View source for Biology:Trombiculidae

{{Short description|Family of trombidiform mites}}
{{Automatic taxobox
| image = Trombicula-mite-larva-with stylostome-2.jpg
| image_alt = Trombiculid mite larva
| image_caption = Trombiculid mite [[Biology:Larva|larva]]
| taxon = Trombiculidae
| authority = Ewing, 1929<ref>{{cite web |url=http://www.biologie.uni-ulm.de/cgi-bin/system/zoosys.pl?id=97056&stufe=5&typ=ZOO&lang=e&sid=T&pr=nix&only=no&B4=ok&syno=y&valid=y |title=Trombiculidae Ewing, 1929 (Family) |work=SysTax - database query |publisher=Universität Ulm |access-date=2009-03-06}}</ref>
| display_parents = 3
| type_genus = 	''[[Biology:Trombicula|Trombicula]]''
| type_genus_authority = Berlese, 1905
| subdivision_ranks = Genera
| subdivision_ref = <ref>{{cite journal|last=Shatrov|first=Andrey B.|author2=Kudryashova, Naina I. |year=2008|title=Taxonomic ranking of major trombiculid subtaxa with remarks on the evolution of host-parasite relationships (Acariformes: Parasitengona: Trombiculidae)|journal=Annales Zoologici |volume=58|issue=2|pages=279–287|doi=10.3161/000345408X326591|s2cid=83569187}}</ref>
| subdivision = 
*''[[Biology:Acomatacarus|Acomatacarus]]''
*''[[Biology:Afropolonia|Afropolonia]]''
*''Anahuacia''
*''Ascoschoengastia''
*''Axiogastia''
*''Blankaartia''
*''Brunehaldia''
*''Chatia''
*''Cheladonta''
*''Doloisia''
*''[[Biology:Euschoengastia|Euschoengastia]]''
*''[[Biology:Eutrombicula|Eutrombicula]]''
*''Gahrliepia''
*''Guntherana''
*''[[Biology:Guntheria|Guntheria]]''
*''Hannemania''
*''Heaslipia''
*''Hirsutiella''
*''Kayella''
*''[[Biology:Leptotrombidium|Leptotrombidium]]''
*''Microtrombicula''
*''Miyatrombicula''
*''Neoschoengastia''
*''[[Biology:Neotrombicula|Neotrombicula]]''
*''Novotrombicula''
*''Ornithogastia''
*''Parasecia''
*''Pseudoschoengastia''
*''Schoengastiella''
*''Schoutedenichia''
*''Speleocola''
*''[[Biology:Trombicula|Trombicula]]''
*''Whartonia''
| range_map = Distribution Trombiculidae.png
| range_map_caption = The distribution of trombiculid species, which is nearly everywhere in the world.
| synonyms = 
| synonyms_ref = 
}}

'''Trombiculidae''' ({{IPAc-en|t|r|ɒ|m|b|ᵻ|ˈ|k|juː|l|ᵻ|d|iː}}), 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.<ref>{{cite journal |author=G. A. Smith |author2=V. Sharma |author3=J. F. Knapp |author4=B. J. Shields |year=1998 |title=The summer penile syndrome: seasonal acute hypersensitivity reaction caused by chigger bites on the penis |journal=Pediatric Emergency Care |volume=14 |issue=2 |pages=116–118 |pmid=9583392 |doi=10.1097/00006565-199804000-00007|s2cid=37926004 }}</ref> Chiggers are often confused with jiggers – a type of flea. Several species of Trombiculidae in their [[Biology:Larva|larva]] stage bite their animal or human host and by embedding their mouthparts into the skin cause "intense irritation"<ref>[http://www.merriam-webster.com/dictionary/chigger Merriam-Webster's Online Dictionary, chiggers] cause intense irritation</ref> or "a wheal, usually with severe itching and [[Medicine:Dermatitis|dermatitis]]".<ref>[http://medical-dictionary.thefreedictionary.com/chigger chigger: Medical dictionary:] "produces a wheal, usually with severe itching and dermatitis"</ref><ref>[http://education.yahoo.com/reference/dictionary/entry/chigger Chigger:] {{Webarchive|url=https://web.archive.org/web/20120926104621/http://education.yahoo.com/reference/dictionary/entry/chigger |date=2012-09-26 }} American Heritage Dictionary</ref><ref>chigger: Dictionary.com, http://dictionary.reference.com/browse/chigger</ref>

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.<ref>{{cite book |author=Ballantine, Todd |title=Tideland treasure: the naturalist's guide to the beaches and salt marshes of Hilton Head Island and the southeastern coast |publisher=[[Organization:University of South Carolina Press|University of South Carolina Press]] |location=Columbia, South Carolina |year=1991 |pages=[https://archive.org/details/tidelandtreasure00ball/page/1 1–4] |isbn=978-0-87249-795-5 |url-access=registration |url=https://archive.org/details/tidelandtreasure00ball/page/1 }}</ref> 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 of [[Biology:Tick|tick]]s are nearly microscopic, measuring 400&nbsp;µm (1/60 of an inch) and have a [[Chrome orange|chrome-orange]] hue.<ref>{{cite book|last=Mandell|first=Gerald L. |author2=Bennett JE |author3=Dolin R |title=Principles and Practice of Infectious Diseases.|edition=6th|publisher=Elsevier Churchill Livingstone|location=Philadelphia|year=2005|chapter=294|isbn=978-0-443-08686-1}}</ref><ref>{{cite book|last=Goldman|first=Lee |author2=Dennis Arthur Ausiello |title=Cecil Medicine|publisher=Elsevier Health Sciences|year=2007|edition=23, illustrated, revised|page=1032}}</ref> There is a marked constriction in the front part of the body in the [[Biology:Nymph|nymph]] and adult stages. The best known species of chigger in North America<ref>''Eutrombicula (Trombicula) alfreddugesi'' is the [http://dailyparasite.blogspot.com/2010/05/may-28-eutrombicula-alfreddugesi.html most familiar [chigger<nowiki>]</nowiki>] in North America."</ref> is the hard-biting ''[[Biology:Trombicula alfreddugesi|Trombicula alfreddugesi]]'' of the Southeastern United States, humid Midwest<ref>"Eutrombicula alfreddugesi." "...[http://www.britannica.com/EBchecked/topic/196741/Eutrombicula-alfreddugesi from the Atlantic coast to the Midwest and southward]..." Encyclopædia Britannica Online, 2011. Web. 10 Aug. 2011.</ref> and Mexico.  In the UK, the most prevalent harvest mite is ''[[Biology:Neotrombicula autumnalis|Neotrombicula autumnalis]]'', which is distributed through Western Europe to Eastern Asia.<ref>''N. autumnalis'' "has not been found in the Nearctic region...." http://www.vetstream.com/lapis/Content/Bug/bug00357</ref>

Trombiculid mites go through a lifecycle of egg, larva, [[Biology:Nymph|nymph]], and adult.<ref name="Durden">{{cite book|last=Durden|first=Lance A.|title=Medical and veterinary entomology|publisher=Academic Press|year=2002|edition=3rd|page=458|isbn=978-0-12-510451-7|url=https://books.google.com/books?id=u4RGXGkRq5YC&q=trombiculidae+%22life+cycle%22&pg=PA458}}</ref> The larval mites feed on the skin [[Biology:Cell|cell]]s of animals. The six-legged parasitic larvae feed on a large variety of creatures, including humans, rabbits, toads, [[Biology:Box turtle|box turtle]]s, [[Biology:Quail|quail]], and even some insects. After crawling onto their [[Biology:Host|hosts]], 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 a [[Biology:Stylostome|stylostome]] and chew up tiny parts of the inner skin, thus causing irritation and swelling. The itching is accompanied by red, pimple-like bumps (papules) or [[Medicine:Hives|hives]] and skin rash or lesions on a sun-exposed area. For humans, itching usually occurs after the larvae detach from the skin.<ref name="PotterKoehler">{{cite web|url=http://edis.ifas.ufl.edu/pdffiles/MG/MG34300.pdf|title=Invisible Itches: Insect and Non-Insect Causes |last=Potter|first=M. F. |author2=P. G. Koehler |date=February 2000|publisher=University of Florida, Depart|pages=1–4|access-date=2009-05-22}}</ref>

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.<ref name="PotterKoehler"/>

==History==
Trombiculidae, from Greek {{lang|el|τρομειν}} ("to tremble") and Latin ''{{lang|la|culex}}'', genitive ''{{lang|la|culicis}}'' ("gnat" or "midge"), was first described as an independent family by Henry Ellsworth Ewing in 1944.<ref>{{cite book |author=Scarborough, John |title=Medical and Biological Terminologies|publisher=University of Oklahoma Press|location=Oklahoma|year=1998|page=122|isbn=978-0-8061-3029-3}}</ref> Then, when the family was first described, it included two subfamilies, Hemitrombiculinae and [[Biology:Trombiculinae|Trombiculinae]]. Womersley added another, Leeuwenhoekiinae, which at the time contained only ''Leeuwenhoekia''. Later, he erected the family Leeuwenhoekiidae for the genus and subfamily, having six genera; they have a pair of submedian [[Biology:Seta|seta]]e present on the dorsal plate.<ref>{{cite journal |author=H. E. Ewing |title=Notes on trombiculid mites with descriptions of Walchiinae n. subf., ''Speotrombicula'' n. g., and ''Eutrombicula defecta'' n. sp |journal=Journal of Parasitology |volume=32 |issue=5 |pages= 435–440 |year=1946 |jstor=3272913 |url=http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1269&context=jrnlparasitology |format=PDF |doi=10.2307/3272913|pmid=20277195 }}</ref>

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, [[Biography:Carl Linnaeus|Carl Linnaeus]] described a single species, ''Acarus batatas'' (now ''Trombicula batatas''). However, most information about chiggers came from problems that arose during and after World War II.<ref>{{cite book |author1=Bowman, Dwight D. |author2=Hendrix, Charles M. |author3=Lindsay, David S. |author4=Barr, Stephen C. |title=Feline clinical parasitology |publisher=Wiley-Blackwell |year=2002 |pages=385–386 |isbn= 978-0-8138-0333-3}}</ref>

== Distribution ==
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 species ''[[Biology:Neotrombicula autumnalis|Neotrombicula autumnalis]]'' are found during the summer and autumn (in [[Social:French language|French]], harvest mites are called ''aoûtat'' because they are common in August<ref>{{cite web|url=http://www.vulgaris-medical.com/encyclopedie/aoutat-522.html|title=Aoûtat: Definition|publisher=Vulgaris - medical|language=fr|access-date=2009-05-19}}</ref>). In the United States, they are found mostly in the Southeast, the South, and the Midwest. They are not present, or barely found, in far northern areas, high mountains, and deserts.<ref>{{cite journal|last=Vater|first=G.|year=2006|title=The geographical distribution of the harvest mite Neotrombicula autumnalis (Acari: Trombiculidae) |publisher=CABI |pages=1–2 |language=de }}</ref> In  North America the species ''[[Biology:Trombicula alfreddugesi|Trombicula alfreddugesi]]'', and the species ''[[Biology:Trombicula hirsti|Trombicula (eutrombicula) hirsti]]'', which are found in {{wipe|Australia}} and are commonly called the scrub-itch mite.<ref>{{cite journal|last=Hirst|first=A.|year=1929|title=On the "scrub itch mite" of North Queensland (''Trombicula hirsti'' Sambon) — a possible carrier of tropical pseudotyphus|journal = Transactions of the Royal Society of Tropical Medicine and Hygiene| volume= 22|issue=5 |pages= 451–452 |url=http://download.journals.elsevierhealth.com/pdfs/journals/0035-9203/PIIS0035920329900675.pdf|doi=10.1016/S0035-9203(29)90067-5}}</ref>

==Life cycle==
[[File:Harvest mite cycle.svg|thumb|left|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.<ref name="Durden"/> 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 {{convert|60|°F|°C|disp=flip}}, 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.<ref name="Durden" />

===Larva===
The larvae, commonly called chiggers, are about {{cvt|170|-|210|µm|in|3}} 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.<ref name="Durden" /><ref name="urlACES Publications : CHIGGERS : ANR-1109">{{cite web |url=http://www.aces.edu/pubs/docs/A/ANR-1109/ |title=ACES Publications : CHIGGERS: ANR-1109 |access-date=2008-06-24}}</ref>

 [[File:Chigger bite.svg|200px|right]]
Chiggers attach to the host, pierce the skin, inject enzymes into the bite wound that digest cellular contents,<ref>{{cite web | last = Finke | first = D.L. | title = University of MD Chigger Fact sheet | date = 1998-10-01 | url = http://www.hgic.umd.edu/_media/documents/hg66.pdf | access-date = 2007-05-25}}</ref> and then suck up the digested tissue through a tube formed by hardened skin cells called a [[Biology:Stylostome|stylostome]].<ref name="IG085">{{cite web |url=http://edis.ifas.ufl.edu/IG085 |title= Chiggers |access-date=2008-06-24}}</ref> 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.<ref name="PotterKoehler"/> The red welt/bump on the skin is not where a chigger laid eggs, as is sometimes believed.<ref name="ReferenceA">About.com: Chiggers Pediatric Dermatology Basics</ref> The larvae remain attached to suitable hosts for three to five days before dropping off to begin their nymphal stage.<ref name="Durden" /> 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.<ref name="ArmaXX">{{cite web |url=http://www.armaxx.com/chigger.html |title=ArmaXX Pest Control |access-date=2008-06-24}}</ref> During dry seasons, chiggers are mostly found underneath brush and shady areas.<ref name="ReferenceA"/><ref>University of Florida: IFAS Extension</ref> Standing still or lying in tall grass gives them more time to climb onto a person.

===Nymph===
Once the larva has engorged 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.<ref>{{cite journal|last=Takahashi|first=M|author2=Misumi, H |author3=Urakami, H |author4=Misumi, M |author5= Matsumoto, I |year=2003|title=Life cycle of Leptotrombidium pallidum (Acari: Trombiculidae), one of the vector mites of scrub typhus in Japan (Author abstract)|journal=Ohara Sogo Byoin Nenpo|volume=45|pages=19–30|issn=0285-3671|url=http://sciencelinks.jp/j-east/article/200401/000020040103A0828660.php}}</ref> 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.<ref name="Durden" />

===Adult===
As deutonymphs and adults, trombiculid mites are independent predators that feed on small arthropods and their eggs, and are also found to eat plant material.<ref name="Durden" /> They live in soil, and are often found when digging in yards or gardens or in compost bins.

Recently (2018), methods based on [[Physics:Autofluorescence|autofluorescence]] microscopy were developed to enable identification of trombiculid mites to the species level on the basis of morphological traits without any special preparation.<ref name="FugmannKumlert2018">{{cite journal|last1=Kumlert|first1=Rawadee|last2=Chaisiri|first2=Kittipong|last3=Anantatat|first3=Tippawan|last4=Stekolnikov|first4=Alexandr A.|last5=Morand|first5=Serge|last6=Prasartvit|first6=Anchana|last7=Makepeace|first7=Benjamin L.|last8=Sungvornyothin|first8=Sungsit|last9=Paris|first9=Daniel H.|title=Autofluorescence microscopy for paired-matched morphological and molecular identification of individual chigger mites (Acari: Trombiculidae), the vectors of scrub typhus|journal=PLOS ONE|volume=13|issue=3|year=2018|pages=e0193163|issn=1932-6203|doi=10.1371/journal.pone.0193163|pmid=29494599|pmc=5832206|bibcode=2018PLoSO..1393163K|doi-access=free}} {{open access}}</ref>

== Effect on humans ==

=== Trombiculosis ===
Trombiculosis, also called trombiculiasis and trombiculidiasis, is the term coined for the rash or infestation caused by trombiculid mite larvae.<ref>{{cite journal |author=Baumann T |title=New treatment for harvest mite infestation |journal=Archives of Internal Medicine |volume=161 |issue=5 |page=769 |date=March 2001 |pmid=11231715 |doi= 10.1001/archinte.161.5.769|url=http://archinte.ama-assn.org/cgi/pmidlookup?view=long&pmid=11231715}}</ref><ref>An "infestation" with ''Trombicula'' mites (chiggers). http://medical-dictionary.thefreedictionary.com/trombiculiasis</ref>

=== Treatment ===
[[File:TrombiculosisSores.jpg|thumb|Chigger-caused lesions on human skin showing characteristic welts]]
[[File:Trombiculid mite larvae attached to human skin.jpg|thumb|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".<ref>[http://nature.mdc.mo.gov/discover-nature/field-guide/chiggers Missouri Department of Conservation]</ref> 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.<ref>[http://www.mayoclinic.org/healthy-living/adult-health/multimedia/poison-ivy/sls-20076702 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."</ref> 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.<ref>2006, [http://www.afpmb.org/sites/default/files/pubs/guides/field_guide.pdf Field Guide to Venomous and Medically Important Invertebrates] Affecting Military Operations: Identification, Biology, Symptoms, Treatment</ref>

According to an Ohio State University Extension Fact Sheet:<ref>William F. Lyon, [http://www.agri.ohio.gov/Public_Docs/Pest_Study_Material/10d%20Mosquito,%20Chigger%20and%20Tick%20Factsheets.pdf] 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."</ref> <blockquote>... After returning from a chigger-infested area, launder the field clothes in soapy, hot water ({{cvt|125|F|C|-1|disp=flip}}.) ... 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.&nbsp;... (The sooner the treatment, the better the results.) </blockquote>

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 3 days, these treatments could possibly kill the mite, reducing further damage.{{Citation needed|date=January 2019}}

=== Chiggers as disease vectors ===
{{Further|Medicine:Scrub typhus}}
Although the harvest mite chigger usually does not [[Biology:Vector (epidemiology)|carry diseases]] in North American [[Earth:Temperate climate|temperate climate]]s, ''[[Biology:Leptotrombidium deliense|Leptotrombidium deliense]]'' is considered a dangerous pest in East Asia and the [[Earth:Oceania|South Pacific]] because it often carries ''[[Biology:Orientia tsutsugamushi|Orientia tsutsugamushi]]'', the tiny bacterium that causes [[Medicine:Scrub typhus|scrub typhus]], which is known alternatively as the Japanese river disease, scrub disease, or ''tsutsugamushi''. The mites are infected by the ''Rickettsia'' passed down from parent to offspring before eggs are laid in a process called [[Biology:Transovarial transmission|transovarial transmission]]. Symptoms of scrub typhus in humans include fever, headache, muscle pain, cough, and gastrointestinal symptoms.<ref>{{cite book|last=Service|first=Mike|title=Medical Entomology for Students |publisher=Published by Cambridge University Press, 2008|edition=4, illustrated, revised|pages=250–252 of 289 pages|isbn=978-0-521-70928-6 |url=https://books.google.com/books?id=wRrof4RLDuwC&q=harvest+mites+scrub+typhus&pg=PA251|year=2008}}</ref><ref>{{cite web |url=https://www.cdc.gov/ncidod/eid/vol9no12/03-0212.htm |title=CDC - Scrub Typhus Reemergence in the Maldives |access-date=2008-06-24}}</ref>

== References ==
{{Reflist}}

== External links ==
* [http://www.ipm.iastate.edu/ipm/iiin/chigger.html Iowa State University Department of Entomology Insect Information Note]
* [https://www.nlm.nih.gov/medlineplus/ency/article/001333.htm NIH Medline Plus]
* [https://web.archive.org/web/20050530073632/http://ohioline.osu.edu/hyg-fact/2000/2100.html Ohio State University Extension Fact Sheet, Entomology, Chiggers, HYG-2100-98]
* [http://www.the-piedpiper.co.uk/th5i.htm#harvestmite ''Trombicula autumnalis'']
* Taxonomic information at [https://www.uniprot.org/taxonomy/92251 UniProt Consortium]

{{Acari}}
{{Taxonbar|from=Q7597354}}

[[Category:Trombiculidae| ]]
[[Category:Acari families]]

{{Sourceattribution|Trombiculidae}}