Larval Chigger Mites Collected from Small Mammals in 3 Provinces, Korea

A total of 9,281 larval chigger mites were collected from small mammals captured at Hwaseong-gun, Gyeonggi-do (Province) (2,754 mites from 30 small mammals), Asan city, Chungcheongnam-do (3,358 mites from 48 mammals), and Jangseong-gun, Jeollanam-do (3,169 for 62 mammals) from April-November 2009 in the Republic of Korea (= Korea) and were identified to species. Leptotrombidium pallidum was the predominant species in Hwaseong (95.8%) and Asan (61.2%), while Leptotrombidium scutellare was the predominant species collected from Jangseong (80.1%). Overall, larval chigger mite indices decreased from April (27.3) to June (4.9), then increased in September (95.2) and to a high level in November (169.3). These data suggest that L. pallidum and L. scutellare are the primary vectors of scrub typhus throughout their range in Korea. While other species of larval chigger mites were also collected with some implications in the transmission of Orientia tsutsugamushi, they only accounted for 11.2% of all larval chigger mites collected from small mammals.

Nested polymerase chain reaction on blood clots for gene encoding 56 kDa antigen and serology for the diagnosis of scrub typhus.

Purpose : Scrub typhus is a zoonotic illness endemic in the Asia-Pacific region. Early diagnosis and appropriate management contribute significantly to preventing adverse outcomes including mortality. Serology is widely used for diagnosing scrub typhus. Recent reports suggest that polymerase chain reaction (PCR) could be a rapid and reliable alternative. This study assessed the utility of these tests for scrub typhus diagnosis. Materials and Methods : Nested PCR to detect the 56 kDa antigen gene of O. tsutsugamushi was performed on blood clots from 87 individuals with clinically suspected scrub typhus. Weil-Felix test and scrub typhus IgM ELISA were performed on serum samples from the same patients. As a gold standard reference test was not available, latent class analysis (LCA) was used to assess the performance of the three tests. Results : The LCA analysis showed the sensitivity of Weil-Felix test, IgM ELISA and PCR to be 59%, 100% and 58% respectively. The specificity of ELISA was only 73%, whereas those of the Weil-Felix test and PCR were 94% and 100% respectively. Conclusion : Nested PCR using blood clots while specific, lacked sensitivity as compared to IgM ELISA. In resource-poor settings Weil-Felix test still remains valuable despite its moderate sensitivity.

Unusually High Number of Eschars on the Face of a Patient with Scrub Typhus

No abstract available.

Geographical Distribution and Relative Abundance of Vectors of Scrub Typhus in the Republic of Korea

A survey to determine the geographical distribution and relative abundance of potential vectors of scrub typhus was conducted from October to November 2006 at 13 localities throughout the Republic of Korea. Apodemus agrarius accounted for 97.6% (80/82) of all rodents, while only 2 Myodes regulus (2/82) were collected. A total of 10,860 chiggers were collected from A. agrarius belonging to 4 genera and 8 species, while only Walchia fragilis (40) was collected from Myodes regulus. Leptotrombidium pallidum (8,137; 74.9%), a vector of scrub typhus, was the predominant species collected from A. agrarius followed by Leptotrombidium scutellare (2,057, 18.9%), Leptotrombidium palpale (279; 2.7%), Leptotrombidium orientale (232; 2.1%), and Leptotrombidium zetum (79; 0.7%), Neotrombicula tamiyai (58; 0.5%), Euschoengastica koreaensis (16; 0.1%), and Cheladonta ikaoensis (2; < 0.1%). L. pallidum was the predominant chigger collected at collection sites in Gangwon (100%), Gyeonggi (87.2%), Chungnam (100%), Chungbuk (100%), Jeonbuk (73.9%), Jeonnam (77.0%), and Gyeongbuk (66.1%) provinces, whereas L. scutellare was the predominant chigger collected in Gyeongnam province (77.9%) and Jeju Island (62.3%). Data suggest a correlation between chigger population abundance and human cases of scrub typhus in Korea.

Acute reversible hearing loss in scrub typhus.

Scrub typhus usually presents as pyrexia with or without multiple organ involvement. Acute hearing loss occurs in about one third of cases and is a useful clue toward the diagnosis. We present two cases of scrub typhus with acute reversible hearing loss from an endemic area. The diagnosis was confirmed by nested PCR.

Patient and sample-related factors that effect the success of in vitro isolation of Orientia tsutsugamushi.

Orientia tsutsugamushi is the causative agent of scrub typhus infection, a major cause of human disease in rural areas of Southeast Asia. Twenty-six blood samples collected from patients with serologically proven scrub typhus during a six month period were sent to Bangkok (535 km from the clinical site) by road at ambient temperature (average daily temperature range: 27.1-29.1 degrees C) for attempted in vitro isolation in Vero cells. O. tsutsugamushi was isolated from 12 samples (sensitivity 46.7%) with the time to isolation ranging from 16 to 37 days [median 27 days, inter-quartile range (IQR) 22.5-33.5 days]. Patient factors such as days of fever and O. tsutsugamushi IgM antibody titer, transport factors such as transit time, and isolate genotype (Karp and Gilliam/Kawasaki) were assessed to determine their influence on the outcome of in vitro isolation. None of the factors significantly influenced the isolation outcome. This study demonstrates that O. tsutsugamushi can often be isolated in vitro from the blood of scrub typhus patients when transported at ambient tropical temperatures for many days.

Epidemiological studies on host animals of scrub typhus of the autumn-winter type in Shandong Province, China.

In order to elucidate the host animals of scrub typhus in Shandong Province, epidemiological studies on host rodents of the autumn-winter type scrub typhus were carried out from 1995 to 2002 at four localities in the Shandong Province. Based upon ecological observations of the composition, seasonal fluctuation of animal hosts, isolation of Orientia tsutsugamushi, detection and identification of serotypes of antibodies to O. tsutsugamushi were conducted. Two thousand eight hundred and eighty-four rodents and insectivores were captured, including 2,055 Apodemus agrarius (71.26%), 408 Cricetulus triton (14.15%), 64 C. barabensis (2.22%), 12 Crocidura suaveolens (0.42%), 313 Rattus (R.) norvegicus (10.85%), 32 Mus (M.) musculus (1.11%). A. agrarius was predominant in the field and the seasonal fluctuation was correlated significantly to that of scrub typhus (r=0.810, p<0.005). R. norvegicus was predominant indoors. The average capture rate per year in the field was 12.76% from 1995 to 1997. Of the total 2,884 rodents and insectivores captured out- and in-doors, 527 were living rodents (including 335 A. agrarius, 119 C. triton, 6 C. barabensis, 2 C. suaveolens, 63 R. norvegicus and 2 M. musculus, and 15,467 chigger mites were collected from them. Two hundred and fifty-three of 335 A. agrarius were parasitized by chiggers, showing 75.52% (253/335) of the infestation rate and 17.53 of the chigger index; 106 C. triton were parasitized by chiggers, showing 89.08% (106/119) infestation rate and 75.93 of the chigger index. The average antibody positive rate of rodents was 14.78%. The seasonal change of the antibody positive rate was higher during December-February (the second year), and varied from 20% to 28%, but the level of antibodies remained relatively low (5.26-16.67%) during March-November. The results of serotyping with 47 antibody-positive sera were as followings: 39 sera were Gilliam types, 7 sera were Karp types, 1 serum was Kato type. Twelve strains of O. tsutsugamushi were isolated from A. agrarius (8 strains), C. triton (3 strains) and R. norvegicus (1 strain), out of the isolated 12 strains, 10 were Gilliam strains, 2 were Karp strains. A. agrarius and R. norvegicus were the main host animals in out- and indoors respectively.

Early diagnosis of scrub typhus in Thailand from clinical specimens by nested polymerase chain reaction.

The early detection of scrub typhus in Thailand by nested polymerase chain reaction (PCR) is presented. The diagnosis of scrub typhus, from clinical samples obtained from hospitals in the northern part of Thailand, by nested PCR was compared to immunofluorescence (IF) and Weil-Felix (WF) tests. The primer pairs used for the nested PCR were designed on the basis of the nucleotide sequence of the gene that encodes the 56-kDa antigen, and RFLP analysis was used for identification. Clotted blood from 80 patients suspected of scrub typhus infection were tested. With the IF test, antibodies for Orientia tsutsugamushi were observed in 38 patients checking IgM and IgG titers. Only 21 patients showed positive seroconversion while 17 patients were negative. For the WF test, only 13 patients gave a positive seroconversion. In the early stage of infection, 19, 13 and 3 patients were detected with a sensitivity of 90.47% (19/21), 61.90% (13/21) and 14.28% (3/21) by the nested PCR, IF and WF test respectively. Two patients who were negative for seroconvesion by IF and WF were positive by nested PCR. Therefore, this suggests that nested PCR is applicable for specific rapid diagnosis at an early stage of scrub typhus in endemic regions.

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.

Laboratory evaluation of repellents against Leptotrombidium deliense, vector of scrub typhus.

BACKGROUND & OBJECTIVES: Scrub typhus, a rickettsial disease transmitted by larvae of Leptotrombidium deliense, is of special importance to the Armed Forces personnel, due to the heightened risk to this disease during movement in mite endemic areas during exercise/war. The disease is best prevented by the use of personal protective measures including repellents. Studies were undertaken to determine the relative efficacy of repellents: diethyl toulamide (DEET), dibutyl phthalate (DBP) with an indigenously developed repellent diethyl phenyl acetamide (DEPA) against the larval trombiculid mite. METHODS: The repellents were tested for persistence on impregnated cloth prior to washing, post washing and ironing by means of a specially fabricated testing kit. Acaricidal efficacy estimation was performed on the treated fabrics and topical application efficacy of repellents on mice was evaluated by a novel animal testing model. RESULTS: DEET and DEPA were found to provide maximum protection (repellence and acaricidal efficacy), could withstand two launderings of the impregnated uniform and also had superior efficacy on topical application (8 h). Ironing was found to significantly reduce the repellence of DEET and DBP. INTERPRETATION & CONCLUSION: The findings of this study point towards the superiority of DEPA and DEET for impregnation of the uniform cloth as well as for topical application for the prevention of scrub typhus amongst the troops.

Diagnosis of scrub typhus in Malaysian aborigines using nested polymerase chain reaction.

A rapid diagnostic system for scrub typhus using nested polymerase chain reaction (PCR) was applied to clinical samples from Malaysian Aborigines. Whole blood from twenty-four patients suspected of scrub typhus infection were tested using nested polymerase chain reaction and sera were evaluated by the indirect immunoperoxidase test. Antibody responses towards Rickettsia tsutsugamushi were observed in seventeen patients with the majority having high titers of IgG antibodies. Seven patients were seronegative. The nested PCR amplified R. tsutsugamushi DNA from six patients, of which two were negative serologically and four had high titers of IgG antibodies. Second samples collected seven days after treatment were negative by PCR testing. Nested PCR is highly sensitive and specific and may be used to provide rapid confirmation of scrub typhus cases in endemic region.

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.

A survey of scrub and murine typhus in the Ancol section of Jakarta, Indonesia.

Rickettsia tsutsugamushi was isolated from L. (L.) arenicola chiggers and three species of rats in an area of scrub and sedge along the Bay of Jakarta. This is the only finding in Indonesia of a cycle of the agent of scrub typhus associated with L. (L.) arenicola. A serologic survey of nearly 300 persons living in two kampungs near the site at which rickettsiae were recovered revealed one individual with antibodies to R. tsutsugamushi. Murine typhus, with a seropositivity rate of 6.5%, may be endemic at low levels.

Early detection of Rickettsia tsutsugamushi in peripheral monocyte cultures derived from experimentally infected monkeys and dogs.

Rickettsia tsutsugamushi organisms were identified in Giemsa and fluorescent antibody stained monocyte cell cultures derived from experimentally infected monkeys and dogs. The identification of organisms in monocyte cell cultures compared favorably with the standard technique of mouse inoculation.

Numbers of Leptotrombidium (Leptotrombidium) deliense (Acarina: trombiculidae) and prevalence of Rickettsia tsutsugamushi in adjacent habitats of peninsular Malaysia.

Numbers of L. (L.) deliense larvae were determined in adjacent habitats over a 16 month period. Both R. argentiventer and R. tiomanicus were highly efficient hosts for L. (L.) deliense. R. argentiventer was host to significantly greater numbers of chiggers per rat than was R. tiomanicus. The 2 habitats were similar in numbers of chiggers collected. No consistent correlation was apparent between numbers of chiggers and any single weather factor, but the chigger population seemed to be adversely affected by a 2 month period during which total evaporation greatly exceeded total rainfall. Direct fluorescent antibody examination of tissues from unfed L. (L.) deliense showed that 2 of 420 larvae (0.5%) contained organisms morphologically resembling R. tsutsugamushi. Considering the vector load and numbers of chiggers being returned to the ground by a given host, a rate of 0.5% appeared adequate to account for the prevalence rate of R. tsutsugamushi observed in the 2 host species.