Malaria epidemiology in low-endemicity areas of the northern coast of Ecuador: high prevalence of asymptomatic infections

Abstract

Background: The recent scale-up in malaria control measures in Latin America has resulted in a significant decrease in the number of reported cases in several countries including Ecuador, where it presented a low malaria incidence in recent years (558 reported cases in 2015) with occasional outbreaks of both Plasmodium falciparum and Plasmodium vivax in the coastal and Amazonian regions. This success in malaria control in recent years has led Ecuador to transition its malaria policy from control to elimination.

Results: This study evaluated the general knowledge, attitude and practices (KAP) about malaria, as well as its prevalence in four communities of an endemic area in northwest Ecuador. A total of 258 interviews to assess KAP in the community indicated that most people in the study area have a basic knowledge about the disease but did not use to contribute to its control. Six hundred and forty-eight blood samples were collected and analysed by thick blood smear and real-time PCR. In addition, the distribution of the infections was mapped in the study communities. Although, no parasites were found by microscopy, by PCR the total malaria prevalence was 7.5% (6.9% P. vivax and 0.6% P. falciparum), much higher than expected and comparable to that reported in endemic areas of neighbouring countries with higher malaria transmission. Serology using ELISA and immunofluorescence indicated 27% respondents for P. vivax and 22% respondents for P. falciparum.

Conclusions: Results suggest that despite a great malaria reduction in Ecuador, transition from control to elimination would demand further improvement in malaria diagnostics, including active case detection to identify and treat parasite asymptomatic carriers, as well as community participation in its elimination.

Keywords: Asymptomatic malaria; Ecuador; Elimination; Knowledge attitude and practices.

Fig. 1

General trend of malaria in Ecuador 2001–2014. A 99% decrease in malaria cases is shown since the year 2001 for total cases (green line) as well as those caused by each of the main parasite species: P. vivax (blue line) and P. falciparum (red line)

Fig. 2

Study area. The study was performed in four locations in the Esmeraldas province (green) in Ecuador (red) which are indicated by color dots on the map

Fig. 3

Plasmodium prevalence in the study area by qPCR. a Distribution of malaria infections in the study area. The size of the circles represents malaria prevalence, with P. vivax in blue and P. falciparum in red. b Percentage of Plasmodium cases by qPCR in the four study communities. El Pedregal had the highest prevalence while Ricaurte had the lowest. c P. vivax and P. falciparum prevalence. P. vivax was the most prevalent parasite in the study area. El Guadual had the highest amount of P. falciparum infections. d Parasitaemia distribution in the four study communities. Parasitaemia varied between 1 and 800 parasites/µl

Fig. 4

Percentage of antibody responders by ELISA. Percentages of antibody respondents to the indicated malaria antigens are shown as bars for the indicated study sites. The antibody response percentages broadly correlated with the malaria prevalence in each of the study sites. Indeed, El Pedregal had a higher percentage of responders for all antigens and a higher malaria prevalence

Fig. 5

Estimated risk of malaria for La Boca (top row), El Pedregal (middle row), and Ricaurte (bottom row). The risk maps (right column) show the correlation between human population density and malaria cases, thus identifying the places where interventions might have the greatest impact. El Guadual was not included in this analysis because the number of samples was too small to perform the algorithm