OBJECTIVES: To investigate the determinants of purchase of insecticide-treated nets (ITNs) and explore the policy implications of the findings for ITN programmes. METHODS: Two surveys were conducted 1 month apart in three villages. The first survey was used to determine stated willingness to pay (WTP) and respondent practices regarding untreated nets and ITNs. The second survey was accompanied by actual sales of ITNs. Pre-tested interviewer-administered questionnaires using three contingent valuation method (CVM) question formats, namely the bidding game (BG), binary with follow up (BWFU) and a structured haggling technique (SH), were administered to different sub-samples of the respondents. The nets were sold at a price of 350 Naira (US dollars 1 = 110 Naira). Bivariate analysis and logistic regression were used to investigate the factors that explain actual WTP. FINDINGS: While 15/158 (9.5%), 21/166 (12.7%) and 35/144 (24.3%) of the respondents in the BG, BWFU and SH stated WTP amounts that were equal to or greater than the price of the net, 19.6%, 24.7% and 24.3% of respondents actually purchased the nets in the three groups respectively. Lower socioeconomic groups were less likely to purchase the nets, while households with a recent attack of malaria and those that stated higher WTP amounts were more likely to purchase nets. Stated WTP was positively associated with actual WTP (p < 0.01). Increased distance of the respondents to the ITNs sales point decreased net purchases (p < 0.05). CONCLUSIONS: Stated WTP was a good predictor of actual WTP. ITNs distribution strategies that will decrease time and travel costs to households are needed to increase net coverage. Also, ITNs financing mechanisms are needed that will ensure that lower socioeconomic groups and those at greater risk of malaria are protected. Governments and donors should take the lead to ensure that ITNs programmes are equitable.

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Who buys insecticide-treated nets? Implications for increasing coverage in Nigeria

We measured ivermectin in plasma, urine, and saliva of nine patients with onchocerciasis. The aim was to establish pharmacokinetic parameters and to assess the most facile medium for use in monitoring compliance. Binding of ivermectin to plasma proteins in vitro was also investigated. The mean (+/- SEM) plasma values for the nine subjects were as follows: weight, 66.3 +/- 2.8 kg; dose, 11.11 +/- 0.4 mg; half-life, 56.50 +/- 7.01 hours; clearance, 142.5 +/- 22.6 L/kg; volume of distribution, 9.91 +/- 2.67 L/kg; area under the plasma concentration-time curve, 1545.3 +/- 190.5 ng/ml.hr; time to reach maximum concentration, 4.7 +/- 0.5 hours; and maximum concentration, 38.2 +/- 5.8 ng/ml. Ivermectin was not detected in the urine of any of the nine subjects. Low levels were found in saliva. Blood specimens remain the only reliable biologic fluid for assessment of compliance after ivermectin oral administration. Ivermectin binds specifically to human serum albumin.

Protein binding and ivermectin estimations in patients with onchocerciasis

Onchocerciasis (river blindness) a parasitic disease caused by the filarial worm Onchocerca volvulus is endemic in much of western Africa and central and southern America. Nigeria is the most endemic country in the world for the disease. While onchocerciasis can be controlled through the mass distribution of ivermectin limited funds have resulted in the coverage of only less than 30% of affected communities with mass distribution of the drug. Findings are reported from an assessment of the levels of willingness to pay (WTP) for local ivermectin distribution in Achi community Oji River Local Government Area (LGA) of Enugu State; Nike Enugu-East LGA of Enugu State; and Toro Toro LGA of Bauchi State. Respondents were randomly selected household heads or household representatives from 404 households in Achi 393 in Nike and 214 in Toro. 92.1-93.3% of respondents were willing to pay 5-100 Naira for the drug to be distributed with a median of 20 Naira or 2-3 times the modelled unit direct economic cost of distributing ivermectin to all eligible community members. Respondents occupation marital status average monthly expenditure of health care manifestations of onchocerciasis type of savings scheme adopted age group level of education and type of property were statistically significant variables affecting WTP.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-3156.1998.00304.x

Willingness to pay for community-based ivermectin distribution: A study of three onchocerciasis-endemic communities in Nigeria

In the Lower Cross River basin in Nigeria, no pre-control entomologic profile of Onchocerca volvulus infection in the local Simulium damnosum population was available prior to the initiation of an ivermectin control program in 1995. A longitudinal entomologic study was therefore carried out over a 12-month period (January- December 2001) at the Agbokim waterfalls and Afi River, which are breeding sites of S. damnosum in the river basin. A total of 9,287 adult S. damnosum were caught on human bait; 9,048 (97.43%) were dissected, of which 313 (3.46%) were infected. Annual biting rates (ABRs) of 42,419 and 28,346 bites per persons per year were recorded at the Agbokim Waterfalls and Afi River, respectively. The annual transmission potential (ATP) was 419 infective larvae per person per year at the Agbokim Waterfalls and 427 at the Afi River. Monthly biting rate and monthly transmission potential varied significantly (P < 0.05) at the two sites. Transmission was highly seasonal from April to September, corresponding to the peak biting period of the vector. The high ATP and ABR values are a measure of the mesoendemicity of onchocerciasis in the river basin. There was a significant F0.05 (1, 10) (P < 0.05) variation in the relative fly abundance from both sites. It was observed that human activities such as farming, fishing, timber cutting, and hunting are done in the early morning and late afternoon, which corresponds to the peak diurnal biting period of the vector. Changes in these practices and attitudes may markedly affect the disease intensity and transmission.

Status of forest onchocerciasis in the Lower Cross River basin, Nigeria: entomologic profile after five years of ivermectin intervention.

Ivermectin levels were measured in breastmilk and plasma of 4 healthy mothers after an oral 150 micrograms/kg dose. Mean +/- S.D. plasma and milk values were 37.9 +/- 0.54 and 14.13 +/- 0.43 (ng/ml) respectively. Steady-state ivermectin levels in milk were low. Our results suggest that exclusion of lactating mothers from mass chemotherapy with ivermectin may be unnecessary.

Ivermectin levels in human breastmilk

Reports on onchocerciasis in Nigeria have been scanty, despite the size of the country and of the problem. A survey of the prevalence and transmission of the disease in the south-eastern communities of Nigeria was commenced, with a year-long study of the vector and the clinical manifestations of the disease in a forest-savannah mosaic area on the Oji river. Microfilaraemia was found in 76% of the population, and nodules in 62%; there were no significant differences between male and female prevalence rates. Skin and ocular lesions of onchocerciasis, including 'Sowda', were common. Flies of the Simulium damnosum complex were found breeding along the entire length of the Oji river and tributaries. Biting occurred all the year round, but peaked in the months of March, April and May.

S. Adibua

Papers

Studies on onchocerciasis in forest-savannah mosaic areas of Nigeria. I. Investigations in Gbaragu, Oji River.