes. It is transmitted from aborting sheep to other susceptible females. Ewe lambs are usually the most susceptible on farms where the organism is present. The bacteria which causes enzootic abortions in ewes is called Chlamydia psittici. Chylamydia causes abortion during the last month of pregnancy and may also result in the birth of lambs that die shortly after birth.
The organism may also cause pneumonia in young lambs, but the chlamydia species that causes abortion is not associated with conjunctivitis or arthritis. Chlamydia abortions can usually be stopped or reduced by treating the entire flock with tetracycline. A vaccine is available. It should be administered 60 days prior to breeding and repeated in 30 days, then annually just prior to breeding.
Leptospirosis
Sheep are generally more resistant to leptospirosis than cattle, swine, and most other domestic animals. Abortion due to this disease may occur during the last month of pregnancy. A blood test of aborting sheep will confirm diagnosis. The problem can be prevented with annual vaccination with a 5-strain leptospirosis vaccine.
Q Fever
Q Fever is a disease caused by the bacterium, Coxiella burnetti. The disease is found worldwide except for New Zealand. Sheep, goats, and cattle are most likely to get Q fever. The most common sign of Q fever is abortion during late pregancy. However, most animals do not show any signs of illness. Animals get Q fever through contact with body fluids or secretions. Q fever is zoonotic (transmissble to people).
Rift Valley Fever
(infectious enzootic hepatitis)
Rift valley disease is a viral disease of sub-Saharan Africa. The virus attacks the liver and causes symptoms ranging from fevers and listlessness to hemorrhage and abortion rates approaching 100% in pregnant sheep. It is transmitted by mosquitos. There is no specific therapy for infected animals.
Vaccination of animals against RVF has been used to prevent disease in endemic areas and to control epizootics. Rift Valley fever has not occurred in the United States. However, there has been concern that it could become permanently established in the U.S. if it does enter the country. Rift Valley fever is more deadly than West Nile virus.
Salmonella
In the U.S., salmonella abortion is a distant fourth in frequency as a cause of abortion in sheep, but probably occurs more often than recognized. The two major factors determining whether a pregnant ewe will abort from Salmonella are stress on the ewe and the number of Salmonella bacteria the ewe ingests.
Abortions may occur earlier in gestation, but are most common in the last month of gestation. Most of the ewes show diarrhea and some will die from metritis, peritonitis and septicemia. Healthy lambs may also contract the disease and die.
Toxoplasmosis
Toxoplasmosis is common cause of abortion in ewes. It is caused by Toxoplasma gondii, a protozoan parasite which causes coccidiosis in cats. Toxoplasma abortion in ewes follows ingestion of feed or water that has been contaminated with oocyte-laden cat feces. The organism migrates to the placenta and fetuses causing their death and expulsion. Ewes will abort during the last month of pregnancy or give birth to dead or weak lambs that usually die from starvation.
Infection in the first two months of gestation results in embryonic death and reabsorption. There is some evidence that Rumensin® and Deccox® will partially prevent toxoplasmosis in pregnant ewes. Limiting cat populations and preventing contamination of sheep feed and water with cat feces will help to prevent disease outbreaks. There is no vaccine available in the U.S. for toxoplasmosis.
Vibrio
(Campylobacteriosis, vibriosis)
Vibrio is the second most common cause of abortion in ewes. Abortion during the last month of pregnancy, stillborn lambs, and the birth of weak lambs are common signs of vibrio abortion The organisms which cause vibrio abortion are Campylobacter jejuni or Campylobacter fetus. Ewes are infected by oral ingestion. The incubation period from the time of infection and abortion is only two weeks. Vaccination can be effective in the face of an outbreak.
Feeding of antibiotics has also been shown to be effective. Disease spread can be prevented by isolating the aborting ewe, disposal of the fetuses and membranes and disinfecting the affected area. Infected ewes usually recover after aborting and are immune to reinfection. A vaccine is available. It should be administered prior to breeding and repeated in 60 to 90 days, then annually.