Wikipedia

Trombiculidae

Not to be confused withTrombidiidae,similar in name and appearance, but a different family of mites.

Trombiculidae(/trɒmbɪˈkjuːlɪdiː/), commonly referred to in North America aschiggersand in Britain asharvest mites,but also known as berry bugs, bush-mites, red bugs or scrub-itch mites, are a family ofmites.[3]Chiggers are often confused withjiggers– a type offlea.Several species of Trombiculidae in theirlarvastage bite their animal host and by embedding their mouthparts into the skin cause "intense irritation",[4]or "awheal,usually with severe itching anddermatitis".[5][6][7]Humans are possible hosts.

Trombiculidae
Trombiculid mite larva
Trombiculid mitelarva
Scientific classificationEdit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Order: Trombidiformes
Suborder: Prostigmata
Infraorder: Anystina
Superfamily: Trombidioidea
Family: Trombiculidae
Ewing,1929[1]
Type genus
Trombicula
Berlese, 1905
Genera[2]
The distribution of trombiculid species, which is nearly everywhere in the world.

Trombiculidae live in forests and grasslands and are also found in the vegetation of low, damp areas such as woodlands, berry bushes, orchards, along lakes and streams, and even in drier places where vegetation is low, such as lawns, golf courses, and parks.[8]They are most numerous in early summer when grass, weeds, and other vegetation are heaviest. In their larval stage, they attach to various animals, including humans, and feed on skin, often causing itching. These relatives ofticksare nearly microscopic, measuring 400 μm (1/60 of an inch) and have achrome-orangehue.[9][10]There is a marked constriction in the front part of the body in thenymphand adult stages. The best known species of chigger in North America[11]is the hard-bitingTrombicula alfreddugesiof theSoutheastern United States,humidMidwest[12]andMexico.In the UK, the most prevalent harvest mite isNeotrombicula autumnalis,which is distributed through Western Europe to Eastern Asia.[13]

Trombiculid mites go through a lifecycle of egg, larva,nymph,and adult.[14]The larval mites feed on the skincellsof animals. The six-legged parasitic larvae feed on a large variety of creatures, including humans, rabbits, toads,box turtles,quail,and even some insects. After crawling onto theirhosts,they inject digestive enzymes into the skin that break down skin cells. They do not actually "bite", but instead form a hole in the skin called astylostomeand chew up tiny parts of the inner skin, thus causing irritation and swelling. The itching is accompanied by red, pimple-like bumps (papules) orhivesand skin rash or lesions on a sun-exposed area. For humans, itching usually occurs after the larvae detach from the skin.[15]

After feeding on their hosts, the larvae drop to the ground and become nymphs, then mature into adults, which have eight legs and are harmless to humans. In the postlarval stages, they are not parasitic and feed on plant material. The females lay three to eight eggs in a clutch, usually on a leaf or among the roots of a plant, and die by autumn.[15]

History

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Trombiculidae, fromGreekτρομειν( "to tremble" ) andLatinculex,genitiveculicis( "gnat" or "midge" ), was first described as an independent family byHenry Ellsworth Ewingin 1944.[16]Then, when the family was first described, it included two subfamilies, Hemitrombiculinae andTrombiculinae.Womersley added another, Leeuwenhoekiinae, which at the time contained onlyLeeuwenhoekia.Later, he erected the familyLeeuwenhoekiidaefor the genus and subfamily, having six genera; they have a pair of submediansetaepresent on the dorsal plate.[17]

References to chiggers, however, go as far back as sixth-century China, and by 1733, the first recognition of trombiculid mites in North America was made[citation needed].In 1758,Carl Linnaeusdescribed a single species,Acarus batatas(nowTrombicula batatas). However, most information about chiggers came from problems that arose during and after World War II.[18]

Distribution

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Trombiculid mites are found throughout the world. In Europe and North America, they tend to be more prevalent in the hot and humid regions. In northern Europe, including the British Isles where they are called harvest mites, the speciesNeotrombicula autumnalisare found during the summer and autumn (inFrench,harvest mites are calledaoûtatbecause they are common in August[19]). In the United States, they are found mostly in the Southeast, the South, and theMidwest.They are not present, or barely found, in far northern areas, high mountains, and deserts.[20]In North America, the speciesTrombicula alfreddugesi,and the speciesTrombicula (eutrombicula) hirsti,which are found inAustraliaand are commonly called the scrub-itch mite.[21]

Life cycle

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The life cycle of a harvest mite

The length of the mite's cycle depends on species and environment, but normally lasts two to 12 months. The number of cycles in a year depends on the region. For example, in a temperate region, only three per year may occur, but in tropical regions, the cycle might be continuous all year long.[14]Adult harvest mites winter in protected places such as slightly below the soil surface. Females become active in the spring, and once the ground temperature is regularly above 16 °C (60 °F), they lay eggs in vegetation, up to 15 eggs per day. The eggs are round and are dormant for about six days, after which the nonfeeding prelarvae emerge, with only three pairs of legs. After about six days, the prelarvae grow into their larval stage.[14]

Larva

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The larvae, commonly called chiggers, are about 170–210 μm (0.007–0.008 in) in diameter, normally light red in color, and covered in hairs; they move quickly relative to size. The larvae congregate in groups on small clods of soil, in matted vegetation, and even on low bushes and plants, where they have more access to prospective hosts.

The larval stage is the only parasitic stage of the mite's lifecycle. They are parasites on many animals. About 30 of the many species in this family, in their larval stage, attach to various animals and feed on skin. This often causes intensely itchy, red bumps in humans.[14][22]

A diagram of thestylostome,or the hardened tube of dead cells formed by the larval form of the Trombiculidae when feeding.

Chiggers attach to the host, pierce the skin, inject enzymes into the bite wound that digest cellular contents,[23]and then suck up the digested tissue through a tube formed by hardened skin cells called astylostome.[24]They do not burrow into the skin or suck blood, as is commonly assumed. Itching from a chigger bite may not develop until 24–48 hours after the bite, so the victim may not associate the specific exposure with the bite itself.[15]The red welt/bump on the skin is not where a chigger laid eggs, as is sometimes believed.[25]The larvae remain attached to suitable hosts for three to five days before dropping off to begin their nymphal stage.[14]They tend to attach where clothing has restrictions, such as belt lines, or behind the knees when wearing jeans.

During the wet season, chiggers are usually found in tall grass and other vegetation.[26]During dry seasons, chiggers are mostly found underneath brush and shady areas.[25][27]Standing still or lying in tall grass gives them more time to climb onto a person.

Nymph

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Once the larva has gorged itself on skin and has fallen off its host, it develops to its nymph stage. The nymph is sexually immature, but more closely resembles the adult.

This stage consists of three phases, the protonymph, deutonymph, and tritonymph. The protonymph and tritonymph morphologies are unusual in species of Trombiculidae. The protonymph phase combines larval and protonymph characteristics with deutonymph and tritonymph morphology.[28]The protonymph is an inactive transitional stage. The active deutonymph develops an additional pair of legs (for a total of eight). Lastly, it re-enters inactivity during its transitional tritonymph phase before growing to adulthood.[14]

Adult

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Adult trombiculid mite.

As deutonymphs and adults, trombiculid mites are independent predators that feed on smallarthropodsand their eggs, and are also found to eat plant material.[14]They live in soil, and are often found when digging in yards or gardens or in compost bins.

Recently (2018), methods based onautofluorescencemicroscopy were developed to enable identification of trombiculid mites to the species level on the basis of morphological traits without any special preparation.[29]

Effect on humans

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Trombiculosis

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Main article:Trombiculosis

Trombiculosis, also called trombiculiasis and trombiculidiasis, is the term coined for the rash or infestation caused by trombiculid mite larvae.[30][31]

Treatment

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Chigger-caused lesions on human skin showing characteristic welts
A trombiculid mite larva attached to human skin

Because chigger wounds are a complex combination of enzymatic and the resulting mechanical damage, plus allergy and immune responses, plus possible secondary bacterial infection subject to local influences, no one remedy works equally well for most people.

The chiggers' digestive enzymes in the saliva cause "the intensely itchy welts".[32]The itching can be alleviated through use of over-the-counter topical corticosteroids and antihistamines. According to Mayo Clinic, the chiggers "fall off after a few days, leaving behind red, itchy welts", which normally heal on their own within one to two weeks.[33]Hot showers or baths also help reduce itching. In cases of severe dermatitis or secondary infection associated with chigger bites, a doctor should be consulted.[34]

According to an Ohio State University Extension Fact Sheet:[35]

... After returning from a chigger-infested area, launder the field clothes in soapy, hot water (50 °C (125 °F).)... As soon as possible, take a good hot bath or shower and soap repeatedly. The chiggers may be dislodged, but you will still have the stylostomes, causing the severe itch. Scratching deep to remove stylostomes can cause secondary infections. For temporary relief of itching, apply ointments of benzocaine, hydrocortisone, calamine lotion, New Skin, After Bite, or others recommended by your pharmacist or medical doctor.... (The sooner the treatment, the better the results.)

Home remedies to "suffocate" the mite, such as applying clear nail polish, rubbing alcohol, or bleach, may have little benefit since the mites do not burrow into the skin. However, since the mite may still be attached for up to three days, these treatments could possibly kill the mite, reducing further damage.[36]

Chiggers as disease vectors

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Further information:Scrub typhus

Although the harvest mite chigger usually does notcarry diseasesin North Americantemperate climates,Leptotrombidium delienseis considered a dangerous pest in East Asia and theSouth Pacificbecause it often carriesOrientia tsutsugamushi,the tiny bacterium that causesscrub typhus,which is known alternatively as the Japanese river disease, scrub disease, ortsutsugamushi.The mites are infected by theRickettsiapassed down from parent to offspring before eggs are laid in a process calledtransovarial transmission.Symptoms of scrub typhus in humans include fever, headache, muscle pain, cough, andgastrointestinal symptoms.[37][38]

References

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  1. ^"Trombiculidae Ewing, 1929 (Family)".SysTax - database query.Universität Ulm.Retrieved2009-03-06.
  2. ^Shatrov, Andrey B.; Kudryashova, Naina I. (2008). "Taxonomic ranking of major trombiculid subtaxa with remarks on the evolution of host-parasite relationships (Acariformes: Parasitengona: Trombiculidae)".Annales Zoologici.58(2): 279–287.doi:10.3161/000345408X326591.S2CID83569187.
  3. ^G. A. Smith; V. Sharma; J. F. Knapp; B. J. Shields (1998). "The summer penile syndrome: seasonal acute hypersensitivity reaction caused by chigger bites on the penis".Pediatric Emergency Care.14(2): 116–118.doi:10.1097/00006565-199804000-00007.PMID9583392.S2CID37926004.
  4. ^Merriam-Webster's Online Dictionary, chiggerscause intense irritation
  5. ^chigger: Medical dictionary:"produces a wheal, usually with severe itching and dermatitis"
  6. ^Chigger:Archived2012-09-26 at theWayback MachineAmerican Heritage Dictionary
  7. ^chigger: Dictionary,http://dictionary.reference /browse/chigger
  8. ^Ballantine, Todd (1991).Tideland treasure: the naturalist's guide to the beaches and salt marshes of Hilton Head Island and the southeastern coast.Columbia, South Carolina:University of South Carolina Press.pp.1–4.ISBN978-0-87249-795-5.
  9. ^Mandell, Gerald L.; Bennett JE; Dolin R (2005). "294".Principles and Practice of Infectious Diseases(6th ed.). Philadelphia: Elsevier Churchill Livingstone.ISBN978-0-443-08686-1.
  10. ^Goldman, Lee; Dennis Arthur Ausiello (2007).Cecil Medicine(23, illustrated, revised ed.). Elsevier Health Sciences. p. 1032.
  11. ^Eutrombicula (Trombicula) alfreddugesiis themost familiar [chigger]in North America. "
  12. ^"Eutrombicula alfreddugesi." "...from the Atlantic coast to the Midwest and southward... "Encyclopædia Britannica Online, 2011. Web. 10 Aug. 2011.
  13. ^N. autumnalis"has not been found in the Nearctic region...."http:// vetstream /lapis/Content/Bug/bug00357
  14. ^abcdefgDurden, Lance A. (2002).Medical and veterinary entomology(3rd ed.). Academic Press. p. 458.ISBN978-0-12-510451-7.
  15. ^abcPotter, M. F.; P. G. Koehler (February 2000)."Invisible Itches: Insect and Non-Insect Causes"(PDF).University of Florida, Depart. pp. 1–4.Retrieved2009-05-22.
  16. ^Scarborough, John (1998).Medical and Biological Terminologies.Oklahoma: University of Oklahoma Press. p. 122.ISBN978-0-8061-3029-3.
  17. ^H. E. Ewing (1946)."Notes on trombiculid mites with descriptions of Walchiinae n. subf.,Speotrombiculan. g., andEutrombicula defectan. sp "(PDF).Journal of Parasitology.32(5): 435–440.doi:10.2307/3272913.JSTOR3272913.PMID20277195.
  18. ^Bowman, Dwight D.; Hendrix, Charles M.; Lindsay, David S.; Barr, Stephen C. (2002).Feline clinical parasitology.Wiley-Blackwell. pp. 385–386.ISBN978-0-8138-0333-3.
  19. ^"Aoûtat: Definition"(in French). Vulgaris - medical.Retrieved2009-05-19.
  20. ^Vater, G. (1982)."The geographical distribution of the harvest mite Neotrombicula autumnalis (Acari: Trombiculidae)".Zoologische Jahrbucher, Abteilung fur Systematik, Okologie und Geographie der Tiere(in German).109(3). CABI: 329–356.ISSN0044-5193.
  21. ^Hirst, A. (1929)."On the" scrub itch mite "of North Queensland (Trombicula hirstiSambon) — a possible carrier of tropical pseudotyphus "(PDF).Transactions of the Royal Society of Tropical Medicine and Hygiene.22(5): 451–452.doi:10.1016/S0035-9203(29)90067-5.
  22. ^"ACES Publications: CHIGGERS: ANR-1109".Retrieved2008-06-24.
  23. ^Finke, D.L. (1998-10-01)."University of MD Chigger Fact sheet"(PDF).Retrieved2007-05-25.
  24. ^"Chiggers".Retrieved2008-06-24.
  25. ^abAbout: Chiggers Pediatric Dermatology Basics
  26. ^"ArmaXX Pest Control".Retrieved2008-06-24.
  27. ^University of Florida: IFAS Extension
  28. ^Takahashi, M; Misumi, H; Urakami, H; Misumi, M; Matsumoto, I (2003)."Life cycle of Leptotrombidium pallidum (Acari: Trombiculidae), one of the vector mites of scrub typhus in Japan (Author abstract)".Ohara Sogo Byoin Nenpo.45:19–30.ISSN0285-3671.
  29. ^Kumlert, Rawadee; Chaisiri, Kittipong; Anantatat, Tippawan; Stekolnikov, Alexandr A.; Morand, Serge; Prasartvit, Anchana; Makepeace, Benjamin L.; Sungvornyothin, Sungsit; Paris, Daniel H. (2018)."Autofluorescence microscopy for paired-matched morphological and molecular identification of individual chigger mites (Acari: Trombiculidae), the vectors of scrub typhus".PLOS ONE.13(3): e0193163.Bibcode:2018PLoSO..1393163K.doi:10.1371/journal.pone.0193163.ISSN1932-6203.PMC5832206.PMID29494599.
  30. ^Baumann T (March 2001)."New treatment for harvest mite infestation".Archives of Internal Medicine.161(5): 769.doi:10.1001/archinte.161.5.769.PMID11231715.
  31. ^An "infestation" withTrombiculamites (chiggers).http://medical-dictionary.thefreedictionary /trombiculiasis
  32. ^"Chiggers".Missouri Department of Conservation.
  33. ^Mayo Clinic, Healthy Lifestyle, Slide show: Poison ivy and other summer skin irritants- Chiggers "fall off after a few days, leaving behind red, itchy welts."
  34. ^2006,Field Guide to Venomous and Medically Important InvertebratesAffecting Military Operations: Identification, Biology, Symptoms, Treatment
  35. ^William F. Lyon,[1]Ohio State University Extension Fact Sheet, Entomology, Chiggers], HYG-2100-98 - Ohioline, --gives other "Control Measures" for chiggers, including: "Keep moving since the worst chigger infestations occur when sitting or laying down in a sunny spot at midday with temperatures above 60°F."
  36. ^Unknown[permanent dead link‍]
  37. ^Service, Mike (2008).Medical Entomology for Students(4, illustrated, revised ed.). Published by Cambridge University Press, 2008. pp. 250–252 of 289 pages.ISBN978-0-521-70928-6.
  38. ^"CDC - Scrub Typhus Reemergence in the Maldives".Retrieved2008-06-24.
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