Download Infectious abortion remains one of the major flock health problems

Infectious abortion remains one of the major flock health
problems faced by sheep farmers and can have a significant
impact on production. Costs are variably quoted as between
£40 and £65 per aborted ewe, but will be more when lamb
prices are high.
Sporadic losses do occur, but once the abortion rate starts to become more than 2% (or sudden clusters) it is very
suggestive that an infectious organism is involved and further investigation by post-mortem and blood sampling is
strongly recommended.
The two main pathogens diagnosed are Chlamydophila abortus (Enzootic abortion (EAE) and Toxoplasma gondii.
According to MSD Animal Health Flock Check results for 2010-2011, 86% of the blood samples submitted tested
positive for Toxoplasmosis; 62% for EAE, with 43% testing positive for both.
Enzootic abortion
EAE usually causes the birth of a stillborn lamb in the 2-3 weeks prior to the expected lambing date. Other ewes
will get infected by ingestion of infected material (vaginal discharge, afterbirth). Normally, ewes that abort become
immune but occasionally a ewe can retain the organism and excrete this at the next oestrus cycle/lambing. Ewe
lambs born to infected ewes can become infected and abort in their first pregnancy.
Vaccination at least four weeks prior to tupping remains the best way of preventing the disease alongside general
biosecurity measures. Whenever an abortion is seen it is important to isolate the aborted ewe and dispose of all
infected material. In the face of an outbreak, treatment with an Oxytetracycline antibiotic can be used to reduce the
number of abortions.
This will not reverse the damage already done to the placenta in those ewes that are very close to lambing. Even
though Oxytetracycline can’t save these lambs, lambs from healthy ewes can be fostered onto these ewes. It is
vital that these are not kept as replacements.
Toxoplasma
Toxoplasma is one of the most successful organisms in the world as it is capable of infecting most warm blooded
animals (including humans). The sheep is an intermittent host that can get infected by ingesting oocysts (eggs)
shed by the definite host, the cat. Even just a brief visit from an infected cat can significantly contaminate barns and
pastures. One cat dropping contains enough oocysts to infect over a hundred ewes. These oocysts can survive in
the environment for up to 12-18 months.
It causes resorption, abortion and birth of mummified or weakly lambs, with early infections causing infertility in the
ewes. Investigation is still ongoing as to whether the infection can be vertically transferred from mother to foetus,
but this is felt to be a very minor route of infection.
This disease can be prevented by using the available vaccine up to 3 weeks prior to tupping. Both vaccines last for
several years and are usually given once.
Other infections
Other causes of abortion include Campylobacter, Salmonella, Listeria, Border disease and Q-fever.
Campylobacter is particularly seen in intensively managed flocks at the end of lambing when heavy contamination
and unhygienic environments occur. The main source of infection is carrier sheep with risks from wild birds being
another source. Salmonella is mostly associated with abortion and death in ewes.
As several of the organisms involved cause a significant zoonotic risk (especially in pregnant women) adhering to
strict personal hygiene methods whilst handling sheep is very important.
Recommended flock biosecurity and biocontainment measures include:







Isolate aborted ewes to prevent infection from vaginal discharges (eg. Chlamydia can remain in discharges
for up to 2 weeks), this includes ewes that gave birth to full-term death or weakly lambs
Remove all infected material like bedding (Chlamydia can survive in bedding for up to 6 weeks)
If possible, keep the flock closed or if buying in replacements try and source them from a flock with a high
health status.
When buying in replacements from an unknown source vaccination for EAE and Toxoplasmosis is
recommended
Tag all ewes affected for future blood sampling or culling
If more than 2% of the flock is affected submit samples to the lab for further diagnosis.
Do not keep ewe lambs fostered onto aborted ewes.
Nanja Verkuijl from Cliffe - XLVets