Developmental Stages of Brugia pahangi in the Final Host

Abstract

Morphologic details of the larval and adult stages of B. pahangi in cats are described. The third molt occurs 8 or 9 days after inoculation of infective larvae; both sexes are about 2 mm long at this time. Males are 6 or 7 mm long when they molt for the fourth time at about 23 days; females are 10 to 13 mm long when they molt at between 27 and 33 days. Sex differences in the growth curve first occur during the fourth stage. Females reach maximum size at about 120 days, males at about 45 days. The largest male seen was 20 mm long, the largest female, 63 mm long. Mating occurs at about 33 days and microfilariae appear in the vagina at about 55 days. The original description of B. pahangi is expanded to encompass features observed in specimens ranging in age from 55 to 321 days. The most distinctive features of the male of Brugia species are those of the spicules. The presence or absence of caudal cuticular bosses in females and the character of the esophagus are unreliable differential features. The location of the vulva distinguishes B. pahangi from B. patei, but not from aperiodic B. malayi. The marked discrepancy in location of the vulva between B. malayi recovered from man and those from animals raises the question of the exact status of different of B. malayi. It is suggested that B. malayi may be a species complex. The histological features of the larval stages and of the immature and mature adults are described for possible use in the identification of filariae observed in human or animal tissues. Details of the development of filariae after their entry into the final host have been described in only a few instances. Menon et al. (1944) studied Conispiculum flavescens in the lizard, Calotes versicolor, but were unable to find molting forms. The first complete filarial life cycle to be described was that of Litomosoides carinii in cotton rats (Scott et al., 1951). Since that time, Chabaud (1954) has studied Dipetalonema blanci in Meriones lebicus (a rodent), and Kume and Itagaki (1955) and Orihel (1961) have described the development of Dirofilaria immitis in dogs. The postarthropod morphologic development of human-adapted filariae has been studied only by Edeson and Buckley (1959, aperiodic Brugia malayi in cats), and by Received for publication 12 January 1962. *A portion from a dissertation submitted to the Graduate School of Tulane University in partial fulfillment of the requirements for the degree of Doctor of Philosophy. This investigation was conducted under the sponsorship of the Commission on Parasitic Diseases, Armed Forces Epidemiological Board, and supported in part by the Office of the Surgeon General, Department of the Army. t Present address: Department of Tropical Health, Schools of Public Health and Medicine, American University of Beirut, Beirut, Lebanon. Edeson et al. (1960b, B. pahangi in cats). The latter reported few morphological details beyond the length of larvae and adults recovered at different times after inoculation; no molting forms were found. Filarial infections suitable for laboratory study have generally been limited to forms only distantly related to human parasites. B. pahangi (Buckley and Edeson, 1956) Buckley, 1958, has several advantages in this respect; it has on at least one occasion (Edeson et al., 1960a) matured in man, while an earlier attempt to infect a human volunteer failed to result in a patent infection but caused marked symptoms (Buckley, 1958a, b). The cat can be infected easily with this parasite, and in this animal it inhabits the afferent lymphatics near the lymph nodes (Edeson et al., 1960b). A further indication of its potential usefulness in experimental studies is the relatively wide range of suitable intermediate hosts (Edeson et al., 1960b; Schacher, 1962). The purpose of the present paper was to expand the preliminary work of Edeson et al. (1960b) concerning the morphology of the developmental stages of B. pahangi in the definitive host. The histologic features of larvae and of immature and mature adults have been described for possible use in identifying filarial