著者

岩本 功

出版者

長崎大学熱帯医学研究所

雑誌

熱帯医学 (ISSN:03855643)

巻号頁・発行日

vol.14, no.3, pp.124-137, 1972-09

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For explanation of the mechanism of microfilarial periodicity, it is a basic problem to know the survival time of microfilaria in the host. Therefore, there have been reported several papers concerning the experimental investigations on it. Viewing these papers reported in the past, however, there is found a great difference in the survival times obtained by each investigator. This disagreement may due to the irrationality of procedual method employed in these studies. In the present study, the author attempts to discuss the longevity and viability of microfilaria in various conditions from the results obtained by using a new method originated by us. When the heparinized blood containing microfilaria is maintained in a test-tube, living microfilariae swarm together near the boundary area between the blood plasma and the blood cell sediment. Microfilariae were isolated from there by pippett, removed to the various kind of media in the watch-glass and then incubated in the glass capillaries. Under microscope, the activity of each microfilaria was checked until all microfilariae died and the numbers were counted every 8 hours. When the commulative mortality was drawn on logarithmic scale. a straight regression line could be obtained. The theoretical mean survival time can be represented by the 50 per cent value of mortality on this regression line. For this observation, microfilaria of Dirofilaria immitis and Wuchereria bancrofti were used and the total numbers in each group of the experiment were approximately 1,000-3,000. First of all, the viability was tested at various temperatures and in various media such as distilled water, physiological saline solution, and the blood plasma of animals and human beings. When one compares the mortality curves given by different temperatures from 5℃ to 37℃, it becomes clear that the survival time in vitro of microfilaria depends much on the temperature. Generally speaking, the survival time was longer in refrigerator at 5℃ than at room temperature of 20℃, while it was signifcantly short at 37℃. In physiological saline solution, the mean survival time of D. immitis microfilaria expressed by 50 per cent value was 216 hours at 5℃, 61 hours at 21℃, 9 hours at 37℃ respectively, but in each group, the last microfilaria was remained alive for 426 hours, 352 hours and 48 hours after all others died out. The survival time was also influenced by the kind of media in which microfilariae were incubated, for example, the mean survival time of D. immitis microfilaria at room temperature was approximately 74 hours in distilled water, 61 hours in physiological saline solution and 216 hours in the rabbit blood plasma, and it was longest in the blood plasma of non-infected dogs as long as 254 hours. It was of interest to note that the blood plasma of infected dog tend to reduce the survival time of D. immitis microfilaria. The survival time of bancroftian type microfilaria in vitro as compared to that of dog heart worm was relatively short in any conditions, especially the viability was found markedly inhibited in the blood plasma of animals other than human being. This finding suggest that bancroftian filarial worm has the high specificity in adaptation to the host. In order to see the longevity of microfilaria in vivo, the living microfilariae were transfused intraveneously into fresh animals. In the dogs received intraveneous transfusion of the blood containing about 950,000-5,700,000 microfilariae of D. immitis, the microfilaria continued the emigration into the peripheral circulation for a long time at least more than 50 days, showing a nocturnal sub-periodic fluctuation in the number. However, the microfilariae transfused into rabbits disappeared from the peripheral blood within 21 days, during which the periodicity was rather indistinct. On the other hand, it was noticed that W. bancrofti microfilaria could not be demonstrated in the blood streams of recipient dog and rabbit, even if a large number of the larvae were given. However, of the animals which were autopsied immediately after tte transfusion, a moderate number of the living larva was usually recovered in the various organs such as the lung, liver and kidney.1)体外での仔虫の死亡経過は時間の対数と関係があり,50%値(MfMD_<50>)を求め,その仔虫群の平均生存時間とすることが出来る.2)仔虫の生存時間は5℃で最も長く,37℃になると早く死亡する.3)夫々対応宿主の血漿内で最も長く生存するが,感染宿主血漿は抑制的に働く.4)いかなる条件のもとでもバンクロフト仔虫は犬糸状虫のそれより生存時間が短く,人以外の動物血漿では早く死亡する.5)犬糸状虫仔虫は犬に移注されると長期にわたり末梢血中に出現し,夜間出現性を最後まで維持する.家兎の場合はにれより速やかに消失し,早期より夜間出現性の乱れがみられる.6)バンクロフト糸状虫仔虫は犬,家兎に移注を行っても末梢血内に出現せず,一部内臓や大血管に集積される.本論文要旨の一部は第21,22回日本寄生虫学会南日本支部大会(1968,1969)及び第38回日本寄生虫学会総会において報告した.稿を終るに当り,終始御指導,御校閲頂いた恩師片峰大助教授に深甚の謝意を表します.