Multiplicity of infection and parasite load of Plasmodium vivax in individuals with recurrences of the communities of cahuide and lupuna of the Peruvian Amazon

In Peru, most cases of Plasmodium vivax infections are concentrated in the region of Loreto, where infections are of interest because the presence of recurrences, most of them with low parasite load and asymptomatic. The presence of latent hypnozoites makes it difficult to classify recurrent P. vivax infections as relapses, recrudescences or re-infections. The characteristic of the different recurrences has not been defined adequately in this region despite obvious relevance to malaria control and elimination. This study aimed to determine the relationship between parasite load and multiplicity of infection (MOI) of P. vivax in addition to determine the type of recurrence in individuals from the communities of San José de Lupuna and Cahuide of the region of Loreto. After a follow-up from August 2012 to March 2014, 123 individuals were selected with recurrences in both communities. Generalized linear mixed models (GLMM) were used to evaluate the relationship between parasite load measured by qPCR and MOI of P. vivax determined by genotyping 17 microsatellite markers among these individuals. Additionally the type of recurrence in a minor group of these individuals was determined by the STRUCTURE analysis. The relationship found between parasite load and MOI was inverse (p <0.001). The parasitemia were lower in episodes of recurrence but with no significant results. In addition most recurrences were heterologous, therefore probably they are the result of reinfection by different clones, however it is also possible that there have been heterologous relapses. These results indicate that the MOI of P. vivax in individuals of these communities does not influence the immune response to control parasitemia in episodes of recurrence, even if those correspond to reinfections.