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What causes toxoplasmosis:
Toxoplasma gondii is a parasite that can infect cats, but uses humans and sheep as an intermediate host. Sheep get infected by pasture, food or water contaminated by cat faeces. Cats get infected by eating infected mice or birds. The Toxoplasma eggs in cat faeces survive for long periods (>500 days) at room temperature in moist conditions.
Clinical signs of toxoplasmosis:
The signs range from resorption or abortion if infected early in pregnancy, to no signs at all if infected very late in pregnancy. Most signs occur if infected in mid-pregnancy when lambs are stillborn, weak or mummified. The placenta can show dark red cotyledons with white spots.
Diagnosis of toxoplasmosis:
As abortion can be caused by many organisms and also stress it is important to get a diagnosis. It is best to send the placenta (!) and the fetuses as fresh as possible to a veterinary lab, so correct samples can be taken. Blood samples of aborted ewes can be taken for antibody testing, but this only indicates the ewe has been infected in the past and does not necessarily proof it as the cause of abortion.
Treatment of toxoplasmosis:
Treatment of toxoplasmosis is not easy. If the lambing period is quite long, decoquinate (Deccox) can be added to the food, and prevent lamb mortality in ewes before infection becomes established. If diagnosed early before serious damage is done to the placenta, some sulfa antibiotics can be effective.
Prevention of toxoplasmosis:
Young cats are the most likely source of infection, although sick older animals can shed infection again as well. Limiting breeding of cats can be useful. Once an outbreak of abortion has started, it is advised to dispose of dead lambs and infected placentas. Sheep to sheep transmission is not very common, but is it advised to disinfect the lambing pens with 5% ammonium (few minutes), 95% ethanol (for an hour) or 10% formalin (for 24 hrs) to kill the eggs.
The best way to prevent toxoplasmosis is by vaccination. Ewes need to be vaccinated once at least 3 weeks before tupping. Ewe lambs can be vaccinated from 5 months of age. Vaccination lasts for two lambing seasons.
Zoonotic implications of toxoplasmosis:
Toxoplasma infected lambing flocks can pose a very real threat to pregnant women. Pregnant women should therefore stay away from (lambing) sheep at all times.
In an emergency please telephone (01793) 522483 (24hrs).
Drove Veterinary Hospital, 252 Croft Road, Swindon, Wiltshire SN1 4RW. |
