Natural Infections and Behavior of Trypanosoma rangeli and Trypanosoma cruzi in the Vector Rhodnius prolixus in Colombia

Abstract

r: Hemolymph, salivary glands, and feces of wild-caught Rhodnius prolixus were examined periodically for trypanosome infections. Dissection of a random sample of bugs revealed spontaneous loss of Trypanosoma rangeli in 18% and of T. cruzi in 12% of infections during a mean observation period of 3 months. In T. rangeli-infected bugs repeated examinations increased the observed hemolymph infection rates from around 7% to 26%, and in the whole lot of investigated bugs from 1% to 4%. The presence of T. cruzi in the intestine did not exclude T. rangeli or prevent its invasion of the hemolymph and salivary glands. In half of the T. rangeli and over 10% of T. cruzi infections the flagellates were undetected in feces. In 97% of T. cruzi and 52% of T. rangeli infections the flagellates were in the rectum, and in 53% of T. cruzi and 83% of T. rangeli infections they were in the slender midgut. In two T. rangeli infections flagellates were found in the hemolymph only; all bugs with flagellates in the hemolymph transmitted infection when fed on mice. It is suggested that examination of all organs from a random sample of a large collection of bugs will provide more reliable information than will examination of feces only from the whole lot. Bugs with T. rangeli or T. cruzi infection took a blood meal significantly less frequently than did those without infection. Prevalence ratios of Trypanosoma cruzi and T. rangeli in triatomid bugs reported from various countries of America were summarized by Dias in 1956. These records usually were based on one examination of feces from each bug. The natural occurrence of T. rangeli in hemolymph and salivary glands has apparently been reported only by Pifano and Mayer (1949) in Rhodnius prolixus in Venezuela, by Groot (1952) in R. prolixus in Colombia, and by the Gorgas Memorial Laboratory (1966) in R. pallescens in Panama. Epidemiological interpretation of such data requires more detailed information on the detection and behavior of the trypanosomes in the vector bugs. Reported here are the results of serial examinations of bugs collected in Colombia. Described also are survey procedures which reflect more adequately the extent and significance of natural infections of T. rangeli and T. cruzi in the vector. Preliminary observations on the distribution of R. prolixus in Colombia, Received for publication 20 March 1969. * Supported by the Tulane University International Center for Medical Research and Training, Grant TW-00143 from the National Institute of Allergy and Infectious Diseases, NIH, U. S. Public Health Service. t Present address: Division of Research in Epidemiology and Communications Science, WHO, Geneva. the rates of natural trypanosome infection in the vectors, and the behavior of 10 isolated strains of T. rangeli were reported earlier (D'Alessandro, 1963). MATERIALS AND METHODS Triatomid bugs were collected in houses during June and July of 1962 in 4 states of Colombia (Magdalena, Santander, Cundinamarca, Tolima). R. prolixus was the only species found. On arrival in the laboratory, the bugs were placed in individual containers and the hemolymph of each 4thand 5th-instar nymph and adult was examined. The bugs were then allowed to feed on uninfected mice, a separate mouse being used for each bug in which parasites in the hemolymph were either undetermined or present, or the same mouse for several negative bugs. A sample of naturally voided feces from each bug was examined for flagellates. Thereafter, the bugs with flagellate-positive feces were given an opportunity to feed on a mouse every 8 to 10 days, or after a molt. The hemolymph of 4thand 5th-instar nymphs and adults was always examined after molting, before each blood meal, and 4 to 5 days later. When flagellates were found in the hemolymph, an attempt was made to detect them also in the salivary glands, either by transmission of the infection to mice or by dissection of the glands. Only bugs with flagellates in the feces after the first meal were fed again, and the feces, hemolymph, and salivary glands were subsequently examined. Because of the large number to be studied at the same time the bugs that had no flagellates in the feces after the first meal were not fed again, although the hemolymph was examined