Markers of Loa loa infection in permanent residents of a loiasis endemic area of Gabon

Different markers of infection were analyzed in 56 permanent residents of a Loa loa endemic village in Gabon. The population was divided into those with parasitological evidence of L. loa infection and those with no history of loiasis over the period of observation (c. 5 years). 26.7% of villagers had L. loa microfilariae, 33.9% had an ocular passage of an adult worm, and 17.8% had calabar oedema. Several other clinical symptoms were present in both groups of individuals, but none was considered to be pathognomonic for L. loa infection. Most of the villagers were polyparasitized, with Plasmodium falciparum and gastrointestinal parasites being particularly prevalent. Mansonella perstans was present in 80% of the villagers and was equally distributed between L. loa microfilaraemic and amicrofilaraemic individuals. Eosinophil levels were elevated in the whole population, and were not significantly different between the groups who were infected and non-infected with L. loa. Polyclonal immunoglobulin (Ig) E levels were high in both the Ambinda villagers and in Gambian serum from patients infected with M. perstans alone and there was no significant difference between the levels of L. loa specific IgG in the Ambinda villagers and the Gambian patients. However, the level of L. loa specific IgG4 was elevated in 75.6% of amicrofilaraemic individuals and could discriminate between most individuals infected with L. loa and those infected with M. perstans, suggesting that this is the best determinant of infection status in the absence of L. loa microfilariae.