''Leptotrombidium'' () is a genus of

mite Mites are small arachnids (eight-legged arthropods) of two large orders, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari. However, most recent genetic analyses do not recover the two as eac ...

s in the family

Trombiculidae Trombiculidae (), commonly referred to in North America as chiggers and in Britain as harvest mites, but also known as berry bugs, bush-mites, red bugs or scrub-itch mites, are a family of mites. Chiggers are often confused with jiggers – a ...

, that are able to infect humans with

scrub typhus Scrub typhus or bush typhus is a form of typhus caused by the intracellular parasite '' Orientia tsutsugamushi'', a Gram-negative α-proteobacterium of family Rickettsiaceae first isolated and identified in 1930 in Japan.Orientia tsutsugamushi ''Orientia'' is a genus of bacteria in family Rickettsiaceae. They are obligate intracellular, gram-negative Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gr ...

'' infection) through their bite. The larval form (called chiggers) feeds on rodents, but also occasionally humans and other large mammals. They are related to the harvest mites of the North America and Europe. Originally, rodents were thought to be the main reservoir for ''O. tsutsugamushi'' and the mites were merely vectors of infection: that is, the mites only transferred the contagion from the rodents to humans. However, the mites are now known to only feed once in their lifetimes, which means that transmission from rodent to human via the mites is impossible (for it to have been possible, the mite would have to feed at least twice, once on the infected rodent and again on the human who would then be infected). Instead, the bacterium persists in the mites through

transovarial transmission Transovarial or transovarian transmission (transmission from parent to offspring via the ovaries) occurs in certain arthropod vectors as they transmit pathogens from parent to offspring. This process, used by a wide variety of parasites, is also kn ...

, where infected mites transmit the infection to their unborn offspring. ''Leptotrombidium'' mites are therefore both vector and reservoir for ''O. tsutsugamushi''. The infection predominantly affects female mites, and does not appear to otherwise harm the mites.

Life history

The larvae are pale orange in colour and feed on liquified skin tissue, not blood, as their mouth parts (chelicerae) are too short to reach the blood vessels. They have three pairs of legs. The larvae most commonly target rodents, but also attach to humans. For humans, the bite is painless, but pain commonly develops only after the larvae detach from the skin, leaving red papules that may then develop into an eschar. The larval stage lasts for 1 to 2 weeks. After feeding, the larvae drop to the ground and become nymphs. Nymphs are brick-red in colour and have four pairs of legs. The nymphal stage lasts for 1 to 3 weeks. Nymphs mature into adults which have four pairs of legs, the first pair being the largest. They are harmless to humans. In the postlarval stage, they are not parasitic and feed on plant materials. Females lay eggs singly, which hatch in about a week. Lifespan of the adult is about 6 months.

Taxonomy

* '' L. akamushi'' is endemic to Japan and is the reservoir for the Kato

serotype A serotype or serovar is a distinct variation within a species of bacteria or virus or among immune cells of different individuals. These microorganisms, viruses, or Cell (biology), cells are classified together based on their shared reactivity ...

of ''O. tsutsugamushi''; * '' L. deliense'' is the main vector in the south of China and in Thailand; it is also endemic to Litchfield Park, in the

Northern Territory, Australia The Northern Territory (abbreviated as NT; known formally as the Northern Territory of Australia and informally as the Territory) is an Australian internal territory in the central and central-northern regions of Australia. The Northern Terri ...

, where is carries the Litchfield serotype. * '' L. pallidum'' is endemic to Japan and is the reservoir for Karp and Gilliam serotypes; * '' L. scutellare'' is endemic to Japan and is the reservoir for Kawasaki and Kuroki serotypes.

References

{{Authority control Parasitic arthropods of humans Trombiculidae Arachnids of Asia Acari genera