Seasonal Variations in Biting Density and Infectivity of Simulium damnosum Complex in Ezeagu and Oji-River Local Government Areas of Enugu State, Nigeria

Background and Objectives: Onchocerciasis is a parasitic filarial disease of the tropics, having serious effects on global public health and the economy of endemic countries. Nigeria is among the most endemic countries, necessitating much research and control program interests. This study determined the rate of transmission of onchocerciasis in Oji-River and Ezeagu Local Government Areas of Enugu State, Nigeria. Methodology: Human landing sampling method was used to collect black flies. Parity assessment was conducted to determine the age of fly populations. Parous flies were further dissected to detect the presence or absence of Onchocerca larvae. Biting rates and transmission potentials were calculated using standard methods. The principal vector groups in the study area were identified morphologically. Results: A total of 352 adult female flies were collected during the study period. These were identified as members of the forest species of the S. damnosum complex. There were significant differences between monthly abundances of black flies caught during the entire study period (P < 0.04). Comparison of the monthly biting rates (MBRs) showed a significant difference in (P < 0.02). The MBR was lowest in February but highest in October. Generally, parity rate of over 50 % was observed throughout the period except for November. None of the flies dissected was infective. Diurnal biting activities of black flies between the months were significantly different from each other (P < 0.01). Conclusions: Onchocerciasis transmission is low in the studied area, and is largely by means of the forest black flies as these were the only observed group. None of the dissected flies was found to be infective. The findings of this study will be of tremendous benefit to policy makers in the National Onchocerciasis Elimination Programme. It calls for a continuous monitoring of onchocerciasis disease conditions in the study area.

Bancroftian filariasis among the Mbembe people of Cross River state, Nigeria.

Background & objective: Bancroftian filariasis is a major public health and socioeconomic problems in the humid tropical and subtropical regions of the world. A study was undertaken to investigate the status of the disease in some rural communities of Cross River State, Nigeria, with a view to enriching the epidemiological baseline data of the disease in Nigeria. Methods: A total of 897 Mbembe people living in six major villages of Obubra Local Government Area of Cross River State, Nigeria were examined between December 2008 and June 2009 for lymphatic filariasis due to Wuchereria bancrofti. Results: Out of the 897 persons examined, 139 (15.5%) were positive for microfilariae in their blood smear. Infection varied significantly among villages (p <0.05) but was not sex-specific (p >0.05). The overall mean microfilarial density among the total population was 9.9 mf/50 μl. The occurrence of microfilaria in the peripheral blood of the infected persons was neither age nor sex specific (p >0.05). The most important clinical manifestations were hydrocele (9.7%) and lymphoedema (2.3%). Overall disease prevalence was (6.8%). Conclusion: Government effort on the Community Directed Treatment with Ivermectin (CDTI) project should be complimented with albendazole distribution to the endemic communities. Environmental sanitation should also be intensified to eliminate the breeding sites of the mosquito vectors.

Transmission dynamics of Simulium damnosum in rural communities of Akwa Ibom State, Nigeria.

BACKGROUND & OBJECTIVES: Onchocerciasis is endemic in some parts of Akwa Ibom State, Nigeria. This study describes the entomological parameters of transmission in three rural communities of Akwa Ibom State, prior to ivermectin intervention in 2004. METHODS: Blackflies were caught using human bait and 90% of the flies were dissected for parity. All parous flies were further dissected for the presence of filaria larvae. Monthly and annual biting rate, and transmission potential were calculated using standard methods. RESULTS: A total of 4296 adult Simulium damnosum were caught on human bait, 4119 were dissected of which 208 (5.1%) were infected with Onchocerca volvulus larvae. Transmission parameters varied significantly (p < 0.05) in the three villages. Annual biting rates, ranged from 9490 to 11,218 bites per person per year. The annual transmission potential ranged from 131 to 189 infective larvae per person per year, monthly biting rate and monthly transmission potential varied significantly (p < 0.05) in the three villages. Transmission was highly seasonal occurring during the peak of rainy season from August to October. There was no transmission during the dry periods--November to March, and the early rainy periods--April to May. The diurnal biting activity of the fly exhibited a bimodal pattern with a morning peak (0900-1000 hrs) and a more marked evening peak (1600-1700 hrs). INTERPRETATION & CONCLUSION: The results indicate that there is a temporal and spatial variation in the transmission dynamics of S. damnosum in the study area.

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.

Longitudinal evaluation of repellent activity of Ocimum gratissimum (Labiatae) volatile oil against Simulium damnosum

To determine the repellent activity of Ocimum gratissimum volatile oil against Simulium damnosum (blackflies), a 12 month (January-December 2003) field study was conducted in three onchocerciasis endemic communities (Idomido, Obio camp, and Ikot Adaha) in Ini Local Government Area of Akwa Ibom State, Nigeria. The result revealed that topical application of 20 percent (v/v) concentration of the oil with liquid paraffin as a base, reduced the biting rate of S. damnosum by 90.2, 81.6, and 79.7 percent, in Idomido, Obiocamp, and Ikot Adaha respectively. The oil gave protection against the bite of S. damnosum for at least 3 h. A total of 710 adults S. damnosum were caught by individuals treated with Ocimum oil, as against 4296 caught by the control group. When the flies caught by the treated individuals were dissected none of them was infected with microfilariae of Onchocerca volvulus. Human-vector contact and onchocerciasis transmission could be reduced by the topical application of the volatile oil during the peak biting periods of the vector.