Differential pathogenicity of Brugia malayi, B. patei and B. pahangi in immunodeficient nude mice.

Immunodeficient nude mice chronically parasitized by subperiodic Brugia malayi developed an elephantoid appearance with persistent lymphoedema of limbs and massive lymphangiectasis of subcutaneous vessels containing viable adult worms. Removal of worms reversed the process. The syndrome was not caused by B. patei or B. pahangi and was not correlated with the presence or absence of microfilaremia. Histologic examination of elephantoid mice revealed dilated and tortuous lymphatics containing small nonobstructive lymph thrombi composed of small mononuclear cells and multinucleate giant cells. Draining lymph nodes were not enlarged or congested and mast cells in oedematous tissue were not degranulated. Analysis of lymph aspirated from dilated lymphatics showed increased total protein content: bacterial sepsis was not detected. This work suggests that viable adult B. malayi exert direct pathologic effects upon lymphatics and that this parasite is more pathogenic than related Brugia spp.