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Feature | Diversity and Multiplicity of P. falciparum infections among asymptomatic school children

In our today’s featured article, we publish a scientific research paper written by a young Gunjurian molecular biologist Abdoulie O. Touray, et al on “Diversity and Multiplicity of P. falciparum infections among asymptomatic school children in Mbita, Western Kenya”


The research paper which is based on Malaria parasite genetic diversity was recently published in the leading scientific publishing journal, “Scientific Reports” which is a member of the Nature Publishing Group.

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Diversity and Multiplicity of P. falciparum infections among asymptomatic school children in Mbita, Western Kenya


By Abdoulie O. Touray, Victor A. Mobegi, Fred Wamunyokoli & Jeremy K. Herren


Multiplicity of infection (Moi) and genetic diversity of P. falciparum infections are important surrogate indicators for assessing malaria transmission intensity in different regions of endemicity. Determination of Moi and diversity of P. falciparum among asymptomatic carriers will enhance our understanding of parasite biology and transmission to mosquito vectors. this study examined the Moi and genetic diversity of P. falciparum parasite populations circulating in Mbita, a region characterized as one of the malaria hotspots in Kenya. the genetic diversity and multiplicity of P. falciparum infections in 95 asymptomatic school children (age 5–15 yrs.) residing in Mbita, western Kenya were assessed using 10 polymorphic microsatellite markers. An average of 79.69% (Range: 54.84–95.74%) of the isolates analysed in this study were polyclonal infections as detected in at least one locus.


A high mean Moi of 3.39 (Range: 2.24–4.72) and expected heterozygosity (He) of 0.81 (Range: 0.57–0.95) was reported

in the study population. the analysed samples were extensively polyclonal infections leading to circulation of highly genetically diverse parasite populations in the study area. These findings correlated with the expectations of high malaria transmission intensity despite scaling up malaria interventions in the area thereby indicating the need for a robust malaria interventions particularly against asymptomatic carriers in order to attain elimination in the region.


Malaria continues to be a major public health problem in many parts of the world despite numerous national and international efforts in combatting the ongoing disease transmission. Although enormous success in the fight against the disease has been registered, reports have indicated an insignificant progress in the reduction of global malaria cases for the period 2014–20181. An increase in the global incidence of malaria cases from 219 million in 2017 to 228 million in 2018 with a staggering 405 000 related deaths was registered1,2. Sub-Saharan Africa bears the greatest malaria cases and death rates compared to other regions like South-East Asia, Eastern Mediterranean, Western Pacific, and the Americas with an unprecedented 213 million malaria cases1.


In Kenya, about 74 percent of the total population are reported to be at risk of malaria infection and regions such as the coastal areas and western part of the country records the highest transmission intensity 3,4. Children registered the highest prevalence of the disease and recorded an average of 8 percent and 15 percent among younger (<5 years) and older (5–15 years) age categories respectively5. Older children living in endemic envi- ronments around lake shores recorded a much higher prevalence of about 38 percent 6. In a bid to attain its goal of a “Malaria-free Kenya”, the country has implemented many malaria control and eradication interventions including; the use of Artemisinin based Combination Therapy (ACT) as a first line of treatment, Long-Lasting Insecticidal Net (LLIN), Intermittent Presumptive Treatment in pregnancy (IPTp), Indoor Residual Spraying (IRS) and Rapid Diagnostic Test (RDT) for efficient parasite diagnosis 7,8.


A larger proportion of malaria morbidity and mortality studies were centred on preschool-aged children (2–4 years of age). This group contributes a substantial number of incidence to the global malaria burden each year 9–11. The management and epidemiology of malaria in school-age children as a group has initially received

little attention in comparison to the pregnant women and children under the age of five years groups 11–14. In many endemic settings, malaria contributes immensely to the annual school absenteeism and poor academic performance among school children 9,13,14. Older children in high malaria transmission areas develop parasite specific immunity against Plasmodium parasite and this contributes to reduction in clinical malaria episodes and high prevalence of asymptomatic parasite carriers 15–17.


As a result, malaria asymptomatic school children might not be absent from school due to clinical malaria episodes but may serve as major reservoir for the transmission of the disease 11,18,19.

Overall, progress towards malaria control and elimination has stalled across all World Health Organisation (WHO) regions. The stagnancy in the global fight against the disease is partly due to decreased funding from international donors 1,20–23.


However, the high prevalence of asymptomatic carriers especially among older children 19,24–28, high recombination rates among distinct P. falciparum clones in endemic settings leading to emergence of highly diverse parasite isolates, rapid emergence and distribution of drug resistant P. falciparum parasite strains 29–33, and prevalence of infections characterized by multiple genetically distinct parasite strains are some of the major contributing factors hindering the global malaria control and elimination 31,34,35. In highly endemic environments, many individuals carry multiple parasite clones 36–38. This may have both positive and negative implications in the fight against malaria. The carriage of multiple distinct parasite clones by an individual is reported to enhance the development of multiple strain specific anti-parasite immunity. However, due to an intense intra-host competition, harbouring multiple distinct parasite clones is also implicated in high gametocyte production and emergence of highly virulent and drug resistant parasite strains 32,39–43.


Multiplicity of infection (MOI) and genetic diversity of P. falciparum infection are important surrogate tools for the determination of malaria transmission intensity in different regions of endemicity 44–46. These indices of P. falciparum parasite infections are also used in determining the impact of some key malaria interventions like drug and vaccine efficacy studies 29,47,48. Numerous studies about multiplicity and diversity of P. falciparum infections have been carried out in various WHO regions using different tools including size-polymorphic antigens and microsatellite markers followed by agarose gel and capillary electrophoresis respectively, single nucleotide polymorphism genotyping, amplicon ultra-deep sequencing and whole genome sequencing 36,49. The use of molecular genotyping of polymorphic antigenic markers like merozoite surface protein (MSP) 1 and 2, glutamate rich protein (Glurp) for parasite diversity studies are faced with some criticisms due to the fact that these genes are implicated to be under strong immune selection 44,50–52.


Amplicon ultra-deep sequencing and whole genome sequencing techniques have high sensitivity and specificity particularly to detect minority clones in case of multi- clonal infections 52. However, the costs and time factors attached to the use of these techniques are relatively high thereby limiting their application especially in resource scarce settings. Microsatellite markers are highly poly- morphic, widely distributed in the Plasmodium genome, perceived to be selection neutral and readily amplifiable using cheap methods like PCR 35,53,54. These criteria have made them an ideal tool for the estimation of parasite genetic diversity and MOI 36,46,48.


While studies about asymptomatic Plasmodium parasite carriage among school children have been reported 18,26,28,55, studies on diversity level and multiplicity of P. falciparum infections among this group still remained scanty. This study was carried out to investigate the diversity and multiplicity of P. falciparum infections among asymptomatic school children (age 5–15 yrs.) in one of the highly malaria endemic regions of Kenya in order to provide an up-to-date critical information for monitoring parasite transmission dynamics and effective evaluation of the impact of currently implemented malaria control interventions in the area.


Materials and Methods ethics statement.


The Kenya Medical Research Institute (KEMRI) Scientific and Ethics Review Unit (SERU) granted approval for the original study (KEMRI/RES/7/3/1). Consent for sample reuse was part of the original consent form. Study participants were only enrolled after obtaining a written informed consent from their parents or legal guardians. Participants above 12 years also provided assent in addition to parental consent. All experiments were performed in accordance with the relevant guidelines and regulations.


Study site and sample collection. Study site. The study was conducted in Mbita sub-county, situated in the shores of Lake Victoria in Homa Bay County formerly Nyanza Province in western Kenya. The district is bordered from the north, west and south by Lake Victoria and located between latitudes 0° 21′ and 0° 32′ South and longitudes 34° 04′ and 34° 24′ East. The area of the district is about 163.28 km2 and is approximately 400 km west of the capital city of Kenya, Nairobi. Mbita sub-county has a population of about 115,896 and the major economic activities include subsistence farming, fishing, small scale businesses and domestication of animals like sheep, goat, chicken, pig and cattle56. Majority of the residents live in a compound system which comprises of one or more households together.


The housing structures range from traditional mud with grass thatched huts to modern concrete and corrugated iron buildings56. The region experiences two periods of rainfall, from March to June and then October to November each year57 and is characterized as one of the HIV hotspots with some of the poorest health indicators in Kenya. Due to the biannual rainfall pattern and the proximity to the shores of Lake Victoria, the region experiences a perennial transmission of malaria thereby making the disease the leading cause of morbidity and mortality among children in the region 58.




The rest of the scientific paper can be accessed by following the link below:


https://www.nature.com/articles/s41598-020-62819-w



Editor’s note:

Abdoulie O. Touray is a PhD candidate in Molecular Biology and Biotechnology, and affiliated with the Pan African university, Institute of Basic Science, Technology and Innovation (PAUSTI) and International centre of Insect Physiology and Ecology (ICIPE) in Nairobi, Kenya. His broader research interest is in infectious diseases specifically in the area of host-pathogen interactions, disease biomarkers, vaccine and drug targets discovery. Abdoulie‘s current research is centred on Malaria genetics and genomics to identify transmission blocking target genes for novel drug and vaccine discovery. He was trainee scientific officer at the Medical Research Centre (MRC Gambia) prior to leaving for his MSc. Degree in Istanbul, Turkey.

Abdoulie O. Touray


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