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Pregnancy confers an increased risk for disease in both animals and people, due to changes in the immune system function. These changes affect cell mediated immunity (CMI) to a greater degree than humoral immunity. Thus, those infections that are controlled largely by CMI may be more easily established during pregnancy. Some of the zoonotic disease agents for which CMI plays an important role in resistance include Chlamydia psittaci, Coxiella burnetii, and Toxoplasma gondii.
Chlamydia psittaci (EAE - Enzootic Abortion of Ewes)
This agent is an important cause of abortion in sheep. It is seen on many South Dakota farms and has been associated with abortion in women after exposure to infected sheep. The common clinical symptoms in the women included fever, cephalgia, nausea, and malaise, with some cases presenting with sore throat, vomiting, and photophobia. Affected women may develop more serious symptoms, including disseminated intravascular coagulation and renal, hepatic, or myocardial involvement.
The epidemiology of EAE in sheep is poorly understood. In sheep, the agent is transmitted by contact with infected uterine/vaginal discharge or aborted fetal tissue. In the human cases described, infections appeared to take place when the women were in contact with lambing ewes or with ovine abortions. It is likely that this is the time period of highest zoonotic risk. It would be best for pregnant women to avoid contact with aborting or sick ewes, and to minimize contact with lambing ewes. If contact is unavoidable, gloves should be worn, hands washed thoroughly after contact, and barn clothes removed before entry to the house. Additional stressors and fatigue should be avoided so to not further compromise the pregnant women's natural resistance.
Coxiella burnetii (Q fever)
Coxiella burnetii is a rickettsia with predilection for the uterus and mammary gland. Sheep, cattle, goats, and cats can be infected with this organism. The prevalence of infection in these animals is probably high, but the infections are nearly always asymptomatic. The organism can be infectious in raw, but not pasteurized, milk. Large numbers of organisms can be shed in uterine and placental discharges following a normal delivery. The organism is very hardy in the environment and forms spores in adverse conditions.
The infectious dose for humans is believed to be exceedingly low. Infections may be acquired by direct contact with uterine discharges, contaminated wool or straw, or by indirect contact with inanimate objects (clothes) contaminated by uterine discharges. Large outbreaks of Q fever have been associated with exposure to dust from roads travelled heavily by sheep.
Q fever in humans is typically a mild, self-limiting febrile illness. Immunosuppressed or pregnant women may exhibit more severe symptoms including pneumonia, hepatitis, fetal death, and neurologic manifestations. In as many as 10% of patients, Q fever can result in chronic endocarditis.
Physicians should be aware that Q fever may present as an unresponsive flu-like disease. Pregnant women should minimize exposure to uterine and placental discharges, especially those of sheep. The potential for aerosol infection is pronounced in situations of high sheep density and dusty conditions. If contact with sheep is unavoidable, pregnant women should wear protective garments, avoid excessive dust, and possibly wear a dust filtering mask.
Toxoplasma gondii
Toxoplasma gondii is a recognized pathogen causing abortion in sheep. The disease in sheep is largely a result of exposure to feed contaminated with the Toxoplasma gondii oocyst. These oocysts are shed by cats for a short period of time in the cat's life.
The potential for direct transmission of toxoplasmosis from an aborted sheep fetus to humans is low. However, if toxoplasmosis abortion has been diagnosed, then it is likely that a cat was present on the farm that was shedding the oocyst. Therefore, the potential for cat-human transmission did (or does) exist.
Pregnant women should minimize contact with cat feces, litterboxes, or places cats are known to defecate. Toxoplasma oocysts are usually shed for only a short period (several weeks) of a cat's life. However, if cats are allowed to defecate in livestock feed, they can contaminate the feed and expose both sheep and humans.
If a cat is kept as a pet, pregnant women should not empty the litterbox - insist that another family member do that. On the farm, cat populations should be controlled to the point that the population is manageable. After petting or handling the cat, hands should be washed. It is usually not necessary to completely eliminate cats to avoid toxoplasmosis.
There are many other potential zoonotic organisms, including Salmonella, Listeria, and Campylobacter. In general, pregnant women need to exercise special caution and avoid contact with sick animals, especially those exhibiting diarrhea and any animal aborting. Personal hygiene is very important. Handwashing and changing clothes before entering the home are a must. Lastly, the kitchen is not the place for cleaning syringes, needles, or equipment. The potential for contamination of food preparation surfaces is great. As always, proper rest, nutrition, exercise, and stress avoidance will help minimize health problems in situations where contact with animals is unavoidable.