Baseline malaria vector transmission dynamics in communities in Ahafo mining area in Ghana

Epidemiology and likelihood of asymptomatic malaria among community dwellers in the Fanteakwa south district of Ghana

Background

Data on the asymptomatic burden of malaria in endemic areas is essential for Ghana's malaria elimination efforts. Consequently, the situation of asymptomatic malaria in the Fanteakwa South District (FSD) is determined in this study. The FSD is predominantly forested with more rural than peri-urban communities. Additionally, artisanal mining is prevalent in the district. Despite that the forgoing could promote high incidence of malaria, the burden of asymptomatic malaria and associated factors in the district have never been determined.

Methods

This community-based cross-sectional study was conducted in four randomly selected communities in the FSD in the Eastern region of Ghana. The participating households were systematically selected, of which one household member was randomly enrolled in the study. With prior consent, 2 mL of whole blood was collected from the participants. Subsequently, the study variables were obtained from the enrolees using a structured questionnaire. The malaria status of the enrolled participants was determined using the CareStart™ malaria rapid diagnostic test kit (mRDT) (USA). The multiple logistic regression model was used to fit the model to predict the groups at risk of P. falciparum infection in the district.

Results

In total, 412 study participants were enrolled. The overall prevalence of asymptomatic malaria in the district was 43.4 % (179/412). The prevalence rate was 36.9 %, 27.7 %, 50 % and 58.8 % (<0.001) respectively for the Dwenase, Bosusu, Nsutam and Osino communities. Living at Bosusu (p = 0.045, AOR = 0.23, 95 % CI: 0.05-0.96), Dwenase (p < 0.001, AOR = 0.12, 95 % CI: 0.04-0.30) and Nsutam (p < 0.001, AOR = 0.19, 95 % CI: 0.08-0.45) were less likely to contract malaria compared to Osino dwellers. Furthermore, pregnant women (p = 0.024, COR = 0.35, 95 % CI: 0.14-0.9) and individuals who do not share mosquito nets with others (p = 0.017, COR = 0.47, 95 % CI: 0.25-0.88) were less likely to contract malaria. Moreover, being an adolescent (p = 0.048, COR = 1.93, 95 % CI: 1.00-3.73), living in mining communities (p = 0.002, COR = 1.97, 95 % CI: 1.27-3.05), being nocturnally active (p = 0.001, AOR = 4.64, 95 % CI: 1.97-11.31), living in a medium quality house (p = 0.031, AOR = 2.31, 95 % CI: 1.09-5.00), schooling in the district (p < 0.001) and body temperature above >37.5 °C (<0.001), were predictors of asymptomatic malaria.

Conclusions

The burden of asymptomatic malaria is high in the Fanteakwa South district. In this context, the implementation of the 'mass strategy' recommended by the World Health Organization will play a key role in eliminating malaria in the district.

Larval habitat diversity and Anopheles mosquito species distribution in different ecological zones in Ghana

Background

Understanding the ecology of larval malaria and lymphatic filariasis mosquitoes in a changing environment is important in developing effective control tools or programmes. This study characterized the breeding habitats of Anopheles mosquitoes in rural communities in different ecological zones in Ghana during the dry and rainy seasons.

Methods

The spatio-temporal distribution, species composition, and abundance of larval Anopheles mosquitoes in breeding habitats were studied in five locations in three ecological zones of Ghana. These were Anyakpor (coastal savannah area), Duase (forest area), and Libga, Pagaza, and Kpalsogu (Sahel savannah area). Larvae were collected using standard dippers and were raised in the insectary for identification.

Results

Out of a total of 7984 mosquito larvae collected, 2152 (27.26%) were anophelines and were more abundant in the rainy season (70.82%) than in the dry season (29.18%). The anophelines comprised 2128 (98.88%) An. gambiae s.l., 16 (0.74%) An. rufipes, and 8 (0.37%) An. pharoensis. In the coastal savannah and forest zones, dug-out wells were the most productive habitat during the dry (1.59 larvae/dip and 1.47 larvae/dip) and rainy seasons (11.28 larvae/dip and 2.05 larvae/dip). Swamps and furrows were the most productive habitats in the Sahel savannah zone during the dry (0.25 larvae/dip) and rainy (2.14 larvae/dip) seasons, respectively. Anopheles coluzzii was the most abundant sibling species in all the ecological zones. Anopheles melas and An. arabiensis were encountered only in the coastal savannah and the Sahel savannah areas, respectively. Larval habitat types influenced the presence of larvae as well as larval density (p < 0.001). The land-use type affected the presence of Anopheles larvae (p = 0.001), while vegetation cover influenced larval density (p < 0.05).

Conclusion

The most productive habitats were dug-out wells in the coastal savannah and forest zones, and furrows from irrigated canals in the Sahel savannah zone. Anopheles coluzzii was the predominant vector species in all the ecological zones. The abundance of Anopheles breeding habitats and larvae were influenced by anthropogenic activities. Encouraging people whose activities create the larval habitats to become involved in larval source management such as habitat manipulation to stop mosquito breeding will be important for malaria and lymphatic filariasis control.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04701-w.

Anopheles gambiae (Diptera: Culicidae) Susceptibility to Insecticides and Knockdown Resistance Genes Prior to Introduction of Indoor Residual Spraying in 11 Districts in Ghana

BACKGROUND

An insecticide susceptibility study was carried out on Anopheles gambiae sensu lato vectors in 11 districts in Ghana between October 2012 and January 2013.

METHODS

An. gambiae s.l. larvae were collected, bred under standard conditions, and 3-5 d postemerged females were used for bioassay. Between 22 and 25 female An. gambiae s.l. fed only 10% sugar were used for testing. Exposure was for 1 h (2 h for fenitrothion). An gambiae that were knocked down were recorded every 10 min and mortalities recorded 24 h posttest. Eleven insecticides from four chemical classes were used: organochlorines, organophosphates, carbamates, and pyrethroids. Subsamples of An gambiae were analyzed by polymerase chain reaction for species and knockdown resistance (kdr) allele determination.

RESULTS

Malathion was effective in killing An. gambiae in seven districts, fenitrothion in three districts, and propoxur in one district. The organophosphate and carbamate insecticides were effective in killing An. gambiae compared to pyrethroids and organochlorines. Of the limited samples analyzed, An. gambiae sensu stricto (39/110), An. coluzzii (66/110), and An. arabiensis (5/110) were identified. Few kdr (11/110) susceptible mosquitoes were detected. Homozygous kdr^RR (65/110) and heterozygous kdr^RS (8/110) genotypes were identified.

CONCLUSIONS

An organophosphate insecticide is considered appropriate for indoor residual spraying (IRS) in the 11 districts earmarked for the IRS program in Ghana.