Sheep abortions pose serious risk to humans too
Last updated 22:02, Tuesday, 15 April 2008
Abortion is still one of the major causes of economic loss to the sheep industry in the UK. It causes concerns for animal welfare and, in some cases, poses a risk to the health of shepherds and others who come into contact with sheep at lambing time.
Abortions may be caused by infectious agents or have a non-infectious cause. In any flock there will be a small number (around 2 per cent) of sheep which abort or produce stillborn lambs with no infectious agent present. These may be due to genetic factors, illness, injury to the ewe, or nutritional problems.
Abortions caused by infectious agents can have a much more serious impact. Abortion “storms” can occur where 40 to 50 per cent of a flock may abort. A number of infectious agents have been identified, the most significant of which are enzootic (chlamydial) abortion, toxoplasmosis, listeriosis, salmonella, campylobacter, leptospirosis and Q-fever.
Enzootic abortion and toxoplasmosis together account for more than 50 per cent of all sheep abortions in the UK. The others are less common but can cause significant damage in infected flocks. All can cause illness in humans.
Q-fever and leptospirosis are relatively uncommon in sheep. Both cause a mild, transient illness in the ewe, which if pregnant when infected will subsequently abort. Infection is spread from ewe to ewe by contact with aborted material and post-lambing discharges, and if not diagnosed early can cause large losses. Spread of infection can be limited by isolation of infected animals and treatment with antibiotic.
Infection in humans is characterised by severe, flu-like symptoms. Both infections can become more serious in older or otherwise frail patients.
Campylobacter, salmonella and listeria are all potential “food poisoning” bugs in humans. In the ewe campylobacter usually causes abortion mid-pregnancy and causes moderate illness in the ewe at the time of abortion. Infection is spread by ingestion of contaminated material.
Salmonella causes serious illness in the ewe at the time of abortion, with abortions occurring from mid-pregnancy onwards. Illness can be so severe that the ewe may die.
Listeria is a bacteria found in the soil that can cause problems when soil contamination of feed occurs (eg when sheep are fed turnips or with soil contamination of silage). Infection with listeria can present as either diarrhoea, abortions or encephalitis (infection in the brain). The diarrhoea and encephalitis can be fatal.
Rarely, all three can be seen in the same outbreak. Early identification will allow any further spread to be cut by the appropriate use of antibiotics.
Infection in humans can cause severe and long-term gastro-enteritis.
Toxoplasmosis is the second most important cause of abortion in sheep in the UK. It can cause abortion storms affecting 40 to 50 per cent of a flock.
Toxoplasmosis is normally a gut infection in cats, but contamination of sheep feed with cat faeces allows the infection to spread to sheep. Sheep will become immune to toxoplasmosis without illness unless they are pregnant when they are first infected. Pregnant ewes can suffer from early embryonic death, foetal death and mummification, abortion, stillbirths or production of live but infected and sickly lambs.
There is no effective treatment once a ewe is infected. However, the disease can be prevented by vaccinating ewes before they become pregnant.
Humans are unlikely to catch toxoplasmosis from sheep, but run the same risk as the sheep in catching it from cat faeces. It causes flu like symptoms in healthy people, but can cause severe illness in immunocompromised patients and miscarriages in pregnant women.
Enzootic abortion is the most damaging of the infectious abortions in sheep. It causes abortions in the last fortnight of pregnancy, but causes no illness in the ewe.
It is spread from sheep to sheep at lambing time by contact with aborted material.
It differs from the other infectious causes of abortion in two ways – firstly, ewes will pick up the infection at lambing time, but will not abort until the following year; secondly, once a ewe is infected she is infected for life. She may not abort again after the first abortion but will always be a source of infection for other sheep. Any female lambs produced or reared by an infected ewe will be infected and will abort their first pregnancy.
Enzootic abortion can cause abortion storms when it is first introduced to a flock, with losses as high as 45 to 50 per cent. It then becomes established within the flock causing abortion rates of at least 5 to 10 per cent each year.
Antibiotics will reduce the weight of infection, and may allow more lambs to be born alive, but will not remove the infection; the problem will still be there the following year.
Vaccination is the only effective control for most flocks. The aim is to protect breeding ewes before they become pregnant, but vaccines are available that can be used in the face of an outbreak. This does not prevent ewes that are already infected from aborting, but can prevent other ewes in the group from picking up the infection.
Enzootic abortion will also infect people, causing sometimes serious flu-like symptoms. In pregnant women, the disease is much more serious, causing miscarriages, severe illness and sometimes death.
Many of the causes of abortion in sheep will look the same. Accurate identification of the disease or diseases is essential for effective control.
It is advisable to have aborted lambs and afterbirths examined at the laboratory. Your vet will be able to advise.
The most important thing to remember is that all of these infectious abortion agents can also infect people. Careful hygiene is therefore essential, and pregnant women should take care not to come into contact with sheep at lambing time.
