Filariasis due to Loa loa and Manspnella perstans: distribution in the region of Okondja, Haut-Ogooué Province, Gabon, with parasitological and serological follow-up over one year

Abstract
The prevalence of Loa loa and Mansonella perstans filariasis has been determined in 6 rural villages in eastern Gabon. Between 18·9 and 27·2% of people carry L. loa microfilariae with an overall microfilarial rate of 25·1%. The microfilarial rate for M. perstans was more variable, between 33·3 and 62·2% (average 49·1%). No significant difference was seen in the microfilarial rate with age over 15 years for either parasite, but men were infected more frequently than women. Anti-L. loa antibody titres were measured, using a homologous microfilarial antigen in ELISA. Taking the parasitological and immunological evaluations together, only 10% of the sample population appear to be free of these filarial infections. L. loa and M. perstans microfilaraemia and corresponding serology were also investigated twice in 150 people at a one-year interval. 99·1% of the cases who had no circulating L. loa microfilaria in March 1984 still did not show any 12 months later. Similarly, 97·1% of the untreated, microfilaraemic cases still harboured this parasite a year later. The same was not observed for M. perstans, since microfilariae appeared or disappeared in 26·7% of the cases. This suggests different dynamics for the two filarial infections. Variation in individual anti-L.loa antibody titres was low. The possibility of a genetic influence on the expression of loiasis is discussed.

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