The bovine parasite Onchocerca ochengi is a nodule-dwelling filarial nematode, closely related to O. volvulus, the causal
agent of human River Blindness, and, sharing with it, the same vector. This brief review, based on a presentation at the
BSP Autumn Symposium 1999, describes recent work supported by the WHO Drug Development Research Macrofil
programme and the Edna McConnell Clark Foundation vaccine development programme, to research the chemotherapy
and immunology of onchocerciasis utilising this model system, with experimental infections in Liverpool and field
infections in northern Cameroon. In a series of chemotherapeutic trials involving 10 compounds in 20 treatment regimes,
the comparability of drug efficacy against O. ochengi with that described against O. volvulus has been demonstrated.
Repeated, long-term treatment with oxytetracycline has been shown to be macrofilaricidal and the effect is hypothesized
to be related to action on Wolbachia endobacteria, abundant in O. ochengi. Avermectins/milbemycins are not macrofilaricidal
(even in high and repeated long-term treatments) but induce sustained abrogation of embryogenesis. In
prospective, field exposure experiments with naive calves, prophylactic treatments with ivermectin and moxidectin
prevented the development of adult worm infection, raising the possibility that drug-attenuated larval challenge infections
may induce immunity. Putatively immune adult cattle exist in endemically exposed populations, and these have been
shown to be significantly less susceptible to challenge than age-matched naive controls, whereas radically drug-cured,
previously patently-infected cattle were not. Experimental infections with O. ochengi have revealed the kinetics of the
immune response in relation to parasite development and demonstrate analogous responses to those reported in O. volvulus
infection in humans and chimpanzees. In an immunization experiment with irradiated L3 larvae, cattle were significantly
protected against experimental challenge – the first such demonstration of the experimental induction of immunity in a
natural Onchocerca host–parasite system. Taken collectively, these studies not only demonstrate the similarity between the
host–parasite relationships of O. ochengi in cattle and O. volvulus in humans, but promise to advance options for the control
of human onchocerciasis.