フィラリア仔虫の脱鞘現象について(II)

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The author reported previously an interesting evidence that some kinds of microfilaria provided with sheath actively cast off the sheath on agar plates or thick blood films which were prevented from dryness. As the next step, a series of the study was attempt to research the biological meanings of this phenomenon and factors stimulating the ex-sheathing process. Present paper describes the findings concerning the effect of temperature and some other environmental conditions on this phenomenon. For the experiment, Wuchereria bancrofti and Brugia pahangi microfilariae were used. As described before, the thick blood films containing microfilariae were stained with silver deposition technique or Giemsa solution after keeping them in a moist chamber for various periods. On the other hand, living microfilariae were observed on agar plates using a phase contrast microscope. First of all, in order to see the influence of temperature to the ex-sheathing, the thick blood drops and agar plates containing microfilariae were kept at various temperature of 5℃, 10℃, 15℃, 20℃, 27℃, 32℃, and 37℃, and numbers of sheathless microfilariae appearing during incubation at the respective temperature were counted every two hours or four hours. On the thick blood specimens incubated in 15℃ or 20℃, more than 50 per cent of bancroftian larvae already cast off the sheath within 4 hours, 80 per cent in 8 hours and about 90 per cent in 12 hours. Similar results were obtained by the observation of living larvae on the agar plates, for example, 90 per cent of bancroftian larvae ex-sheathed within 8 hours and also 98.2 per cent of pahangian larvae within 1 hour. At higher or lower temperature the rate generally declined. At 5℃ and 37℃, none or only less than 10 per cent of larvae came out of the sheath, indicating an extreme inhibition of the process. If the agar plates were exposed to 20℃ after keeping them for 8 hours at 5℃, ex-sheathing was found to be accelerated, the rate reaching up to 65.5 per cent of bancroftian larvae and 85 per cent of pahangian larvae within 4 hours. On the contrary, the microfilariae which were incubated in 37℃ for 4 hours could not recover their activity casting off the sheath. It is obvious, therefore, that the process of ex-sheathing in vitro is influenced significantly by the temperature of the environment, and that the most suitable temperature ranges from 15℃ to 20℃. The ideal conditions of agar plate for the living larva were tested. Concerning the saline concentration in agar plate, it can be said that the presence of saline is indispensable for living microfilaria. Lack of saline or its high concentration over 2 per cent brought a strong osmotic effect to kill microfilaria. The best concentration of saline was found in the proximity of 0.9 per cent corresponding to that of physiological saline solution, on which bancroftian microfilariae ex-sheathed in 83.2 per cent of them within 8 hours. Hydrogen ion concentration of agar plate is also an important factor influencing the activity of microfilaria. On an observation of pahangian microfilariae, the naked larvae appeared in the highest rate as many as about 80 per cent of the population on the agar plates adjusted to neutral ranging from pH 5.8 to 6.8. Acid and alkaline media seemed to be undesirable for keeping the activity of microfilaria. When the most ideal conditions of agar plate and environmental temperature were given, fresh microfilariae were found to begin immediately a characteristic movement to and fro inside the sheath and the ex-sheathing occured progressively according to increase of the incubation hours.
長崎大学熱帯医学研究所,Institute of Tropical Medicine, Nagasaki Universityの論文
1971-12-30

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