PLASMODIUM FALCIPARUM POPULATION GENOMIC DIVERSITY ALONG THE SLOPE OF MOUNT CAMEROON
Tobias O Apinjoh1,2, Robert V. Nyingchu1, Rachiel F. Daniels2, Mary-Carmen Frinwie1, Ngum Ndeh1, Judith K. Anchang-Kimbi1, Hanesh F. Chi1, Rolland B. Tata1, Regina N. Mugri1, Eleanor M. Fon1, Delphine A. Tangoh1, Timothy Farrell2,3, Eric A. Achidi1, Selina Bopp2, Dan Neafsey2,3, Sarah K. Volkman2, Dyann F. Wirth2,3
1University of Buea, Buea, Cameroon
2Harvard TH Chan School of Public Health, Boston, USA
3Broad Institute of Harvard and MIT, Cambridge, USA
Malaria remains a global concern, especially in sub-Saharan Africa, despite significant investments in control interventions. In some endemic settings, information on the genetic diversity of the parasite, which will inform future vaccine and drug trials is limited.
This study characterized the genomic diversity of Plasmodium falciparum populations from different altitudinal zones, with a view to identifying population substructure due to differences in parasite prevalence levels.
- falciparum infected individuals were enrolled through cross-sectional surveys in 2013 and 2015 from localities at varying altitudes along the slope of mount Cameroon. Malaria parasitaemic blood screened by light microscopy and parasite’s genotype determined using a barcode containing a panel of 24 SNPs.
Of the 301 participants enrolled, 176 (58.5%) had single (monogenomic) infections while 125 were polygenomic, with complex parasite populations. The proportion of polygenomic infections was high overall (41.6%, 122/293) and increased (p=0.052) in 2015 (46.4%, 77/166) when compared to 2013 (35.3%, 48/136). In 2013, polyclonal infections were highest (p=0.038) in participants from low altitude areas (59.1%, 13/22) when compared to their intermediate (30.4%, 28/92) and high (31.8%, 7/22) altitude counterparts. Principal component analysis of individual allele frequencies did not identify any parasite population substructure accruing to varying minor alleles in time and space. The overall pairwise Fst of parasite populations across the three altitudinal zones and between 2013 and 2015 was low, with at most 3.5% of the overall allelic variation, due to differences between the populations. The overall complexity of infection (COI, 1.35) did not vary with altitude (p=0.106) and time (p=0.161), although it was higher (p=0.022) in participants at low compared to those from intermediate altitude in 2013.
These results indicate enormous diversity, a broadly mixing population and no evidence for recent bottlenecks due to enhanced interventions. We are currently using whole genome sequencing to gain higher resolution of these populations.
Tobias Obejum Apinjoh, PhD
University of Buea, Buea, Cameroon