The Salmonella group of bacteria for many years has been prominent in the causation of disease amongst the human race and various species of animals. This group, which was formerly known as the typhoid and paratyphoid group, derived its former name from the fact that one member of the group previously known as B. typhosus and now as S. typhi, is the cause of typhoid or enteric fever of man. In animal disease the commonest conditions and those of greatest economic significance caused by Salmonella types of organisms are Necrotic Enteritis of pigs and Pullorum Disease of poultry.
Upon more than one occasion, workers in America have described a disease in sheep which, as a result of research, they have attributed as being due to infection by Salmonella organisms. Until recently, Australian investigators have not encountered a similar type of infection in sheep here. In an article at present in the press by Mr. W. L. Hindmarsh, Director of Veterinary Research, a description is given of what is the first record of a mortality in sheep in this country due to an infection with one of the Salmonella group.
This mortality occurred on a property close to the metropolitan area of Sydney, and involved the loss of several hundred sheep. The particular strain of Salmonella, recovered from several of the cases involved in this mortality was identified as S. typhi murium or what was previously known as B. aertryeke, an exceedingly virulent member of this group and one that has frequently been demonstrated as the cause of severe outbreaks of food poisoning, or what was formerly known as Ptomaine poisoning in man, and with a high rate of mortality.
The history and circumstances of the cases investigated by Mr. Hindmarsh are of interest. The paddocks in which the mortalities had been experienced for some time were used as holding and fattening paddocks by a large company, and their experience had been that sheep placed in these paddocks commenced to die some four days after their arrival and the mortality rate would increase to as high as 40 deaths per day. The greatest losses were encountered during the hot summer months, particularly when the water supply was low and comprised a series of stagnant pools in the bed of a creek which was fast drying up. Bacteriological examination of the water from these pools revealed the presence of the same particular Salmonella as that recovered from the body tissues of the dead sheep, thus substantiating the suspicion that the water supply was the source of infection.
It is emphasised that Salmonella infections are primarily an infection of the intestinal tract, the organism being ingested either with the food or drinking water. The latter, it will be recalled, is the common source of infection of the human subject with S. typhi, the cause of typhoid or enteric fever, particularly in certain European countries and Asia. In November last, Mr. D. J. Walker, Inspector of Stock at Narrabri, investigated a mortality amongst sheep on a property in his district, and as the result of the submission of specimens to the Veterinary Research Station, a Salmonella was recovered upon bacteriological examination. In a little over a month later Mr. Walker investigated a somewhat similar mortality which we were able also to establish as being due to a Salmonella infection, but the particular strain of Salmonella was different to that recovered from the first outbreak. In the first mortality S. bovis morbificans was identified, this particular Salmonella having been described upon very few occasions in the world's literature. In the second outbreak, the particular Salmonella was identified as a varient of S. typhi murium and one which will probably be added as a new strain to the already long list of Salmonellae, the group now comprising over a hundred different types.
As a guide in forming an opinion under field conditions that a particular mortality in sheep may be due to a Salmonella, the following facts should be considered:
The losses are experienced during the hotter summer months, particularly when water supplies are getting low. Affected sheep almost invariably show diarrhoea, which frequently progresses to a dysentery characterised by the faeces consisting almost entirely of blood and mucus. The sheep are very debilitated, and prefer to remain lying, and if made to rise stand trembling and will walk with a staggering gait. Respiration is rapid and shallow, visible mucous membranes are congested and the temperature will rise to as high as 107º.
Subjects for post-mortem examination should be either sheep killed in the advanced stages of the condition or which have been dead not longer than an hour. Dead sheep which have been exposed to the sun when the shade temperature is over 100ºF are of little value for bacteriological examination.
The most constant features seen upon post-mortem examination are congestion and petechiation of the kidneys. The abamasum is markedly congested, the condition extending down the small intestines to the caecum, the walls of which are frequently thickened. The lungs are usually markedly congested and sub-epicardial haemorrhages are present on the heart.
In submitting specimens for bacteriological examination—and in this connection it must be pointed out that only as a result of bacteriological examination can diagnosis be definitely established - should be taken from heart blood, liver, kidney, spleen, mesenteric lymphatic glands and small bowel.
In adopting control measures, it is essential that the affected flock be seen daily and any sick animals removed and isolated from the main flock. Affected animals are voiding the causal Salmonella organisms in their faeces and so increasing the chance of contamination of the pasturage and water supplies. In the event of the above measures failing to check the mortality, consideration must be given to the chlorination of the tanks and other water supplies.
In conclusion, it is necessary to point out that Salmonella infections of sheep, as in pigs, are of very definite significance from the point of view of public health. Man is particularly susceptible to Salmonella infection, and the eating of meat in an underdone state from a sheep in the incipient stages of infection would almost certainly give rise to infection of the individual.
Thus the necessity for the adoption of early control measures is obvious.