Abstract

Analyses were performed to assess how the dose and frequency of administration of the natural infective stage (L3) affects events in the peripheral blood of an infected host. A blood sample was collected from different mandrills (Mandrillus sphinx) infected once with 1000 L3 Loa loa, 250 L3 four times, 100 L3 once and 25 L3 four times. Enzyme-linked immunosorbent assay (ELISA) was used to measure levels of microfilaria-specific IgG and Western blotting to identify antigens. Fluctuation in the number of neutrophils, eosinophils and monocytes was seen during prepatency and patency in relation with some L3 doses. The density of microfilaria in the peripheral blood showed that animals that received 1000 L3 had the highest density of microfilaria as compared to those that received 250L3 ×4, 100L3 ×1 or 25L3 ×4. In contrast, the microfilaria-specific IgG level was higher in animals that received doses of 25 L3 ×4 as compared to those that received 1000 L3 ×1 (p< 0.001) but comparable with the level in the groups that received 250 L3 ×4 or 100 L3 ×1 (p>0.05). Identification of microfilaria antigens recognized by this specific IgG on Western blotting revealed the presence of 23-, 20- and 14-kDa antigens specifically in animals that developed patent infection. These results suggest that the regimen of L3 administration may have an effect on the level of humoral immune response and to some extent on the density of microfilaria.

Key words:  Loa loa, Helminths, larvae, immunology, primate.