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.

Anthelmintic efficay of nauclea latifolia extract against gastrointestinal nematodes of sheep: in vitro and vivo studies

Direct effects of Nauclea latifolia extracts on different gastrointestinal nematodes of sheep is described. In vivo and in vitro studies were conducted to determine possible anthelmintic effect of leaf extracts of Nauclea latifolia toward different ovine gastro intestinal nematodes. A larval development assay was used to investigate in vitro; the effect of aqueous and ethanolic extracts of N. latifolia towards strongyles larvae. The development and survival of infective larvae (L3) was assessed and best-fit LC50 values were computed by global model of non-linear regression analysis curve-fitting (95CI). Twenty sheep harbouring naturally acquired gastrointestinal nematodes were treated with oral administration of ethanolic extracts at a dose rate of 125 mg/kg; 250 mg/kg and 500mg/kg to evaluate therapeutic efficacy; in vivo. The presence of the extracts in the cultures decreased the survival of larvae. The LC50 of aqueous and ethanolic extract were 0.704 and 0.650 mg/ml respectively and differ significantly (P0.05; paired t test). Faecal egg counts (FEC) on day 12 after treatment showed that the extract is effective; relative to control (1-way ANOVA; Dunnett's multiple comparison test); at 500mg/kg against Haemonchus spp; Trichostrongylus spp (p0.05); Strongyloides spp (P 0.01); at 250mg/kg against Trichuris spp (P 0.01) and ineffective against Oesophagostomum spp (p0.05). The effect of doses is extremely significant; the day after treatment is sometimes significant while interaction between dose and day after treatment is insignificant (2-way ANOVA). N. latifolia extract could therefore find application in the control of helminth in livestock; by the ethnoveterinary medicine approach

Comparative in-vitro studies on the efficacy of ivermectin against gastrointestinal sheep nematode

Purpose: This study was designed to evaluate the relative efficacy of various brands of ivermectin injection available for use in clinical veterinary practice in Nigeria. Method: Ivermectin injections were evaluated by a larval development assay (LDVA), using the larvae of Strongyles (predominantly Haemonchus contortus) of sheep. The effect of standard solutions of the drug from the various brands on the transformation of L1 to L3 and survival of L3 larvae was used to assess bioactivity. The 50% lethal concentration (LC50) was determined from regression line obtained by probit transformation of the biological data. The LC50 values for each of the brands were compared with that of the innovator brand (Ivomec Super) for any significant difference. Results: The LC50 values obtained for the five brands varied widely. It ranges from 1.1±0.17 ng/ml for the innovator brand to 2.3±0.3, 3.0±0.3, 8.0±0.2 and 17.0±0.3 ng/ml for the other four brands. The biological assays performed on each of the five brands were of comparable precision. LC50 for Ivomec super was significantly different from those of the other four brands (Student's t test, p < 0.01). Conclusion: The bioactivities of brands of ivermectin injections available in Nigeria are significantly different. This is a probable reason for the varied treatment response to various brands of ivermectin injection in veterinary practice in Nigeria. This justifies the need for drug regulatory bodies in Nigeria to ensure that ivermectin injections registered for use in Nigeria meets approved standards before the drugs are allowed to be imported into the country