Brugia beaveri: microscopic morphology in host tissues and observations on its life history

The filaria Brugia beaveri is a parasite of raccoons (Procyon lotor) in Louisiana. Its microfilariae, which circulate in the peripheral blood without any periodicity, develop to the infective stage in mosquitoes. The filaria can be transmitted in the laboratory to other raccoons, the domestic cat, and jirds (Meriones unguiculatus). The prepatent period is 70-107 days depending on the definitive host. Adult worms are found in lymphatics and associated subcutaneous tissues of raccoons and in the heart, lungs, and testes ofjirds. In host tissues, the parasite is recognized by its small diameter and the morphology of the body wall. There is a thin cuticle, which is characteristically thickened in the lateral fields; in males, a lateral, internal cuticular ridge is sometimes present. The hypodermis forms large lateral chords and less conspicuous dorsal and ventral chords. Muscle cells are coelomyarian; in females there is an average of 4 cells per body quadrant and in males about 4-6. Internal organs are easily identified as to type, but do not provide any clues to species identification. Brugia beaveri is a filarial parasite of raccoons and possibly other wild mammals in the southeastern United States. Only 1 other species of Brugia, B. leporis, a parasite of rabbits in Lou- isiana, has been reported from the U.S. (Eberhard, 1984, 1986). However, a microfilaria indistinguishable from that of B. leporis has been found in rabbits in Massachusetts, and an undeter- mined species of Brugia was found in a lymph node from a domestic cat in California (Beaver and Wong, 1988; Eberhard et al. 1991). These species of Brugia must be regarded as po- tential agents of human zoonotic infections that are reported with increasing frequency in the U.S. (Orihel and Beaver, 1989). Unfortunately, there is a dearth of information regarding bru- gian filariasis in animals in the U.S. and little or no knowledge of the microscopic anatomy of the species that have been de- scribed. Although Orihel and Beaver (1989) provided a list of morphological features of these filariae in tissues that identify them as Brugia, species identifications are still not possible. The morphologic description of B. beaveri presented in this report represents an initiative to fill that void. Some additional details of the parasite's biology and life cycle not previously reported are included as well.