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This article was published in 1949
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
TROMBIDIOSIS IN SHEEP IN N.S.W.
W. E. CROGAN. B.V. Sc. Inspector of Stock, Braidwood.
Gill, Moule and Riek (1945) reported the occurence in Queensland of an infection of sheep by the mite Trombicula sarcina; this mite being very prevalent in the Clermont-Springsure district of that State, but apparently being confined to that area. Mactier (1948) reported the first outbreak of this condition noted officially in New South Wales; the locale being the Warialda District in the North-west of this State.
This communication concerns the location and treatment of an outbreak of Trombidiosis in the Narrabri District; also in the North-west. It is reported for the similarity of its course with that of the outbreak described by Gill et al.; and by reason of the fact that it does present solute new features. Resolution occurred too soon to do more than demonstrate the inefficiency of lime-sulphur solution on treatment by single application; and forestalled the intention to test the efficiency of new dips containing Gammexane.
HISTORY
On 27th April, 1948, a reported sickness in sheep was investigated on a small property of 1,200 acres, situated 25 miles from Narrabri on the foothills of the Nandewar Ranges and not far from Mt. Kaputar. The property is very hilly, with several gullies running through it, and the two paddocks concerned in this outbreak are typical of the general topography of the area. The two paddocks were of 300 acres (containing the wethers) and 400 acres (carrying the ewes), and each was more or less strewn with rocks of volcanic origin. The soil consisted mainly of heavy black earth, samples of which were examined by Mr. Robinson of the N.S.W. Department of Agriculture, who confirmed the fact that they were of the typical black earth variety as described by Prescott (1944) and found by Gill and his co-workers to be the ruling type at Clermont. The feed consisted mainly of native grasses, with clovers on the heavier flats; both Variegated and the Scotch thistle being prevalent. The timber was mainly box, kurrajong and pine; with isolated clumps of wild orange, olive (Notelaea microcarpa) and pimelea (p. pauciflora)
About three weeks earlier the owner had noted that the wethers were affected with a scaliness of the legs and fetlocks. The condition obviously caused considerable irritation as the sheep were biting and rubbing their legs continually; and the spread must have been very rapid, since at my visit it was found that from 90 to 100 per cent. of the mob of 200 wethers were affected. All stages of infestation were seen—from newly affected to almost healed—but most of these sheep were in the most advanced stages. The average case was affected from the top of the hooves to the knee and hock; all legs being involved and the infected area being covered with scabs and crusts; in many cases pus being present under and between the scabs. A thorough search was made for Foot Lice; with negative results. The whole condition could be best described as an itching dermatitis with loss of wool and scaliness of the skin.
A horse also was examined and found to be suffering from a scaley dermatitis of the face, muzzle and inner surface of the hind legs. This condition obviously was very itchy, as the animal was biting frequently at any affected parts which could be reached. The dermatitis in this case was not confined to non-pigmented areas as in Trefoil Dermatitis; but was generalised over areas of varying colour.
The 200 wethers and the horse were running on the 300-acre paddock. A flock of ewes on an adjoining paddock of similar country did not show any sign of infection at that time.
An examination of skin scrapings, taken from the sheep, at Glenfield Veterinary Research Station revealed mites identical with Trombicula sarcina. Gill, Moule and Riek's article, already cited, now was consulted, and the lesions of the Narrabri cases found to be identical with those described in the Clermont outbreak.
TREATMENT
The legs of all affected sheep wore immersed thoroughly in a solution of lime-sulphur (1 gallon of concentrate to 20 gallons of water); and the results of this trentment assessed three weeks later. The owner stated that during the first week a considerable improvement was apparent, as the scabby lesions cleaned up to a great extent. During the next week, however, about 20 per cent. of the wethers appeared to have become re-infected and the treatment was repeated. On the horse the condition, following the first lime-sulphur treatment, had been reduced to a few small patches only; and these responded to a second treatment.
At this period it was noted that about 20 per cent. of the neighbour- ing flock of 250 ewes now showed signs of re-infestation for the first time. As stated, these ewes were running in an adjoining 400 acre paddock, of very similar topogrnphy in that in which the wethers had been grazing throughout the outbreak. In addition, and perhaps indicating that the wave of infection then was at its peak, the owner himself became infected and began to suffer as much as the sheep. He was covered from feet to neck with very small, black areas which were intolerably itchy. Treatment consisted of a bath containing a strong mixture of kerosene; this apparently effecting a cure.
Both ewes and wethers were treated with lime-sulphur at this stage, and when the property was visited just one month after the initial inspection it was found that the condition had resolved almost completely. All the ewes appeared normal, while about 1 per cent. of the wethers showed signs of recent infection. From further skin scrapings T. sarcina was identified readily at the McMaster Animal Health Laboratory.
DISCUSSION
The cessation of the outbreak was considered by both the owner and the writer to be due to a series of heavy frosts which occurred during the preceding week. Our experience with the first lime-sulphur treatment had shown that it killed the mite present on the sheep but did not have any residual effect sufficient to prevent re-infestation. (NOTE. The suggestion made by Mactier (ibid.) that this condition might resolve without treatment well might he kept in mind when assessing the value of any particular treatment—Editorial Committee).
From a comparison of the features of the Narrabri and the Queensland outbreaks it is obvious that the physical conditions were very similar; though in our case there was a slight difference in seasonal incidence, as the Narrabri outbreak occurred in the autumn and subsided towards mid-winter, i.e., from the end of March to the end of May. Symptoms were identical, and the excellent photographs of the A.V.J. article could have been taken from our sheep.
Landowners in the Narrabri now have no recollection of ever having seen this condition before, and consequently the question arises, as to why an isolated outbreak should occur in the District. Kangaroos and wallaroos were running in small numbers in the adjoining State Forest but according to the owner very few ever were seen on his property. Unfortunately, none of these animals were secured for examination. Rabbits were trapped in large numbers on the property, but all were found to be free from any indication of infection with Trombicula. The only explanation might lie with the wave of field mice which occurred in the Narrabri District at the time. None could be examined but it is quite possible, of course, that these mice could have been the vectors.
In any case, it can be concluded from this outbreak that the distribution of the mite is more general than thought formerly. It appears likely that further outbreaks will occur in the area; in which case the opportunity should be taken to test the efficacy of treatment with a Gammexane preparation, since from experience against other parasites such a preparation not only should produce a good initial kill, but also should exert a residual effect sufficient to prevent re-infestation. In addition, the use dibutyl thallate might be kept in mind for the protection of humans involved. A solution smeared on the boots and trouser legs appeared in our case to exert a repellant effect so far as the mites were concerned.
ACKNOWLEDGEMENTS
Our thanks are due to Mr. Robinson of the N.S.W. Department of Agriculture for soil examination; Mr. D. A. Gill, M.R.C.V.S., McMaster Animal Health Laboratory; Mr. R. A. Anderson, Chief Botanist and Curator of the Botanic Gardens, Sydney; and to The Chief, Division of Animal Industry, for permission to publish this article.
REFERENCES
Gill, D. A., Moule, G. R. and Reik, R. F. (1945)—Aust. vet. J., 21: 22.
Mactier, L. A. W. (1948)—Year Book, Institute Inspectors of Stock, N.S.W., 71.
Prescott, J. A. (1944)—Bull. Counc. sci.industr. Res. Aust., 177.