Population dynamics of onchocerca volvulus microfilariae in human host after six years of drug control.

BACKGROUND & OBJECTIVES: Mass administration of ivermectin drug was carried out annually between 1995 and 2001 in three villages that were endemic for onchocerciasis in the Lower Cross River Basin, Nigeria. The aim of this study was to evaluate the population dynamics (dispersion patterns, distribution, prevalence and intensity) of Onchocerca volvulus microfilariae in their human host after six years of ivermectin treatment. METHODS: A total of 1014 subjects from three rural areas in Etung Local Government Area of Cross River State, Nigeria were screened for skin microfilariae using standard parasitological method of diagnosis. RESULTS: Ivermectin drug intervention had significantly reduced the prevalence of skin microfilariae (PMF) from 69.3% pre-control to 39.3% and community microfilarial load (CMFL) from 7.11 to 2.31 microfilariae per skin snip. Males (45%) were significantly (p <0.05) more infected than females (34%). Both microfilarial prevalence and intensity increased with age. Pearson correlation test between intensity and age was not significant (r = 0.37; p >0.05). The correlation between age-dependent parasite prevalence and mean abundance was also not significant (r = 0.42; p >0.05). The degree of dispersion as measured by variance to mean ratio (VMR), coefficient of variation (CV) and exponent 'K' of the negative binomial model of distribution showed that the parasite aggregated, clumped and overdispersed in their human host. The relative index of potential infection of each age group showed that adults between the age of 21 and 50 yr accounted for 52.7% of microfilariae positive cases. INTERPRETATION & CONCLUSION: Aggregated and overdispersion of O. volvulus observed in this study showed that active transmission could still be going on, because the tendency of the vector, Simulium damnosum ingesting more microfilariae was high due to the aggregated and overdispersed nature of the parasite with its host.

Macrofilaricidal effects of chloroquine on adult Onchocerca volvulus by local infiltration of palpable onchocercal nodules

O efeito macrofilaricida da infiltração local, com uma alta concentração de cloroquina, dentro da cápsula do nódulo oncocercótico sobre o verme adulto de Onchocerca volvulus foi determinado. Seis semanas depois da infiltração, estudos histopatológicos de nódulos simple demonstraram todos os vermes adultos mortos. Em conglomerados de nódulos a ação da cloroquina foi só sobre os vermes adultos do nódulo infiltrado, não acontecendo a difusão da droga aos nódulos adjacentes. A infiltração de cloroquina a nódulos novos ou de recente formação reduz a carga de vermes adultos dos indivíduos parasitados e pode ser uma alternativa para os altos custos das nodulectomias.

The macrofilaricidal effects of local infiltration of high concentrations of chloroquine into the capsule of onchocercal nodules on adult worms of Onchocerca volvulus was determined. Six weeks post infiltration, histological examination of single nodules showed all adult worms to be dead. With nodule conglomerates, there was localized action of chloroquine only on the adult worms in the infiltrated nodule, with no diffusion of the drug to adjacent nodules. Chloroquine infiltration of young, recently formed nodules to reduce the adult worm load of infected individuals may be an alternative method to costly nodulectomy.