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This study was developed with the aim of characterizing Plasmodium vivax circumsporozoite protein genotypes on the Island of São Luís, Maranhão. Blood samples were taken for direct parasitological examination (thick blood film) from 126 individuals. Among these individuals, 109 samples were also taken for molecular diagnosis by means of the polymerase chain reaction. The parasitological examination showed the presence of Plasmodium vivax in two symptomatic individuals, while the molecular study was positive for Plasmodium vivax in seven individuals (two symptomatic and positive from the thick blood film and five asymptomatic and negative from the thick blood film). Two samples showed an association with Plasmodium falciparum. Genotyping of the Plasmodium vivax samples showed that the VK 210 variant was present. This was associated with the VK 247 variant in two samples.

The routine test for diagnosing malaria is still the thick blood smear, despite its known decreased sensitivity and specificity in situations of low parasite density and mixed infections. The polymerase chain reaction is increasingly being used for molecular detection and identification of Plasmodium species, due to its higher sensitivity and specificity. Nested PCR was performed on whole-blood samples from 344 patients with acute febrile syndrome who came to a tertiary healthcare center in Manaus (State of Amazonas) for diagnostic confirmation of malaria. No malaria cases caused by Plasmodium malariae were detected through the blood smear or PCR. Co-positivity of 96.7%, co-negativity of 62.2% and kappa coefficient of 0.44 were observed between PCR and thick blood smear for Plasmodium falciparum. For Plasmodium vivax, co-positivity of 100%, co-negativity of 78.1% and kappa coefficient of 0.56 were observed. For mixed infection, co-positivity of 100%, co-negativity of 84.9% and kappa coefficient of 0.26 were observed. Polymerase chain reaction detected a high number of mixed infections in the samples analyzed, but its routine use for diagnosing malaria still deserves further discussion.