Confirmation of cultured parasite P. vivax Chesson strain using characteristics of the ribsomal 18S RNA gene. (a Upper) Amplification products for a Plasmodium specific region of the 18S rRNA gene. The two bands represent the sporozoite (top) and blood stage (bottom) forms of the gene. Type specimen Chesson strain (Che) can be clearly distinguished not only from P. falciparum (Pf), P. cynomolgi (Pc), and P. knowlesi (Pk), but from the Central American strain of P. vivax (Sal). The type specimen is identical to monkey reared parasites at the beginning of culture (V0) and after five cycles (V5). (Lower) Southern blot of the seven samples with an oligo probe specific for the blood stage gene of P. vivax. Size standards are shown in M (100 bp ladder). (b Upper) Amplification profiles of cDNA derived from rRNA by reverse transcriptase–PCR for two additional primate species, P. malariae (Pm) and P. ovale (Po), as well as for culture cycles 3 (V3), 5 (V5), and 8 (V8). Southern blots with the same probe as in a are shown below.