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This article was published in 1950
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Tetanus in Sheep

AN UNUSUAL OUTBREAK

G.E. CHARLES, B.V.Sc., Inspector of Stock, Forbes.

Towards the end of November, 1949, a watercourse on the western edge of the town of Grenfell was flooded as a result of heavy rain over its catchment. It broke its banks and ran with considerable force through the sewage treatment works, carrying with it both residue and untreated sewage, which were swept downstream until the creek lost its identity as such and became a swamp with undefined banks on a property about 3 miles to the South.

Some 5 or 6 days later the owner noted that some of the sheep grazing in the paddocks containing this swamp had developed a stilted gait and appeared to be off their feed. Deaths commenced approximately 8 days later, and continued at the rate of about one (1) per day. No advice was sought until midway through January, by which time about 30 had died. At the time of the first visit to the property the only cases seen were what the owner described as early cases and the symptoms resembled calcium imbalance, which was supported by the lushness of the pastures, and serum samples were submitted in order to ascertain the calcium and magnesium content; which was found normal. This was supported by the lack of response to calcium and magnesium injections. At the same time the possibility of tetanus was considered to be a very definite one, but positive diagnosis was not considered wise until the mineral balance had been determined.

The pastures implicated consisted of a great variety of grasses, many borne down the creek by floods, and included rye grass, spear and corkscrew, couch, paspalum and others; also native trefoils, clovers, and considerable numbers of saffron and star thistles, which were to be of considerable importance in the light of subsequent findings.

A further visit was paid on 28 January, 1950, when a further 11 sheep had died, and two cases in extremis were seen showing stilted gait, trismus, tetanic spasms and opisthotonus. Post-mortem examination revealed no abnormality except slight grass-seed penetration. A definite diagnosis of tetanus was made and the owner advised as to preventive measures.

However, this did not solve the problem, which was to ascertain the source of infection and the mode of entry of the organisms. This was desirable as no wounds were apparent either ante- or post-mortem, and since the course of the disease was so unlike the typical outbreak of tetanus which usually is associated with marking or shearing, with the deaths occurring over a brief period; whereas this outbreak lasted over a period of weeks with a daily death roll of one or two. Consequently, on 15 February, 1950, a further visit was paid to the property and soil samples were collected from the affected paddocks; as well as a composite sample of dry residue and soil from the effluent discharge of the treatment works. This latter was taken as Hutyra and Marek (1) report that human faeces contain tetanus spores, and if Clostridium tetani could be isolated from this sample it would reveal a likely source of contamination, in view of the history given above.

These samples were submitted to the Veterinary Research Station and, following examination, the Director of Veterinary Research reported as follows:—"Examination of these samples has resulted in the recovery of Cl. tetani from all four samples. The recovery of this organism, in each case, indicates that the concentration of these organisms on this property must be fairly high." Despite the fact that Cl. tetani is a common soil saprophyte, its recovery from soil with such ease and in such large numbers is apparently not usual and the opinion was expressed that the term "fairly high" was conservative.

It would appear from this finding, coupled with the presence of large numbers of star and saffron thistles in the paddocks, that those parts of the sheep carrying no wool, such as the face and legs, became heavily contaminated with the spores of Cl. tetani while the sheep were grazing over the contaminated ground and that these were inoculated into the sheep by thistle pricks, and to a lesser extent by grass-seed penetration.

This outbreak of a comparatively common disease is recorded as being of interest for the following reasons:—

(a) The prolonged period over which deaths occurred,
(b) The somewhat unusual mode of infection, and
(c) The probable implication of the sewage treatment works as a source of contamination.

Acknowledgment:

The permission of Mr. J. N. Henry. D.V.O. to quote from official papers is gratefully acknowledged.

Reference:

(1) Hutyra and Marek. "Special Pathology and Therapeutics of the Diseases of Domestic Animals." Bailliere, Tindall & Cox, London.

 


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