Mites

PARASITES ARACHNIDA

Astigmata Introduction

Mites are one of the most successful and divers vertebrate group. The species of veterinary importance are parasitic, although a few non-parasitic mites are also important, such as orbatid and forage mites.

Mites are very small, on average under 0.3mm in length and for this reason often go unnoticed. They spend the majority of their life cycle on the host and cause mange.

The taxonomy of mites is complex as there are over 8 families. In this article the families are split according to their location on the host into sub-surface (burrowing) and surface (non-burrowing) mites.

Burrowing Mites

Sarcoptidae

Sarcoptes

Recognition

• Small, round mite

• Short legs
  • Project only a short distance from body margin

• Dorsal spines
  • Arranged in rows

• Dorsal spines

• Terminal anus

Life Cycle

• 3 weeks life cycle

• Female lays eggs in epidermis in an egg laying pocket

• Female feeds on liquid ozzing from damaged tissue

• The eggs hatch in 1 week

• 6 legged larvae released which crawl to skin surface

• The larvae then burrow back into the epidermis into moulting pockets

• Larvae moult to become 8 legged nymphs

• Nymphs moult twice before becoming adults

• Adult males emerge and look for females for mating

Transmission

• Close contact

• Adults and larvae can be transferred from one skin surface to another

Pathogenesis

• Erthema with papule formation

• Scale and crust formation
  • Alopecia

• Intense pruritis for one week
  • Self-inflicted trauma
  • Scab formation

• Wrinkling anf thickening of skin

• Hypersensitivity may develop
  • Rash develops

• Sarcoptes scabiei
  • In scabies

• Strains of S. scabiei can be passed between different animals and cause clinical signs although the infection is likely to resolve spontaneously and be unlikely to establish

Sarcoptic Mange

Diagnisis

• Skin scraping until capillary blood appears
  • Adults, eggs, immature mites and faecal pellets looked for

• Place material on a microscope slide

• Add 10% KOH

• Warm slide over bunson flame

Treatment

• Acaricide
  • For more information on acaricides click here

• Treat both infected and in-contact animals

• Older products have to be given in repeat treatments

• Avermectins are effective in farm animals

• Selamectin is available as a good spot-on for dogs

• Control for pigs:
  • Treat sows before entering the farrowing pen
  • Treat boars at 6 month intervals

Knemidocoptes

• K. mutans
  • Scaly leg in poultry

• K. pilae
  • Scaly leg in psittacines

Demodex

• Demodex in demodicosis

Notoedres

• Notoedres cati in notoedric skin infestation

Non-Burrowing Mites

Psoroptes

• In psoroptic skin infestation

Psoroptes cuniculi

• Parasite of rabbits
• Epizootiology
  • Common among conventional rabbits; transmitted via contact.
• Clinical
  • The ears are painful and itch intensely; affected rabbits shake their heads and scratch their ears. The inner surfaces of the pinnae are covered with brown, scaly, fetid material, and the skin beneath is raw. Mites are grossly visible.
• Pathology
  • Histologically, there is chronic erosive and proliferative eosinophilic dermatitis. The mites are non-burrowing and thus are found only in the exudate, not in the tissue.
• Diagnosis
  • Appearance; examination for mites (low magnification).
• Control
  • Infestations are difficult to eliminate from a colony, although ivermectin is said to be effective.

Chorioptes bovis

• In skin infestation

Otodectes cynotis

• in otodectic skin infestation

Cheyletiella sp.

• Cheyletiella yasguri
• In skin infestation

Trombicula

• In skin infestation