[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Ectoparasites](https://durgical.com/en/microbiology/groups/ectoparasites/) › Trombicula, Cheyletiella and bird mites

# Trombicula, Cheyletiella and bird mites

- Parasite
- For completeness

Tiny mites from grass, pets or birds that bite people and cause intense itch. In Asia and the Pacific, chiggers also carry scrub typhus.

Updated Nov 13, 2026

Also called: chiggers, harvest mites, coloradillas, walking dandruff (Cheyletiella), bird mites (Dermanyssus, Ornithonyssus)

## Quick facts

**Type**
Parasite · [Ectoparasites](https://durgical.com/en/microbiology/groups/ectoparasites/)

**Gram / shape**
Chigger larvae

**Spread**
Chiggers · Cheyletiella · Bird and rodent mites

**Causes**
Trombiculosis · Cheyletiellosis and bird

**Treatment**
Bites

On this page

- The basics Key points
- At a glance
- Morphology
- Transmission
- Life cycle
- Memory aid
- What the colours mean

- Clinical Virulence factors
- Diseases it causes
- Clinical picture
- Diagnosis

- Treatment Treatment
- Prevention

- Study Test yourself

- Connections Connections

## Key points

- Only the chigger larva bites; it feeds on tissue fluid, not blood.
- Itchy papules where clothing is tight: ankles, waistband, folds.
- Chiggers (Leptotrombidium) carry scrub typhus: eschar plus fever; doxycycline.
- Cheyletiella and bird mites: human scrapings negative, look at the pet or the nest.
- Animal mites do not reproduce on human skin.

## At a glance

**Shape**
Chigger larvae: round, bright red to orange, six legs; Cheyletiella: large hook-like mouthpart palps

**Family**
Trombiculidae (chiggers); Cheyletiellidae; Dermanyssidae and Macronyssidae (bird and rodent mites)

**Type**
Mites (arachnids, Acari); temporary ectoparasites, and chiggers as vectors

**Size**
Chigger larvae about 0.2 mm, barely visible; Cheyletiella about 0.4 mm

## Morphology

- Only the six-legged chigger larva feeds on animals; nymphs and adults live free in the soil.
- Cheyletiella lives on the skin surface of dogs, cats and rabbits, in moving scales.
- Bird mites are greyish until they feed and turn red with blood.

## Transmission

- Chiggers: larvae climb onto skin from grass, bushes and forest floor, often at the waistband, ankles and skin folds.
- Cheyletiella: close contact with an infested pet; the mite does not burrow or complete its cycle on people.
- Bird and rodent mites: they leave abandoned nests near windows, roofs or air vents and bite people when hosts are gone.
- Scrub typhus: Orientia tsutsugamushi is passed in the bite of an infected chigger larva.

**Reservoir:** Grassland, bushes and forest margins (chiggers); Dogs, cats and rabbits (Cheyletiella); Pigeons, poultry and nesting birds; rats and mice (bird and rodent mites); Wild rodents and the mites themselves (Orientia, through mite eggs)

**Vector:** Leptotrombidium chiggers transmit Orientia tsutsugamushi (scrub typhus) in rural Asia, the Indian subcontinent and northern Australia.

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Life cycle

- Adult chiggers live in soil and feed on small arthropods and their eggs.
- The female lays eggs in soil; six-legged larvae hatch and wait on vegetation for a host.
- The larva attaches, digests skin cells with saliva and feeds on tissue fluid, not blood, for a few days.
- It drops off, becomes a free-living nymph and then an adult in the soil.
- Cheyletiella completes its whole cycle on the pet in a few weeks; bird mites complete theirs in the nest.

## Virulence factors

- Chigger saliva forms a feeding tube (stylostome) in the skin that triggers intense itch.
- The itch begins hours after the bite and lasts days, long after the larva has dropped off.
- Animal mites cause hypersensitivity dermatitis without true infestation of human skin.
- Scratching leads to impetigo and other secondary infections.

## Diseases it causes

- Trombiculosis: intensely itchy papules where clothing presses
- Cheyletiellosis and bird or rodent mite dermatitis (gamasoidosis)
- Scrub typhus, carried by chiggers in Asia and the Pacific [Rickettsial infections (spotted fever) →](https://durgical.com/en/conditions/rickettsial-infections/)
- Papular urticaria from mite bites

## Clinical picture

- Chiggers: clusters of red, very itchy papules at the ankles, legs, waistband and skin folds after time in grass.
- Cheyletiella: itchy papules on the arms, chest and abdomen where the pet is held.
- Bird mites: itchy papules on exposed skin, sometimes with tiny moving mites seen on walls or bedding.
- Scrub typhus: fever, headache, lymph nodes and a dark eschar at the bite site.

## Diagnosis

- Clinical, from the distribution of lesions and exposure (grass, pets, birds' nests).
- Human skin scrapings are negative in Cheyletiella and bird mite dermatitis: examine the pet's scales or the nest.
- Scrub typhus: serology or PCR; treatment starts on clinical suspicion.

## Treatment

Bites: wash the skin after exposure, topical corticosteroids and oral antihistamines for itch. Treat the pet through a veterinarian and remove birds' nests; scrub typhus is treated with doxycycline or azithromycin.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

- [Doxycycline](https://durgical.com/en/pharmacology/doxycycline/)
- [Azithromycin](https://durgical.com/en/pharmacology/azithromycin/)
- [Hydrocortisone](https://durgical.com/en/pharmacology/hydrocortisone/)
- [Cetirizine](https://durgical.com/en/pharmacology/cetirizine/)

## Prevention

- Long clothes tucked into socks and repellents in grass and scrub; bathe and wash clothes after outings.
- Treat infested pets and wash their bedding.
- Remove pigeon and other birds' nests from windows, roofs and air conditioners; control rodents.
- Permethrin-treated clothing for field work in scrub typhus areas.

## Memory aid

The red larva clings where the belt and the sock pinch; if the pet is scaly or the nest is empty, look there, not on the patient.

## Test yourself

Think of the answer, then tap the question to see it.

## Which stage of the chigger bites humans?

Only the six-legged larva; nymphs and adults live free in the soil.

## Where on the body are chigger bites typically found?

Where clothing is tight or skin folds: ankles, legs, waistband, groin and armpits.

## Why are skin scrapings usually negative in Cheyletiella dermatitis?

Because the mite does not burrow or live on human skin; it is found on the infested pet.

## Which disease do chiggers carry in Asia and the Pacific?

Scrub typhus, caused by Orientia tsutsugamushi.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/trombicula-cheyletiella-and-bird-mites/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

## Connections

## Related 5

- [Orientia tsutsugamushi](https://durgical.com/en/microbiology/orientia-tsutsugamushi/)
- [Sarcoptes scabiei](https://durgical.com/en/microbiology/sarcoptes-scabiei/)
- [Demodex folliculorum and Demodex brevis](https://durgical.com/en/microbiology/demodex-folliculorum-and-demodex-brevis/)
- [Amblyomma, Rhipicephalus and Ornithodoros](https://durgical.com/en/microbiology/amblyomma-rhipicephalus-and-ornithodoros/)
- [Pulex, Xenopsylla and Ctenocephalides](https://durgical.com/en/microbiology/pulex-xenopsylla-and-ctenocephalides/)

## Related conditions 1

- [Rickettsial infections (spotted fever)](https://durgical.com/en/conditions/rickettsial-infections/)

[← Back to the group: Ectoparasites](https://durgical.com/en/microbiology/groups/ectoparasites/)

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [About Scrub Typhus | Typhus Fevers | CDC](https://www.cdc.gov/typhus/about/scrub.html) (CDC, 2025); [Arthropod infestations. Arachnid bites and stings](https://dermnetnz.org/cme/arthropods/arachnid-bites-and-stings) (DermNet, 2023).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/microbiology/trombicula-cheyletiella-and-bird-mites/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/trombicula-cheyletiella-and-bird-mites/