Micro-epidemiology of mixed-species malaria infections in a rural population living in the Colombian Amazon region

Abstract

Malaria outbreaks have been reported in recent years in the Colombian Amazon region, malaria has been re-emerging in areas where it was previously controlled. Information from malaria transmission networks and knowledge about the population characteristics influencing the dispersal of parasite species is limited. This study aimed to determine the distribution patterns of Plasmodium vivax, P. malariae and P. falciparum single and mixed infections, as well as the significant socio-spatial groupings relating to the appearance of such infections. An active search in 57 localities resulted in 2,106 symptomatic patients being enrolled. Parasitaemia levels were assessed by optical microscopy, and parasites were detected by PCR. The association between mixed infections (in 43.2% of the population) and socio-spatial factors was modelled using logistic regression and multiple correspondence analyses. P. vivax occurred most frequently (71.0%), followed by P. malariae (43.2%), in all localities. The results suggest that a parasite density-dependent regulation model (with fever playing a central role) was appropriate for modelling the frequency of mixed species infections in this population. This study highlights the under-reporting of Plasmodium spp. mixed infections in the malaria-endemic area of the Colombian Amazon region and the association between causative and environmental factors in such areas.

Figure 1

Geographical locations of the 57 localities where samples were collected (this map was modified from a map downloaded from the Instituto Geográfico Agustín Codazzi, IGAC)^,. Images are freely accessible and modifiable in accordance with IGAC policies.

Figure 2

Cumulative frequency of Plasmodium species and their contribution to malaria in 1,750 people in whom parasitic DNA was identified using molecular techniques. P.v = Plasmodium vivax, P.m = Plasmodium malariae and P.f = Plasmodium falciparum.

Figure 3

Relative frequency of parasite infection and Plasmodium spp. distribution with respect to the area sampled [area 1 (n = 344), area 2 (n = 257), area 3 (n = 566) and area 4 (n = 828)]. Part (a) shows the distribution of parasite infection frequency with respect to the Plasmodium spp. infection status. Blue represents the uninfected target population. Green represents the proportion of the target population infected by a single species. Dark red represents the proportion of the target population with a mixed species infection. Part (b) shows the relative frequency of Plasmodium spp.

Figure 4

Multiple correspondence analysis (MCA). Part (a) represents the mode on axes 1 and 2. Part (b) represents the mode on axes 1 and 3. Part (c) represents the mode on axes 2 and 3. The variables contributing towards each profile are highlighted; green indicates the positive pole and red indicates the negative pole variables.