The lymphatic pathology of Brugia pahangi in the Mongolian jird

We studied the sequence of histopathologic changes associated with Brugia pahangi (Nematoda: Filarioidea) infections in lymphatic vessels in the spermatic cord of the Mongolian jird (gerbil), Meriones unguiculatus. Intravascular granulomas caused mainly by disintegrating worms were seen in 67% of jirds necropsied on, or after, 35 days postinoculation, whereas none of 20 jirds examined before this day showed dying larvae. These granulomas usually evolved without vascular occlusion. Other granulomatous foci, often with a thrombuslike core, sometimes harbored microfilariae or microfilarialike materials. The perilymphatic cellular infiltrate consisted mostly of eosinophils, lymphocytes, and plasma cells. Large numbers of eosinophils were seen in the early weeks, but later declined, while lymphocytes increased to become the predominant cell in old infections. Irregular fibrosis of some valves and portions of the lymphatic walls were seen as early as the 2nd wk postinoculation. Lymphatic changes in the jird are similar to those described in other hosts infected with filariae, but remained moderate. Living worms appeared to be the stimulus for many observed changes. Most pathologic alterations were well established by 3 or 4 mo and showed little qualitative change during the remaining 4 mo of the study.