Toxoplasma Abortion in Sheep
A protozoal parasite, Toxoplasma gondii, causing 20-30% of ewe abortions in this country.
The Disease Cycle:
Cats, notably kittens, are important in the parasite life cycle and the parasite cysts shed in cat faeces may be eaten by pregnant ewes. An important factor is hay feeding – wild cats frequently raise kittens in haybarns, the hay becomes soiled and the use of this hay in winter ensures that a large number of ewes can come in contact with the infective cysts. These resistant cysts may also last up to two years in hay or soil.
However, toxoplasmosis also occurs when no hay is used and it is worth noting that a single gram of faeces from a cat that is shedding toxo (not all do) contains enough toxoplasma to abort up to 2000 ewes!
Importantly, the parasite is not passed from ewe to ewe and once infected, the ewe is strongly immune.
Depending on the stage of pregnancy at which the ewe is exposed to Toxoplasma, you may see:
- a. More dry ewes, as very early abortions may go unnoticed.
- b. Small, premature lambs aborted in late pregnancy.
- c. Weak lambs born near full-term but die soon after birth.
With so much opportunity for infection, Toxoplasmosis has been shown to cause an average 8% drop in lambing percentages, even on farms where a Toxoplasmosis problem was not thought to exist.
There are few consistent specific signs of Toxoplasma infection in aborted lambs and these should be submitted to the veterinary clinic for post mortem and sampling.
What do you do?
Until Toxoplasma is confirmed as the cause of the abortions, you should collect and destroy all products of abortion and isolate aborted ewes for 7-10 days. This is aimed at limiting spread of possible Campylobacter abortion, the other major cause of abortion in New Zealand sheep.
Unfortunately, there is nothing you can do to halt the outbreak this year.
In future, a vaccine, TOXOVAX, can be used to artificially infect non pregnant ewes so that they have lifelong immunity.
The vaccine costs approximately $1.62 excl. per ewe and is given to replacement stock at least four weeks before tupping. In the first year, as a minimum, all incoming replacement ewes should be vaccinated – either hoggets or two tooth ewes.
Note that if you intend to mate hoggets you will need to make your selection and get the vaccination done at least a month before mating begins. Use of Toxovax when mating/lambing hoggets is considered “best practice”.
Ideally, in severe cases, older ewes should also be vaccinated, especially four and six tooth ewes.
Aborted ewes will already be immune.
The vaccine is manufactured to order so you must place your order at least three weeks before the date required.
NOTE: This is a live vaccine and, as such, pregnant women should not handle the vaccine.