Molecular investigation of mixed malaria infections in southwest Saudi Arabia.

Objective: To investigate the incidence of mixed-species (MS) malaria infection, and compare the results with microscopically confirmed cases of malaria.

Methods: During 2010, blood spots collected from 371 clinically suspected cases of malaria were microscopically examined in a cross-sectional study. The DNA was extracted from the samples, and a nested polymerase chain reaction (PCR) was performed. The results obtained by the 2 methods were compared.

Results: From the microscopic analysis it was determined that 369 samples (99.5%) were positive for Plasmodium falciparum (P. falciparum) and 2 were Plasmodium vivax (P. vivax) mono-infections. There were no mixed malaria infections. The PCR analysis, however, showed that in 7 cases (1.9%) the infection was caused by MS malaria comprising of P. falciparum and P. vivax, 2 of these representing the cases that were microscopically diagnosed as P. vivax mono-infections. All cases were negative for Plasmodium malariae, Plasmodium ovale, and Plasmodium knowlesi.

Conclusions: Mixed malaria infections are currently overlooked when using microscopy. The PCR assays are essential complementary techniques that should be used with microscopic examination of blood smears.