PLASMODIUM INUI IS NOT CLOSELY-RELATED TO OTHER QUARTAN PLASMODIUM SPECIES

Plasmodium inui (Halberstaedter and von Prowazek, 1907), a malarial pa rasite of Old world monkeys that occurs in isolated pockets throughout the Celebes, Indonesia, Malaysia, and the Philippines. has traditiona lly been considered to be related more closely to Plasmodium malariae of humans (and its primate counterpart Plasmodium brasiliantum), than to other primate Plasmodium species. This inference was made in part b ecause of the similarities in the periodicities or duration of the ase xual cycle in the blood, the extended sporogonic cycle, and the longer period of time for development of the pre-erythrocytic stages in the liver Both P. inui and P. malariae have quartan (72 hr) periodicities associated with their asexual cycle, whereas other primate malarias, s uch as Plasmodium fragile and Plasmodium cynomolgi, are associated wit h tertian periodicities (48 hr), and Plasmodium knowlesi, with a quoti dian (24 hr) periodicity. Phylogenetic analyses of portions of ortholo gous small subunit ribosomal genes reveal that P. inui is actually mon closely related to the Plasmodium species of the ''vivax-type'' linea ge than to P. malariae. Ribosomal sequence analysis of many different, geographically isolated, antigenically distinct P. inui isolates reve als that the isolates are nearly identical in sequence and thus member s of the same species.