Leptotrombidium

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Leptotrombidium
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Arachnida
Subclass: Acari
Order: Trombidiformes
Family: Trombiculidae
Subfamily: Trombiculinae
Genus: Leptotrombidium
Nagayo et al., 1916

Leptotrombidium /ˌlɛptɵtrɒmˈbɪdiːəm/ is a genus of mites in the family Trombiculidae, that are able to infect humans with scrub typhus (Orientia tsutsugamushi infection) through their bite.[1] 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.

It was originally thought that rodents were the main reservoir for O. tsutsugamushi and that the mites were merely vectors of infection: that is, the mites only transferred the contagion from the rodents to humans.[2][3] However, it is now known that the mites only feed once in their lifetime, 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).[4] Instead, the bacterium persists in the mites through transovarial transmission,[5][6][7] where infected mites transmit the infection to their unborn offspring. Leptotrombidium mites are therefore both vector and reservoir for O. tsutsugamushi.[4] The infection predominantly affects female mites,[8] and does not appear to otherwise harm the mites.

Life history

The larva is pale orange in colour and feeds on liquified skin tissue, not blood, as their mouth parts (chelicerae) are too short to reach the blood vessels.[9] They have 3 pairs of legs. The larvae most commonly target rodents, but will also attach to humans.[4] For humans, the bite is painless, but pain commonly develops only after the larva detaches from the skin, leaving a red papule that may then develop into an eschar.[10]

The larval stage lasts for 1 to 2 weeks. After feeding, the larvae drop to the ground and become nymphs. Nymph is brick-red in colour and has 4 pairs of legs. Nymphal stage lasts for 1 to 3 weeks. Nymphs mature into adults which have 4 pairs of legs, first pair being the largest. They are harmless to humans. In the post larval stage, they are not parasitic and feed on plant materials.[11] Female lays eggs singly, which hatch in about a week. Lifespan of adult is about 6 months.

Taxonomy

  • L. akamushi is endemic to Japan and is the reservoir for the Kato serotype of Orientia tsutsugamushi;[1]
  • L. deliense is the main vector in the south of China[12] and in Thailand;[13] it is also endemic to Litchfield Park, in the Northern Territory, Australia, where is carries the Litchfield serotype.[14]
  • L. pallidum is endemic to Japan and is the reservoir for Karp and Gilliam serotypes;[1][15]
  • L. scutellare is endemic to Japan and is the reservoir for Kawasaki and Kuroki serotypes.[1][15]

References

  1. ↑ 1.0 1.1 1.2 1.3 "Scrub typhus (tsutsugamushi disease) in Japan, 1996–2000". Byogen Biseibutsu Kenshutsu Joho Geppo 22: 211–212. 2001. 
  2. ↑ Philip CB (1948). "Tsutsugamushi disease (scrub typhus) in World War II". J Parasitol 34 (3): 169–191. doi:10.2307/3273264. JSTOR 3273264. 
  3. ↑ Fox JP (1948). "The long persistence of Rickettsia orientalis in the blood and tissues of infected animals". J Immunol 59 (2): 109–114. 
  4. ↑ 4.0 4.1 4.2 Pham XD, Suzuki H, Takaoka H (2001). "Distribution of unengorged larvae of Leptotrombidium pallidum and other species in and around the rodent nest holes". Southeast Asian J Trop Med Public Health 32 (3): 553–57. PMID 11944716. 
  5. ↑ Walker JS, Chan CT, Manikumaran C, Elisberg BL (1975). "Attempts to infect and demonstrate transovarial transmission of R. tsutsugamushi in three species of Leptotrombidium mites". Ann NY Acad Sci 266: 80–90. doi:10.1111/j.1749-6632.1975.tb35090.x. 
  6. ↑ Takahashi M, Murata M, Nogami S, Hori E, Kawamura A, Tanaka H (1988). "Transovarial transmission of Rickettsia tsutsugamushi in Leptotrombidium pallidum successively reared in the laboratory". Jpn J Exp Med 58: 213–218. 
  7. ↑ Frances SP, Watcharapichat P, Phulsuksombati D (2001). "Vertical transmission of Orientia tsutsugamushi in two lines of naturally infected Leptotrombidium deliense (Acari: Trombiculidae)". J Med Entomol 38 (1): 17–21. doi:10.1603/0022-2585-38.1.17. PMID 11268685. 
  8. ↑ Roberts LW, Rapmund G, Gadigan FG (1977). "Sex ratios in Rickettsia tsutsugamushi-infected and noninfected colonies of Leptotrombidium (Acari: Trombiculidae)". J Med Entomol 14 (1): 89–92. 
  9. ↑ Roberts LW, Robinson DM, Rapmund G, et al. (1975). "Distribution of Rickettsia tsutsugamushi in organs of Leptotrombidium (Leptotrombidium) fletcheri (Prostigmata: Trombiculidae)". J Med Entomol 12 (3): 345–348. 
  10. ↑ Kitaoka M, Asanuma K, Otsuji J (1974). "Transmission of Rickettsia orientalis to man by Leptotrombidium akamushi at a scrub typhus endemic area in Akita Prefecture, Japan". Am J Trop Med Hyg 23 (5): 993–9. PMID 4451238. 
  11. ↑ Takahashi M, Misumi H, Urakami H, et al. (2003). "Life cycle of Leptotrombidium pallidum (Acari: Trombiculidae), one of the vector mites of scrub typhus in Japan". Ohara Sogo Byoin Nenpo 45: 19–30. 
  12. ↑ Wang S, Jiang P, Huang J, et al. (2001). "Demonstration of the natural foci of tsutsugamushi disease in Nan Peng Lie Islands in China". The Southeast Asian journal of tropical medicine and public health 32 (3): 541–46. PMID 11944714. 
  13. ↑ Frances SP, Watcharapichat P, Phulsuksombati D, Tanskul P, Linthicum KJ (1999). "Seasonal occurrence of Leptotrombidium deliense (Acari: Trombiculidae) attached to sentinel rodents in an orchard near Bangkok, Thailand". J Med Entomol 36 (6): 869–874. PMID 10593093. 
  14. ↑ Odorico DM, Graves SR, Currie B, et al. (1998). "New Orientia tsutsugamushi strain from scrub typhus in Australia". Emerg Infect Dis 4 (4): 641–4. doi:10.3201/eid0404.980416. PMC 2640248. PMID 9866742. 
  15. ↑ 15.0 15.1 Kawamori F, Akiyama M, Sugieda M, et al. (1992). "Epidemiology of Tsutsugamushi disease in relation to the serotypes of Rickettsia tsutsugamushi isolated from patients, field mice, and unfed chiggers on the eastern slope of Mount Fuji, Shizuoka Prefecture, Japan". J Clin Microbiol 30 (11): 2842–2846. PMC 270539. PMID 1452653. 
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