The indirect hemagglutination test and the bentonite flocculation test utilizing a saline extract of Dirofilaria immitis have been evaluated. The test was reactive with sera from individuals with infections of Acanthocheilonema perstans and showed higher titers for symptomatic patients with microfilariae in the blood. In a group of 42 symptomatic patients, 92% of 13 microfilariae-positive patients and 62% of 29 microfilariae-negative patients showed positive serologic tests. In a group of 15 asymptomatic individuals with microfilariae in the blood, 67% were positive. From a group of 295 asymptomatic-microfilariae-negative individuals, 21 sera (7%) were positive.
Testing 632 sera from 295 normal missionaries, 84 normal Americans, and 253 individuals with various other parasitic and bacterial infections, an over-all non-specific response of 10% was obtained, utilizing the following criteria for a positive serologic test: (1) a hemagglutination titer of 1:200 or higher with a positive flocculation of 1:5 or higher, or (2) a hemagglutination titer of 1:400 with a negative flocculation reaction. Sera from 141 patients with helminth diseases showed a non-specific rate of 21%. This high rate was due to cross-reactions with trichinosis sera (35%) schistosomiasis (20%) and ascariasis (27%). Since the schistosomiasis and ascariasis sera were from individuals born in an area endemic for filariasis, the reactions may represent a serologic response to past experience with filariasis. Only 5% of 112 sera from individuals with non-helminthic diseases and 5% of 84 sera from normal individuals were positive.