Report on protective inoculation against tick fever : an account of an experimental inquiry into its effect on cattle, and on meat and milk, together with some notes on protective measures other than inoculation / by FrankTidswell.

  • Tidswell, Frank, 1867-1941.
Date:
1899
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Licence: Public Domain Mark

Credit: Report on protective inoculation against tick fever : an account of an experimental inquiry into its effect on cattle, and on meat and milk, together with some notes on protective measures other than inoculation / by FrankTidswell. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

    6/20 (page 2)
    (c) The Disease can he artificially produced by the Inoculation of Blood from a Sick Animal. The observations just mentioned apply to the disease as it occurs in the ordinary course of nature. It was shown, however, that the disease can be set up artificially by injectin blood taken from a sick animal under the skin, or into the veins, of a healthy one. The disease could be thus transmitted throu<^h a series of any number of animals. The blood was found to retain its infective properties after the apparently perfect recovery of the animal from tick fever. It was therefore made'clear that the tick is not the essential cause of the fever, and further inves- ti<j;atious showed that the real agent is a micro-organism which lives in and upon the blood of affected animals. To this micro-organism Smith and Kilbourne gave the name of Pyrosoma hiyeminum, on account of its microsco]jical appearances. Its constant presence in the blood of animals suffering or recovered from tick fever furnished the e.vplanation of the infectivity of the blood when artificially injected. {d) In nature Tides carry and Inoculate the JMicro-orjanism. Numerous experiments indicated that in nature the disease can only be conveyed by the cattle ticks,* which it is presumed, inoculate the micro-organism in much the same way as cau be done with the injection syringe. It was found that the micro-organisms are transmitted from the old ticks through the eggs and young to any cattle to which these particular young ticks happen to attacdi themselves. Adult female ticks taken direct from sick cattle laid their eggs in glass boxes kept in the laboratory. In due course the young ticks hatched out, and they produced the disease on being placed on healthy cattle in stables away from all infected ground. Hence it appears that the adult tick in withdrawing the blood of infected cattle takes with it the micro-organisms, and that these are transferred through the eggs to the next generation of ticks. The fact that each female usually lays over 2,000 eggs explains the way in which the disease becomes widely disseminated. The micro-organism, though discoverable in the blood of all infected animals, has not been detected in the bodies of the ticks, possibly on account of its assuming a different, and as yet unknown, form in the tick. When, where, and how the micro-organism first became associated with the tick is unknown. The association is accidental, for there are ticks which do not produce tick fever. (e) Comment. The American researches established the role of the tick in tick fever. The tick is the means by which the real causal micro-organisms gets into the blood of cattle, and also the means by wdiich it eventually gets out again. The researches of Dr. J. Sidney Hunt, Government Pathologist, and ]\Ir. C. J. Pound, Director of the Stock Institute, Brisbane, have shown that the American results apply also to the disease as it occurs in Queensland. The intervention of two different parasites, the tick and the micro-organism, in the causation of tick fever, though marvellous, is not without parallel in the realm of disease. Similar symbiotic roles are ])layed by the Tse-tse ily and the micro-organism of the African cattle disease, “Nagana”; by the mosquito and the micro-organism of malaria ; and, it is said, by the common flea and the micro-organism of plague. In all four cases the production of the disease is not an essential attidbute of the insect concerned, but a fortuitous circumstance due to their capability of acting as conveyors of the real pathogenic microbe. There are cattle ticks which do not communicate tick fever, just as thei’e are mosquitoes which do not communicate malaria. B. IxiMUNITY AFTER NATURAL TiCK FeVER. (a) Certain animals possess natural immunity. Tick fever is not known to attack animals other than bovines. Ticks attach themselves to horses, sheep, marsupials, birds, snakes, &c., and may even mature upon them (7), but they do not set up tick fever in these animals. The animals appear 11 be, by nature, insusceptible to the disease, and hence are said to possess natural immunity. It must be admitted that some doubt exists in the case of sheep. The American observers came to the conclusion that sheep were not susceptible, but they only report one experiment in which blood w'as injected into a lamb (1, page 8:i). By similar experiments on twai sheep in Queensland, Dr. Hunt set up a fever in both. One recovered, and one was killed in a dying state. Post-mortem examination did not reveal the characteristic lesions of tick fever, and the examination for micro-organisms was indefinite. The blood from one of the .sheep injected into a bullock “ produced no well-marked disease” (7, page 28). The evidence is, perhaps, no more than suspicious, but it is possible that tick fever, like tuberculosis, occasionally occurs in sheep. As Dr. Hunt remarks, the subject merits further study. (h) Cattle are naturally susceptible, hut come to possess an acquired, immunity after having suffered from the disease. Cattle are by nature susceptible to tick fever; but, after having suffered from it, they exhibit more or less resistance to a second attack. They come to possess an acquired immunity. In America the permanent distribution of ticks is limited to the States south of a boundary known as Salmon’s line. Although the cattle south of this line are ahvays more or less tick infested, they show no visible signs of having tick fever. But immediately northern cattle are taken to the south the ticks invade them and set up tick fever. The absence of fever in the south is not due to lack of virulence on the part of the ticks, but to the immunity of the .southern cattle. (c) American Experiments on Immunity. The American observers furnished the proof that this immunity of Southern cattle was not natural, but due to previous attacks. Their experiments w'ere performed by the exposure of Southern cattle to the ticks at the Experimental Station, near Washington. A steer, aged 2 years ; 3 heifers, aged 1^, 3, and 3 years ; and 5 cows, aged 5, r>, 5, i, and 0 years, from North Carolina and Texas, were exposed, with neg.ative results in all cases, whilst northern cattle cxqioscd at the same time all took the disease. Two of the southern cow’s had calved after their arrival at the station, .and the c.alves were exposed with the mothers. Both calves took the fever. Although descended from immune parents, the calves were not themselves immune. The experiments thus show that the immunity of the southern cattle is not natural, but acquired. Another * Notliiiifc is known as to the p ssibi ity of other suctional insects spreading the disease.