High Prevalence of Asymptomatic Malarial Anemia and Association with Early Conversion from Asymptomatic to Symptomatic Infection in a Plasmodium falciparum Hyperendemic Setting in Cameroon

Abstract

Asymptomatic malarial parasitemia is highly prevalent in Plasmodium falciparum endemic areas and often associated with increased prevalence of mild to moderate anemia. The aim of this study was to assess the prevalence of anemia during asymptomatic malaria parasitemia and its interplay with persistent infection in highly exposed individuals. A household-based longitudinal survey was undertaken in a malaria hyperendemic area in Cameroon using multiplex nested polymerase chain reaction to detect plasmodial infections. Residents with P. falciparum asymptomatic parasitemia were monitored over a 3-week period with the aid of structured questionnaires and weekly measurements of axillary temperatures. Of the 353 individuals included (median age: 26 years, range 2–86 years, male/female sex ratio 0.9), 328 (92.9%) were positive for malaria parasitemia of whom 266 (81.1%) were asymptomatic carriers. The prevalence of anemia in the study population was 38.6%, of which 69.2% were asymptomatic. Multivariate analyses identified high parasitemia (> 327 parasites/µL) and female gender as associated risk factors of asymptomatic malarial anemia in the population. Furthermore, risk analyses revealed female gender and anemia at the time of enrolment as key predictors of early development of febrile illness (< 3 weeks post enrolment) among the asymptomatic individuals. Together, the data reveal an extremely high prevalence of asymptomatic malaria parasitemia and anemia in the study area, unveiling for the first time the association of asymptomatic malarial anemia with early clinical conversion from asymptomatic to symptomatic infection. Furthermore, these findings underscore the negative impact of asymptomatic malaria parasitemia on individual health, necessitating the development of appropriate control and preventive measures.

Clinical characteristics of Plasmodium falciparum infection among symptomatic patients presenting to a major urban military hospital in Cameroon

“…Considering 10–14-year-olds for example, this group had a higher prevalence of P. falciparum infection than young children or adults, and over 80% of anaemia was associated with malaria infection. The role of malaria in the burden of anaemia in Cameroon may extend even to asymptomatic malaria infection as a recent longitudinal study across multiple villages in Cameroon’s Central Region found asymptomatic malaria infection (diagnosed by PCR) was associated with 69.2% of anaemia in the study population [ 41 ]. Despite this association, the relationship between anaemia and malaria in children remains complex.…”

Asymptomatic carriage ofPlasmodium falciparumin children living in a hyperendemic area occurs independently of IgG responses but is associated with a balanced inflammatory cytokine ratio

“…The longevity of asymptomatic falciparum malaria has been studied in several settings with the prevalence in naturally occurring infections ranging from 2 months in Vietnam (8), 5–6 months in a longitudinal study in Ghana (13) and 6–9 months in Myanmar (14). Over the course of our 3-month study, we have shown that there is a high rate of persistent asymptomatic parasite carriage in Cameroon (43). Mathematical modelling of existing data indicates that asymptomatic P. falciparum infections could last for as long as 13-years (68).…”

“…(45). Genotyping of msp2 gene was performed by nested PCR on P. falciparum PCR positive samples as previously described (43,46).…”

“…A total of 353 residents of the Esse health district of Cameroon were screened for malaria using multiplex nested PCR. Overall, 328 residents (92.9%) were positive for Plasmodium infection, of which (266) 81.1% were asymptomatic and 63 (18.9%) were symptomatic (43). Given that the aim of this study was to determine the host immunological determinants in the maintenance of the asymptomatic infections, only a subset of individuals with known status during the longitudinal follow-up period were included in the analysis.…”

Systems biology of malaria explored with nonhuman primates

“…Specifically, E03 [ 131 ] showed that rhesus macaques infected with P. coatneyi develop chronic infections after receiving subcurative artemether treatment and that they recapitulate the decrease in haemoglobin levels characteristic of persistent infection in humans [ 45 , 488 ]. A recent study with kra monkeys infected with P. knowlesi showed evidence of a similar phenotype, but without the administration of subcurative anti-malarial treatment (see E07 below) [ 268 ].…”