Introduction

Classification

Taxonomy

• Family: Trombiculidae.
• Genus: Neotrombicula/Trombicula.

Active Forms

Clinical Effects

Epidemiology

Habitat

• Damp, but drained, usually chalky soil with only the larva becoming parasitic.
• The natural hosts are usually small rodents, eg field-mice, but larvae will attach themselves to any grazing animals, humans working in the fields, eg harvest time, or humans, dogs, cats, etc walking over the often low-lying fields.

Lifecycle

• See lifecycle diagram .
• Only the larvae are parasitic.

Transmission

• The mites are acquired from the chalky soils that they favor.
• Larvae will climb up to 8 cm on grass, harvested corn stalks, etc to locate and attach to a host.

Pathological effects

• A hypersensitivity reaction (presumably in response to antigens in saliva and feeding tunnel) that persists for days to weeks after the mite has been removed or fallen off.

• The proteolytic enzymes and hypersensitivity reaction lead to severe pruritis and irritation.
• The dog persistently licks or scratches.
• Marked hyperaemia at site(s) of attachment with formation of red nodules and wheals often up to 2 cm, with exudation of tissue fluid to form a yellow crust over very reddened skin.
• If the yellow exudate crust is lifted, the mites are attached underneath.
• The 'feeding tunnel' in the dermis becomes surrounded with inflammatory cells.
• Secondary infection can lead to pustule formation.

Other Host Effects

• Larva attaches to host for up to 4-5 days and feeds on host's tissue fluids.
• Attachment and feeding is aided by cytolytic enzymes that dissolve tissues.
• A 'feeding tunnel' is formed of a hardened hyaline material secreted by the mite and this penetrates through the epidermis.

Control

Control via animal

Treatment

• Remove any visible mites.
• Treat with acaricide.
• Anti-inflammatory therapy is useful as the hypersensitivity reaction persists after the mites have been removed.
• Antibacterial therapy Therapeutics: antimicrobial drug may be useful if secondary infection present.

Prevention

• Restrict access to known infested areas in late summer/autumn.
• Apply repellents if dog is known to frequent known infested soils in the autumn (efficacy seems variable and also will depend on the dog not licking off the repellent).

Control via chemotherapies

Acaricides

• Amitraz Amitraz.
• Dichlorvos/fenithrothion (not available in US).
• Phosmet.
• Fipronil Fipronil.
• Permethrin spot-on.

Repellents

• Benzyl benzoate (unlicensed use in dog).
• DEET (NN-diethyl-m-toluamide) (not available in UK).
• Can also apply long-acting collars (amitraz, diazonin, chlopyirifos) (not available in UK).

Diagnosis

Further Reading

Publications

Refereed papers

• Recent references from PubMed and VetMedResource.