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Observations on the pathogenicity for white rats of a strain of Trypanosoma rhodesiense
;-)4.~ TRANSACTIONS OF THE ROYAL SOCIETY oF TROPICAL MEDICINE AND HYGIENE.
Vol.XXXII. No.3 November, 1938.
OBSERVATIONS
ON T H E
P A T H O G E N I C I T Y FOR W H I T E
RATS
OF A S T R A I N OF T R Y P A N O S O M A RHODESIENSE. BY
J. F. CORSON, M.D., D.P.H., Research Laboratory, Tinde, Tanganyika Territory.
A strain of Trypanosoma rhodesiense was obtained in October, 1934, by feeding laboratory-bred Glossina morsitans on an untreated infected man in Kahama, Tanganyika Territory. The strain was transmitted by one of the infected flies to a sheep and was afterwards maintained in sheep by cyclical passages through G. morsitans, twenty-four passages having been made up to May, 1938. At the thirteenth passage, in October, 1936, a branch line through antelopes was begun. Infective flies were isolated by feeding them singly on white rats and were used to infect man and various animals including white rats. Inoculations of white rats were also made from time to time from infected animals and man. Altogether, 177 white rats were infected by inoculation from 58 vertebrate hosts consisting of 17 men, 27 sheep, 9 monkeys and 5 antelopes, and 197 rats were bitten and infected by 80 isolated infective G. morsitans which had become infected by feeding on 19 vertebrate hosts consisting of one man, 9 sheep and 9 antelopes. The antelopes included 4 reedbuck, 3 dikdik, a duiker, a bushbuck, an impala, a Thomson's gazelle and an eland. The blood of the rats was examined but the virulence of the strain was estimated from the life of the rats and, to a less degree, by the incubation period. So far as I can judge no change in virulence for white rats has taken place since the beginning of the experiment, but the number of rats infected from an animal was usually small and the tests can only be regarded as, at most, enabling a rough estimate of virulence to be made. As appeared in a somewhat similar experiment (CoRSON, 1934) the infections in white rats showed little variation in course and duration ; no species of animal and no individual animal seemed to have any influence on the virulence of the trypanosomes and no differences were apparent between individual flies in this respect. As rats are so susceptible to infection they are probably not so suitable as man for showing differences between flies.
:344
T. RHODt~SIENSE
The incubation periods and length of life in rats infected by flies were, on the whole, shorter than in rats inoculated with the syringe. It happened sometimes that a subcutaneous injection of 1 c.e. of the undiluted blood of a volunteer--whose blood showed scanty trypanosomes under the microscope--into each of two rats, failed to produce infection. It would be interesting to test the serum of an infected untreated man on his own trypanosomes in vitro. In a rather small number of experiments with T. rhodesiense, including the present one, I have found that the duration of life in groups of five or ten infected white rats usually ranged from the shortest to about twice that period, e.g., from 40 to 80 or 90 days or from 20 to 40 or 50 days according to the virulence of the strain used ; exceptionally a rat would live much longer or die rather sooner. About the same range was observed in mice, and it is probable that at least as much variation occurs in monkeys and guineapigs. Reedbuck " Mongi 2 " and Thomson's Gazelle 5.--Both antelopes were infected by single flies of the seventh passage through sheep, the reedbuek by Fly BE 46 and the gazelle by Fly BE 100. The infections in subinoeulated rats were similar ; four rats inoculated from the reedbuck in March and April, 1936, showed incubation periods of 6 and 7 days and lived 42, 44, 48 and 55 days; while eighteen rats inoculated from the gazelle (ten on 17th April and eight on 23rd June, 1936) had incubation periods of 5, 6 and 7 days and lived 38, 43, 43, 43, 44, 45, 46, 48, 48, 49, 50, 54, 56, 60, 61, 61, 69 and 91 days. Although the trypanosomes of the two antelopes seemed to be similar, the results of feeding laboratory-bred G. morsitans on them were very different. The trypanosomes of the reedbuck infected the salivary glands of a large proportion of those flies which lived for a month after feeding on it, viz., 47 per cent. in March, 1936 (CORSON, 1936) ; and 52 per cent. in another experiment made a month later, in which forty-nine of ninety-four dissected flies showed infected salivary glands. On the other hand two attempts to infect flies from the gazelle failed. In the first experiment about 120 flies were put to feed on the gazelle on 23rd May, 1936, and seventy-five were successfully dissected on 19th and 20th June ; the state of the blood of the gazelle on the day of feeding was unfortunately not recorded and it cannot be assumed that trypanosomes were seen. In the second attempt 144 flies were put to feed on the gazelle on 28th June, 1936, and most of them fed ; a thick film of the antelope's blood showed six trypanosomes in 400 fields. On 25th and 26th July seventy-six flies were successfully dissected. The rabbits which were used to feed the flies also did not become infected. The blood of the gazelle was perhaps less suitable than that of the reedbuck for the development of the trypanosomes in the flies ; if the difference depended on an endogenous cycle of the trypanosomes in the vertebrate host, the conditions must have been very favourable both times in the reedbuck and very unfavourable both times in the gazelle.
J. F. coasoN.
845
SUMMARY. White rats were used as test animals in an experiment to see whether a strain of T. rhodesiense would lose its infectivity to man or undergo other changes in its characters during maintenance in ruminant animals. T h e rats were infected by the bites of isolated G. morsitans and also by inoculation from the infected animals and volunteers. N o change in virulence was observed. T h e infections in rats produced by inoculation and by the bites of flies which had fed on the same hosts were similar, but those produced by the flies appeared to be rather more acute• T h e infections of a reedbuck and a T h o m s o n ' s gazelle were apparently similar, as tested in white rats ; but when G. morsitans were fed on these animals those which fed on the reedbuck showed a large proportion with infected s~tlivary glands, while no fly with infected salivary glands was found among those which fed on the gazelle. REFERENCES. CORSON, J . F . (1934). The influence of the dose. of trypanosomes and of the body weight in experimental infections of white rats with Trypanosoma rhodesiense. Ann. trop. Med. Parasit., 28, 4. • (1936). A second note on a high rate of infection of the salivary glands of Glossina morsitans after feeding on a reedbuek infected with Trypanosoma rhodesiense. Trans. R. Soc. trop. Med. Hyg., 80, 2.
Vol.XXXII. No.3 November, 1938.
OBSERVATIONS
ON T H E
P A T H O G E N I C I T Y FOR W H I T E
RATS
OF A S T R A I N OF T R Y P A N O S O M A RHODESIENSE. BY
J. F. CORSON, M.D., D.P.H., Research Laboratory, Tinde, Tanganyika Territory.
A strain of Trypanosoma rhodesiense was obtained in October, 1934, by feeding laboratory-bred Glossina morsitans on an untreated infected man in Kahama, Tanganyika Territory. The strain was transmitted by one of the infected flies to a sheep and was afterwards maintained in sheep by cyclical passages through G. morsitans, twenty-four passages having been made up to May, 1938. At the thirteenth passage, in October, 1936, a branch line through antelopes was begun. Infective flies were isolated by feeding them singly on white rats and were used to infect man and various animals including white rats. Inoculations of white rats were also made from time to time from infected animals and man. Altogether, 177 white rats were infected by inoculation from 58 vertebrate hosts consisting of 17 men, 27 sheep, 9 monkeys and 5 antelopes, and 197 rats were bitten and infected by 80 isolated infective G. morsitans which had become infected by feeding on 19 vertebrate hosts consisting of one man, 9 sheep and 9 antelopes. The antelopes included 4 reedbuck, 3 dikdik, a duiker, a bushbuck, an impala, a Thomson's gazelle and an eland. The blood of the rats was examined but the virulence of the strain was estimated from the life of the rats and, to a less degree, by the incubation period. So far as I can judge no change in virulence for white rats has taken place since the beginning of the experiment, but the number of rats infected from an animal was usually small and the tests can only be regarded as, at most, enabling a rough estimate of virulence to be made. As appeared in a somewhat similar experiment (CoRSON, 1934) the infections in white rats showed little variation in course and duration ; no species of animal and no individual animal seemed to have any influence on the virulence of the trypanosomes and no differences were apparent between individual flies in this respect. As rats are so susceptible to infection they are probably not so suitable as man for showing differences between flies.
:344
T. RHODt~SIENSE
The incubation periods and length of life in rats infected by flies were, on the whole, shorter than in rats inoculated with the syringe. It happened sometimes that a subcutaneous injection of 1 c.e. of the undiluted blood of a volunteer--whose blood showed scanty trypanosomes under the microscope--into each of two rats, failed to produce infection. It would be interesting to test the serum of an infected untreated man on his own trypanosomes in vitro. In a rather small number of experiments with T. rhodesiense, including the present one, I have found that the duration of life in groups of five or ten infected white rats usually ranged from the shortest to about twice that period, e.g., from 40 to 80 or 90 days or from 20 to 40 or 50 days according to the virulence of the strain used ; exceptionally a rat would live much longer or die rather sooner. About the same range was observed in mice, and it is probable that at least as much variation occurs in monkeys and guineapigs. Reedbuck " Mongi 2 " and Thomson's Gazelle 5.--Both antelopes were infected by single flies of the seventh passage through sheep, the reedbuek by Fly BE 46 and the gazelle by Fly BE 100. The infections in subinoeulated rats were similar ; four rats inoculated from the reedbuck in March and April, 1936, showed incubation periods of 6 and 7 days and lived 42, 44, 48 and 55 days; while eighteen rats inoculated from the gazelle (ten on 17th April and eight on 23rd June, 1936) had incubation periods of 5, 6 and 7 days and lived 38, 43, 43, 43, 44, 45, 46, 48, 48, 49, 50, 54, 56, 60, 61, 61, 69 and 91 days. Although the trypanosomes of the two antelopes seemed to be similar, the results of feeding laboratory-bred G. morsitans on them were very different. The trypanosomes of the reedbuck infected the salivary glands of a large proportion of those flies which lived for a month after feeding on it, viz., 47 per cent. in March, 1936 (CORSON, 1936) ; and 52 per cent. in another experiment made a month later, in which forty-nine of ninety-four dissected flies showed infected salivary glands. On the other hand two attempts to infect flies from the gazelle failed. In the first experiment about 120 flies were put to feed on the gazelle on 23rd May, 1936, and seventy-five were successfully dissected on 19th and 20th June ; the state of the blood of the gazelle on the day of feeding was unfortunately not recorded and it cannot be assumed that trypanosomes were seen. In the second attempt 144 flies were put to feed on the gazelle on 28th June, 1936, and most of them fed ; a thick film of the antelope's blood showed six trypanosomes in 400 fields. On 25th and 26th July seventy-six flies were successfully dissected. The rabbits which were used to feed the flies also did not become infected. The blood of the gazelle was perhaps less suitable than that of the reedbuck for the development of the trypanosomes in the flies ; if the difference depended on an endogenous cycle of the trypanosomes in the vertebrate host, the conditions must have been very favourable both times in the reedbuck and very unfavourable both times in the gazelle.
J. F. coasoN.
845
SUMMARY. White rats were used as test animals in an experiment to see whether a strain of T. rhodesiense would lose its infectivity to man or undergo other changes in its characters during maintenance in ruminant animals. T h e rats were infected by the bites of isolated G. morsitans and also by inoculation from the infected animals and volunteers. N o change in virulence was observed. T h e infections in rats produced by inoculation and by the bites of flies which had fed on the same hosts were similar, but those produced by the flies appeared to be rather more acute• T h e infections of a reedbuck and a T h o m s o n ' s gazelle were apparently similar, as tested in white rats ; but when G. morsitans were fed on these animals those which fed on the reedbuck showed a large proportion with infected s~tlivary glands, while no fly with infected salivary glands was found among those which fed on the gazelle. REFERENCES. CORSON, J . F . (1934). The influence of the dose. of trypanosomes and of the body weight in experimental infections of white rats with Trypanosoma rhodesiense. Ann. trop. Med. Parasit., 28, 4. • (1936). A second note on a high rate of infection of the salivary glands of Glossina morsitans after feeding on a reedbuek infected with Trypanosoma rhodesiense. Trans. R. Soc. trop. Med. Hyg., 80, 2.