Plasmodium falciparum: genetic diversity of several strains infectious for the squirrel monkey (Saimiri sciureus)

The squirrel monkey, Saimiri sciureus, is a useful experimental host for the human malaria parasite Plasmodium falciparum. Twelve strains of P. falciparum, including monkey-adapted strains, culture-derived strains, and one human isolate were injected into naive, splenectomized Saimiri monkeys of karyotype 14-7. Several parameters were recorded following inoculation such as parasitemia, body temperature, standard hematological parameters, gametocytemia, rosette formation, autoagglutination, as well as HRPI and PfEMP3 expression. Each strain was injected into two to four monkeys and induced a reproducible course of infection. Four distinct patterns of parasite development were observed. For each strain, a multilocus genotype was established by PCR using several polymorphic (Pf60, RESA, RESA2, MSA1, MSA2, Pf332, TRAP, GLURP, CSP, and HRPI) or conserved (EBA175, GARP, MDRI, and RNA POL III) markers. RFLP analysis was conducted for the Pf11.1 locus. This genotyping approach showed that 3 strains presented strictly similar patterns, typical of FUP/SP parasites. A group of 7 other strains presented a highly similar FUP/CP (FCR3-like) genetic background, while 4 other strains showed unique patterns. Infectiousness did not depend on a RESA deletion, as several strains developed successfully while present ng a wild-type RESA gene. Conversely, an interesting correlation was found between allelic diversity at the HRPI locus and the course of blood stage infection. The data presented here provide the first precise genotyping of several monkey-adapted strains, allowing a more rational approach in the study of the role of parasite diversity on host/parasite interactions.