An outbreak of Anthrax in cattle recently occurred in the Macquarie Marshes.
In this Marsh area the Macquarie River spreads out into a large number of shallow channels which fill rapidly with any rise in the river, and then overflow to flood the whole of the surrounding low-lying country. The grey clay soil is impassable except to cattle when it is wet.
The whole Marsh region is covered with a dense growth of Mirandas, which grow to a height of from nine to ten feet, Reeds (sedges), Noogoora Burr and Swamp Grasses. The whole growth is locally known as the Reed Beds. Through these Reed Beds there is quite a heavy growth of timber.
There are few fences as frequent flooding soon carries them away. Because of the type of vegetation and the marshy nature of the country the area is used almost exclusively for cattle fattening. The plains surrounding the Marshes are primarily sheep country.
When cattle are first introduced to the Marshes they are held in a small area for several days until they become familiar with it, then they are left. When the stock are mustered, cattle from adjoining properties are drafted out, and the owners notified. The control, or apparent lack of control, of stock in the area would appear lax but, in reality, it is the only system which can be practised and is efficient under the conditions prevailing.
Anthrax was first confirmed in the Marshes in 1938 when it occurred on a property on the Northern extremity. No further cases were reported until 1962 when the loss of ten sheep and a cow on the adjoining property was confirmed as Anthrax. In 1963 a property, some 24 miles North reported the loss of 24 cattle. Again Anthrax was confirmed. In this outbreak two dogs returned to the station with Anthrax after being absent for ten days. The wife of the manager, who treated the dogs, also became infected. Fortunately the condition was diagnosed and all these cases responded to treatment.
In February, 1965, a further outbreak occurred on properties just North of the 1963 outbreak area. This was by far the most extensive outbreak which had yet occurred. On four properties, known to be involved, there were 284 cattle deaths, and on one further property there were two deaths which were considered very highly suspicious. The difficult nature of the country, which means that cattle are seen infrequently, makes early detection of an outbreak and satisfactory control of movement impossible.
When cattle were being mustered for inoculation in the 1965 outbreak the sighting of both sick pigs and kangaroos was reported. There is no doubt that pigs were affected with Anthrax. Pigs were seen with swollen jowls as far as eight miles from the outbreak area. On at least one property pigs were seen to die while cattle were being inoculated. Although extensive inquiries and investigations were made, there was no evidence that kangaroos were ever affected. It was reported that some sick and weak kangaroos, which were shot, were carrying an extremely heavy lice infestation.
As is well known, the Macquarie Marshes carry a very heavy wild pig population. To demonstrate the extent to which these pigs were responsible for spreading infection, it was reported that cattle were seen to die in a paddock adjacent to the yards where inoculation was being carried out. The carcasses were dragged a short distance away. During the night wild pigs were heard fighting over the carcasses, which were avidly devoured. In another case a bull was seen 24 hours after death when only bones and remnants of hide remained. Three months after the original outbreak it was stated that pigs were still dying and still showing swollen jowls on one, at least, of the outbreak properties. It is quite obvious that these pigs must have heavily contaminated the whole of the Marsh area.
All mustering in the area is carried out on horseback. Horses become so fatigued dragging through the mud that they cannot work for longer than two or three days. When mustering, the horses are able to follow the cattle pads but are not able to go into the swamps. This means that it is only under drought conditions that a complete muster could be obtained.
No losses occurred after inoculations were commenced so it seems that inoculation succeeded in halting the outbreak. As an indication of the numbers involved, 10,640 cattle were inoculated, as well as large numbers of sheep. The aim was to place a ring of inoculated cattle round the outbreak properties, and, although this aim was not achieved in its entirety, it can be said that most stock on, or adjoining outbreak properties have been inoculated.
As an example of the losses experienced, one owner, who lost 196 head, stated that these could be valued conservatively at £40 per head, which meant that his losses through deaths were £7,840.
Anthrax has frequently been associated with the growth of new pastures which bring spores to the surface of the soil and so cause infection. In this case there was a quick growth of lush pasture in the wake of the receding flood waters and this may have been the cause of the initial outbreak. There is no doubt that the feral pig was the main factor in the further spread of the disease.