Seasonal Occurrence of Leptotrombidium deliense (Acari: Trombiculidae) Attached to Sentinel Rodents in an Orchard near Bangkok, Thailand

Abstract

Leptotrombidium deliense Walch that attached to sentinel laboratory mice and the roof rat, Rattus rattus (L.), placed in an orchard habitat near Bangkok, Thailand, were studied between April 1993 and April 1995. A single L. deliense larva was attached to only 1 of 51 laboratory mice placed in the study area between April and September 1993. Overall, 89/202 (44.1%) R. rattus had 1 or more L. deliense larvae attached, and Orientia tsutsugamushi (Hayashi), the etiologic agent for scrub typhus, was isolated from liver/spleen samples of 2/202 (1.0%) rats placed in an endemic area for a single night. A total of 474 L. deliense attached to sentinel R. rattus, of which 314 larvae successfully fed to repletion and were recovered, and 2 (0.6%) of these were naturally infected with O. tsutsugamushi. The occurrence of L. deliense was influenced by rainfall, with more chiggers attached to rodents in the wetter months of the year. The study showed that the risk of exposure to infection with O. tsutsugamushi is greater during the wetter months of the year, and that only a relatively small number of chigger attachments are needed to infect potential hosts.

Use of a sentinel host system to study the questing behavior of Ixodes spinipalpis and its role in the transmission of Borrelia bissettii, human granulocytic ehrlichiosis, and Babesia microti.

“…Because previous attempts to collect I. spinipalpis in this region by dragging were unsuccessful, a sentinel host system was employed. Sentinel birds are commonly used to monitor arbovirus activity, 20 whereas sentinel mammals have been employed to study Scrub typhus rickettsia 21,22 and Leishmania 22 activity, as well as to collect vector mites. 21,22 Our results suggest that employing this method of studying the questing behavior of I. spinipalpis ticks was successful in detailing specific ecological niches of activity, as well as directly demonstrating this tick's ability to transmit multiple human pathogens.…”

Experimental infection and transmission ofOrientia Tsutsugamushiin adultLeptotrombidium deliensefollowing inoculation with cultured rickettsiae

“…The mean production of 333 eggs per female in injected adults was greater than 146 eggs per female in 174 adults (Frances et al, 1999a) and 218 eggs per female in 11 adults (Frances et aL, 1999b) which were reared from larvae attracted to rodents. However, engorgement on mice was poor, with only 7% of larvae placed recovered as engorged (Table 3), compared with 75% in a previous study (Frances et al, 2000).…”

Distribution of rickettsioses in Oceania: Past patterns and implications for the future

“…In Australia, distribution of published scrub typhus cases and seropositivity appears to be restricted to areas receiving more than 1500 mm of precipitation annually (Campbell and Domrow, 1974;Currie et al, 1996;Frances, 2011). Concordantly, a Thai study found that trombiculid mite larvae were more abundant on hosts in the wetter months than the drier months (Frances et al, 1999). However, in contrast to this tropical distribution, positive serology to O. tsutsugamushi has been reported in large numbers by Australia's national disease surveillance (NNDSS) in the sub-tropical to temperate states South Australia between 2004 and 2011, and in small numbers in Victoria, New South Wales and Tasmania (NNDSS, 2013) ( Table 1).…”