Bionomics and vectorial role of anophelines in wetlands along the volcanic chain of Cameroon

Entomological indicators of Plasmodium species transmission in Goma Tsé-Tsé and Madibou districts, in the Republic of Congo

BACKGROUND

Malaria remains a major public health problem in the Republic of Congo, with Plasmodium falciparum being the deadliest species of Plasmodium in humans. Vector transmission of malaria is poorly studied in the country and no previous report compared rural and urban data. This study aimed to determine the Anopheles fauna and the entomological indices of malaria transmission in the rural and urban areas in the south of Brazzaville, and beyond.

METHODS

Indoor household mosquitoes capture using electric aspirator was performed in rural and urban areas during raining and dry seasons in 2021. The identification of Anopheles species was done using binocular magnifier and nested-PCR. TaqMan and nested-PCR were used to detect the Plasmodium species in the head/thorax and abdomens of Anopheles. Some entomological indices including the sporozoite infection rate, the entomological inoculation rate and the man biting rate were estimated.

RESULTS

A total of 699 Anopheles mosquitoes were collected: Anopheles gambiae sensu lato (s.l.) (90.7%), Anopheles funestus s.l. (6.9%), and Anopheles moucheti (2.4%). Three species of An. gambiae s.l. were identified including Anopheles gambiae sensu stricto (78.9%), Anopheles coluzzii (15.4%) and Anopheles arabiensis (5.7%). The overall sporozoite infection rate was 22.3% with a predominance of Plasmodium falciparum, followed by Plasmodium malariae and Plasmodium ovale. Anopheles aggressiveness rate was higher in households from rural area (1.1 bites/night) compared to that from urban area (0.8 ib/p/n). The overall entomological inoculation rate was 0.13 ib/p/n. This index was 0.17 ib/p/n and 0.092 ib/p/n in rural and in urban area, respectively, and was similar during the dry (0.18 ib/p/n) and rainy (0.14 ib/p/n) seasons.

CONCLUSION

These findings highlight that malaria transmission remains high in rural and urban area in the south of Republic of Congo despite the ongoing control efforts, thereby indicating the need for more robust interventions.

Burden of mosquito-borne diseases across rural versus urban areas in Cameroon between 2002 and 2021: prospective for community-oriented vector management approaches

BACKGROUND

Over the past two decades, Cameroon has recorded one of the highest rates of urban population growth in sub-Saharan Africa. It is estimated that more than 67% of Cameroon's urban population lives in slums, and the situation is far from improving as these neighbourhoods are growing at an annual rate of 5.5%. However, it is not known how this rapid and uncontrolled urbanization affects vector populations and disease transmission in urban versus rural areas. In this study, we analyse data from studies conducted on mosquito-borne diseases in Cameroon between 2002 and 2021 to determine the distribution of mosquito species and the prevalence of diseases they transmit with regards to urban areas versus rural areas.

METHODS

A search of various online databases, such as PubMed, Hinari, Google and Google Scholar, was conducted for relevant articles. A total of 85 publications/reports were identified and reviewed for entomological and epidemiological data from the ten regions of Cameroon.

RESULTS

Analysis of the findings from the reviewed articles revealed 10 diseases transmitted by mosquitoes to humans across the study regions. Most of these diseases were recorded in the Northwest Region, followed by the North, Far North and Eastern Regions. Data were collected from 37 urban and 28 rural sites. In the urban areas, dengue prevalence increased from 14.55% (95% confidence interval [CI] 5.2-23.9%) in 2002-2011 to 29.84% (95% CI 21-38.7%) in 2012-2021. In rural areas, diseases such as Lymphatic filariasis and Rift valley fever, which were not present in 2002-2011, appeared in 2012-2021, with a prevalence of 0.4% (95% CI 0.0- 2.4%) and 10% (95% CI 0.6-19.4%), respectively. Malaria prevalence remained the same in urban areas (67%; 95% CI 55.6-78.4%) between the two periods, while it significantly decreased in rural areas from 45.87% (95% CI 31.1-60.6%) in 2002-2011 to 39% (95% CI 23.7-54.3%) in the 2012-2021 period (*P = 0.04). Seventeen species of mosquitoes were identified as involved in the transmission of these diseases, of which 11 were involved in the transmission of malaria, five in the transmission of arboviruses and one in the transmission of malaria and lymphatic filariasis. The diversity of mosquito species was greater in rural areas than in urban areas during both periods. Of the articles reviewed for the 2012-2021 period, 56% reported the presence of Anopheles gambiae sensu lato in urban areas compared to 42% reported in 2002-2011. The presence of Aedes aegypti increased in urban areas in 2012-2021 but this species was absent in rural areas. Ownership of long-lasting insecticidal nets varied greatly from one setting to another.

CONCLUSIONS

The current findings suggest that, in addition to malaria control strategies, vector-borne disease control approaches in Cameroon should include strategies against lymphatic filariasis and Rift Valley fever in rural areas, and against dengue and Zika viruses in urban areas.

High genetic complexity but low relatedness in Plasmodium falciparum infections from Western Savannah Highlands and coastal equatorial Lowlands of Cameroon

To determine the diversity and connectivity of infections in Northwestern and Southwestern Cameroon, 232 Plasmodium falciparum infections, collected in 2018 from the Ndop Health District (NHD) in the western savannah highlands in the Northwest and the Limbe Health District (LHD) in the coastal lowland forests in the Southwest of Cameroon were genotyped for nine neutral microsatellite markers. Overall infection complexity and genetic diversity was significantly (p < 0.05) lower in NHD than LHD, (Mean MOI = 2.45 vs. 2.97; Fws = 0.42 vs. 0.47; Mean He = 0.84 vs. 0.89, respectively). Multi-locus linkage disequilibrium was generally low but significantly higher in the NHD than LHD population (mean ISA= 0.376 vs 0.093). Consequently, highly related pairs of isolates were observed in NHD (mean IBS = 0.086) compared to those from the LHD (mean IBS = 0.059). Infections from the two regions were mostly unrelated (mean IBS = 0.059), though the overall genetic differentiation across the geographical range was low. Indices of differentiation between the populations were however significant (overall pairwise Fst = 0.048, Jost's D = 0.133, p < 0.01). Despite the high human migration across the 270km separating the study sites, these results suggest significant restrictions to gene flow against contiguous geospatial transmission of malaria in west Cameroon. Clonal infections in the highland sites could be driven by lower levels of malaria prevalence and seasonal transmission. How these differences in genetic diversity and complexity affect responses to interventions such as drugs will require further investigations from broader community sampling.

Diversity and behavioral activity of Anopheles mosquitoes on the slopes of Mount Cameroon

BACKGROUND

Malaria remains endemic in Cameroon, with heterogeneous transmission related to eco-climatic variations, vector diversity and spatial distribution. The intensification of malaria prevention and control through the free distribution of insecticide-treated nets in recent years may have altered the composition, geographic distribution and natural infection rate of Anopheles species, with implications for malaria transmission dynamics. The present study seeks to assess the vectorial diversity, dynamics and infectivity across different seasons and altitudes in relationship to parasite prevalence around the slopes of Mount Cameroon, southwestern region.

METHOD

Mosquitoes were sampled (indoors and outdoors) in 11 eco-epidemiological settings at low (18-197 m), intermediate (371-584 m) and high (740-1067 m) altitude by nightly human landing catches. The mosquitoes were identified morphologically and Anopheles gambiae sibling species identified by PCR. Parity status was ascertained by examining the ovaries and the entomological inoculation rates (EIR) determined by Plasmodium falciparum circumsporozoite antigen ELISA of the head-thorax. The prevalence of Plasmodium infection across target communities was assessed using rapid diagnostic tests.

RESULTS

A total of 7327 (18.0 mosquitoes/trap/night) mosquitoes were trapped, mainly during the rainy season (5678, 77.5%) and at low altitude (3669, 50.1%). Anopheles spp. (5079, 69.3%) was the most abundant genera and An. gambiae complex (2691, 36.7%) the major vector, varying with altitude (χ² = 183.87, df = 8, P < 0.001) and season (χ² = 28.14, df = 4, P < 0.001). Only An. gambiae (s.s.) was identified following molecular analysis of An. gambiae complex siblings. The overall biting peak for An. gambiae complex was 2-3 a.m. Anopheles cinctus was the most abundant secondary vector in the area. The average EIR in the area was 2.08 infective bites per person per night (ib/p/n), higher at low (2.45 ib/p/n) than at intermediate altitude (1.39 ib/p/n) and during the rainy (1.76 ib/p/n) compared to the dry season (0.34 ib/p/n). Anopheles funestus was most infectious overall (28.1%, 16/57) while An. gambiae had the highest inoculation rates averaging 1.33 ib/p/n. Most Anopheles species across all altitudes and seasons were parous, highest in communities with the highest proportion of malaria parasite infections.

CONCLUSION

Anopheles gambiae (s.s.) remains the major malaria vector in the area and An. cinctus possibly a secondary vector of the disease in the slopes of Mt. Cameroon. The seasonal and altitudinal effects on the distribution of these mosquitoes may have implications for the transmission of malaria and its control strategies in the area. Regular monitoring of the bionomics of local Anopheles vector species and targeted control interventions in the 'hotspots' is necessary to curb the prevalence of the infection and incidence of disease.

Impact of long lasting insecticidal nets on asymptomatic malaria during pregnancy, in a rural and urban setting in Cameroon

According to the world malaria report more malaria cases were reported in 2020 than in 2019, due to disruptions in the distribution of insecticide treated nets, caused by the COVID-19 pandemic. Consequently a projected 34.32% (11.6 million out of 33.8 million) pregnancies were exposed to malaria in the WHO African Region in 2020. This study was therefore designed to assess the impact of long lasting insecticidal nets (LLINs) on asymptomatic malaria in the pregnant women attending the Foumbot District Hospital (rural setting) and the Bamenda Regional Hospital (urban setting). This was a hospital based cross-sectional study done within three months from February to April 2021. A structured questionnaire and the CareStart™ Pf Malaria HRP2 qualitative rapid diagnostic test were used for data collection. Data were analysed using descriptive statistics, and Chi-square test. The relative risk, attributable risk, odds ratio, and likelihood ratio of malaria occurrence in exposed patients were determined by Chi-square (and Fisher's exact) test. The prevalence of asymptomatic malaria was 10.14% (63/621), with a higher prevalence among the pregnant women in the rural setting (12.21%; 37/303), than the urban setting (8.18%; 26/318). As indicated by the attributable risk, 21% of malaria incidence was attributed to absence of LLINs distribution in neighborhoods of the rural setting meanwhile 10% of malaria incidence is attributed to absence of LLINs distribution in neighborhoods of the urban setting. Regular screening for asymptomatic malaria in pregnancy and consistent free distribution of LLINs are recommended in endemic areas, especially in the rural settings.

Malaria Transmission and Vector Resistance to Insecticides in a Changing Environment: Case of Simbock in Yaoundé-City, Cameroon

Ecological upheavals resulting from uncontrolled urbanization can lead to significant changes in vector borne diseases’ profiles, thus requiring a thorough revision of their prevention and control strategies. The current study aimed at characterizing malaria vector populations in the Simbock neighborhood of Yaoundé-city (Cameroon), in relation to its urbanization scheme. Adult mosquitoes were captured by human landing catches (HLC) in- and outdoors prior to (2000–2006) and during infrastructural development (2014–2016). Anophelines were morphologically identified and analyzed for Plasmodium (P.) falciparum circumsporozoite protein detection using the ELISA technique. Species of the Anopheles (An.) gambiae complex were identified using SINE-PCR. Adult An. gambiae s.l. from larvae collected between 2014 and 2017 were tested for susceptibility to insecticides (0.1% bendiocarb, 4% DDT, 0.75% permethrin and 0.05% deltamethrin) with or without piperonyl butoxide (PBO) synergist, using WHO standard bioassays. The Hot Oligonucleotide Ligation Assay was used to detect the knockdown resistance (kdr) L995F/S mutations. Overall, nine malaria vector species were identified in 2000-2006, mostly An. moucheti (49%), An. nili (13.5%) and An. gambiae s.l. (12%); the six remaining species were represented at less than 3% each. However, only three species were found in 2014-2016, with increasing proportions of An. gambiae s.l. (67%) and An. funestus (32%) (P&lt;0.0001). An. gambiae s.l. consisted An. coluzzii (&gt; 85%) and An. gambiae (&lt;15%) species during the two study periods. Plasmodium falciparum infection rates were 2.1% and 1.0% in 2000-2006 and 2014-2016 respectively (P=0.4), with decreasing entomological inoculation rates (EIR) from 0.34 infective bites per man per night (ib/m/n) to 0.02 ib/m/n (P&lt;0.0001). Anopheles gambiae s.l. was resistant to DDT and permethrin [&lt;40% mortality rates (MR)], and deltamethrin (65-89% MR), but fully susceptible to bendiocarb (100% MR). Pre-exposure of mosquitoes to PBO resulted in 90-100% MR to deltamethrin but not to permethrin. Furthermore, the two kdr L995F/S resistance alleles were recorded at 0.64 and 0.006 frequencies respectively. This study highlights a shift from rural to urban malaria transmission in Simbock, coupled with DDT and pyrethroid resistance in An. gambiae s.l. Combination vector control interventions, e.g., PBO nets and bendiocarb indoor residual spraying are needed in such areas.

An update on the mosquito fauna and mosquito-borne diseases distribution in Cameroon

The expansion of mosquito-borne diseases such as dengue, yellow fever, and chikungunya in the past 15 years has ignited the need for active surveillance of common and neglected mosquito-borne infectious diseases. The surveillance should be designed to detect diseases and to provide relevant field-based data for developing and implementing effective control measures to prevent outbreaks before significant public health consequences can occur. Mosquitoes are important vectors of human and animal pathogens, and knowledge on their biodiversity and distribution in the Afrotropical region is needed for the development of evidence-based vector control strategies. Following a comprehensive literature search, an inventory of the diversity and distribution of mosquitoes as well as the different mosquito-borne diseases found in Cameroon was made. A total of 290 publications/reports and the mosquito catalogue website were consulted for the review. To date, about 307 species, four subspecies and one putative new species of Culicidae, comprising 60 species and one putative new species of Anopheles, 67 species and two subspecies of Culex, 77 species and one subspecies of Aedes, 31 species and one subspecies of Eretmapodites, two Mansonia, eight Coquillettidia, and 62 species with unknown medical and veterinary importance (Toxorhynchites, Uranotaenia, Mimomyia, Malaya, Hodgesia, Ficalbia, Orthopodomyia, Aedeomyia, and Culiseta and Lutzia) have been collected in Cameroon. Multiple mosquito species implicated in the transmission of pathogens within Anopheles, Culex, Aedes, Eretmapodites, Mansonia, and Coquillettidia have been reported in Cameroon. Furthermore, the presence of 26 human and zoonotic arboviral diseases, one helminthic disease, and two protozoal diseases has been reported. Information on the bionomics, taxonomy, and distribution of mosquito species will be useful for the development of integrated vector management programmes for the surveillance and elimination of mosquito-borne diseases in Cameroon.

Urban malaria in sub-Saharan Africa: dynamic of the vectorial system and the entomological inoculation rate

Sub-Saharan Africa is registering one of the highest urban population growth across the world. It is estimated that over 75% of the population in this region will be living in urban settings by 2050. However, it is not known how this rapid urbanization will affect vector populations and disease transmission. The present study summarizes findings from studies conducted in urban settings between the 1970s and 2020 to assess the effects of urbanization on the entomological inoculation rate pattern and anopheline species distribution. Different online databases such as PubMed, ResearchGate, Google Scholar, Google were screened. A total of 90 publications were selected out of 1527. Besides, over 200 additional publications were consulted to collate information on anopheline breeding habitats and species distribution in urban settings. The study confirms high malaria transmission in rural compared to urban settings. The study also suggests that there had been an increase in malaria transmission in most cities after 2003, which could also be associated with an increase in sampling, resources and reporting. Species of the Anopheles gambiae complex were the predominant vectors in most urban settings. Anopheline larvae were reported to have adapted to different aquatic habitats. The study provides updated information on the distribution of the vector population and the dynamic of malaria transmission in urban settings. The study also highlights the need for implementing integrated control strategies in urban settings.

Microcytic and Malarial Anaemia Prevalence in Urban Children ≤15 Years in the Mount Cameroon Area: A Cross-Sectional Study on Risk Factors

BACKGROUND

Anaemia, a common nutritional deficiency, is a public health problem in the Mount Cameroon area. This study determined the prevalence and possible risk factors of microcytic and malarial anaemia in children less than ≤15 years residing in the Buea and Limbe municipalities in the Mount Cameroon area.

METHODS

A total of 566 children were clinically examined in a cross-sectional study from December 2018 to August 2019 for anaemia and malaria parasites. Blood samples collected were used in evaluating full blood count with the aid of an automated haemoanalyser, and malaria parasite was confirmed by microscopy. Anaemia was defined based on WHO standards while microcytic anaemia and malarial anaemia were defined as microcytosis + anaemia and malaria + anaemia, respectively. Factors that showed significance in the bivariate analysis were entered into a multinomial logistic regression to determine risk factors for microcytic and malarial anaemia.

RESULTS

The overall prevalence for anaemia, microcytosis, microcytic anaemia, and malarial anaemia was, respectively, 68.7%, 48.9%, 36.9%, and 19.6% with microcytic anaemia representing 53.7% of all anaemic cases. Risk factors for microcytic anaemia included child age of 1-5 years (P=0.007), forest ethnicity (P=0.019), parents being farmers (P=0.038) or jobless (P=0.009), and having moderate malaria parasitaemia (P=0.048) while those for malarial anaemia were child age of 6-10 years (P=0.008), parents' age of 26-35 years (P=0.049), parents being jobless (P=0.023), and consuming plantains 3-4 times (P=0.024) a week.

CONCLUSION

Microcytic anaemia is getting to be a severe public health concern while malarial anaemia is a mild public health issue in children residing in urban areas of Mount Cameroon. Parents' occupation was directly linked to all anaemia forms; hence, any intervention to curb anaemia should consider aspects that will raise the socioeconomic status of the population.

Performance assessment of a widely used rapid diagnostic test CareStart™ compared to microscopy for the detection of Plasmodium in asymptomatic patients in the Western region of Cameroon

While malaria remains a serious public health concern, its rapid or prompt diagnosis in remote areas is important in the fight against the disease. The study aimed to evaluate the performance of widely used Rapid Diagnostic Test (RDT) kits for routinely detection of Plasmodium asymptomatic patients. A total of 400 asymptomatic participants of both sexes aged between 1-89 years from Menoua Division (Santchou and Dschang) were tested for malaria infection using both microscopy and CareStart™ RDT. The prevalence of malaria was higher when using the standard gold tool (Microscopy) (26.0%) compared to RDT (21.8%) with a significant difference (P < 0.05). However, a strong agreement was observed between both tests (kappa = 0.883; P < 0.0001). RDT CareStart™ sensitivity and specificity were 83.65% and 100% respectively while the positive predictive value and negative predictive value were 100% and 95.57% respectively. RDT sensitivity increased with parasite density while false negative (40.4%; n = 17) were observed only when parasite density was low (<500 parasites per microliter of blood). RDT kits appear to be good tools in areas where malaria diagnosis through microscopy is not feasible. However, the low sensibility observed when parasite density is low could be a concern.

Evaluation of malaria preventive measures among adult patients attending the Bamendjou and Foumbot district hospitals of the West Region of Cameroon

BACKGROUND

Although a significant decrease in entomological and epidemiological indicators was reported in Cameroon since the introduction of insecticide-treated bed nets, malaria prevalence remains high also in some parts of the West Region of Cameroon. This study was designed to evaluate malaria preventive measures among patients attending the Bamendjou and Foumbot District hospitals of the West Region of Cameroon.

METHODS

This was a cross-sectional study carried out within a period of 3 months, from January to March 2020. Data was obtained using a structured questionnaire and laboratory analysis. The CareStart™ Pf Malaria HRP2 qualitative rapid diagnostic test was used for malaria diagnosis. The questionnaire was designed to collect information on respondent's socio-demographic characteristics, and the use of malaria preventive measures. Data were analysed using descriptive statistics, regression analysis, and Chi-square (and Fisher's exact) test.

RESULTS

A total of 170 study participants were recruited in Foumbot and 197 in Bamendjou. Malaria was significantly (P < 0.0001) more prevalent in Foumbot (47.06%) than in Bamendjou (19.8%). In Foumbot, non-use of insect repellent spray (P = 0.0214), insect repellent body cream (P = 0.0009), mosquito spray (P = 0.0001) and not draining stagnant water (P = 0.0004) predisposed to higher risk of malaria. In Bamendjou, non-use of insect repellent spray (P = 0.0012), long-lasting insecticidal bed nets (P = 0.0001), window and door nets (P = 0.0286), predisposed to a higher risk of malaria.

CONCLUSIONS

Malaria prevalence was high among the study participants especially in Foumbot. An adequate follow-up to ensure effective execution of the recently launched third phase of LLINs distribution campaign in Cameroon is recommended. Additionally, integrated vector management is required to ensure effective control of malaria transmission in Foumbot and Bamendjou.

Influence of a Major Mountainous Landscape Barrier (Mount Cameroon) on the Spread of Metabolic (GSTe2) and Target-Site (Rdl) Resistance Alleles in the African Malaria Vector Anopheles funestus

Increased levels of insecticide resistance in major malaria vectors such as Anopheles funestus threaten the effectiveness of insecticide-based control programmes. Understanding the landscape features impacting the spread of resistance makers is necessary to design suitable resistance management strategies. Here, we examined the influence of the highest mountain in West Africa (Mount Cameroon; 4095 m elevation) on the spread of metabolic and target-site resistance alleles in An. funestus populations. Vector composition varied across the four localities surveyed along the altitudinal cline with major vectors exhibiting high parity rate (80.5%). Plasmodium infection rates ranged from 0.79% (An. melas) to 4.67% (An. funestus). High frequencies of GSTe2^R (67–81%) and Rdl^R (49–90%) resistance alleles were observed in An. funestus throughout the study area, with GSTe2^R frequency increasing with altitude, whereas the opposite is observed for Rdl^R. Patterns of genetic diversity and population structure analyses revealed high levels of polymorphisms with 12 and 16 haplotypes respectively for GSTe2 and Rdl. However, the reduced diversity patterns of resistance allele carriers revealed signatures of positive selection on the two genes across the study area irrespective of the altitude. Despite slight variations associated with the altitude, the spread of resistance alleles suggest that control strategies could be implemented against malaria vectors across mountainous landscapes.

Review of malaria situation in Cameroon: technical viewpoint on challenges and prospects for disease elimination

Malaria still has a devastating impact on public health and welfare in Cameroon. Despite the increasing number of studies conducted on disease prevalence, transmission patterns or treatment, there are to date, not enough studies summarising findings from previous works in order to identify gaps in knowledge and areas of interest where further evidence is needed to drive malaria elimination efforts. The present study seeks to address these gaps by providing a review of studies conducted so far on malaria in Cameroon since the 1940s to date. Over 250 scientific publications were consulted for this purpose. Although there has been increased scale-up of vector control interventions which significantly reduced the morbidity and mortality to malaria across the country from a prevalence of 41% of the population reporting at least one malaria case episode in 2000 to a prevalence of 24% in 2017, the situation is not yet under control. There is a high variability in disease endemicity between epidemiological settings with prevalence of Plasmodium parasitaemia varying from 7 to 85% in children aged 6 months to 15 years after long-lasting insecticidal nets (LLINs) scale-up. Four species of Plasmodium have been recorded across the country: Plasmodium falciparum, P. malariae, P. ovale and P. vivax. Several primate-infecting Plasmodium spp. are also circulating in Cameroon. A decline of artemisinin-based combinations therapeutic efficacy from 97% in 2006 to 90% in 2016 have been reported. Several mutations in the P. falciparum chloroquine resistance (Pfcrt) and P. falciparum multidrug resistance 1 (Pfmdr1) genes conferring resistance to either 4-amino-quinoleine, mefloquine, halofanthrine and quinine have been documented. Mutations in the Pfdhfr and Pfdhps genes involved in sulfadoxine-pyrimethamine are also on the rise. No mutation associated with artemisinin resistance has been recorded. Sixteen anopheline species contribute to malaria parasite transmission with six recognized as major vectors: An. gambiae, An. coluzzii, An. arabiensis, An. funestus, An. nili and An. moucheti. Studies conducted so far, indicated rapid expansion of DDT, pyrethroid and carbamate resistance in An. gambiae, An. coluzzii, An. arabiensis and An. funestus threatening the performance of LLINs. This review highlights the complex situation of malaria in Cameroon and the need to urgently implement and reinforce integrated control strategies in different epidemiological settings, as part of the substantial efforts to consolidate gains and advance towards malaria elimination in the country.

A combination of metabolic resistance and high frequency of the 1014F kdr mutation is driving pyrethroid resistance in Anopheles coluzzii population from Guinea savanna of Cameroon

BACKGROUND

The scale-up in the distribution of long-lasting insecticidal nets (LLINs) and indoor residual spraying has significantly reduced malaria burden and mortality. However, insecticide resistance, among other factors, is responsible for a recent rebound in malaria transmission in 2015-2016, threatening the progress so far made. As a contribution towards understanding patterns of resistance and its mechanism in the field we characterized a population of Anopheles gambiae (s.l.) from Gounougou, a Guinea savanna of north/central Cameroon.

RESULTS

Indoor collection conducted in September 2017 identified Anopheles coluzzii and Anopheles arabiensis as the unique Anopheles vector species, with abundances of 83 and 17%, respectively. Analysis of infection with TaqMan assays using heads/thoraces of indoor collected females of An. coluzzii revealed a low Plasmodium falciparum parasite rate of 4.7%. Bioassays conducted with female An. coluzzii revealed extreme resistance, with low mortalities of only 3.75 ± 1.25%, 3.03 ± 1.59% and 1.45 ± 1.45%, respectively, for permethrin, deltamethrin and DDT. In contrast, high susceptibility was obtained with the organophosphates and carbamates, with mortalities in the range of 98-100%. Synergist assays with piperonyl butoxide (PBO) recovered some susceptibility with increased mortality for permethrin to 14.88 ± 8.74%, and for deltamethrin to 32.50 ± 10.51% (~27-fold increase compared to mortalities with deltamethrin alone, χ² = 29, df = 1, P < 0.0001). These correlated with the results of cone bioassays which revealed complete loss of efficacy of Olyset®Net (0% mortality) and PermaNet®2.0 (0% mortality), and the considerable loss of efficacy of Olyset®Plus (mortality of 2 ± 2%), PermaNet®3.0 side panel (mortality of 2 ± 2%) and PermaNet3.0® roof (mortality of 16 ± 5.1%). Time-course bioassays conducted with deltamethrin established a high intensity of resistance, with LT₅₀ of 309.09 (95% CI 253.07-393.71, Fiducial), and a resistance ratio of 93.09 compared with the fully susceptible Ngoussou laboratory colony. TaqMan genotyping revealed a high frequency of the 1014F allele (65.25%) in the An. coluzzii populations. Sequencing of a fragment of the voltage-gated sodium channel identified a single An. arabiensis female harbouring the 1014S kdr mutation.

CONCLUSIONS

This finding of high pyrethroid and DDT resistance in An. coluzzii from north-central Cameroon is a major obstacle to malaria control using pyrethroid bednets and indoor residual spraying with DDT.

Automatic Detection of Open and Vegetated Water Bodies Using Sentinel 1 to Map African Malaria Vector Mosquito Breeding Habitats

Providing timely and accurate maps of surface water is valuable for mapping malaria risk and targeting disease control interventions. Radar satellite remote sensing has the potential to provide this information but current approaches are not suitable for mapping African malarial mosquito aquatic habitats that tend to be highly dynamic, often with emergent vegetation. We present a novel approach for mapping both open and vegetated water bodies using serial Sentinel-1 imagery for Western Zambia. This region is dominated by the seasonally inundated Upper Zambezi floodplain that suffers from a number of public health challenges. The approach uses open source segmentation and machine learning (extra trees classifier), applied to training data that are automatically derived using freely available ancillary data. Refinement is implemented through a consensus approach and Otsu thresholding to eliminate false positives due to dry flat sandy areas. The results indicate a high degree of accuracy (mean overall accuracy 92% st dev 3.6) providing a tractable solution for operationally mapping water bodies in similar large river floodplain unforested environments. For the period studied, 70% of the total water extent mapped was attributed to vegetated water, highlighting the importance of mapping both open and vegetated water bodies for surface water mapping.

Comparative analysis of IgG and IgG subclasses against Plasmodium falciparum MSP-119 in children from five contrasting bioecological zones of Cameroon

Background

Studies reporting the natural immune responses against malaria in children from different geographical settings in endemic areas are not readily available. This study was aimed at comparing the immune responses against Plasmodium falciparum MSP-1₁₉ antigen in children from five contrasting bioecological zones in Cameroon.

Methods

In a cross-sectional survey, children between 2 and 15 years, were enrolled from five ecological strata including the south Cameroonian equatorial forest, sudano-sahelian, high inland plateau, high western plateau, and the coastal strata. The children were screened for clinical malaria (defined by malaria parasitaemia ≥ 5000 parasites/µl plus axillary temperature ≥ 37.5 °C). Their antibody responses were measured against P. falciparum MSP-1₁₉ antigen using standard ELISA technique.

Results

In all, 415 children comprising 217 (52.3%) males participated. Total IgG and IgG1–IgG4 titres were observed to increase with age in all the strata except in the sudano-sahelian and high inland plateau strata. Total IgG and IgG1–IgG4 titres were significantly higher in the coastal strata and lowest in the high inland plateau (for IgG1 and IgG2) and sudano-sahelian strata (for IgG3 and IgG4). Titres of the cytophilic antibodies (IgG1 and IgG3) were significantly higher than the non-cytophilic antibodies (IgG2 and IgG4) in all the strata except in the sudano-sahelian and high inland plateau strata. Total IgG and IgG subclass titres were significantly higher in children positive for clinical malaria compared to negative children in all study sites except in the high western plateau and coastal (for IgG1 and IgG3), and the sudano-sahelian strata (for all antibodies). Furthermore, a significant positive correlation was observed between parasite density and IgG2 or IgG4 titres in all study sites except in the south Cameroonian equatorial forest and sudano-sahelian strata.

Conclusions

This study showed that antibody responses against MSP-1₁₉ vary considerably in children from the different bioecological strata in Cameroon and could be linked to the differential exposure to malaria in the different strata. Furthermore, the rate of antibody acquisition was not observed to increase in an age-dependent manner in low transmission settings.

Electronic supplementary material

The online version of this article (10.1186/s12936-019-2654-9) contains supplementary material, which is available to authorized users.