Observations on Trypanosoma lewisi and Grahamella sp. in the Blood of Rats from the Hamakua District, Island of Hawaii

Abstract

During the course of an investigation on wild rodent flea control in the enzootic plague region of the Island of Hawaii, observations were made on Trypanosoma lewisi in several species of rats inhabiting a wild gulch area of the Hamakua District. These observations were not the result of an organized study of blood parasites, since the original purpose of the investigation was to use T. lewisi as an indicator of the pulicidal effect of insecticides affecting rat fleas. It was thought that a significant reduction in the rat flea population would be reflected by a declining curve of new trypanosome infections in young susceptible rats. Unfortunately, the field investigations did not last long enough to allow an adequate evaluation of the above hypothesis. A search of the literature has not revealed any reports on the blood protozoa of rats in the Hawaiian Islands. Furthermore, no evidence has been found on the incidence of blood protozoa in commensal rat species living in wild situations. Recent studies by Eyles (1952) and Calero (1952) review evidence on the incidence of Trypanosoma lewisi in rats from the American continent. Seven different studies cited by these authors, and their own investigations, show the incidence of T. lezwisi in the Norway rat to vary from 0.5 to 47.5 percent. On the contrary, a study in Quebec, Canada, failed to demonstrate any blood protozoa in the brown rat (Firlotte, 1948). As far as can be determined, there is scant information on blood parasites of the black rat and its subspecies. Swellengrebel (1913) presented data on T. lewisi in Rattuzs rattus rattus in Eastern Java; all of his data were based on rats with a body length under 150 mm. Dore (1918) found 30% of R. norvegicus from sewers and 12% from wharves and grain stores infected with 7'. lewisi in Auckland, New Zealand. This author also suggested that in New Zealand Rattus exulans, a member of the group to which the Hawaiian rat belongs, declined in numbers due to infection with T. lewisi. If this hypothesis is true it would substantiate the idea that T. lewisi is a relatively new parasite in rats of the Malaysian concolor group. Laird (1951) obtained 65 R. norvegicus from buildings in Wellington, New Zealand and found 3 individuals infected with T. lewisi. The average dimensions of 100 trypanosomes recorded by this author are in substantial agreement with the mensural data given in the present report. The present note will record observations on Trypanosoma lewisi mainly in the Hawaiian rat, Rattus hawaiiensis, in subspecies of the black rat, primarily Rattus rattus alexandrinus, and to a lesser extent in R. norvegicus. Data also are presented here on an apparently unknown species of Grahamella