Toxoplasmosis Abortion in sheep
What is Toxoplasmosis ?
Toxoplasmosis is caused by a parasite called Toxoplasma gondii. It results in
abortion and barrenness in ewes and as such can have a large economic impact.
How do sheep become infected?
Cats become infected by eating raw tissue containing the cysts. The Toxoplasma
then multiplies in the cat’s guts to produce millions of eggs that can contaminate food
stores, pasture and water supplies. The eggs can persist in the environment in this
way for months or years depending on local conditions such as moisture and
temperature.
The key source of infection for sheep is eggs in food and water and the key source of
infection for cats is tissue cysts in rodents such as mice and in small birds.
Infection before pregnancy
If the sheep becomes infected before she is pregnant they suffer a passing fever that
is not usually noticed by the farmer. After this infection they will develop a solid
immunity and will be effectively protected from Toxoplasmosis in the future. However
if the ewe becomes infected whilst pregnant the consequences can be very serious
for the developing lambs
Infection in early or mid pregnancy
If infection occurs in early pregnancy then the likely outcome is death of the lamb. If
this occurs very early then the lamb may be reabsorbed and the ewe will either return
to service or may remain barren. If lamb death occurs later in pregnancy the dead
lamb or lambs will be aborted usually a few days before the expected lambing date.
Infection in late pregnancy
Infection in late pregnancy is less likely to be fatal to the lambs as their ability to fight
infection improves as they develop, however they may still die and be aborted or
stillborn. Lambs that survive the infection may be weak at birth or die in the first few
days of life. It is not unusual for ewes to produce one dead lamb alongside one or
more live lambs. The dead lamb may be small or mummified.
Ewes that become infected during pregnancy also develop a solid immunity and
therefore animals that have aborted once to toxoplasmosis are very unlikely to do so
again.
Diagnosis of Toxoplasmosis
The best way to diagnose the infection is to submit the dead lambs plus the placenta
(cleaning) to the VLA centre after speaking with ourselves. Tests to look to antibodies
can be done on blood samples from aborted ewes. This again should be discussed
with ourselves.
There is often a subsidised testing scheme sponsored by one of the vaccine
companies.
Vaccination
The most effective way to protect sheep is to vaccinate them. The vaccine Toxovax
gives a life-long immunity with one vaccination. Replacement ewes can be
vaccinated from 5 months of age and non-pregnant healthy ewes can be vaccinated
at any time apart from the 4-week period before tupping. DO NOT VACCINATE
PREGNANT SHEEP. Toxovax is a live vaccine, which is fragile, so needs care when
handling it and should not be administered by susceptible people (pregnant women
or immunocompromised people).
Drug Therapy
Significant lamb losses due to toxoplasmosis may be reduced by feeding the
coccidiostat decoquinate (Deccox) during pregnancy. It should be added to the feed
to provide 2mg/kg bodyweight/day from mid pregnancy. It is most effective if it is
already being fed to susceptible ewes at the time the encounter the infection rather
than after infection is established. This should be discussed with ourselves before
being used. However this is usually a more expensive option than vaccination.
As always, please contact ourselves for advice and information.