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This article was published in 1981
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Vibrionic Abortion in Sheep
S.J. Whittaker, B.V.Sc., Veterinary Inspector, Glen Innes/Inverell
This paper deals with an abortion storm that occurred in a group of crossbred ewes on a Glen Innes property during the spring of 1980.
The property concerned is situated in the eastern part of the Glen Innes Board on light granite soil. It has been heavily 'supered' and is almost completely pasture improved. The stocking rate averages about 3 ewes per acre.
Although the winter had been very mild with few frosts having occurred, the area had been in the grip of drought for some ten months and was also experiencing a wingless grasshopper plague at that time. As a result paddock feed was particularly scarce and the ewes involved in the abortion storm had been hand fed grain sorghum (fed on the ground) for 'some five months' prior to lambing.
Approximately 1,500 mixed age cross bred ewes were running on the property at the time. These ewes were running in adjacent paddocks in groups of 700, 500 and a third group of 300 which consisted of ewes which had been drafted off the other two groups as being 'shy feeders'. The group of 300 were not being hand fed at all and had been given the paddock with the best available pasture. Most of the ewes had been running on the property for some years and no recent introductions had occurred.
Abortions were first noted in the group of 700 ewes about ten days before lambing was due to commence. Abortions continued at an alarming rate for the next 2 weeks after which time they fell to a trickle.
Approximately 250 out of the group of 700 ewes aborted and 50 ewes out of the group of 500 aborted. No abortions occurred at all in the group of 300 ewes, i.e. the group which were not being hand fed.
POST-MORTEM FINDINGS
Most of the aborted lambs examined were normal looking, near term lambs. 80% of lambs had breathed but had not walked or suckled. The large number of mummified and decomposing lambs recorded in other vibriosis outbreaks were certainly not seen in this case. Some foeti, however, did appear malformed due to the dropsical affects of subcutaneous fluid accumulation.
Apart from dropsical subcutaneous tissue, 40% of lambs examined showed a marked fibrinous peri-hepatitis peritonitis - an enlarged liver and pale, cream-coloured necrotic foci up to 2cm in diameter in the liver would seem to be a typical finding in lambs that have been aborted as a result of ovine vibrionic infection.
Findings such as oedema of the chorio-allantois along the course of the main blood vessels and enlarged, soft cotyledons, were not seen in this outbreak but many ewes were noted as having retained foetal membranes and an accompanying fetid, brown vaginal discharge. No ewes died, however, as a result of metritis.
BACTERIOLOGY
Camphylobacter fetus, sub species intestinalis was isolated on primary culture from the abomasum and lungs of 2 ex 5 lambs submitted to R.V.L. for examination.
DISCUSSION
There are a number of possible sources of infection with C. fetus var intestinalis. The organism may be present in the foetus, placenta and uterine discharge of aborting sheep. The ewe may continue to contaminate her environment for up to 2 weeks after abortion but the organism is rarely recovered from the ewe's vaginal tract following the cessation of post abortion discharge. However, Moule records that the organism may be passed via the vagina up to 68 days after abortion.
C. fetus var intestinalis has also been isolated from the contents of the rectum, colon, caecum and the ileo-jejunum of clinically normal sheep. The organisms have been isolated from the faeces of sheep 3 - 20 months of age, and more frequently from sheep 2 - 8 years of age. C. fetus var intestinalis can apparently exist as a saprophyte in the intestines of cattle, sheep and pigs.
Crows, magpies and other birds have also been implicated in the past as a possible source of infection. When crows have been dosed with C. fetus var intestinalis their faeces have been shown to remain infective for at least 42 days. Such infected faeces have been given orally to susceptible pregnant ewes to produce abortion with recovery of the organism from the aborted lambs.
Although rams have been shown to be capable of spreading the infection at the time of service the primary mode of infection of the ewe is obviously via the oral route.
Most ewes lose the infection rapidly and do not remain carriers. All the evidence suggests that infection during the early stages of gestation is not likely to be harmful.
However, ewes exposed to the organism in the latter half of pregnancy are susceptible to abortion. The incubation period is about 2 - 3 weeks. Moule records that bacteraemia follows within 3 days of oral infection. The organisms then invade the foetus, cause secondary changes in the placenta and induce abortion.
It is interesting to speculate on the source of infection in this outbreak. The owner had noted 2 or 3 odd abortions in the group of 700 ewes, about 2 weeks prior to the commencement of the abortion storm. Bearing in mind that this group of ewes was being hand fed and they were obviously in close contact with one another these few early abortions would seem to be the most likely cause of the abortion storm.
There was no history of recent introductions onto the property and so the possibility of a recently introduced carrier would not seem possible. Crow activity in the area was described by the owner as being high.
In summary and from an epidemiological viewpoint, it is interesting to note that in this case we have a classic series of events coming together at the right point in time to cause a disease outbreak - namely, a disease source (the early aborting ewes); a susceptible population (ewes in late pregnancy); and close contact between the two (via hand feeding). The importance of close contact in the rapid transmission of the disease is shown by the fact the susceptible group of 300 ewes which were not being hand fed suffered no abortions. The point is further emphasised by the fact that 30 ex 1100 hand fed ewes in a neighbour's paddock also aborted as a result of vibrionic infection.
IMMUNITY
There is some dispute as to the degree of immunity attained following vibrionic abortion. However, it would seem significant that both overseas and Australian experience with the disease shows abortion due to vibriosis seldom recurs in the same flock.
CONTROL
Aborted foetuses should be promptly collected and either burnt or buried deeply. Aborting ewes should be isolated as a group as soon as possible. Some authorities recommend the treatment of aborting eves with antibiotics to prevent metritis. No ewes were treated in this outbreak and no losses were recorded.
PREVENTION
Lack of knowledge about the nature of the disease and of methods of diagnosing the possible carrier state impose difficulties in recommending means of control and prevention.
A vaccine is in use in overseas countries but the sporadic nature of outbreaks would seem to make continuous vaccination programmes uneconomical in this country.
REFERENCES
Moule, G.R. (1969) - The Management of Breeding Sheep in Australia. Univ. of Syd. Post Grad. Found. Pub. NO. 6
Hungerford, T.C. - Diseases of Livestock
Clarke, B. - C.S.I.R.O., Parkville, Victoria. Personal communication