Onchocerciasis is a neglected tropical disease caused by the filarial nematode,
Onchocerca volvulus. It afflicts some 37 million people globally, with 99 % of all the cases living in sub-Saharan Africa [
1]. Onchocerciasis was estimated to account for 18.3 million disability-adjusted life years (DALYs) in sub-Saharan Africa within 20 years [
2]. It is the second leading infectious cause of blindness worldwide [
3]. The debilitating symptoms of onchocerciasis are attributed to inflammatory reactions to dead or dying
O. volvulus microfilariae (mf) in the skin and eyes [
4,
5]. The mf of
O. volvulus is the stage of the parasite ingested during a blood meal on humans by the black fly (of genus,
Simulium), in which the mf develop to the infective third stage larvae (L3), which may be transmitted to another person when bitten by the infected fly. Ivermectin, a microfilaricide is the only recommended drug used in many onchocerciasis elimination programs to break the transmission cycle by killing the
O. volvulus mf. This drug is unfortunately, only a microfilaricide, and a major challenge with ivermectin treatment is the fact that it also kills
L. loa mf in blood, a situation that often leads to severe adverse events (encephalopathy and death) in individuals with high
L. loa mf load [
6]. In addition, there is evidence of resistance or low response rate of mf to ivermectin [
7,
8], emphasizing the need for new therapeutic options.
Efficacious small animal models in onchocerciasis for in vivo screens and preclinical studies, capable of closely mimicking the natural infection in humans are an urgent, unmet need. Immunocompetent rodents are non-permissive to natural infections of
O. volvulus [
9], but experimentally injected
O. lienalis mf have been shown to survive in mice, especially in inbred CBA mice [
10,
11]. The severe-combined immunodeficient (SCID) mice have been exploited as a model for onchocerciasis and are permissive to mf of
O. lienalis [
12]. The
O. lienalis mf mouse model has been validated with ivermectin and other filaricides [
10,
13]. However,
O. ochengi in cattle is the closest in phylogeny to
O. volvulus [
14] and many onchocerciasis drug tests in vitro [
15‐
18] and in naturally infected cows [
19‐
21] have been done based on
O. ochengi. However, the cow is too big, requires huge quantities of drugs, thereby rendering it too expensive for routine screening. Consequently, most funding bodies are reticent in considering the cow as a useful model for onchocerciasis. Both
O. ochengi and
O. volvulus are transmitted by the same black fly vectors of genus,
Simulium. O. ochengi is confined to Africa and combines many important features of the human infection with
O. volvulus [
21].
O. ochengi also forms nodules with close resemblance to those of
O. volvulus [
22]
, which can be enumerated by palpation in situ or removed for analysis during immunological or chemotherapeutic studies. Moreover, both parasites are equally susceptible to the filaricides, ivermectin and suramin [
23], and tetracyclines [
24]. Molecular and biochemical comparisons reveal almost identical antigenic and genomic profiles [
25]. Given that
O. ochengi is readily available and can be obtained at relatively low cost, it is currently regarded as a more practical model in onchocerciasis drug screens [
26]. However, no small laboratory animal has been reported as a model to screen drugs on
O. ochengi mf. This study therefore, was aimed at developing and validating such a model for onchocerciasis based on the use of
O. ochengi, and verifying the usefulness of the model for
L. loa mf counter screens.