The purpose of this review is to provide an overview of published data and available information on malaria situation in RoC and to identify gaps in knowledge in order to contribute in research-based solutions adapted for the country. In the present review, as the first goal, we attempted to determine if there was any change in malaria epidemiology in RoC from 1992 to 2015, with regard to malaria parasites and vectors and in the presentation of the disease as well. The year 1992 was chosen because the first national policy for malaria control established by the NMCP was adopted that year. Besides, all the research institutions including those involved in malaria research were nationalized.
As a summary, during almost 24 years, a total of 28 studies published in peer reviewed journals were conducted the RoC in relation to different aspects of malaria infection. Concerning malaria burden, lower rates of malaria parasite infection in children and adults were observed in studies conducted from 2009 to 2015 compared to those conducted from 1992 to 2006 regardless of the diagnostic method (microscopy or PCR). This is suggestive of a decline malaria prevalence and incidence during the past 7 years and might be attributable to the scaling-up of malaria interventions in the country with the support of Global fund for HIV/AIDS, malaria and tuberculosis, including the use ACT which are freely provided to children of ?15 years in public health facilities since 2008 associated with mass distribution of LLINs from 2008 to 2012. Further evidence on sustainability of the trend to the years later is important to ascertain such attributes.
With regard to Plasmodium species distribution, P. falciparum is by far the predominant malaria parasite occurring in the country accounting for almost 100% of malaria cases [11]. This observation on the extreme predominance of P. falciparum in the RoC is in accordance with findings from studies conducted in other Central African countries [39, 40].
The genetic diversity of P. falciparum was characterized trough different studies and the MOI was also determined. These two parameters are known to be good indicators of the level of premunition of populations living in endemic areas and correlate with the extent of the parasite population diversity as well as the transmission intensity [41, 42]. They are also important determinants of malaria control interventions. Overall, a significant diversity of P. falciparum population has been observed in all the studies and this is representative of areas with holo- or hyper-endemic malaria transmission. The High genetic diversity remains similar before and after introduction of ACT in 2006 and scaling up of control measures in the RoC. This implies that most of the parasite clones are still persisting and the interventions did not have impact on specific P. falciparum clones. Lower values of the MOI (1.3–1.7) have been obtained in studies conducted after these interventions than those conducted before (2.2–2.3). This trend, in addition to low rates of parasite carriage observed in studies conducted after 2006 may suggest that the implemented control measures have resulted in a substantial decrease of transmission. However, this needs to be assessed by conducting entomological studies that allow determination of the EIR in each area, which correlate well with the level of malaria transmission.
Vector control is one of the main interventions for an effective malaria control programme. To be successful, this intervention needs to rely on availability of data on vector population, level of transmission and insecticide resistance. Unfortunately, only one publication was found [33] and this reflects a major gap in knowledge about the malaria situation in RoC. In that study, 523 An. gambiae complex specimens were collected and the specimen identification revealed that all were An. gambiae s.s., of which, 95.4% were further molecularly characterized as the S-form. Importantly, these vectors were found to be highly resistant to multiple insecticide classes. This review would classify entomological research as a key priority in the country. Moreove, as An. funestus, An. coustani and An.hancocki were found to be potential minor malaria vectors [5], their implication in malaria transmission and the level of resistance to insecticides have yet to be further elucidated.
Since the utilization of ACT for the treatment of uncomplicated malaria, monitoring studies are required to detect any emergence of artemisinin resistant strains as it has been already reported from South East Asia [43, 44]. Overall in vivo efficacy studies conducted so far provided evidence of good efficacy of currently recommended ACT in RoC. It is observed that only one study analysed mutations on P. falciparum K13 propeller gene in isolates from RoC [32], and it would be important that local scientists screen regularly isolates from different parts of the country. Chloroquine and SP were banned for the treatment of uncomplicated malaria in the RoC since 2006 due to high level of parasite resistance. Studies conducted five to seven years after their withdrawal still show high rates of parasites carrying mutations associated with resistance to these two molecules. This would like to suggest that these molecules remain inactive, despite the fact that SP is still used as intermittent preventive treatment in pregnant women. Moreover, the presence of the 540 dhps mutation (in P. falciparum isolates collected in 2011–2012) [36], which was absent before SP withdrawal [23], and higher level of quintuple dhfr/dhps mutations might suggest that SP resistance become more pronounced.
As a second key priority highlighted by this review is the limited number of publications on malaria in pregnancy in RoC. For instance, there is no data on malaria parasites collected from pregnant women before the introduction of ACT and the first data were published in 2013 [9]. The researchers from Congo working on malaria are also involved in the Central Africa Network on Tuberculosis, HIV/AIDS and Malaria (CANTAM) which aims at building capacities for the conduct of clinical trials. Therefore, it would be of interest to test alternative drugs for preventing malaria during pregnancy in Congolese women.