A Microsporidian Parasite of Anopheles gambiae in Liberia

Abstract

In connection with a survey of wild Anopholes gambiae for natural infections of malaria, conducted at the Liberian Institute, Harbel, Liberia, West Africa, one of us made some thousands of midgut dissections during the period from June 1955 until April 1956 (Fox, 1957). From time to time a wild mosquito was found to be infected with a microsporidian parasite. The rate of this natural infection was not recorded but was exceedingly low. Colonies of A. gambiae had been maintained at the Institute continuously for the previous 4 years without difficulty. During the summer of 1956 an outbreak of nosematosis occurred, quickly reaching nearly epizootic proportions and spreading to the colony of A. melas. Because infected mosquitoes are not suitable for use in malaria study, the colonies had to be destroyed. A few infected strains were kept for further study of the parasite. The purpose of the present paper is to record the pathology of the microsporidian infection, identified as Nosema stegomyiae, in adult A. gambiae and to present certain observations on nosematosis in mosquitoes. Nosema stegomyiae (Marchoux, Salimbeni and Simond), 1903, has reniform or comma-form spores 4-7 microns long and 2-3 microns wide. It invades the gut, muscles, air sacs, coelomic lining, neural ganglia and ovaries of adult mosquitoes, and was originally observed as a parasite of Aedes. N. stegomyiae Lutz and Splendore, 1908, described as a new species, and N. anophelis Kudo, 1924, are synonyms. Two other microsporidia parasitize mosquitoes: Thelohania grassi Nicholson, 1921, had earlier been recorded but not described by Grassi (1901), Ross (1906), Stephens and Christophers (1908); Plistophora culicis Weiser, 1947, with spores 5 microns long and plasmodia 15 microns in diameter, has been found and fully detailed by Garnham (1956) and Canning (1957). Both these species sometimes invade the larvae. One of us (JW) is preparing a monographic revision of the microsporidia.