Morphology of the Microfilaria of Brugia pahangi and of the Larval Stages in the Mosquito

Abstract

The detailed morphology of the microfilariae of B. pahangi following several methods of preparation is described. Possible features which will allow its rapid differentiation from the microfilariae of B. malayi and of B. patei are the size and proportions of the cephalic space. Among eleven species of Louisiana mosquitoes tested, Anopheles quadrimaculatus, A. crucians, and Psorophora confinnis were susceptible to infection with B. pahangi. Although infective larvae were recovered from all three species, encapsulation of some larvae was seen in A. quadrimaculatus and P. confinnis. As the chemical nature of the encapsulating material is not known, it is suggested that the term "chitinization reaction" be dropped. In the development of B. pahangi in the mosquito, the first molt occurs between 4 and 5 days and the second molt at about 8 days, after which the larvae are immediately infective. During the first 3 days of development, micro-filarial structures are rearranged and the nerve ring is obliterated. Cell multiplication during this period is minimal; cell growth is marked and larvae become much shorter. The developmental period just preceding the first molt is distinguished by rapid cell multiplication, lengthening of the body, and differentiation of internal structures. The cephalic space of the microfilaria does not form the buccal cavity or any other structure of the infective larva but is shed undeveloped at the first molt. It is suggested that the supernumerary nuclei of the terminal caudal appendage of the microfilaria may be the retained polar bodies. The tail of the microfilaria containing the supernumerary chromatin dots is retained throughout the first and second stages of development. If not dislodged by dissection procedures, its presence affords a reliable distinguishing feature for separating the first- and second-stage larvae of B. pahangi from those of other genera, but not of congeneric species. Infective larvae of B. pahangi could not be distinguished from those of B. malayi. The sex of individual larvae can be identified in late second stage by the position of the genital primordium which is at or just behind the esophago-intestinal junction in males, and at the midesophageal level in females. In light of this and other findings, it is suggested that the R1 cell does not form the genital primordium but develops into the intestine, and that the R2-4 cells are incorporated into the rectum.