Onchocerciasis of cattle and man: serological recognition of parasite specific and cross-reactive antigens

Abstract

The endemicity of human onchocerciasis in NorthI Cameroon can be related to the presence of cattle. In the Adamawa highland, an area (if intensive cattle breeding, human onchocerciasis is hypoendemic, although the trans­ mission of O. volvulus infective third-stage larvae is much higher than in the hyperendemic savanna area, where cattle breeding is almost non-existing (Wahl, 1991). Onchocerciasis-associated eye lesions and blindness very rarely occur in the highland, whilst in the savanna region, severe onchocerciasis in the human population is frequent (Renz et al., 1987). Simulium squamosum, the vector of human onchocerciasis in this area also transmits O. ochengi, a cattle filaria, which out-numbers the infective larvae of O. volvulus in man-biting flies by a factor of over ten in the highland area. It is believed, that the ongoing and intensive transmission of this bovine species to man induces cross-protective immunity against forthcoming lar­ vae of O. volvulus (cf. abstracts Renz et al., Wahl et al). In this study we first compared the protein composition of O. ochengi and O. volvulus and then examined the antigen recognition by sera from patients living in the highland (cattle breeding) or savanna area. It was of particular inte­ rest to identify O. ochengi antigens that refer to contact of highland patients with this cattle filaria. Using one- and two dimensional electrophoresis the two filariae showed a high homology. However some speciesspecific proteins could be identified in O. ochengi and O. volvulus extracts, with molecular weights of 32, 6.3, 5.3 kDa and 16, 94, 9.1, 5.6 and 5.1 kDa, respectively. Sera from cattle recognized a major O. ochengi-specific antigen duplett of 28 kl)a, whilst other specific antigens migrated between 10-20 kDa. Using Tricine-SDS-PAGE and immunoblotting human sera identified a possible O. ochengispecific antigen of 7 kDa. Comparison of the two patient groups from the savanna (with high microfilarial density in the skin) and highland (few microfilariae or skin-negative) revealed distinct diffe­ rences in respect to their antigen recognition ; low molecu­ lar weight antigens of both filaria species were recognized