MIXED INFECTIONS
Infections caused by two or more species of malaria parasites are not so uncommon in many of the areas where these kinds are endemic. Frequently, however, these infections are missed by microscopists due to different reasons. First of all, in mixed infections, one species is usually more numerous than the others, making it very important not to stop the microscopic examination as soon as the first species is diagnosed. Besides, as it happens in many laboratories, if only thin blood films are examined for diagnosis, low parasitemia of one species can be masked by the predominant species present. In this case, as previously seen, the correct approach for an optimal diagnosis is to first examine the thick blood film to more easily detect low parasitemias and thus find the diagnostic stage of the species of malaria present, that, in case of doubt, must be confirmed on thin blood films. It is to remember, however, that the diagnosis of these particular cases need very expert microscopists. The mixed infection most frequently encountered in sub-tropical zones is the P. falciparum and P. vivax combination. In Africa, the more common association is between P. falciparum and P. malariae, even though the P. falciparum and P. ovale combination also exist. In Asia, triple infections of P. falciparum, P. malariae, P. vivax are not so uncommon, while coinfection of all four species is a very rare finding [47][70].