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.

Urban malaria is becoming a major health priority across Africa. A study was undertaken to assess the importance of urban pollution and agriculture practice on the distribution and susceptibility to insecticide of malaria vectors in the two main cities in Cameroon.

Malaria transmission in Africa is a dynamic and complex system that is so far superficially understood. Further knowledge is required to improve control of the disease. In the present report, we highlight the contribution of the so-called "secondary" malaria vectors to the overall parasite transmission intensity in several sites across Cameroon, through a retrospective analysis of surveys from the Organisation de Coordination pour la lutte Contre les Endémies en Afrique Centrale database. In total, 48,490 female anophelines belonging to 21 different species were collected between October 1998 and March 2003. Anopheles gambiae Giles, Anopheles arabiensis Patton, Anopheles funestus Giles, Anopheles nili (Theobald), and Anopheles moucheti Evans represented 89% of the total anopheline fauna. Beside these major vectors, malaria parasites or their circumsporozoite proteins were found in nine secondary malaria vectors: Anopheles ovengensis Awono-Ambene et al., Anopheles carnevalei Brunhes et al., Anopheles coustani Laveran, Anopheles hancocki Edwards, Anopheles marshallii (Theobald), Anopheles paludis Theobald, Anopheles pharoensis Theobald, Anopheles wellcomei Theobald, and Anopheles ziemanni Grtünberg. The mean infection rate of secondary vectors (1.36%) was significantly (P < 0.001) lower than that of major vectors (3.08%). An. pharoensis and An. ovengensis were repeatedly found infected by Plasmodium falciparum Welch and contributed substantially to the total malaria transmission intensity in some areas where they were abundant. Both species have strong exophilic and/or exophagic habits such that they might elude vector control directed against endophilic and endophagic malaria vectors.

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 theAnopheles gambiaecomplex 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.

Malaria remains a major public health threat in Cameroon and disease prevention is facing strong challenges due to the rapid expansion of insecticide resistance in vector populations. The present review presents an overview of published data on insecticide resistance in the main malaria vectors in Cameroon to assist in the elaboration of future and sustainable resistance management strategies. A systematic search on mosquito susceptibility to insecticides and insecticide resistance in malaria vectors in Cameroon was conducted using online bibliographic databases including PubMed, Google and Google Scholar. From each peer-reviewed paper, information on the year of the study, mosquito species, susceptibility levels, location, insecticides, data source and resistance mechanisms were extracted and inserted in a Microsoft Excel datasheet. The data collected were then analysed for assessing insecticide resistance evolution. Thirty-three scientific publications were selected for the analysis. The rapid evolution of insecticide resistance across the country was reported from 2000 onward. Insecticide resistance was highly prevalent in both An. gambiae (s.l.) and An. funestus. DDT, permethrin, deltamethrin and bendiocarb appeared as the most affected compounds by resistance. From 2000 to 2017 a steady increase in the prevalence of kdr allele frequency was noted in almost all sites in An. gambiae (s.l.), with the L1014F kdr allele being the most prevalent. Several detoxification genes (particularly P450 monooxygenase) were associated with DDT, pyrethroids and bendiocarb resistance. In An. funestus, resistance to DDT and pyrethroids was mainly attributed to the 119F-GSTe2 metabolic resistance marker and over-expression of P450 genes whereas the 296S-RDL mutation was detected in dieldrin-resistant An. funestus. The review provides an update of insecticide resistance status in malaria vector populations in Cameroon and stresses the need for further actions to reinforce malaria control strategies in the coming years.

In the city of Yaoundé in Cameroon malaria is predominately transmitted by the M and S molecular forms of Anopheles gambiae and both are resistant to the pyrethroid insecticides and DDT. Mutations in the target site of these insecticides, present at a high frequency in malaria vectors in this city, contribute to this resistance profile. To identify additional resistance mechanisms, the expression profile of multiple DDT-resistant field populations of M and S molecular forms was compared to laboratory-susceptible populations. The prevalence of DDT resistance was highest in the S form population originating from the cultivated site of Nkolondom (mortality after WHO bioassay = 4%). A high prevalence of DDT resistance was also found in two urban M form populations, Messa from a pristine unpolluted environment (DDT mortality = 54%), and Gare, where the breeding sites are heavily polluted with organic matter (DDT mortality = 38%). Microarray analysis showed that several transcripts coding for detoxification enzymes (P450s, GSTs and UDPGTs) and ABC transporters were upregulated in the three populations. Despite the presence of multiple detoxification genes over expressed in the DDT-resistant subset of these field populations, only three were commonly over expressed in resistant populations from all three environments. Two of these genes, CYP6M2 and GSTD1-6, encode enzymes that have been previously shown to metabolize DDT. Analogous to target site resistance, genes involved in metabolic resistance to DDT are also shared between the M and S forms of An gambiae. Alternative explanations for this occurrence are explored.