Mixed infections detected by nested PCR from archival thick blood films

The detection of Plasmodium species for clinical management in the field have relied mainly on microscopy. Otherwise, there are studies that showed that microscopy alone fail to detection a high proportion of mixed infections, in comparison with PCR-based methods. The precise detection of mixed infections is important to guarantee the adequate treatment, since the specific treatment used depends on the infecting species. This study aimed to determine the frequency of mixed P. falciparum/P. vivax/P. malariae infections in southeastern of Para state (Amazon Region, Brazil) using archival thick blood films as source of Plasmodium DNA to nested PCR and compared to microscopic results. The frequency of mixed infections of blood samples from individuals from southeastern Para collected from 2000 to 2010 was determined using nested PCR from archival thick blood films. These findings were compared with microscopy results, read by two independence technicians. From 113 blood films initially diagnosed by microscopy, nested PCR showed that 24.8% were mixed infections. These findings were double the frequency detected by microscopy. Otherwise, nested PCR failed in detecting two mixed infections (P.falciparum + P. vivax and P. vivax + P. malariae). The correct detection of mixed infections is extremely important mostly in co-exist P. falciparum/P. vivax/P. malariae areas to safeguard appropriate treatment to patients and to ensure epidemiological malaria vigilance. This can involve the use of other diagnostic tools, including rapid diagnostic tests and molecular methods, able to detecting low parasitaemias or mixed infections, which contribute to the strengthening of laboratory capacity in endemic areas, mainly in countries targeting pre-elimination.