Slapping as a Factor in Transmission of Kala-Azar by Sandflies (Phlebotomus).

Abstract

The results in the experimental transmission of kala-azar thus far have been uniformly negative. 1 , 2 Shortt, attempting transmission by means of sandflies, attributes his negative results to insufficient susceptibility of the experimental animals rather than to inability of the fly to expel the flagellates from its buccal cavity into the wound while feeding. We are inclined to believe that the negative results might have been due to the overlooking of one natural factor not previously considered, namely, the crushing of the fly by slapping the itching skin, where the fly is feeding. To ascertain the importance of this factor in the transmission of kala-azar, a method has been worked out, imitating as far as possible the natural conditions under which the flies feed and are crushed.

The sandflies, P. major, are fed with the blood-parasite mixture on the feeding stage within 24 hours after hatching, 3 and are then kept in the ice box at 21° C. After 6 to 10 days, they are allowed to refeed and, while feeding, are crushed by slapping. This is occasionally done as late as the 18th day, if the flies have had a second feeding.

1. The feeding stage. This stage is like the one for the blood-parasite mixture, except that the dish is only 1/2 inch in diameter. The flannel is cut a little smaller than the dish and is cut in 2 equal halves. It is then pressed and saturated with defibrinated rabbit blood, and covered with a piece of skin from a normal hamster. Strictest asepsis is necessary in these preparations, but the heavily contaminated external surface of the skin is not sterilized for reasons which are given below. The prepared feeding stage is placed on the electric heater set at 35° C., and the slapper is adjusted to the skin surface.