Behavioural aspects of the life cycle of Loa. Behavioural aspects of parasite transmission

In the Cameroon rain-forest, infections with Loa loa in man show diurnally periodic microfilariae, which are transmitted by Chrysops silaceus Aust. and C. dimidiatus Wulp, species whose habits bring them into close association with man [cf. RAE/B 49, p. 52]. Three species of monkey are infected with a simian species of Loa, which shows nocturnally periodic microfilariae and is transmitted by the crepuscular and nocturnal, canopy-dwelling C. langi Beq., and C. centurionis Aust. The human and simian parasites appear to have evolved by adaptive radiation in two separate host-vector complexes. Hybridisation between the two parasites is still possible under experimental conditions, but in nature, as a result of the behavioural patterns of the microfilariae, their definitive hosts and their vectors, the exchange of parasitic material between the two complexes appears to be minimal and to a great extent self-eliminating.