Introduction/Causative Agent: Toxoplasmosis is caused by the parasite Toxoplasma gondii, which is ingested by cats when they eat raw meat or birds and mice. Domestic cats are the host species where the parasite reaches full maturity. This parasite lives in the small intestine of the host animal and its eggs are shed in the feces. Once shed, the eggs are hardy, and have been known to live in the environment for over 1 year. Once the eggs have hatched, they are able to infect sheep and goats, and many other vertebrates, including humans. Sheep and goats are often infected with Toxoplasma gondii when they graze or feed on roughage contaminated with cat feces. Toxoplasma gondii can cause abortion and stillbirths in adult ewes/does. It can also cause the birth of weak lambs and kids.
Clinical Signs: The most common clinical sign noticed in sheep and goats is abortion. In most cases, the adult ewe or doe does not show any signs of infection before or after the abortion. If clinical signs are noticed, they usually include fever and neurological problems. Ewes that are infected before breeding usually will not abort. Those that are infected early in their pregnancy (30-60 days) will often resorb or mummify the fetus.
Diagnosis: One on-farm way to determine if Toxoplasma gondii is a possible cause for an abortion is to examine the placenta. The cotyledons will often have small areas of necrosis and calcification that appear grayish to yellow. These areas are better identified after the cotyledons are washed with saline. Noticing these lesions is not a guarantee that Toxoplasma gondii is the problem, but it does place it higher on a list of possible causes.
Another way of diagnosing this disease is by testing a blood sample taken from the fetus or a newborn (before it has had a chance to nurse any colostrum). It is also possible to test the placenta, and fetal fluids, brain, muscles, or lungs for the presence of the Toxoplasma gondii organism. If these samples are collected, they should be chilled and sent on ice, but not frozen.
Samples of the ewe’s or doe’s blood can be tested for antibodies; however, finding a high titer to Toxoplasma gondii can often be misleading due the fact that high blood titers can remain from one season to the next. On the other hand, if a ewe does not have any titers, then the cause of the abortion is not likely to be Toxoplasma gondii. Other tests such as the indirect fluorescent antibody (IFA) test and the enzyme-linked immunosorbent assay (ELISA) can also be used for diagnosis.
Treatment: Once a diagnosis has been made, there are usually not many animals that will require treatment. If a ewe or doe is extremely ill from the infection, supportive care (fluids and nutrition support) is required. Sulfamethazine and products like monensin (15-30 mg/head/day) can be used to help control infections.
Prevention: In the United States, there is no vaccine currently available for toxoplasmosis. Therefore, the best prevention is not allowing cats to have access to sheep and goats, particularly when sheep and goats are pregnant. This would include preventing cats from defecating on pastures and hay used for feeding. Cats should also be kept away from feeders, water, and bedding used by sheep and goats.
Some reports indicate that feeding monensin (Rumensin) or decoquinate (Deccox) throughout gestation can decrease the number of abortions. Monensin should be fed at 15-30 mg per head per day, and decoquinate should be fed at 2 mg per kg of body weight per day.
Public Health Concerns: Because toxoplasmosis is transmissible to humans (zoonotic), anyone who has contact with cat feces should wear rubber gloves, and take caution to not contaminate equipment and common areas. It is also essential that when a sheep or goat aborts, extra care should be taken to avoid contaminating contact with the aborted fetus, placenta, and fetal fluids. Unless they are to be used for diagnostics, the fetus and placenta should be burned or buried to prevent the spread of disease. Humans become infected with toxoplasmosis when they accidentally ingest Toxoplasma gondii parasite eggs. Women who are considering pregnancy and think they may have come in contact with toxoplasmosis in the past, should see their physician before becoming pregnant. This disease can cause miscarriage, stillbirth, and serious birth defects in a human fetus. Pregnant women should avoid handling the fetus, placenta, or fluids associated with an abortion in a ewe or doe. They should also avoid contact with cat feces.
Infected female animals may shed Toxoplasma gondii in their milk. Therefore, it is essential that all sheep and goat milk be pasteurized before human consumption.