A Study On The Malaria Vector (Anopheles spp) in A Sudano-Sahelian Savannah Area Of Borno State North Esthern Nigeria And The Insect Growth Regulator Pyriproxyfen (S-31183)

Abstract

Malaria is a major problem in the Sudano-sahel Northeastern Nigeria with the highest prevalence of malaria in pregnancy of 64.5 percent. Little is known about the major malaria vector and its role in malaria transmission. Longitudinal entomological and parasitological surveys were conducted to better understand the relationship of the key components in malaria transmission dynamics .Anopheles mosquitoes were sampled using pyrethroid spray collection and identified morphologically and by molecular methods of Polymerase chain reaction (PCR). Enzyme linked immunosorbent Assay (ELISA) was used for the bloodmeal analysis and mosquito infectivity by circumsporozoite detection. Malariometric indices were determined following the World Health Organization procedures. A total of 1030 female Anopheles mosquitoes were caught consisting of five species, namely, 1026 (99.6%) of Anopheles gambiae complex further identification using PCR showed the predominant sibling species were An. arabiensis Patton 95%(n=221) and An. gambiae s.s. 5%(n=12). Other Anopheles mosquitoes collected were morphologically identified as An. pharoensis, An. squamosus and An. rhodesiense. Results showed that the population of Anopheles arabiensis was significantly higher than that of Anopheles gambiae s.s (P<0.05). Mosquito infection was determined by ELISA method for the detection of Plasmodium falciparum sporozoites 7(2.4%) were positive for P.falciparum circumsporozoite antigen. All seven were An.arabiensis. Indoor collection was significantly higher than the outdoor collection (P<0.01). Mosquito blood feeding source determined by direct ELISA showed human bloodmeal was (98%, 94/96) for indoor collections and (2%, 2/96) for outdoors (P<0.01). The Human Blood Index (HBI) was 0.98. The results implicate xvi An.arabiensis as the main malaria vector in the area. Of a total of 692 children consecutively screened over a period of one year, significant difference (p<0.05) in infection rates was observed between the males and the females. The levels of parasitaemia asexual parasite were significantly related to age (p<0.05).The majority of infected children (68.0%) were aged between 12-60 months and their asexual parasite density was between 1000-5000 of whole blood. The month of September recorded the highest geometric mean parasite density (GMPD) of 13,655 while the lowest parasite densities were observed during the dry season months of March, April, and May while gametocytaemia was not significantly affected by the age of the patients nor the season (p>0.05). Overall average Inhibition of Emergence (IE) rates were 86% for the first week (0-7days) then peaked to 100% during the second week (8-14days) and declined to 73% (15-21days) on the third week and finally to 36% on the fourth week (22-28day). Percentage Inhibition of Emergence between 0.1 and 0.5mg (a.i)/l treatments were not different (P> 0.05). In planning effective site specific malaria vector control programmes under the Integrated Vector Management (IVM) program of the Federal Government of Nigeria, results of this study has highlighted the need to give special consideration to the predominance of a single malaria vector An. arabiensis in the Sudanosahel and the strong seasonality of malaria in contrast to other regions of Nigeria. Findings also demonstrated the potentials of pyriproxyfen as an effective mosquitoes larvicide for consideration under the Integrated Vector Management (IVM) program for use in Sudanosahel Northeastern Nigeria.