On April 27, 1964, an owner near Bogan Gate, some 30 miles northwest of Forbes, reported that three sows were dead and a further three were sick. The property was visited the same day. The pigs were being fed a ration of hammer-milled wheat and lucerne hay and had access to a poor grazing paddock, the soil being of a red, sandy nature.
The affected sows showed general malaise and leg weakness, but were reluctant to lie down. There was only a slight elevation of temperature and respiration was shallow and thoracic.
Decomposition was very advanced in the dead sows, but all of them showed evidence of enteritis and up to 5 lb. of sand in the caecum and colon. A diagnosis of sand impaction was made and appropriate treatment prescribed for the sick pigs, with a poor prognosis.
On May 26, 1964, the owner reported that the three sick sows had died and that he had a further case. The affected sow showed the same symptoms as the ones previously seen. She frequently adopted a dog sitting position for short periods and then stood up again. There was a massive oedematous swelling involving the right face, throat, neck and prescapular area. The skin over the right submaxillary region was necrotic and oozing blood-stained fluid. The swelling interfered with respiration and mouth breathing was obvious.
As the swelling was unilateral it was considered that the condition was probably a Clostridial infection rather than Anthrax. However, penicillin was prescribed at a dosage of two million units per day and the sow appeared to respond. A smear of the fluid from the submaxillary region was negative for Anthrax.
The sow died on May 29, having received eight million units of penicillin. She had drunk water about midday that day and appeared brighter, but was found dead late in the afternoon. An autopsy was done on May 30. Decomposition was advanced. There was a marked swelling still present in the right submaxillary and throat regions, the skin being purplish red in colour, and there was a sanguineous nasal discharge. Visible mucous membranes were cyanotic but there was no anal discharge.
The abdominal cavity contained approximately 200 ml. of bloodstained fluid. The liver was decomposed and there was extensive gas formation. The spleen showed gas formation and less advanced decomposition. The stomach appeared normal but was full of undigested wheat despite the fact that the sow had not eaten for four days. The intestinal tract appeared normal, apart from a slight congestion of the mucosa. The kidneys exhibited a congested cortex and numerous sub-capsular petechiae. The thoracic cavity contained some bloodstained fluid, the lungs were decomposed and the heart was flabby and showed scattered sub-epicardial petechiae.
The right throat and submaxillary region showed a massive thickening due to inflammatory reaction. The muscles were pale and the cut surfaces exuded a clear fluid. The submaxillary lymph node was indurated and haemorrhagic.
Pipettes of kidney, spleen, submaxillary lymph node and submaxillary tissue were taken and submitted for bacteriological examination. Smears from the pipette contents revealed Clostridial forms in the spleen material, no organisms in the submaxillary tissue, and organisms suggestive of Anthrax in the submaxillary lymph node. Culture resulted in typical Anthrax colonies being recovered from the submaxillary lymph node, while no significant growth was recovered from the other tissues and anaerobic culture was negative.
The source of the infection was never determined definitely, but it is suspected that a cow, which died on the property and whose udder only was eaten by the first sows to die, may have been the source. The boar and weaners were not affected although running at all times with the sows. The outbreak is recorded as being of interest in that first the swelling was at all times unilateral, and secondly the penicillin treatment failed to cure the infection, although it probably controlled the systemic infection, leaving surviving organisms in the submaxillary lymph node. Possibly the marked inflammatory reaction in this area resulted in a much-reduced circulation and consequently only a low concentration of penicillin reached the lymph node.