Neotropical primates of the Cebidae and Callitrichidae, in their natural habitats, are frequently infected with a variety of trypanosomes including Trypanosoma cruzi, which causes a serious zoonosis, Chagas' disease. The state of trypanosome infection after a 30-day quarantine period was assessed in 85 squirrel monkeys (Saimiri sciureus) and 15 red-handed tamarins (Saguinus midas), that were wild-caught and exported to Japan as companion animals or laboratory animals, for biomedical research, respectively. In addition to many microfilariae of Mansonella (Tetrapetalonema) mariae at a prevalence of 25.9%, and Dipetalonema caudispina at a prevalence of 3.5%, a few trypomastigotes of Trypanosoma (Megatrypanum) minasense were detected in Giemsa-stained thin films of blood from 20 squirrel monkeys at a prevalence of 23.5%. Although few T. minasense trypomastigotes were found in Giemsa-stained blood films from tamarins, a buffy-coat examination detected trypanosomes in 12 red-handed tamarins (80.0%), and PCR amplification of a highly variable region of the small subunit ribosomal RNA genes (SSU rDNA) for Trypanosoma spp. detected the infection in 14 of the 15 tamarins (93.3%). Nucleotide sequences of the amplicons were identical for trypanosomes from tamarins and squirrel monkeys, indicating a high prevalence but low parasitemia of T. minasense in imported Neotropical nonhuman primates. Based on the SSU rDNA and 5.8S rDNA, the molecular phylogenetic characterization of T. minasense indicated that T. minasense is closely related to trypanosomes with Trypanosoma theileri-like morphology and is distinct from Trypanosoma (Tejeraia) rangeli, as well as from T. cruzi. Using some blood samples from these monkeys, amplification and subsequent sequencing of the glycosomal glyceraldehyde-3-phosphate dehydrogenase (gGAPDH) gene fragments detected 4 trypanosome genotypes, including 2 types of T. cruzi clade, 1 type of T. rangeli clade, and 1 T. rangeli-related type, but failed to indicate its phylogenetic position based on the gGAPDH gene. Furthermore, species ordinarily classified in the Megatrypanum by morphological criteria do not form a clade in any molecular phylogenetic trees based on rDNA or gGAPDH genes.

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