Probing the composition of Plasmodium species contained in malaria infections in the Eastern region of Ghana

Abstract

Background: Asymptomatic falciparum and non-falciparum malaria infections are major challenges to malaria control interventions, as they remain a source of continual infection in the community. This becomes even more important as the debate moves towards elimination and eradication. This study sought to quantify the burden of Plasmodium malaria infection in seven communities in the Eastern Region of Ghana.

Methods: The cross-sectional study recruited 729 participants aged 85 years old and below from 7 closely linked communities. Finger pricked blood was used to prepare thick and thin blood smears as well as spot filter paper and an histidine rich protein 2 (HRP2) rapid diagnostic test kit (RDT). Genomic DNA was extracted from the filter paper dry blood spot (DBS) and used in PCR to amplify the Plasmodium 18S rRNA gene using species specific PCR.

Results: 96.6% of the participants were identified as afebrile, with axillary temperatures below 37.5 °C. PCR identified 66% of the participants to harbor malaria parasites, with 9 P. malariae and 7 P. ovale mono-infections accounting for 2.2% and P. falciparum combined with either 36 P. malariae or 25 P. ovale infections, accounting for 13.3%. Parasite prevalence by microscopy (32%) was similar to the RDT positivity rate (33%). False positive RDT results ranged from 64.6% in children aged between 5 and 9 years to 10% in adults aged 20 years and above. No significant differences were observed in falciparum and non-falciparum parasite carriage at the community level, however young adults aged between 15 and 19 years had the highest prevalence (34.8% (16/46)) of P. falciparum and P. malariae parasite carriage whilst children aged between 5 and 9 years had the highest level (11.4% (14/123)) of P. ovale carriage.

Conclusion: The high rate of misidentification of non-falciparum parasites and the total absence of detection of P. ovale by microscopy suggests that more sensitive malaria diagnostic tools including molecular assays are required to accurately determine the prevalence of carriers of non-falciparum parasites and low density P. falciparum infections, especially during national surveillance exercises. Additionally, malaria control interventions targeting the non-falciparum species P. malariae and P. ovale parasites are needed.

Keywords: Falciparum; Malariae; Ovale; Plasmodium; RDT; Submicroscopic.

Fig. 1

A map of Ghana highlighting study sites located within the Eastern Region

Fig. 2

Prevalence of PCR detectable Plasmodium species within the study sites. A Venn diagram showing the frequency as counts of each of the Plasmodium species identified by PCR

Fig. 3

Prevalence of P. falciparum detected by varying diagnostic tools. A Venn diagram showing the detection of P. falciparum by microscopy, RDT and P. falciparum specific PCR

Fig. 4

The distribution of PCR detectable Plasmodium species within the study sites. OB, Obosono; TB, Towoboase; OK, Okomfo; AK, Akwensu; AW, Awensu; AM, Amokope; YB, Yaw Boadi; mono species infection; pf: Plasmodium falciparum (red), pm: Plasmodium malariae (yellow), po: Plasmodium ovale (blue), multi species infection; pf + pm (orange); pf + po (purple); pf + pm + po (black). Prevalence is expressed as the % of total parasites identified in each site

Fig. 5

Comparison of diagnostic tools. A bar graph showing the prevalence of P. falciparum (Pf), P. malariae (Pm) and P. ovale (Po) as estimated by species specific PCR (P), microscopy (M) and RDT (R). values shown represent frequency expressed as a % of the total number of samples (729)