Characterization of an Indoor-Resting Population of Anopheles arabiensis (Diptera: Culicidae) and the Implications on Malaria Transmission in Tubu Village in Okavango Subdistrict, Botswana.

Comprehensive knowledge on vector dynamics is lacking in Botswana and yet essential for effective indoor residual spraying. This study assessed some of the entomological indices that contribute to malaria transmission by an indoor-resting population of Anopheles arabiensis Patton (Diptera: Culicidae) in Tubu village, Okavango subdistrict. The pyrethroid space-spray technique and hut searches were used to sample mosquitoes. Species and bloodmeal source identification were done using the polymerase chain reaction techniques. The infective status was determined by the enzyme-linked immuno-sorbent assay test. The human blood indices (HBI), human-biting rates (HBR), and vector densities were computed. Anopheles arabiensis was the sole vector and member of the Anopheles gambiae Giles complex identified. Significant changes in vector densities were observed over seasons, while nonsignificant differences were observed among the huts (P > 0.05). The main source of bloodmeal was cattle (46.8% [65]). There were no significant differences in HBI (P > 0.05) and HBR (P > 0.05) between the seasons. All the 271 mosquitoes tested for sporozoite infection were negative. The results showed that seasonal variations in vector densities corresponded to the traditional malaria and nonmalaria seasons. The vector population was relatively more zoophagic. The HBI and HBR were not influenced by the seasons. None of the endophilic mosquitoes tested (N = 271) was positive for sporozoites. Our study provided some relevant basic information to the local malaria control program that may be used to strategize their operations if malaria elimination has to be achieved by 2017.

Malaria and schistosomiasis risks associated with surface and sprinkler irrigation systems in Zimbabwe.

A comparative assessment of the malaria and schistosomiasis risks associated with surface and sprinkler irrigation systems in Zimbabwe was carried out. The risk assessment of the two diseases was done in accordance with the three standard components of health impact assessment, namely (i) community vulnerability, (ii) environmental receptivity, and (iii) capability of health services to respond to malaria and schistosomiasis. Records of the two diseases were obtained from four health centres serving two surface irrigation schemes and two sprinkler irrigation schemes. For comparison records were also obtained from health centres serving nearby dryland areas. Incidence of schistosomiasis as estimated from recorded new cases of the disease was much higher in surface irrigation schemes than in sprinkler irrigation schemes. For malaria it was the other way around. These findings were confirmed by rapid risk assessments. Malaria risk factors were more prominent in sprinkler irrigation schemes, whereas more schistosomiasis risk factors were identified in surface irrigation schemes. These observations were attributed to poorly maintained infrastructure and inadequate landscape-levelling, which created mosquito breeding sites within the fields in the case of sprinkler schemes, and to poor drainage structures, which created snail-breeding sites in the case of surface-irrigation schemes. Importantly, poor maintenance of sprinkler scheme infrastructure accounted for more disease promoting features than the engineering designs per se. This study demonstrated the value of complementing routinely collected health data with rapid assessment procedures for appraisal of commonly reported diseases.

Absence of insecticide resistance in Anopheles gambiae s.l. (Diptera: Culicidae) after four decades of residual house spraying in Gokwe District, Zimbabwe.

Field tests showed that Anopheles gambiae s.l. from 4 villages in Gokwe District, Midlands Province, Zimbabwe, were susceptible to 4% DDT, 0.025% deltamethrin, 0.025% alpha-cypermethrin, and 0.1% lambdacyhalothrin. In the laboratory, F1 progeny of field-caught females that were identified as Anopheles arabiensis Patton were completely susceptible to deltamethrin, alpha-cypermethrin, lambdacyhathrin, and DDT. The use of insecticides in Gokwe district has not yet induced detectable resistance in An gambiae s.l.

The efficacy and residual life span of two alphacypermethrin insecticide formulations (Fendona 6% suspension concentrate and Fendona Dry 15%) treated on mosquito bed nets.

OBJECTIVE: To compare the effects of mosquito nets treated with two formulations of alpha-cypermethrin insecticide with a view to recommending the most appropriate formulation for use to treat mosquito nets. DESIGN: Assessment of insecticide potency under conditions of ordinary use. SETTING: Chilonga rural irrigation community in south east Lowveld Zimbabwe, a holoendemic area of year round malaria transmission. SUBJECTS: Convenience sample of 20 household heads (volunteers) was issued with treated mosquito nets. INTERVENTION: Following mosquito net treatment and distribution, bioassay tests were carried out monthly for a period of six months on insecticide and placebo treated nets. Questionnaires were administered once, one month post treatment of nets. MAIN OUTCOME MEASURES: Median mosquito knock down times of mosquitoes exposed to insecticide treated nets and community attitude towards the use of insecticide treated nets. RESULTS: Average time taken to knock down the median mosquito progressed from 2.3 minutes to 13.0 minutes for Fendona Dry 15% and from 4.1 minutes to 7.8 minutes for Fendona 6% SC over the six month period. The average time taken to knock down the median mosquito three months post-washing were 13.0 minutes and 7.4 minutes for Fendona Dry 15% and Fendona 6% SC respectively as against more than 30 minutes in controls. Both insecticides exhibited some wash resistance properties. The side effects reported were sneezing, itching, skin rash and smelling. Questionnaire data suggested that alphacypermethrin treated mosquito nets were welcomed. CONCLUSIONS: Both insecticide formulations proved to be suitable candidates. This was because of their insecticidal potency, wash resistance properties and acceptance by the community.