Cytogenetic studies of some species complexes of Anopheles in Thailand and Southeast Asia.

Recent studies on cytogenetics, behavioral, geographical and distinct morphological characters on adult, pupal and larval stages have revealed that "balabacensis" is a species complex. Anopheles dirus the mainland species, is distributed widely in Thailand and is renowned for its role as primary vector of human malarial parasites. Further, evidence from cytogenetic and taxonomic studies suggests that "An. dirus" is a species complex comprising at least four distinct species provisionally designated: dirus A, B, C and D. These cryptic species are distinguishable only partially morphologically, but can be separated on the basis of metaphase chromosomes using the Giemsa and Hoechst 33258 staining techniques. Apparently, these siblings show distinct patterns of geographic distribution in Thailand and Peninsular Malaysia. The recognition of dirus as a complex of species in Thailand and Peninsular Malaysia requires a re-evaluation of the role that the individual members of this complex have in the transmission of malaria parasites in this region. Cytological analysis of gene rearrangements in ovarian polytene chromosomes has shown that An. maculatus is a sibling-species complex consisting of at least four species in Thailand provisionally designated: maculatus A, B, C and G. These siblings are sympatric in some populations. Furthermore, species B is so highly polymorphic for chromosome rearrangements that four geographic forms can be recognized. It is not known whether these four forms are subspecies or yet further species within the species B complex. These sibling-species must be differentiated in order to understand any differential capabilities in their transmission of human malaria parasites. Anopheles nivipes was elevated from synonymy under An. philippinensis to full species status by Reid, a decision recently confirmed by cross mating experiments. The Thailand Malaria Division does not differentiate these two species and only identifies An. philippinensis, yet, An. nivipes is by far the most common of the two species in Thailand. Furthermore, preliminary surveys of the ovarian polytene chromosomes of several widely separated populations of An. nivipes in Thailand have revealed at least two distinct chromosomal types of nivipes based on fixed inversions on the X chromosomes.

Sporozoite-induced Plasmodium cynomolgi infections in captive born Macaca fascicularis.

Capability of captive born cynomolgus monkeys to substitute for rhesus in the Plasmodium cynomolgi radical curative antimalarial drug development model was examined. Eighteen monkeys divided into 3 groups were given standard or high doses of sporozoites intravenously. One group of 4 received 0.8 - 1.6 X 10(6) and a second group of 8 received 0.3 - 1.0 X 10(7) sporozoites. The third group of 6 was splenectomized and then received 3.0 - 4.0 X 10(6). The 2 groups of intact monkeys developed a persistent low level parasitemia; however, gametocyte production was poor. The splenectomized group developed a persistent parasitemia with a higher mean, which more closely resembled rhesus parasitemias. A high, post-patent leukocytosis consisting primarily of lymphocytes was observed in this group. Good gametocyte production resulted in the splenectomized group and oocysts were produced from all lots of Anopheles dirus which fed on them. Following clearance of blood forms, relapse potential was demonstrated in the 2 splenectomized monkeys tested. In this study the splenectomized captive born cynomolgus appeared to be capable of supplementing rhesus as an antimalarial drug testing model.

Rickettsia tsutsugamushi strains found in chiggers collected in Thailand.

R. tsutsugamushi strains found in chiggers collected from 3 different sites throughout Thailand were antigenically characterized. Monotypic infections were observed in 76.7% of the chiggers. Karp was the most predominant strain, followed by TA716, TA763, TA686 and Kato. This study represents the first confirmed report of R. tsutsugamushi infection in 8 different chigger species in Thailand.