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This article was published in 1974
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Anthrax Moree 1974
by G.W. Eggleston, B.V.Sc.
Seddon (1965) describes Anthrax as an acute usually septicaemic infectious disease affecting a wide variety of domestic and wild animals and man.
He states that the incubation period may be from 48 hours to seven days and cattle may show weakness or inappetence for up to 3 days before death.
Post-mortem findings, he states, are usually those of blood stained discharges coming from natural orifices. Putrefaction usually occurs very rapidly and the carcase is soon distended with gas.
The blood is usually dark and tarry and clots very poorly. The speen is usually greatly enlarged, the contents being dark and pulpy.
The deaths at Moree in 1973 were in the Watercourse area which is an area of 250,000 acres which is low lying and which floods periodically with small rises in the Gwydir River.
One of these floods occurred in January 1973 and as the flood receded the warm humid conditions and moist ground made ideal conditions for the anthrax outbreak to occur. Although in other areas of N.S.W. anthrax occurs on hard dry ground, we only seem to get it in the swampy areas of the Watercourse at Moree.
One of the major difficulties was that the textbook signs described by Seddon were not seen in at least 50% of cases.
In the first case a grazier reported 6 cows dying. Anthrax was immediately considered. On examining the animals externally no bloody discharges could be seen and the animals gave no appearance at all of having Anthrax. It was then decided to take blood smears as a precaution and to do a post-mortem. The spleen in the beast was of a normal size and quite firm. The only abnormal thing seen in this beast was a small necrotic patch on the diaphragmatic surface of the liver. A diagnosis of black disease was tentatively made and the owner advised to keep in touch if any more died. The slides taken were broken on the way to the house, however portions of these slides were looked at under the microscope at the local hospital and not a sign of Anthrax could be seen.
This type of situation with a lack of any clinical signs continued on the neighbouring property and it wasn't until there were about 50 cattle dead that any bloody discharges were seen.
Cows would be normal one minute and then ten minutes later would give a stagger and drop dead. It appeared we had to take blood smears in the first 12 hours after a beast died or the Anthrax organism wouldn't show up on the smear.
As the weeks progressed, outbreaks were reported in other areas of the Watercourse and these symptomless deaths were still seen. By this time we were encouraging everybody on the Watercourse to vaccinate their cattle to prevent further outbreaks. The general procedure was that once an outbreak was detected, the owner of that property was ordered to vaccinate. The surrounding properties were strongly advised to vaccine and everyone on the Watercourse was generally encouraged to do the same.
In the first outbreak cattle were injected with penicillin by a private practitioner at the same time as they were given the vaccine. Deaths still occurred 15 days post vaccination and it was decided to re-vaccinate the cattle. Deaths stopped 7 days after the second vaccination.
It would appear that the penicillin knocked out the first lot of vaccine. It must also have had some effect on the reticulo endothelial ( sic) system as deaths again occurred in this particular mob on this property 3 months later. All other mobs on the property which had not been injected with penicillin were quite alright.
There was tremendous variation between outbreaks as to the time it took the vaccine to take effect. In some cases it only took four days and in others it took seven. There were two cases where no deaths had occurred before vaccination and deaths occurred after vaccination before the vaccine had had time to take effect.
It has been said by some authorities that once the cold weather comes anthrax outbreaks should cease. This did not occur at Moree. Three outbreaks occurred in June and July after reasonably heavy frosts in the Watercourse area.
In the last case 3 horses died. This was then the only confirmed case of Anthrax occurring in any animal other than cattle.
Vaccination in horses was not recommended with the old spore vaccine and had not been tried with the stern vaccine we now use. To this point 50 horses have been vaccinated and none have showed any signs of swelling and oedema which was seen with the old spore vaccine.
In all, there were 15 outbreaks extending from January to July. Somewhere in the region of 400 cattle died. 60,000 head of cattle were vaccinated on 72 properties. In the end there were only 2 properties in the whole of the Watercourse which didn't vaccinate.
Reference
Seddon H.R. (1965) Diseases of Domestic Animals in Australia - Bacterial Diseases (Vol.2).