Mites, Including Chiggers

James H. Diaz

Keywords

animal mites; chiggers; grain mite; house dust mites; itch mites; mites; Orientia tsutsugamushi; plant mites; red bugs; rickettsialpox; scrub typhus; urticaria

Mites, including chigger and scabies mites, are among the smallest arthropods, with most barely visible without magnification. Only about 25 species of the more than 3000 species of chigger, animal, plant, and scabies mites are of any medical importance, and most of these are simply biting nuisances and do not transmit infectious diseases.¹ Mites are closely related to ticks but not as prodigious at blood-feeding. They also do not transmit as broad a range of infectious microbial diseases as ticks. The most serious diseases transmitted by mites are scrub typhus and rickettsialpox.

Only biting larvae of Asian scrub typhus chiggers (Leptotrombidium spp.) can transmit scrub typhus caused by Orientia tsutsugamushi (formerly Rickettsia tsutsugamushi), and only biting house mouse mites (Liponyssoides sanguineus) can transmit rickettsialpox caused by Rickettsia akari. Both scrub typhus mites and house mouse mites are, like ticks, capable of inheriting bacterial infections by transovarial transmission and maintaining infections in several mite generations as bacteria are passed from adult to juvenile stages (nymphs and larvae) by trans-stadial transmission. Originally considered vectors of a rodent zoonosis, scrub typhus chiggers are the main environmental reservoirs of O. tsutsugamushi in endemic regions with much smaller secondary reservoirs in wild rodents.¹ Common house mice are the zoonotic reservoirs of R. akari, not only in crowded urban apartment buildings in the United States but also in mice-infested buildings, such as sheds and barns, in more rural locations worldwide.²

Mite Taxonomy and Ecology

Mites may be commonly classified as scabies mites (see Chapter 295), trombiculid or chigger mites (also called chiggers, red bugs, and itch mites), human follicle mites, dust mites, and a variety of animal, plant, and wood mites (Table 297-1). All mite species develop close generational associations with their ecosystems and zoonotic reservoirs, often referred to as mite islands.¹ Mite islands usually border cleared land and scrub bush and have several habitat requirements, including grassy vegetation with warm soil temperatures and high humidity, frequently visiting rodent hosts to feed larvae, and sufficient small insect fauna to feed nymphs and reproducing adults. Humans stumbling onto mite islands are at significantly higher risks for multiple larval chigger bites or trombidiosis worldwide or scrub typhus in the endemic regions of Eurasia and Asia.

TABLE 297-1

Mites of Medical Importance

FAMILY GENUS, SPECIES	COMMON NAMES (PLANT OR ANIMAL MITE)	GEOGRAPHIC DISTRIBUTION	MAINTENANCE IN NATURE	CLINICAL MANIFESTATIONS	INFECTIOUS DISEASE TRANSMISSION
Sarcoptidae
Sarcoptes scabiei var. hominis	Scabies (itch) mite (human mite)	Worldwide	Obligate ectoparasite of humans, human reservoir	Classic scabies Atypical scabies	None
Trombiculidae
Neotrombicula autumnalis	European harvest mite (animal mite)	Europe	Free-living ectoparasites of small mammals and birds	Scrub itch (trombidiosis)	None
Eutrombicula alfreddugesi	American chigger mite (animal mite)	Western Hemisphere	Free-living ectoparasites of small mammals and birds	Scrub itch (trombidiosis)	None
Eutrombicula sarcina	Asian chigger mite (animal mite)	Asia, Australia	Free-living ectoparasites of small mammals and birds	Scrub itch (trombidiosis)	None
Leptotrombidium deliense	Asian rodent chigger (animal mite)	Southeast Asia, Japan, Philippines, South Pacific, Australia	Free-living ectoparasites of rodents and insectivores, transovarial/trans-stadial passage of infectious disease agent	Scrub typhus (tsutsugamushi disease)	Orientia tsutsugamushi (formerly Rickettsia tsutsugamushi), causative agent of scrub typhus
Leptotrombidium akamushi, L. pallidum, and L. scutellaris	Japanese rodent chiggers (animal mites)	Japan	Same	Same	Same
Leptotrombidium arenicola and L. fletcheri	Malaysian rodent chiggers (animal mites)	Malaysia	Same	Same	Same
Leptotrombidium pavlovskyi	Russian rodent chigger (animal mite)	Far east of former Soviet Union	Same	Same	Same
Demodicidae
Demodex folliculorum	Hair follicle mite	Worldwide	Obligate ectoparasite of man, human host reservoir in hair follicles	Benign follicular (scaling) dermatitis Chronic blepharitis (demodicidosis)	None
Demodex brevis	Sebaceous gland mite	Worldwide	Obligate ectoparasite of man, human host reservoir in sebaceous glands	May potentiate granulomatous acne	None
Pyroglyphidae
Dermatophagoides pteronyssinus	European house dust mite (human mite)	Worldwide	Free-living ectoparasites of man; live in human bedrooms, especially in mattresses; feed on human skin detritus	House dust mite allergies and asthma	None
Dermatophagoides farinae	American house dust mite (human mite)	Worldwide	Same	Same	None
Dermanyssidae
Liponyssoides sanguineus (formerly Allodermanyssus sanguineus)	House mouse mite	North America, Northern Europe and Asia, Africa	Free-living ectoparasites of field mice, transovarial/trans-stadial passage of infectious disease agent	Rickettsialpox	Yes (Rickettsia akari)
Dermanyssus gallinae	Red poultry (chicken) mite	Worldwide	Free-living ectoparasites of domestic and wild birds	Poultry workers’ dermatitis of hands	None
Macronyssidae
Ornithonyssus bacoti	Tropical rat mite	Temperate and tropical regions worldwide	Free-living ectoparasites of large rodents: Rattus rattus, Rattus norvegicus	Urticarial papulovesicular to pustular dermatitis	None
Ornithonyssus bursa	Tropical fowl mite	Same	Free-living ectoparasites of domestic and wild birds	Pruritic papules in a scabietic distribution: finger webs, axillae, groin, buttocks	None
Laelapidae
Laelaps echidnina	Spiny rat mite	Worldwide, the most prevalent rodent mite species in the United States	Free-living ectoparasites of large rodents: Rattus rattus, Rattus norvegicus	Nonspecific mite-bite dermatitis	None
Pyemotidae
Pyemotes tritici	Grain (straw) itch mite	Worldwide	Free-living ectoparasites of straw-, hay-, grain-, and rice-eating moths, beetles, weevils	Grain workers’ pruritic vesicular eruption	None
Pediculoides ventricosus	European wood beetle itch mite		Free-living ectoparasites of straw-, hay-, grain-, and rice-eating moths, beetles, weevils	Solitary to multiple highly erythematous pruritic macules, some of which have attached macular tracts resembling comet tails	None
Pyemotes herfsi	Oak leaf gall mite	Europe, introduced into the United States	Free-living ectoparasites of gall-making larvae of oak trees	Pruritic, erythematous, vesicular eruptions of limbs, face, and neck	None
Acaridae*
Carpoglyphus lactis	Cheese and dried fruit mites	Worldwide	Free-living ectoparasites of cheeses and dried fruits	Cheese and fruit workers’ dermatitis	None
Tyrophagus putrescentiae	Copra (dried coconut meat or kernel) mite	Copra (dried coconut meat or kernel) growing areas	Free-living ectoparasites of coconut copra	Copra itch	None
Glycyphagidae*
Glycyphagus domesticus	Grocer’s mite	Worldwide	Free-living ectoparasites of fruits and vegetables	Grocer’s itch	None
Glycyphagus destructor	Hay mite	Worldwide	Free-living ectoparasites of cut hay	Hay workers’ and hay wagon riders’ allergy, asthma, rhinitis, conjunctivitis	None