Bacterial microbiome of the chigger mite Leptotrombidium imphalum varies by life stage and infection with the scrub typhus pathogen Orientia tsutsugamushi

Scrub typhus is a mites-borne rickettsiosis caused by the obligate intracellular Gram-negative bacterium Orientia tsutsugamushi. The disease is potentially life threatening and is prevalent in tropical Asia, islands of the western Pacific Ocean and northern Australia where an estimated one million cases occur annually. Orientia tsutsugamushi is transmitted by the bite of larval mites in the genus Leptotrombidium. In the present study, the composition of the microbiome in larvae, deutonymphs and adult males and females from laboratory colonies of L. imphalum that were infected as well as uninfected with O. tsutsugamushi were investigated by high-throughput sequencing of the bacterial 16S rRNA gene. Notably, the bacterial microbiomes of infected adult females were dominated by sequences of O. tsutsugamushi and an unidentified species of Amoebophilaceae, which together comprised 98.2% of bacterial sequences. To improve the taxonomic resolution of the Amoebophilaceae OTU a nearly full length sequence of the 16S rRNA gene was amplified, cloned, and Sanger sequenced. Infected female mites had 89 to 92% nucleotide identity with the Amoebophilaceae family, indicating that the bacterium was likely to be a species of a novel genus. The species composition of bacterial communities varied between mite life stages regardless of their infection status. Uninfected adults exhibited greater species diversity than adults infected with O. tsutsugamushi. In the infected colony, the rate of filial infection with Orientia was less than 100%. Larval and male mites that were PCR-negative for Orientia contained low numbers of sequences of Amoebophilaceae (0.01 and 0.06%, respectively) in their taxonomic profiles, suggesting that a mutualistic relationship exists between the novel species of Amoebophilaceae and O. tsutsugamushi. Our study findings provide the basis for further research to determine the influence of the novel Amoebophilaceae species on the bacterial microbiome and on vector susceptibility to and transovarial transmission of O. tsutsugamushi.

[(ACARI: TROMBICULIDAE) (THE INFESTATION OF SMALL MAMMALS IN SOUTH-EASTERN VIETNAM WITH HARVEST MITES (ACARI: TROMBICULIDAE))]

This investigation was conducted in three provinces of southern Vietnam in September-October 2011. A total of 257 small mammals of 11 species were caught; among them 120 rodents were infected with harvest mites of 8 species (Trom- biculidac). About 4000 mites of nearly 1200 identified species were collected from the small mammals. 17 species of harvest mites were identified. Walchia lupella, Leptotrombidium deliense, Walchia kritochaeta, and Walchia micropelta predominated in the collections. Most species of mites parasitized Rattus rattus (n= 15), Maxomys surifer (n=9), and B.savilei (n=7). The occurrence of Trombiculidaewas high on Bandicota savilei (90.0%), M.sunfer (87.8%), R.rattus (80.9%), and Bandicota indica (71.4%). The largest number of mites was observed in B.savilei and B.indica. The species of the genus Ascoschoengastia parasitized predominantly R.rattus and those of the genus Wachia did M.surifer. W.upella (n=7), L.delense (n=5), and Ascoschoengastiaindica (n=5) were associated with the widest range of nourishers. The species L.delicense known as a carrier of the causative agent of tsutsugamushi fever predominated in synanthropic rodents.

Straelensiosis in dogs: a newly described nodular dermatitis induced by Straelensia cynotis

A distinctive nodular dermatitis induced by Straelensia cynotis, a newly described trombidioid larval mite which resides in hair follicles, was identified in 12 dogs living in France. They all had scattered, small (1 to 3 mm in diameter), pale, firm skin nodules, variable in distribution but always affecting the dorsal regions of the head and trunk; they were distributed over the whole body of seven of the dogs. The animals were otherwise healthy except for three severely infested fox terriers which had a decreased appetite, were lethargic, and whose skin nodules were painful to the touch. The nodules did not induce pruritus. The lesions usually began as erythematous papules which developed into firm pale nodules. The dermatitis resolved within two to 12 months. Topical acaricides were ineffective but the skin nodules regressed after treatments with systemic avermectins. Histologically, each nodule was composed of a dilated follicular ostium containing a well-preserved larval mite, and showed a pseudoepitheliomatous follicular hyperplasia and an abundant perifollicular mucinosis. The larvae were identified as belonging to the genus Straelensia (Acari: Leeuwenhoekiidae). It was clearly established that the three fox terriers had become infested within a fox's den. The nymphs and adults of this species of mite are believed to live in foxes' dens; foxes are considered to be the natural host for the larval stage, and dogs a permissive but occasional host.

First report of a parasitic mite, Leptotrombidium (Hypotrombidium) subquadratum (Lawerence) (Acari: Trombiculidae: Trombiculinae), from dogs and children in the Bloemfontein area, South Africa

Leptotrombidium subqunadratum larvae were collected for the first time in 1994 from dogs in Bloemfontein. The larvae have been collected annually, during the summer months, over a period of 6-7 years. Previously the only known hosts were scrub hare (Lepus saxatilis) (locality unknown) and short-snouted elephant shrew (Elephantulus brachyrhynchus) (Kruger National Park). These mites cause severe itching and dermatitis in humans and dogs.

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.

Trombidiosis-induced dermatitis in white-tailed deer (Odocoileus virginianus)

During a routine blood collection at a wildlife management checkpoint, several white-tailed deer (Odocoileus virginianus) from Lake Russell Wildlife Management Area, Habersham County, Georgia, were observed to have accumulations of orange granular material around the eyes and mouth accompanied by serous exudate, crusting, and alopecia. Microscopic examination of the granular material disclosed numerous larval mites of the family Trombiculidae. Histologic examination revealed severe chronic diffuse plasmacytic dermatitis with intralesional larval trombiculid mites. Several stylostomes were also identified in the tissue sections. This paper describes the gross and histologic changes associated with severe trombiculid infestation in a white-tailed deer and suggests potential causes for this unusual finding.

Lesions associated with infestation of a yellow-footed rock wallaby (Petrogale xanthopus xanthopus) with larvae of Odontacarus (Leogonius) adelaideae (Womersley) (Acarina: Trombiculidae) in South Australia

Dermatitis associated with natural infestation of a yellow-footed rock wallaby (Petrogale xanthopus xanthopus) with larvae of the chigger mite, Odontacarus (Leogonius) adelaideae is described. This record extends the known host range of O. adelaideae and is the first from a native animal in southern Australia.

[The origin of parasitism in trombiculid mites (Acariformes: Trombiculidae)]

On the basis of literary data and original investigations some phylogenetic, ecological and morphological aspects of the origin of parasitism in trombiculid mites are carefully considered for the first time. It is shown that parasitism in this group of trombidiform mites is a relatively young historical phenomenon and was formed after their ontogenesis had differentiated into active and quiescent stages. Therefore, in the life pattern of trombiculid mites the character of individual development, that defines their biotopical restriction, is much more important than the phase parasitism. Primitive organization of the digestive system and extraintestinal digestion, so characteristic of this group, are one of the main reasons of the origin of their parasitism. Under pasture conditions trombiculid mites, that initially were predators-entomophages with bite-sucking mouth parts, pass easily to parasitism on vertebrate animals and become primary lymphophages. They use the vertebrate host's organism exclusively as a source of food and by the extent of polyphagia are very close to free-living blood-sucking insects. Stylostome, that develops during feeding of trombiculid larvae and some other closely related groups of trombidiform mites, is a universal structure for achieving a large amount of food on a wide range of animals during a relatively short period of time and reflects wide host-parasite specificity of these parasitic mites. From the historical view the larvae of trombiculid mites did not pass from one group of hosts to the others, but owing to morphological preadaptation to parasitism passed in a definite historical period, not earlier than Paleogene, to parasitism on all classes of terrestrial vertebrates, especially on mammals, their primary hosts.

Transmission of scrub typhus to human volunteers by laboratory-reared chiggers

Laboratory-reared, Rickettsia tsutsugamushi-infected Leptotrombidium arenicola and L. fletcheri chiggers were fed on 1 and 2 human volunteers respectively. All subjects developed typical clinical signs and symptoms of scrub typhus beginning days 8-10 post chigger attachment (PCA); these included fever, severe headache, myalgia, regional lymphadenopathy, and eschar. The two L. fletcheri subjects developed a transient generalized rash on days 3-4 after the onset of fever, and these two individuals also appeared to suffer a more severe clinical disease. Rickettsemias were detected in all three volunteers beginning on day 7 PCA, 1-3 days before the onset of clinical disease. Rises in indirect fluorescent antibody titers occurred starting on days 13-19 PCA (day 4-11 post fever) and in Weil-Felix OXK titers starting on days 26-22 PCA (days 7-14 post fever). These results strongly suggest that the use of laboratory-reared chiggers is a reliable means of transmitting scrub typhus infections to volunteers.