Half the annual 400,000 infectious abortions in the national sheep flock are from enzootic abortion caused by Chlamydophila abortus (previously called chlamydia). Vaccines exist to control the disease, which is also known as chlamydiosis, but the fact remains that every year flocks continue to suffer significant losses.
The key reason for this is that less than 15% of sheep are vaccinated. If the flock is genuinely closed and enzootic-free this may be justified. However, there is still a biosecurity risk from animals transferring infected material from next door. If the flock is currently enzootic-free it is prudent to vaccinate them, to keep them that way - it is far easier to prevent enzootic abortion in a flock than to try to cure the problem once it has materialised.
If a flock has an abortion problem the first step is to identify and isolate the ewe, put the aborted foetus and placenta in a clean bag and get it tested to find out the cause. Next, it is vital that the area is cleaned up and disinfected. Birthing fluids are highly infective to other ewes, lambs and people – remember this is a zoonotic disease! Having the odd abortion is often accepted by shepherds but if 2-3% of the flock are aborting it is likely that the problem will escalate in subsequent years. Typical abortion storms average 13% losses but figures can reach 50% which can have a dramatic practical and economic impact. Identification of the cause is fundamentally important, simply because chlamydiosis and toxoplasmosis can be managed through strategic vaccination programmes.
Should enzootic abortion be diagnosed then treatment with long-acting oxytetracycline of the remaining in-contact ewes between 105 – 120 days pregnant is the best damage limitation. Oxytetracycline can have some effect against the bacteria when it is in cells and actively multiplying; it has no effect on the extra-cellular form. Relying on oxytetracycline treatment every year is not as cost-effective as vaccination, particularly with extended lambing periods requiring repeat treatments. Ultimately every sheep in the flock can get infected.
Remember that the cost of vaccination with live vaccines can be factored over three or four years’ protection and in many flocks is a one-off cost per ewe. Saving just one abortion in a hundred ewes can make the vaccination economically viable. It is recommended that the whole flock should be vaccinated in the first year and all replacement stock in subsequent years. Live vaccines should be used more than 4 weeks before tupping.
The importance of vaccination programmes was emphasised last year in the face of new research conducted by the Moredun research Institute. Limited data collected had raised alarm with the suggestion that vaccines aimed at preventing abortion in ewes may in fact be causing them. Polymerase Chain reaction (PCR) tests had shown the presence of the vaccine strain in some samples from ewes that had been vaccinated but had subsequently aborted. The presence of the vaccine strain in a sample was not the concern but that the wild strain was not found in the same sample. This could lead to the conclusion that either the vaccine did not work in that animal or that it had caused the abortion. The reality is more likely to be related to vaccinating infected flocks and that in fact the vaccine prevented an abortion storm within the flock. More work is being undertaken this year to investigate further. Currently the advice remains to continue with vaccination programmes as the benefits outweigh the risks.
Disillusioned clients should be reminded that vaccines would not get a marketing authorisation to be sold as veterinary medicines if they didn’t work! However they are not guaranteed to work in sheep that are already infected. If a ewe aborts and another ewe sniffs and licks the birthing fluids, that ewe is likely to abort the next time it is pregnant, even if it is vaccinated in the interim. Lambs can be born infected or become infected and then, even if vaccinated, they can abort at their first (and even second) pregnancy. Ewes that have aborted with enzootic abortion are usually immune, although Dr David Buxton, recently retired from the Moredun Research Institute, had suggested in 20% of ewes that abort or produce weak infected lambs the chlamydophila lies dormant until the next pregnancy when it becomes activated and infects the placenta and foetus.
Prevention is better than cure. Routine vaccination will prevent enzootic abortion in the flock but if the flock already has chlamydophila abortion, vaccination will reduce further losses, reduce excretion and will help to eradicate the problem in the longer term. Be aware that in the following year there may still be some abortions due to the fact that some ewes were likely to have been infected already but the ultimate goal should be to have the flock chlamydophila-free over two to three years.
This article was kindly provided by Ceva Animal Health, makers of CEVAC® Chlamydia:
CEVAC® Chlamydia, Ceva Animal Health’s live enzootic abortion vaccine, is available in a 50 dose or 20 dose bottle. It is quick and easy to administer, using the special, multi-dose injector gun. For further product information contact your local Ceva representative or Ceva Animal Health Ltd, 90 The Broadway, Chesham, Bucks, HP5 1EG or visit the website at www.ceva.uk.com