All South American countries except Chile and Uruguay currently experience transmission of human malaria, which is one of the commonest maladies treated at health clinics in rural areas (Fig.l). Annual parasite indices, the numbers of malaria infections per thousand persons, for 1997 ranged by country from 0.4 in Paraguay to 314.5 in Suriname (PAHO 1998). More than one-half of the slightly less than one million annual registered cases occur in Brazil, with Peru and Colombia following in numerical importance (PAHO 1998). Although the majority of infections are of Plasmodium vivax (Grassi & Feletti), P. falciparum (Welch) and P. malariae (Grassi & Feletti) may be abundant locally (e.g., Branquinho et al. 1993, Arambarú Guarda et al. 1999).