Marked Rise in the Prevalence of Asymptomatic Plasmodium falciparum Infection in Rural Gabon

Abstract

Control strategies implemented a decade ago led to a marked reduction in the prevalence of malaria in many countries. In Dienga, southeastern Gabon, the prevalence of microscopic P. falciparum infection was 7% in 2003, close to the pre-elimination threshold of 5%. The aim of this work was to determine the prevalence of P. falciparum infection in the same community a decade later. A cohort of 370 individuals aged from 3 to 85 years living in Dienga was investigated for P. falciparum infection; during six passages (P) in 15-month period. Demographic data were collected, along with behaviors and attitudes towards malaria. Plasmodium infection was diagnosed by microscopy (ME), followed by PCR to detect submicroscopic infection. The prevalence of P. falciparum infection in P1, P2, P3, P4, P5 and P6 was respectively 43.5% (25.1% ME+, 18.4% PCR+); 40.9% (27.0% ME+, 13.9% PCR+), 52.7% (26.1% ME+, 26.6% PCR+); 34.1% (14.1% ME+, 20% PCR+), 57.7% (25.4.% ME+, 32.3% PCR+); and 46.2% (21.4% ME+, 24.8% PCR+) with an overall average of 45.9% (95%CI [37.0–54.7], 23.2% ME+ and 22.7% PCR+). P4 and P5 prevalences were statically different throughout the six passages. Microscopic prevalence was significantly higher than that observed ten years ago (23% [n = 370] vs 7% [n = 323], p < 0.001). Asymptomatic infections were the most frequent (96%). Gametocytes were detected in levels ranging from 5.9% to 13.9%. Insecticide-treated nets, indoor residual insecticides, and self-medication were used by respectively 33.2% (95%CI [29.0–37.4]), 17.7% (95%CI [15.5–19.9]) and 12.1% (95%CI [10.6–13.6]) of the study population. A near-threefold increase in P. falciparum infection has been observed in a rural area of southeastern Gabon during a 10-year period. Most infections were asymptomatic, but these subjects likely represent a parasite reservoir. These findings call for urgent reinforcement of preventive measures.

Seasonal Variation in the Epidemiology of Asymptomatic Plasmodium falciparum Infections across Two Catchment Areas in Bongo District, Ghana

“…The prevalence of asymptomatic P. falciparum infections by microscopy differed between the age groups surveyed, gradually increasing during childhood and then declining from late adolescences into adulthood. This age-dependent trend in microscopic prevalence was in agreement with previous studies [42][43][44] and was observed at the end of the wet and dry seasons across both catchment areas in BD. These results indicate the importance of understanding the burden of disease and consequences of asymptomatic malaria in the adolescent population, which have traditionally been neglected and rarely targeted for malaria control.…”

“…14,33,53 Recent findings from an area with intense seasonal malaria in Burkina Faso suggests that submicroscopic parasite carriers are an important source of onward transmission, particularly at the end of the dry season, and are responsible for about half of the infectious P. falciparum reservoir. 4 Although our results are similar to previous studies and demonstrate that asymptomatic infections made up a substantial portion of the P. falciparum reservoir across all ages, 42,44,48,54 their ability to produce mature gametocytes and transmit remains vague based on the microscopy results. Further work to evaluate the potential contribution of these asymptomatic infections for onward transmission needs to be assessed and monitored using more sensitive methods if we are to implement appropriate elimination strategies in BD.…”

“…45 The attitudes and behaviors of adolescents are different from those of children and adults, and hence influence their risk of developing and transmitting malaria. 44,46 Although ITNs, ITP p , ITP i , and SMC reduce the morbidity and mortality associated with malaria they are typically targeted toward children £ 5 years of age and therefore do not adequately account for the whole reservoir of P. falciparum infections in the population. Reducing the burden of disease among both adolescents and older age groups needs to be made a priority in regions with stable malaria transmission.…”

Pfmdr1 gene polymorphism of Plasmodium falciparum isolates from asymptomatic individuals of Dienga, southeastern Gabon

“…In Dienga, the prevalence of P. falciparum infection decreased around 2003 [30] but a decade after this prevalence rose markedly [29]. This situation may be associated with a lack of ongoing efforts to fight against the disease (ie local anti-malarial drug use, prevention measures).…”

“…From April 2013 to June 2014, through six field missions, a cohort composed of 370 indiduals was followed to investigate P. falciparum infection [29]. The participants were composed of volunteers permanently living in Dienga; primary school children (≥ 3 years) and adults.…”