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This article was published in 1984
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Abortions & Stillbirths Associated With Mucosal Disease Virus

I.H. MACKAY, B.V.Sc., Veterinary Inspector, CONDOBOLIN

My first introduction to this problem was two weak calves presented at the office a week apart. There was nothing grossly abnormal with either of these calves except for a slight doming of the forehead, incoordination and one could not stand. Both had good sucking reflexes.

I sent the first one home on bottle feeding and it died several days later.

The second I post-mortemed and found nothing abnormal except for a haemorrhagic looking brain. Histopathology of liver, kidney, lungs and heart showed nothing abnormal. There was however congestion of the vessels and haemorrhage from the vessels throughout the cerebellum, cerebrum and brain stern and sub-meningal haemorrhage. It was suggested that this was typical of injury due to dystocia but considering the calf was very small and the cow large I found this difficult to believe.

Stomach contents examined under gram and modified Ziehneilson stained smears and dark field examination of wet preparations showed no organisms.

There was no visible growth on culture and no Campylobacter isolated via selective media.

I then found out more of the history when I visited the property.

The herd was run by two brothers who owned properties some 5 miles from their father. All the cattle had been isolated from any other cattle for 4-5 years and had always remained in good condition throughout the 2-3 year drought.

Cows tested in calf had been 91% in 1980-81, 83% in 1981-82 and 92% this year.

In 1982-83 there were 101 cows and heifers pregnancy tested of which 77 were pregnant (76%).

In the year of 1982-83, 84 cows and 17 heifers were joined for 10 weeks. One week after joining the cows were separated from the heifers and mixed with the boys' father's cattle for approximately eight weeks. This was the only time the cows and heifers were separated before calving.

The father had two mobs of cows. The first mob had calves six months previously, and had produced 4 grossly deformed and 4 dwarfed calves. The second mob were calving when the boys' cattle were mixed with them.

When the cows were reunited with the heifers they were all pregnancy tested.

63 of 84 cows were P.T.I.C.

14 of 17 heifers were P.T.I.C.

59 cows and 14 heifers were retained and run together until the heifers started to calve, at which stage they were separated from the cows and moved closer to the house.

Calving results were as follows:

Heifers - 13 had normal calves

1 calf died of Dystocia

Cows - 10 cows did not calf - aborted

11 stillbirths or weak calves

7 dwarfed calves - 2 of which developed blindness

31 normal calves

That is approximately 50% of the cows P.T.I.C. developed problems during their gestation.

In summary we had no problems in the heifers which seemed very unusual. The cows had significant problems with their calves but were unaffected themselves. The only time the cows were separated from the heifers was for 8 weeks when they were mixed with another herd of cattle that had known problems in their previous calving. It therefore appears obvious that the cows must have developed the problem in this 8 week period.

DIAGNOSIS

Serum was taken from 5 cows that had lost calves and 4 from cows that aborted and they were all tested for:

Brucella - R.B.T. & C.F.T. negative

Leptospira hardjo & pomona - negative

Akabine/Aino - negative

Chlamydia - C.F.T. negative

Calcium all >2.4 (normal >2.25)

Mg. all >0.8 (normal 0.75)

P. all >2.2 (normal 1.3)

All results had given negative results which in my experience was typical of abortion investigations.

It was around this time we had an influx of young cattle from northern N.S.W. Most of these cattle were badly stressed and we had several outbreaks of Mucosal Disease.

While reading up on Mucosal Disease I found out that affected calves, can have slight ataxia to complete lack of co-ordination and lack ability to stand and some may be blind.

This was similar to the calves I had seen so I obtained the references listed from Orange Vet. library.

The first one was 'A Serological survey of Mucosal Disease and Infectious Bovine Rhinotracheitis in Cattle in Australia and New Guinea' T.D. St. George et al. A.V.J. Vol. 43 1967.

A summary of this showed approximately 60% of cattle have neutralising antibodies to M.D. virus and 30% have antibodies to I.B.R. virus. The important difference between the two is that I.B.R. tends to persist and to produce latent and intermittent infections whereas M.D. virus tends to die out in a small closed cattle population.

As the hero in question was a small closed cattle population we can assume that Mucosal Disease may have died out.

The second reference was: 'Bovine virus diarrhoea-mucosal disease virus: Pathogenicity for the foetal calf following maternal infection.' J.T. Done et al. Vet. Record June 7, 1980.

An experiment was carried out where 15 antibody-free heifers were isolated, artificially inseminated and injected with a mixture of 10 different strains of M.D. virus isolated in Britain. The whole cattle population was used as a control. These heifers were injected intramuscularly at 100 days of gestation. There was no apparent clinical illness in the cows but all had seroconverted by day 42. 5 calves aborted within days 136-154 (one set of twins). One foetus became mummified and was retained until 300 days with no effect on the mother.

Ten calves were born alive but all showed intrauterine growth retardation, that is:

a. diffuse stunting in terms of crown anus length and bodyweight

b. selective stunting of vulnerable tissues, e.g., brain, lungs, thymus

c. growth arrest lines in long bones

± gross malformation

± demyelination of C.N.S. & C.N.S. malformation such as: hydrocephalus, microencephaly cerebellar hypoplasia, three showed congenital nervous disease

There were no eye lesions or hydranencephaly as has been described in other Mucosal Disease experiments. Virus was isolated from 80% of the live calves but was not isolated from two calves which had neutralising antibodies to Mucosal Disease virus.

As calves were slaughtered before they sucked, maternal antibodies were not present.

With this information it looked very much like our problem may have been caused by a trans-placental infection of the foetus by Mucosal Disease virus.

To try and prove this I collected sera from the two worst affected calves, two cows that aborted and two cows that had stillborn calves.

All sera were retested for Akabane and Aino virus antibodies and again all showed negative results. Results for M.D. and I.B.R. are as follows:

	M.D. - 'G.D.P.R.''	I.B.R.
calf blind	excess	27
calf part blind	3	27
COW A	2	>81
COW B	2	<47
cow	2	>81
cow with stillborn calf	2	negative

With high levels of antibody to Mucosal Disease virus in the calves and moderate levels in the cows it gave further weight to the diagnosis.

I believed the presence of antibodies to I.B.R. to be insignificant as in my area I always get some level of antibodies to I.B.R. but very rarely get any M.D. virus antibodies. I also believe that in this situation where we had an isolated small mob of cattle, an introduction of M.D. virus could have caused this abortion, stillbirth problem. Whereas I.B.R. would not, due to the fact that I.B.R. tends to persist and M.D. does not.

It is also unlikely that cows would develop problems and not the heifers if I.B.R. was involved.

It was suggested that I collect E.D.T.A. blood samples and serum on the clot from 6 or 7 affected calves.

Seven calves were picked by appearance three months after the initial investigation and the samples were submitted to Glenfield laboratory. Approximately three months later I received the following results:

	G.D.P.R.	Virus Isolation Mucosal Disease
1	1	+
2	3	-
3	excess	-
4	-	-
5	2	+
6	excess	-
7	2	-

It is suggested in the British paper that the Bovine foetus may become immunologically competent in relation to M.D. virus by 90 to 100 days gestation. It is therefore possible to have antibodies present to M.D. virus and still show clinical effects of intra-uterine infection with M.D. virus.

I believe that there is enough circumstantial evidence and supportive laboratory finding to suggest Mucosal Disease virus caused the abortions, stillbirths and poor growth rates in this herd. it is most likely that the Mucosal Disease virus was picked up by the cows when they were mixed with the father's mob of calving cows.

If this were the case, then it would also explain why the heifers were not affected. That is, the cows should have developed immunity by the time they were reintroduced to the heifers and the stage of pregnancy in the heifers would have been more advanced thereby reducing the effect on the foetus if trans-placental infection did occur.