Species Composition of Anopheles (Diptera: Culicidae) in Selected Forested Tourist Areas of Nigeria Endemic for Malaria.

The study was carried out to determine relative abundance, species diversity, of Anopheles species (Diptera: Culicidae) in selected forested areas in Cross River State, Nigeria and the prevalence of malaria infection in the specimens. Mosquitoes were collected using pyrethrum spray catch and Centre for Disease Control light traps modified with yeast and sugar to generate carbon dioxide (CO2) and identified using morphological identification keys. We used a multiplex polymerase chain reaction followed by restriction fragment length polymorphism (PCR-RFLP) to simultaneously distinguish sibling species of the An. gambiae s.l, including separation of An. gambiae s.s. and An. coluzzii (Diptera: Culicidae). The samples were also screened for Plasmodium infection using the enzyme-linked immunosorbent assay. One hundred and four Anopheles specimens were collected during the study of which 97% was An. gambiae complex and 3% was An. rufipes (Diptera: Culicidae). Only 77% of the An. gambiae s.l. was identify to species level. The result shows that 41.6% was An. gambiae s.s. and 34.6% was An. coluzzii. No sporozoite of Plasmodium was detected in the Anopheles species. The study also found a hybrid form of An. gambiae s.s. and An. coluzzii. These findings suggest the first documented evidence of hybrid forms of An. gambiae s.s./An. coluzzii in South Eastern Nigeria although its epidemiological implication is still not clear.

Dynamics of malaria vector indices in two vegetation zones within North Eastern Adamawa State, Nigeria.

Studies profiling community and zonal malaria entomological risk indices are required to identify high risk areas where targeted control resources are most needed or likely to have the greatest impact on reducing risk of malaria infection. This study presents a first report on malaria vector risk indices in two vegetation zones within Adamawa state, Nigeria. Endophilic mosquitoes were collected for one year in selected communities in the Guinea and Sudan savanna zones within the State. Plasmodium falciparum Sporozoite and human blood meal ELISA assays were carried out on the female Anopheles mosquitoes collected. Sibling species composition of the An. gambiae complex were determined using PCR assays. Mean numbers of mosquitoes in the Guinea savanna communities were significantly (t = 7.73, DF = 11, p < 0.001) higher than the Sudan. Man-biting rates (F = 2.76, p = 0.13) of Anopheles mosquitoes were higher in the Guinea but not significantly different from Sudan savanna. Sporozoite rates of mosquitoes within the Guinea savanna were 2.7 times higher than the Sudan. The predominant Anopheles coluzzii species encountered in the state had higher overall human blood indices (0.63) and sporozoite rates (6.9%) compared to An. gambiae (0.39, 1.9%) and An. arabiensis (0.58, 2.3%) respectively. Overall annual human blood indices (0.59) of mosquitoes in Adamawa were lower compared to reports from other States. Prevalence and higher transmission risks indices of endophilic An. coluzzii mosquitoes reveal the need for LLIN and management of relatively permanent An. coluzzii breeding sites in the State. Widespread cattle rearing lifestyle and lower human blood indices of mosquitoes in the study area suggest the need to investigate cattle blood indices of the mosquitoes in the state. Higher entomological risk indices in the Guinea Savanna zone provide baseline information for prioritization of malaria vector control supplies within the State.

Dynamics of malaria vector indices in two vegetation zones within North Eastern Adamawa State, Nigeria

@#Studies profiling community and zonal malaria entomological risk indices are required to identify high risk areas where targeted control resources are most needed or likely to have the greatest impact on reducing risk of malaria infection. This study presents a first report on malaria vector risk indices in two vegetation zones within Adamawa state, Nigeria. Endophilic mosquitoes were collected for one year in selected communities in the Guinea and Sudan savanna zones within the State. Plasmodium falciparum Sporozoite and human blood meal ELISA assays were carried out on the female Anopheles mosquitoes collected. Sibling species composition of the An. gambiae complex were determined using PCR assays. Mean numbers of mosquitoes in the Guinea savanna communities were significantly (t = 7.73, DF = 11, p < 0.001) higher than the Sudan. Man-biting rates (F = 2.76, p = 0.13) of Anopheles mosquitoes were higher in the Guinea but not significantly different from Sudan savanna. Sporozoite rates of mosquitoes within the Guinea savanna were 2.7 times higher than the Sudan. The predominant Anopheles coluzzii species encountered in the state had higher overall human blood indices (0.63) and sporozoite rates (6.9%) compared to An. gambiae (0.39, 1.9%) and An. arabiensis (0.58, 2.3%) respectively. Overall annual human blood indices (0.59) of mosquitoes in Adamawa were lower compared to reports from other States. Prevalence and higher transmission risks indices of endophilic An. coluzzii mosquitoes reveal the need for LLIN and management of relatively permanent An. coluzzii breeding sites in the State. Widespread cattle rearing lifestyle and lower human blood indices of mosquitoes in the study area suggest the need to investigate cattle blood indices of the mosquitoes in the state. Higher entomological risk indices in the Guinea Savanna zone provide baseline information for prioritization of malaria vector control supplies within the State.

Species composition of the Anopheles gambiae complex across eco-vegetational zones in Bayelsa State, Niger Delta region, Nigeria.

BACKGROUND & OBJECTIVES: Correct vector identification is an important task in the planning and implementation of malaria vector control programmes. This study was designed to provide baseline information on the species composition and distribution of members of the Anopheles gambiae complex in three eco-vegetational zones in Bayelsa state, Nigeria. METHODS: Adult mosquitoes were collected by pyrethrum spray catch (PSC) in randomly selected houses during September 2009-August 2010. Anopheles mosquitoes were identified using standard morphological keys. Mosquitoes identified as An. gambiae s.l. were used for species specific PCR-assays. RESULTS: Out of 203 Anopheles gambiae s.l. successfully amplified, 180 (88.7%) were Anopheles gambiae s.s., 14 (6.9%) were An. melas and 9 (4.4%) were An. arabiensis. The variation in the sibling species composition of An. gambiae s.l. was not significant (p >0.05). Anopheles gambiae s.s. was predominant in all the collections with three sibling species occurring in all the eco-vegetational zones. INTERPRETATION & CONCLUSION: The observation of An. melas in the fresh water swamp forest of Yenagoa is of importance in malaria epidemiology. These findings are of importance in the planning and implementation of malaria vector control strategy in the three eco-vegetational zones of Bayelsa state.

Anopheles gambiae s.s. breeding in polluted water bodies in urban Lagos, southwestern Nigeria.

BACKGROUND & OBJECTIVE: Urban malaria is on the rise in Nigeria due to rapid industrialisation and developmental activities. A study was undertaken in Lagos, Nigeria to study the Anopheles breeding in polluted water bodies. METHODS: Anopheles larval breeding habitats were surveyed and water samples from 24 larval breeding sites from four strategic areas in urban Lagos were analysed. The relationship between eight abiotic variables (pH, dissolved oxygen, conductivity, hardness, nitrate, total dissolved solids, turbidity and oil) and density of Anopheles larvae were investigated. The levels of heavy metals (Zn, Co, Cu, Pb, Mn, Fe, Hg and Ni) pollution were analysed by Atomic Absorption Spectrophotometry. RESULTS: Morphological and PCR analysis of 2358 anopheline larvae revealed only the presence of two members of the Anopheles gambiae complex consisting of 93.1% Anopheles gambiae s.s. and 6.9% An. arabiensis. Multiple regression analysis revealed a significant association between occurrence of An. arabiensis larvae and two independent variables: pH and turbidity but not for An. gambiae s.s. The levels of three heavy metals: Fe, Cu and Pb from more than half of the sites surveyed were three times higher than the values obtained in natural breeding sites of An. gambiae s.s. from a rural area of Lagos. Over 85% of An. gambiae s.s. larvae were found in water bodies characterised by low dissolved oxygen (<3 mg/L), high conductivity (>900 uS/cm), turbidity (>180 FAU), oil (>11 mg/L) and heavy metals: Fe, Cu, and Pb (>0.4 mg/L). INTERPRETATION & CONCLUSION: These results indicate that An. gambiae s.s. is adapting to a wide range of water pollution in this urban area. The survival of the mosquito in widespread polluted water bodies across Lagos metropolis could be responsible for the rise in the incidence of malaria.

Dynamics of knockdown pyrethroid insecticide resistance alleles in a field population of Anopheles gambiae s.s. in southwestern Nigeria.

BACKGROUND & OBJECTIVES: Pyrethroid insecticide resistance in the malaria vector Anopheles gambiae Giles is mainly associated with reduced target site sensitivity arising from a single point mutation in the sodium channel gene, often referred to as knockdown resistance (kdr). This resistance mechanism is widespread in West Africa and was reported for the first time in Nigeria in 2002. Here we present changes in the susceptibility/resistance status of the molecular 'M' and 'S' forms of An. gambiae and the frequency of the kdr alleles from 2002-05. METHODS: Adult anophelines were sampled quarterly inside human dwellings from January 2002 to December 2005 and adults reared from wild larvae were identified using morphological keys. Samples belonging to the An. gambiae complex were subjected to PCR assays for species identification and detection of molecular 'M' and 'S' forms. Insecticide susceptibility tests were carried out using standard WHO procedures and test kits only on 2-3 days old adult An. gambiae s.s. reared from larval collections. The kdr genotypes were determined in both live and dead specimens of An. gambiae s.s. using alleles-specific polymerase chain reaction diagnostic tests. RESULTS: The overall collection showed that the molecular 'S' form was predominant (> 60%) but the proportions of both forms in the mosquito populations from 2002-05 were not statistically different. Both forms also occurred throughout the period without apparent relationship to wet or dry season. Insecticide susceptibility tests did not show any significant increase in the resistance status recorded for either Permethrin or DDT from 2002-05, rather, an improvement in the susceptibility status of the mosquitoes to these insecticides was observed from 2004-05 relative to the tests performed in 2002-03. CONCLUSION: The proportion of the molecular 'M' and 'S' form of An. gambiae and the kdr frequencies have not increased significantly from 2002 when it was first reported in Nigeria. However, the findings on susceptible mosquitoes exhibiting the kdr gene need further investigation. Further monitoring of this may provide additional information on the ongoing debate on the possibility of restriction in gene flow and reproductive barriers in these sympatric taxa.

Behaviour and population dynamics of the major anopheline vectors in a malaria endemic area in southern Nigeria.

BACKGROUND & OBJECTIVES: Anopheline mosquitoes consist of a large number of species each of which differs from another in population, resting and feeding behaviour in relation to the prevailing conditions in the locality. A longitudinal study was carried out to investigate the population dynamics, resting and feeding behaviour of the major anopheline species found in a rain forest zone of Nigeria. METHODS: Mosquitoes resting and biting indoors were collected using WHO standard techniques and supplemented with outdoor-biting collections in the study areas between January and December 2004. Samples were sorted and identified microscopically for morphological features while molecular identification was carried out using polymerase chain reaction (PCR) techniques. RESULTS: PCR-based tests showed that both indoor and outdoor collections constitute three groups of Anopheles mosquitoes, An. gambiae s.l. Giles (68.6%), An. funestus Giles (30.7%) and An. moucheti Evans (0.7%). Of the 1342 female Anopheles mosquitoes collected indoors, 799 were caught resting and 543 were caught biting. The outdoor-biting population accounted for 28.8% of the total collections (n=1885). There was no significant difference (p > 0.05) in the biting activities (indoors and outdoors) of these species in four villages. However, An. arabiensis and An. moucheti were more exophagic with >60% of their biting occurring outdoors while An. gambiae and An. funestus were more endophagic with >55% of their biting occurring indoors. The human-vector contact with An. gambiae and An. funestus (indoors) was about 73.3 and 66.7%, respectively as against 27.7% in An. arabiensis and 25.3% in An. moucheti. This gave the corresponding man-biting rates (MBR) of 17.5 bites/man/night for An. gambiae, 14.6 bites/man/night for An. funestus, 6.7 bites/man/night for An. arabiensis and 4.3 bites/man/night for An. moucheti. Moreover, the number of An. gambiae and An. funestus caught resting indoors was significantly higher than the other two species (p < 0.05). The wet season collections showed thatAn. gambiae caught were more than 67% of the total catch while An. arabiensis was predominant in the dry season (chi2 = 75.44, df = 3, p < 0.01). INTERPRETATION & CONCLUSION: The present study highlights some aspects of the behaviour of anopheline mosquitoes in southern Nigeria which is an important component of epidemiological study of malaria. This information provides basis to the understanding of the role played by the identified anopheline species in malaria transmission and a baseline to formulate malaria control programme.

Behavioural biting preference of Culex quinquefasciatus in human host in Lagos metropolis Nigeria.

BACKGROUND & OBJECTIVES: Olfactory cues play an important role in the attraction of major disease vectors towards their host. Hence we intend to investigate the contribution of selected parts of the human host on the behavioural biting preference of Culex quinquefasciatus. METHODS: Two volunteers were trained to collect host seeking female mosquitoes landing to feed on different parts of the lower limbs. The Cx. quinquefasciatus were collected in paper cups with the aid of a flash-light and aspirator. Each paper cup was labeled to represent the selected parts where the mosquitoes were collected. RESULTS: The composition of Cx. quinquefasciatus from the total mosquitoes collected showed that Cx. quinquefasciatus was more predominant (90%) over other species present. The average minimum and maximum atmospheric temperature recorded during the night catches were 27 and 29.5 degrees C while the average relative humidity range was 78-81.6%. The behavioural biting preference results obtained showed that the density of Cx. quinquefasciatus mosquitoes preferring the foot region (298) was significantly higher (p > 0.05) when compared with other different parts of the human host such as the ankle, calf and the thigh. INTERPRETATION & CONCLUSION: The study indicates that the foot region of the human host has a stronger influence in orientating mosquitoes towards the human host. Hence, the exploitation of the characteristic human odour will add to the existing vector control strategies.