Scrub typhus: vector competence of Leptotrombidium chiangraiensis chiggers and transmission efficacy and isolation of Orientia tsutsugamushi.

A total of 4,281 rodents, belonging to 20 species, was collected from three villages in Chiangrai Province, northern Thailand, from January 1994 to December 2001. The predominant species were Rattus rattus, R. losea and Bandicota indica, accounting for 96% of the total. More than 135,000 chigger mites were removed from wild rodents of which 1% were identified as Leptotrombidium chiangraiensis, a new species vector of scrub typhus. Five Orientia tsutsugamushi-infected L. chiangraiensis colonies established from chiggers removed from R. rattus and R. losea rodents. The prevalence of O. tsutsugamushi infection in colonies ranged from 7-89%. Vertical and horizontal transmission efficacies of O. tsutsugamushi were stable between generations among colonies of L. chiangraiensis. The two isolates of O. tsutsugamushi obtained from individual adult L. chiangraiensis mites represent the first successful isolation of this bacterium from individual adult mites. Characterization of the O. tsutsugamushi isolates is under way.

Temporal changes in prevalence of scrub typhus rickettsia (Orientia tsutsugamushi) infecting the eggs of Leptotrombidium imphalum (Acari: Trombiculidae).

Eggs from seven colony lines of the chigger mite Leptotrombidium imphalum (Vercammen-Grandjean & Langston) were examined for infection with Orientia tsutsugamushi (Hyashi), the etiologic agent of scrub typhus. The polymerase chain reaction (PCR) using primers OtP 56.809 and OtM 56.1221, which amplify a 291 bp region of the P56 gene of O. tsutsugamushi, was used to detect scrub typhus within single eggs. All seven chigger mite lines produced infected eggs with varying rates of infection (Li1 = 8.1%, n = 124; Li2 = 45.6%, n = 90; Li3 = 30.1%, n = 144; Li4 = 31.7%, n = 145; Li5 = 21.3%, n = 136; Li6 = 41.6% n = 77; Li7 = 22.5%, n = 110). The 3 wk with the highest infection rates for each line using Fourier analysis were as follows: Li1 = 2, 7, 14; Li2 = 4, 6, 12; Li3 = 3, 6, 12; Li4 = 4, 6, 12; Li5 = 5, 7, 14; Li7 = 4, 6, 12. Li6 only had nine measurements over time; therefore, Li6 was excluded from individual analysis. Infection rates of scrub typhus in eggs occurred in a 2-wk 2-d cycle, using Fourier analysis of combined data. Not only did infection rates vary among the progeny of females, but temporal variation also occurred.

Investigation of the role of Blankaartia acuscutellaris (Acari: Trombiculidae) as a vector of scrub typhus in central Thailand.

Monthly collections of rodents were conducted in Phitsanulok Province, central Thailand in 1993 to investigate the role of the mite Blankaartia acuscurellaris as a vector of scrub typhus. Overall, a total of 41 rodents were collected and examined for the presence of the red colored larvae of B. acuscutellaris and yellow larvae of Leptotrombidium deliense and Ascoshoengastia sp. A total of 787 B. acuscutellaris and 1390 yellow larvae were placed into pools, triturated and isolation of Orientia tsutsugamushi attempted in laboratory mice. The sera of 8 of the collected rodents had elevated antibodies to O. tsutsugamushi indicating active infections; however, O. tsutsugamushi was not isolated from rodent tissues or pools of larvae. The results of this survey suggest that B. acuscutellaris may not be an important vector of scrub typhus, but more studies are needed in endemic areas.

Transmission of Orientia tsutsugamushi, the aetiological agent for scrub typhus, to co-feeding mites.

Experiments were conducted to investigate the potential for transmission of Orientia tsutsugamushi, the aetiological agent for scrub typhus, when naturally infected mite larvae were co-feeding with uninfected larvae. Larvae from colonies of Leptotrombidium deliense and L. imphalum infected with O. tsutsugamushi were used. Transmission of O. tsutsugamushi to previously uninfected L. deliense and Blankaartia acuscutellaris co-fed with infected L. deliense was shown to occur. The overall minimum rate of acquisition was 1.6% (4/258) for L. deliense and 2.5% (3/119) for B. acuscutellaris. When individual infected L. deliense were co-fed with B. acuscutellaris acquisition of O. tsutsugamushi was not detected. However, when 4 and 8 infected larvae were co-fed with B. acuscutellaris acquisition of O. tsutsugamushi was detected. Transmission of O. tsutsugamushi was not observed when uninfected L. deliense were co-fed with infected L. imphalum. This novel transmission route may explain the occurrence of rickettsiae in genera other than Leptotrombidium spp, which are considered to be the main vectors of O. tsutsugamushi.

Seasonal occurrence of Leptotrombidium deliense (Acari: Trombiculidae) attached to sentinel rodents in an orchard near Bangkok, Thailand.

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.

Occurrence of Orientia tsutsugamushi in chiggers (Acari: Trombiculidae) and small animals in an orchard near Bangkok, Thailand.

The ecology of Orientia tsutsugamushi (Hayashi) was studied in chiggers and small animals in an orchard near Bangkok, Thailand. Small animals were trapped monthly between July and November 1992 and examined for the presence of O. tsutsugamushi and ectoparasitic chiggers. A total of 40 Rattus rattus (L.) and 16 Tupaia glis (Diard) was trapped. O. tsutsugamushi was isolated from liver and spleen samples of 30.8% of R. rattus and 18.6% of T. glis. Antibodies to O. tsutsugamushi were detected in 95% of R rattus, and IgG antibodies persisted for up to 10 mo after removing rats from potential reinfection in the field. A total of 1,133 chiggers was identified and examined for the presence of O. tsutsugamushi using a direct fluorescent antibody test, and 2.6% Leptotrombidium deliense Walch, 5.1% Aschoshoengastia indica Hirst, 2.6% A. (Laurentella) sp. #2 and 0.9% A. (Laurentella) sp. #4 were infected. Forty-four pools of chiggers from these animals were triturated and injected into mice. Seven pools were obtained from T. glis and 1 was positive for O. tsutsugamushi, and 3 of 37 pools from R. rattus were positive. A proportion of the engorged chiggers collected was reared to the adult stage, and the progeny of these adults tested for the presence of O. tsutsugamushi. The progeny of 186 females was tested, and the progeny of 2 L. deliense was found to be naturally infected with O. tsutsugamushi.

Redescription of Leptotrombidium (Leptotrombidium) imphalum (Acari: Trombiculidae), with observations on bionomics and medical importance in northern Thailand.

Leptotrombidium (Leptotrombidium) imphalum Vercammen-Grandjean & Langston is redescribed and illustrated. Specimens were collected from the rodents Rattus rattus, Rattus losea, and Bandicota indica in Chiangrai Province, northern Thailand. The species was found on hosts collected on dikes at the margins of rice fields and in adjacent fruit plantations and along irrigation canals, especially in areas covered with the grasses Imperata cylindrica (lalang grass) and Saccharum arudinaceum. The etiological agent of scrub typhus, Orientia (formerly Rickettsia) tsutsugamushi has been isolated from L. (L.) imphalum, rodent hosts, and patients who live and work in the same habitats.

Systematic review of the genus Acropsylla Rothschild, 1911 (Siphonaptera: Leptopsyllidae), with notes on certain fleas from northern Thailand.

Acropsylla (Leptopsyllidae), a genus of fleas from the Indian Subregion of the Oriental Region, is reviewed to include the seasonal and geographical distribution of the known species. Acropsylla girshami Traub, 1950 is proposed as a junior synonym of Acropsylla episema Rothschild, 1911. Keys are provided for the tribe Meopsyllini and for the species of Acropsylla.

A new ecology for scrub typhus associated with a focus of antibiotic resistance in rice farmers in Thailand.

Following the documentation of chloramphenicol-resistant and doxycycline-resistant strains of Orientia tsutsugamushi (Hyashi) in northern Thailand, we conducted ecological and epidemiological studies near the houses of patients hospitalized with antibiotic-resistant infections. New associations between chiggers, rodents, and O. tsutsugamushi in active rice agriculture areas, an ecological habitat not described previously, are reported. Rattus rattus (L.) was the most common species (representing 85.8% of the 1,433 rodents processed), followed by Rattus losea (Swinhoe) (9.4%), Bandicota indica (Bechstein) (3.6%), and Rattus argentiventer (Robinson and Kloss) (1.3%). O. tsutsugamushi was isolated from 30% of the R. rattus and R. losea, 29% of the B. indica, and 33% of the R. argentiventer collected. Mean minimum infection rates were 0.03 in Leptotrombidium chiangraiensis Tanskul & Linthicum, a new species of chigger, and 0.002 in Leptotrombidium imphalum (Vercammen-Grandjean & Langston), a chigger species not previously associated with scrub typhus transmission. Efficient vertical and horizontal transmission of O. tsutsugamushi by L. chiangraiensis and L. imphalum was demonstrated. During a 19-mo period from October 1993 to April 1995, the overall prevalence of human IgM and IgG antibody to O. tsutsugamushi was 25.5 and 47.3%, respectively. L. chiangraiensis and L. imphalum are incriminated as vectors of O. tsutsugamushi in a rice field habitat associated with a focus of antibiotic resistance.

Immunocytochemical methods to study the distribution of Orientia tsutsugamushi in Leptotrombidium (Acari: Trombiculidae) chiggers.

Immunocytochemical methods were developed and tested for their ability to detect the distribution of Orientia tsutsugamushi in paraffin sections of adult chiggers (Leptotrombidium imphalum Vercammen-Grandjean & Langston). Rickettsial antigen was detected by application of a simple direct or amplified immunocytochemistry procedure and an indirect immunofluorescent procedure. In the direct procedure alkaline phosphatase conjugation to the mouse polyclonal antibody to the Karp strain was followed by the HistoMark Red test system to detect rickettsial antigen. The amplification procedure used a similar method but used an unlabeled primary antibody followed by secondary biotinylated antimouse IgG, streptavidin-alkaline phosphatase, and the HistoMark Red test system. The immunofluorescent procedure included a biotinylated secondary antibody followed by addition of a streptavidin-FITC conjugate. Specific tissue tropisms in infected chiggers were observed in the salivary glands, nervous tissue, and ovaries of adult female mites in all procedures; however, nonspecific fluorescence of the chigger limited definitive identification of tissue tropisms with the indirect immunofluorescent procedure.

A new species of Leptotrombidium (Acari:Trombiculidae) collected in active rice fields in northern Thailand.

Leptotrombidium (Leptotrombidium) chiangraiensis Tanskul & Linthicum is described and illustrated as new from specimens collected from the rodents Rattus rattus (L., 1758), Rattus argentiventer (Robinson & Kloss, 1916), Rattus losea (Swinhoe, 1870), and Bandicota indica (Bechstein, 1800) in Chiangrai Province northern Thailand. The new species was collected in active rice fields and adjacent fruit plantation areas. The etiological agent of scrub typhus, Orientia (formerly Rickettsia) tsutsugamushi (Hayashi), has been isolated from patients who live and work in the same habitat where L. chiangraiensis is the predominant Leptotrombidium species.

Pathology of Rickettsia tsutsugamushi infection in Bandicota savilei, a natural host in Thailand.

Following rodent surveys in a rice-growing area of central Thailand where we found Bandicota savilei, B. indica, and Rattus rattus infected with Rickettsia tsutsugamushi, we performed a study of pathogenesis of R. tsutsugamushi in laboratory-reared B. savilei. Eight animals were injected with saline and 19 animals were injected with 4.0 x 10(6) mouse 50% lethal dose units of a strain of R. tsutsugamushi isolated from a human in central Thailand. Animals were evaluated at intervals for IgG and IgM antibodies to R. tsutsugamushi by an indirect immunoperoxidase assay, the presence of the pathogen in liver and spleen by murine inoculation, and the pathology of representative tissues by gross and microscopic examination. The infected animals began to show internal evidence of mild illness 7-14 days after inoculation, and exhibited no changes in behavior. Total white blood cell counts decreased on day seven (including lymphocytes and polymorphonuclear leukocytes), followed by an almost equal increase on day 14. Gross pathology noted at necropsy was limited to slight liver and spleen enlargement accompanied by low numbers of abscesses and fibrinous tags present in the abdominal cavity. In addition to the gross morphologic changes, histopathologic lesions noted were all mild, consisting of vasculitis of the lung, activation of the mononuclear phagocyte system, abdominal mesothelial cell hyperplasia, and peritonitis. Rickettsiae were isolated from liver and spleen on days 0, 7, and 14, but not thereafter. Specific antibody response was first observed on day 14, peaked on day 21, and it decreased to levels observed in uninfected animals between days 120 and 180.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevalence of antibodies to rickettsiae in the human population of suburban Bangkok.

Following a report of three cases of scrub typhus in suburban Bangkok, we performed a serosurvey in the patients' communities. Both IgG and IgM antibodies were measured in an indirect immunoperoxidase assay, using separate spots of antigen from Rickettsia tsutsugamushi (scrub typhus), R. typhi (murine typhus), and TT-118 spotted fever group rickettsiae. Of 215 people donating blood, antibody levels indicative of most recent exposure to R. tsutsugamushi were most prevalent (21%), followed by R. typhi (8%), and TT-118 (4%). Seroprevalence suggesting most recent exposure to R. tsutsugamushi varied by location (range 13-31%), gender (26% of females and 13% of males), age (61-80-year-old individuals were the highest, with a prevalence of 38%), and contact with orchards and orchid farms (29% of those with extensive contact, 38% of those with occasional contact, and 10% of those with no contact). These patterns indicated that exposure to R. tsutsugamushi was related to occupation and behavior, as has been observed in areas of rural transmission. Expansion of metropolitan Bangkok has created a situation in which people employed in agriculture live with people employed in the city. As a result, a serosurvey in suburban Bangkok reveals evidence of murine typhus, which is usually transmitted in urban areas, as well as scrub and tick typhus, which are usually transmitted in rural areas.

Efficacy of common broad spectrum anthelmintics against hook worm, Ascaris and Trichiuris in Hat Yai district, Songkhla Province, Thailand.

1. The third therapeutic scheme should be used in the hospital. 2. The second and third therapeutic scheme may be used in mass treatment. 3. The 4th-6th therapeutic scheme is to be considered, reviewed, and evaluated. 4. Model and technology of permanent worms control is to be studied. 5. The treatment and control of Ascaris were simple. Cure with low reinfection rate and long reinfection period was remarkable. 6. The prevalence rate and reinfection rate of Trichiuris was high, and not so sensitive to any antelmintics. 7. The reinfection rate in the second group was not superior to the first group and the third group. This revealed no effectiveness of ovicidal and larvicidal on the helminthiasis. 8. Reinfection rate in the third therapeutic scheme was the least group. 9. Toxicity and side effect were not found in any anthelmintics. 10. Broad Spectrum Anthelmintics are necessary in mass treatment or blind treatment.

Rickettsia tsutsugamushi in chiggers (Acari: Trombiculidae) associated with rodents in central Thailand.

Chiggers were collected from rodents trapped at two military bases located 10 km apart in central Thailand. One site was swampy and nearly treeless and the other site was well-drained and partially wooded. Although 13 species of chiggers were collected, only three species were found to be positive for Rickettsia tsutsugamushi (Hayashi) Ogata using a direct fluorescent antibody test: Blankaartia acuscutellaris Walch (7.3% infected), Leptotrombidium delinese Walch (3.1% infected), and an undescribed species of Ascoschoengastia near A. indica Hirst (1.2% infected). This was the first record of R. tsutsugamushi in B. acuscutellaris. The Ascoschoengastia species occurred with equal frequency at the two study sites, L. deliense occurred more frequently at the well-drained site, and B. acuscutellaris occurred more frequently at the swampy site. Results suggest that there are important foci of scrub typhus in central Thailand and that B. acuscutellaris may be a vector in this area.

A new species of Leptotrombidium (Acari: Trombiculidae) collected from black plates in Thailand.

A new species, Leptotrombidium (Leptotrombidium) dendrium, is described and illustrated. Specimens were collected from black plates exposed on the ground surface in a secondary forest at Nakhonratchasima and Surin Provinces in northeastern Thailand.

Scrub typhus in suburban Bangkok: first cases.

Three patients, two of whom had eschars, were admitted with fulminant febrile disease suggestive of scrub typhus. Elevated IgG and IgM to Rickettsia tsutsugamushi were detected in all three by IFA. The cases lived in widely separated areas of western Bangkok where fruit trees are grown and claimed not to have left the areas of their homes during the estimated incubation periods. A field survey collected rodents, treeshrews, and mites fro around the homes of each case. R. tsutsugamushi was isolated from one rat and known vector species of mites were found. These are the first confirmed cases of scrub typhus transmission in Metropolitan Bangkok. It is suggested that typhus incidence around Bangkok may be substantial but has been unreported because of widespread self-medication with antibiotics and the difficulties of laboratory diagnosis.

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.