Farmnote 29/1990 [Reviewed February 2006]
By Peter Buckman, Veterinary Officer, Division of Animal Health, South Perth
Ovine vibriosis is an infectious disease of breeding ewes causing abortion in late pregnancy. It is caused by the bacteria Campylobacter fetus. The disease is found in flocks throughout the agricultural region of Western Australia.
The disease
The main feature of ovine vibriosis is abortion in late pregnancy and the birth of dead or weak lambs. In a flock the disease begins with a few ewes aborting, but these usually pass unnoticed. An abortion 'storm' then occurs with several ewes aborting and the number of abortions increasing rapidly over several days.
The average abortion rate in an outbreak is 20 per cent of the flock, but may vary from 5 to 50 per cent. Abortion rates of up to 70 percent have been reported. It is rare for a recovered flock to have outbreaks of vibriosis in successive years.
Signs of the disease
Ewes
In most cases abortion is quite sudden and causes the ewe little trouble. There may be a discharge from the vulva for a few days before the abortion.
Following the abortion, the ewes have a brownish discharge from the vulva for up to two weeks. This discharge contains millions of the infectious bacteria. Up to 5 percent of ewes may die from blood poisoning following infection of the uterus.
Lambs
About 50 per cent of aborted lambs die in the uterus before they are expelled. About 20 per cent of aborted lambs show a number of yellowish areas of degeneration throughout the liver. These areas are rosette-shaped and vary from one to twenty mm in diameter.
There may be blood-tinged fluid in the cavities of the chest, abdomen and around the heart and there is oedema (swelling) of subcutaneous tissues.
Afterbirth (placental membrane)
The membranes show oedema and the cotyledons (buttons) are soft and usually pale orange in colour. This differs from the normal red colour of the cotyledons.
Infection and spread
Ewes are susceptible to infection during the second half of pregnancy. Susceptible ewes contact bacteria from contaminated food or water.
The bacteria enter the bloodstream and pass to the uterus where they multiply in the placenta (afterbirth) infecting the placental membranes. This infection causes an abortion of the developing lamb. Abortion usually occurs one to three weeks after infection.
Aborted lambs and the afterbirth contain large numbers of the vibriosis bacteria. The bacteria are fragile and die quickly in a dry environment.
However, the bacteria survive longer in cool moist conditions. An abortion on to moist ground around a watering point or soak may be followed by a rapid spread of the disease to the rest of the flock. This explains why vibrionic abortion occurs mainly during cold wet seasons.
In Western Australia, there have been some outbreaks of the disease in late summer and autumn. The spread of infection under arid seasonal conditions is associated with the grouping of sheep around areas of hand feeding and watering.
The initial entry of vibriosis to a flock is usually impossible to trace. One means of entry is by domestic carrier animals. These are ewes that have aborted and then carry the bacteria. The organism has been isolated from the gall bladder of ewes that have aborted. These ewes, if brought into a clean flock, become a source of infection.
Cattle may possibly be involved as carriers by harboring the bacteria in their intestines.
A second means of entry is by wild animals and birds carrying the bacteria from one flock to another or from one farm to another. Foxes are believed to spread the disease.
Crows have been found to carry the organism and pass it in their droppings. They are probably the main cause of disease spread during dry periods. The crows are attracted to areas of watering and hand feeding where sheep congregate.
Treatment
There is no practical treatment to prevent abortion caused by this disease. Once the abortion 'storm' commences, the placenta membranes in infected ewes have already suffered damage.
Ewes that have aborted may be treated with antibiotic injections or pessaries to reduce losses from blood poisoning.
Control
- Aborting ewes should be isolated.
- Aborted lambs and placental membranes should be collected and burnt.
- Prevent contamination of feed and water by vaginal discharges and aborted lambs. This includes providing water troughs at dams or soaks.
- Ewes from an infected flock should not be sold for breeding as some may be carrier animals.
- Flocks that experience an abortion 'storm' usually develop good immunity.