Biological Factors Influencing Transmission of Trypanosoma rangeli by Rhodnius prolixus

Abstract

Certain biological factors which might influence transmission of a Venezuelan strain of Trypanosoma rangeli by Rhodnius prolixus are presented with statistical evaluation of their significance. T. rangeli must invade salivary glands of R. prolixus before transmission is possible. When 1st instar nymphs were exposed to an infected meal, survival during nymphal stages decreased. This decrease was statistically significant and indicates that T. rangeli is pathogenic for R. prolixus nymphs. There was no indication that blood from different vertebrate hosts influenced survival. In adult survivors exposed as nymphs as well as in those exposed as adults cycle progressed to salivary glands in a significantly greater percentage of males than females. There was no significant difference in percentage of mature infections between those exposed as 1st instar nymphs and those exposed as adults. There appeared to be no advantage in multiple infective feedings. Following ingestion of Trypanosoma rangeli by Rhodnius prolixus, cyclical process begins with trypanosomes changing form and multiplying in alimentary canal. This first stage of development is a constant feature; second, passage into hemolymph, is not. However, once hemolymph is invaded, development progresses to salivary glands. Transmission of Trypanosoma rangeli by invertebrate host is not possible until salivary gland invasion has occurred. Groot (1954) in a comparative study of biological behavior of four strains of T. rangeli in Rhodnius prolixus reported that in one strain (ariarii) invasion of salivary glands always occurred when flagellates were found in hemolymph and his figures indicated at least 33% with salivary gland involvement. This high percentage of invasion was not observed in all strains. Tobie (1961), working with a cyclically maintained strain, obtained only a 12.5% invasion of salivary glands. The percentage, however, increased after a number of cyclical passages (Tobie, 1964). Grewal (1957) studying pathogenicity of T. rangeli to R. prolixus reported that most of bugs which died or could not molt had hemolymph infections. Only 41 out of 120 survived to become adults and only one of these had a salivary gland infection. This great loss he attributes to heavy parasitosis of insect, the entire system being blocked by