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.

Vectors of scrub typhus and their hosts on a mature oil palm estate.

L. (L.) deliense was the predominant vector of scrub typhus in a mature oil palm estate, but a small number of L. (L.) fletcheri (0.1% from rodents) and L. (L.) vivericola (0.02% from rodents and 8.0% from black plates) was also collected. Although good correlation between L. (L.) deliense collected from rodents and from black plates was not established, either method may serve as a general indicator of population fluctuations over a period of time. For the most part, the vectors of scrub typhus were limited to litter piles, and thus, the possibility of contracting scrub typhus within this type of habitat was minimal.

Rickettsia tsutsugamushi infections in chiggers and small mammals on a mature oil palm estate.

An epidemiological study in a mature oil palm estate in Peninsular Malaysia has demonstrated a low prevalence of R. tsutsugamushi infection in small mammals. The direct fluorescent antibody technique for assaying infections in chiggers proved more sensitive than mouse inoculation. Most infections in both chiggers and rodents were caused by the Karp strain.

Virulence and antigenic properties of Rickettsia tsutsugamushi in a naturally infectei laboratory colony of Leptotrombidium (leptotrombidium) arenicola.

Over 1,200 isolations of R. tsutsugamushi were obtained over 7 generations of L. (L.) arenicola and no reproducible differences in virulence or antigenic markers could be detected among these isolations. The F8 generation yielded rickettsia with the same antigenic makeup and virulence properties as the original female parent mite. When these isolates were inoculated into mice they elicited the same predominant antibody specificities, i.e. they all produced antibody which reacted with the TA 763 and Karp strains. These were the same as the major antigens detected by direct fluorescent antibody staining of the isolates.

The life history of a colony of Leptotrombidium (Leptotrombidium) fletcheri (Womersley & Heaslip) infected with Rickettsia tsutsugamushi.

The life cycle of 5 generations of Leptotrombidium (L.) fletcheri infected with Rickettsia tsutsugamushi and reared under ambient temperatures in Malaysia was presented and compared with a colony reared at a constant 27 degrees C (Neal and Barnett, 1961). In general our colony had a longer generation time (average of 54 days from engorged larvae to adult compared with 37 days) and produced fewer eggs (average of 127.9 compared with 900.0) than the comparison colony. Possible factors causing these differences are discussed.

Chigger (Acarina:Trombiculidae) surveys of the west coast beaches of Sabah and Sarawak.

Leptotrombidium (Leptotrombidium) arenicola Traub, a vector of scrub typhus, had previously been found to occur in the coastal vegetation behind the edge of open sand along the beaches of Peninsular Malaysia. Surveys of the west coast beaches of Sabah and Sarawak were conducted to determine if this species occurs in similar habitat in East Malaysia on the island of Borneo. Leptotrombidium (L.) arenicola was not collected from the eighteen sites studied. Of the 11,982 mite larvae collected, 55 per cent were L.(L.) deliense (Walch), a well-known, widespread vector of scrub typhus.

Murine typhus in a Malaysian village.

A high prevalence of murine typhus was found in the human and rodent populations of Senaling, West Malaysia. In addition to 2 index cases which prompted the investigation, 45% of the humans and 35% of the rodents had IFA titers of 1/50 or greater. Serological studies provided evidence of recent infections in 3 human subjects. In a control group of Malaysian soldiers IFA titers of 1/50 or greater were found in only 13 (5%) of 265 sera tested.