Jump to content

Trombiculidae

From Wikipedia, the free encyclopedia

This is an old revision of this page, as edited by 71.133.254.31 (talk) at 18:29, 7 March 2014 (First paragraph, still trying to define Chigger. Is this controversial? if so see MOS:LEAD --~~~~Doug Bashford). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

"Chigger" redirects here. Not to be confused with Chigoe flea, also called a Jigger.

Trombiculidae
Scientific classification
Kingdom:
Animalia
Phylum:
Arthropoda
Class:
Arachnida
Subclass:
Acari
Order:
Trombidiformes
(unranked):
Parasitengona
Superfamily:
Trombidioidea
Family:
Trombiculidae

Ewing, 1929 [1]
Type species
Trombicula autumnalis
(Shaw, 1790)
Genera[2]
The distribution of trombiculid species, which is nearly everywhere in the world.

Trombiculidae (/trɒmb[invalid input: 'ɨ']ˈkjuːl[invalid input: 'ɨ']diː/ (also called berry bugs, harvest mites, red bugs, scrub-itch mites and aoutas) are a family of mites.[3] The best known of the Trombiculidae are the chiggers. There are two widely recognized definitions of "chigger," the scientific (or taxonomic) definition and the common definitions found in English and medical[4] dictionaries. According to most dictionaries; the several species of Trombiculidae that bite their host in their larval stage and cause "intense irritation"[5] or "a wheal, usually with severe itching and dermatitis,"[6][7] are called chiggers.[8] The scientific definitions seemingly includes many more, but not all species of Trombiculidae.

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.[9] 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 ticks are nearly microscopic, measuring 0.4 mm (1/60 of an inch) and have a chrome-orange hue.[10][11] There is a marked constriction in the front part of the body in the nymph and adult stages. The best known species of chigger in North America[12] is the hard-biting Trombicula alfreddugesi of the southeastern United States, humid Midwest[13] and Mexico; in the UK, the most prevalent chigger, called the "harvest mite", is Trombicula autumnalis, with distribution through Western Europe to Eastern Asia.[14]

Trombiculid mites go through a life cycle of egg, larva, nymph, and adult.[15] The larval mites feed on the skin cells of animals. The six-legged parasitic larva feeds on a large variety of creatures, including humans, rabbits, toads, box turtles, quail, and even some insects. After crawling onto their 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 stylostome and chew up tiny parts of the inner skin, thus causing severe irritation and swelling. The severe itching is accompanied by red, pimple-like bumps (papules) or hives and skin rash or lesions on a sun-exposed area. For humans, itching usually occurs after the larvae detach from the skin.[16]

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 stage, they are not parasitic and feed on plant materials. The females lay three to eight eggs in a clutch, usually on a leaf or under the roots of a plant, and die by autumn.[16]

History

Trombiculidae, from Greek τρομειν ("to tremble") and Latin culex, gen. culicis ("gnat" or "midge"), was first described as an independent family by Henry Ellsworth Ewing in 1944.[17] Then, when the family was first described, it included two subfamilies, Hemitrombiculinae and 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 setae present on the dorsal plate.[18]

References to chiggers, however, go as far back as sixth century China, and by 1733 the first recognition of trombiculid mites in North America were made. In 1758, 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.[19]

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 the more temperate regions, they are found only during the summer (in French, harvest mites are called aoûtat because they are common in August[20]). 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, in high mountains and in deserts.[21] In the British Isles, the species Trombicula autumnalis is called harvest mites, in North America the species Trombicula alfreddugesi, and the species Trombicula (eutrombicula) hirsti which are found in Australia and are commonly called the scrub-itch mite.[22]

Life cycle

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, there might only be three per year, but in tropical regions the cycle might be continuous all year long.[15] Adult harvest mites overwinter in protected places such as slightly below the soil. Females become active in the spring, and once the ground temperature is regularly above 60 °F (16 °C), she lays eggs, up to 15 eggs per day in vegetation when soil temperatures are 60 °F (16 °C). The eggs are round in shape. The eggs are dormant for about six days, after which the non-feeding pre-larvae emerge, with only three pairs of legs. After about six days, the pre-larva grows into its larval stage.[15]

Larva

The larvae, commonly called chiggers, are about 0.17–0.21 mm (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 earth, 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 life cycle. 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 an intensely itchy, red bump in humans (who are accidental hosts).[15][23]

Chiggers attach to the host, pierce the skin, inject enzymes into the bite wound that digest cellular contents,[24] and then suck up the digested tissue through a tube formed by hardened skin cells called a stylostome.[16] 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.[16] The red welt/bump on the skin is not where a chigger laid eggs, as is sometimes believed.[25] The larva remains attached to a suitable host for three to five days before dropping off to begin its nymph stage.[15]

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]

Chiggers as disease vectors

Further information: Scrub typhus

Although the harvest mite chigger usually does not carry diseases in North American temperate climates, the Leptotrombidium deliense is considered a dangerous pest in East Asia and the South Pacific because they often carry Orientia tsutsugamushi, the tiny bacterium that causes 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 transovarial transmission. Symptoms of scrub typhus in humans include fever, headache, muscle pain, cough, and gastrointestinal symptoms.[28][29]

Handling chigger bites

Chigger bites on human skin showing characteristic welts

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.

Itching can be alleviated through use of over-the-counter topical corticosteroids and antihistamines. Hot showers or baths also will help reduce itching. In cases of severe dermatitis or secondary infection associated with chigger bites, a doctor should be consulted.[30] Some swear by the application of petroleum jelly or by painting nail polish over the chigger bite, under the belief that the nail polish will suffocate the chiggers buried under the skin. However, this 'treatment' is based on common misconception, as chiggers do not actually bury themselves in skin. Rather, the digestive enzymes in the saliva are what cause the severe itching sensation.[31]

The myth of chiggers burrowing under the skin is more or less perpetuated by these 'treatments' effects, in so much as they cause the victim to refrain from scratching the affected area, thereby allowing the skin to heal sooner.

Nymph

Once the larva has engorged itself on skin and has fallen off its host, it develops to its nymph stage. The nymphs are sexually immature but more closely resemble the adult.

This stage consists of three phases, the protonymph, deutonymph, and tritonymph, respectively. The protonymph and tritonymph morphology are unusual in species of Trombiculidae. The protonymph phase combines larval and protonymph characteristics with deutonymph and tritonymph morphology.[32] 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.[15]

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.[15] They live in soil, and are often found when digging in yards or gardens.

Trombiculiasis

Main article: Trombiculosis

Trombiculiasis, also called trombiculidiasis, is the term coined for the rash or infestation caused by trombiculid mites.[33][34]

References

  1. ^ "Trombiculidae Ewing, 1929 (Family)". SysTax - database query. Universität Ulm. Retrieved 2009-03-06.
  2. ^ Shatrov, Andrey B. (2008). "Taxonomic ranking of major trombiculid subtaxa with remarks on the evolution of host-parasite relationships (Acariformes: Parasitengona: Trombiculidae)". Annales Zoologici. 58 (2). Warsaw: 279–287. doi:10.3161/000345408X326591. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  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. PMID 9583392.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  4. ^ Medical Definition from Merriam-Webster, Chigger, 2; "...and causes intense irritation" Retrieved March 7, 2014
  5. ^ Merriam-Webster's Online Dictionary, chiggers cause intense irritation
  6. ^ chigger: Medical dictionary: "produces a wheal, usually with severe itching and dermatitis"
  7. ^ Chigger: American Heritage Dictionary
  8. ^ chigger: Dictionary.com, http://dictionary.reference.com/browse/chigger
  9. ^ 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. ISBN 0-87249-795-X.
  10. ^ Mandell, Gerald L. (2005). "294". In 6th (ed.). Principles and Practice of Infectious Diseases. Philadelphia: Elsevier Churchill Livingstone. ISBN 978-0-443-08686-1. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)CS1 maint: extra punctuation (link) CS1 maint: numeric names: editors list (link)
  11. ^ Goldman, Lee (2007). Cecil Medicine (23, illustrated, revised ed.). Elsevier Health Sciences. p. 1032. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  12. ^ Eutrombicula (Trombicula) alfreddugesi is the most familiar [chigger] in North America."
  13. ^ "Eutrombicula alfreddugesi." "...from the Atlantic coast to the Midwest and southward..." Encyclopædia Britannica Online, 2011. Web. 10 Aug. 2011.
  14. ^ N. autumnalis "has not been found in the Nearctic region...." http://www.vetstream.com/lapis/Content/Bug/bug00357
  15. ^ a b c d e f g Durden, Lance A. (2002). Medical and veterinary entomology (3rd ed.). Academic Press. p. 458. ISBN 978-0-12-510451-7.
  16. ^ a b c d Potter, M. F. (March 1995. Revised February 2000. Reviewed January 2006.). "Invisible Itches: Insect and Non-Insect Causes" (PDF). University of Florida, Depart. pp. 1–4. Retrieved 2009-05-22. {{cite web}}: Check date values in: |date= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help) Cite error: The named reference "url" was defined multiple times with different content (see the help page).
  17. ^ Scarborough, John (1998). Medical and Biological Terminologies. Oklahoma: University of Oklahoma Press. p. 122. ISBN 0-8061-3029-6.
  18. ^ H. E. Ewing (1946). "Notes on trombiculid mites with descriptions of Walchiinae n. subf., Speotrombicula n. g., and Eutrombicula defecta n. sp" (PDF). Journal of Parasitology. 32 (5): 435–440. doi:10.2307/3272913. JSTOR 3272913.
  19. ^ Bowman, Dwight D.; Hendrix, Charles M.; Lindsay, David S.; Barr, Stephen C. (2002). Feline clinical parasitology. Wiley-Blackwell. pp. 385–386. ISBN 0-8138-0333-0.{{cite book}}: CS1 maint: multiple names: authors list (link)
  20. ^ "Aoûtat : Definition" (in French). Vulgaris - medical. Retrieved 2009-05-19.
  21. ^ Vater, G. (2006). "The geographical distribution of the harvest mite Neotrombicula autumnalis (Acari: Trombiculidae)" (in German). CABI: 1–2. {{cite journal}}: Cite journal requires |journal= (help)
  22. ^ Hirst, A. (1929). "On the "scrub itch mite" of North Queensland (Trombicula hirsti Sambon) — 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.
  23. ^ "ACES Publications : CHIGGERS : ANR-1109". Retrieved 2008-06-24.
  24. ^ Finke, D.L. (1998-10-01). "University of MD Chigger Fact sheet" (PDF). Retrieved 2007-05-25.
  25. ^ a b About.com: Chiggers Pediatric Dermatology Basics
  26. ^ "ArmaXX Pest Control". Retrieved 2008-06-24.
  27. ^ University of Florida: IFAS Extension
  28. ^ Service, Mike (2008). Medical Entomology for Students (4, illustrated, revised ed.). Published by Cambridge University Press, 2008. pp. 250–252 of 289 pages. ISBN 978-0-521-70928-6.
  29. ^ "CDC - Scrub Typhus Reemergence in the Maldives". Retrieved 2008-06-24.
  30. ^ 2006, Field Guide to Venomous and Medically Important Invertebrates Affecting Military Operations: Identification, Biology, Symptoms, Treatment
  31. ^ Missouri Department of Conservation
  32. ^ Takahashi, M (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. Japan: 19–30. ISSN 0285-3671. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  33. ^ Baumann T (March 2001). "New treatment for harvest mite infestation". Archives of Internal Medicine. 161 (5): 769. doi:10.1001/archinte.161.5.769. PMID 11231715.
  34. ^ An "infestation" with Trombicula mites (chiggers). http://medical-dictionary.thefreedictionary.com/trombiculiasis
Retrieved from "https://en.wikipedia.org/w/index.php?title=Trombiculidae&oldid=598582124"