The ears of the African elephant: unexpected high seroprevalence of Plasmodium ovale and Plasmodium malariae in healthy populations in Western Africa

Abstract

Background: Malaria Is A Life-Threatening Pathology In Africa. Plasmodium Falciparum And Plasmodium Vivax Attract The Most Focus Because Of Their High Prevalence And Mortality. Knowledge About The Prevalence Of The Cryptic Pathogens Plasmodium Ovale And Plasmodium Malariae Is Limited. Thanks To Recombinant Tools, Their Seroprevalence Was Measured For The First Time, As Well As The Prevalence Of Mixed Infections In A Malaria-Asymptomatic Population In Benin, A Malaria-Endemic Country.

Methods: A Panel Of 1,235 Blood Donations Collected Over Ten Months In Benin Was Used For Validation Of The Recombinant Tools. Recombinant P. Falciparum, P. Malariae, P. Ovale MSP1, And P. Falciparum AMA1 Were Engineered And Validated On A Biobank With Malaria-Infected Patients (N = 144) Using A Species-Speific ELISA Test (Recelisa). Results Were Compared To An ELISA Using A Native P. Falciparum Antigen (NatELISA).

Results: Among Microscopically Negative African Blood Donors, 85% (1,050/1,235) Present Antibodies Directed To Native P. Falciparum, 94.4% (1,166/1,235) To rPfMSP1 And rPfAMA1, 56.8% (702/1,235) To rPoMSP1, 67.5% (834/1235) To rPmMSP1 And 45.3% Of The Malaria Seropositive Population Had Antibodies Recognizing The Three Species.

Conclusion: A High Rate Of Antibodies Against P. Ovale And P. Malariae Was Found In Asymptomatic Blood Donors. The Proportion Of Mixed Infections Involving Three Species Was Also Unexpected. These Data Suggest That Determining Seroprevalence For These Cryptic Species Is An Appropriate Tool To Estimate Their Incidence, At The Eve Of Upcoming Anti-P. Falciparum Vaccination Campaigns.

Figure 1

Seroprevalence of antibodies detected by native P. falciparum or a set of recombinant proteins from Plasmodium (r Pf AMA1 and rMSP1 from P. falciparum , P. ovale and P. malariae ) in 1,235 Beninese blood donors.

Figure 2

Venn diagram showing a distribution of mixed malaria infections among 1,220 malaria antibody-positive Beninese blood donors.

Figure 3

Seasonal evolution of seroprevalence for antibodies detected by native P. falciparum antigen and recombinant proteins r Pf AMA1 + r Pf MSP1, r Po MSP1, and r Pm MSP1 in 1,235 malaria blood donors in Benin; LRS: long rainy season (May to July); SDS: short dry season (August to September); SRS: short rainy season (October to November); LDS: long dry season (December to March).

Figure 4

Distribution of positive samples according to the ELISA’s index for P. falciparum, P. malaria and P. ovale recombinant antigens. The cut-off value was calculated by multiplying the negative control wells’ average optical density (OD) by three. The antibody (Ab) index of each sample was calculated by dividing its OD value by the cut-off value. The sample was considered positive if the Ab index was >0.7, and negative if the Ab index was ≤0.7.