Mites (fur and ear)

Prevalence
  • External parasites are seen occasionally, especially if a break in the barrier with wild mice/rats entering the facility occurs
  • Infestation is common and persistent in contemporary laboratory rodent colonies
 
Significance
  • If infestation and clinical signs and lesions are severe - animals are not suitable for research
  • Mites may induce changes in the immunological reactions of the host animal which may impact research and compromise experimental results
  • Sequelae may still interfere with research even when infestation is inapparent
  • Zoonotic nature of some mites may also be a health hazard to workers
Disease
  • Most commonly isolated from the dorsal regions near the tail, between the scapulae or on the head, neck or flank (also common on the ventral abdomen, inguinal areas, and cheeks)
  • Clinical signs:
    • inflammation, lymphadenopathy, erythema, ruffled fur, scratching and mild alopecia to severe pruritus, self-mutilation, and ulcerative dermatitis often complicated by bacterial infection
  • General malaise conditions - weight loss, decreased fertility, and shortened lifespan
  • Burdens vary depending on length of infestation, mouse strain and age, and conspecific grooming
  • Nude and hairless animals are not susceptible to fur mites and immunocompetent animals mount a robust humoral response (effective treatment is imperative)
Transmission
  • Direct contact with infested animal and/or through the environment of that animal (soiled bedding or partially cleaned cages)
  • If presence was overlooked during quarantine, mites could enter the facility on imported animals and spread rapidly and inadvertently
  • Mites will infect neonates as soon as pelage start to grow at about 1 week of age
Diagnosis
  • Preferred - Sticky tape preparations (pelage, perianal region and neck pluck)
  • Direct examination of the pelt with or without magnification
  • Pulled hair tufts
  • Skin scrape of head and dorsal thoracolumbar regions
  • Ear swabs of rabbits for identification of Psoroptes cuniculi (speciation is possible on light microscopy)
  • PCR
Strains
  • Fur mites:
    • Mice: Demodex musculi; Myocoptes musculinus; Myobia musculi; Radfordia affinis
    • Rats: Ornithonyssus bacoti (zoonotic); Radfordia ensifera; Demodex musculi;
    • Guinea Pigs: Chirodiscoides caviae; Trixacarus caviae (zoonotic); Demodex musculi;
    • Rabbits: Cheyletiella parasitivorax (zoonotic); Demodex musculi
  • Ear mites:
    • Rabbits: Psoroptes cuniculi
Duration
  • Animals may maintain infestation for a long period of time without treatment.
 
Durability
  • Physical cleaning of surfaces should remove mites
  • Nonviable eggs, empty casings and mite parts can remain on coat for months post treatment
Screening
  • At the least, prior to the introduction of new animals.
Prevention and Control
  • Pathogen exclusion, quarantine and testing, and control by effective treatment methods and periodic monitoring is important
  • An Avermectin class drug in treatment has powerful broad-spectrum antiparasitic activity against most endo- and ectoparasites
  • Rederivation is an option
 
Reading
  • S. T. Bino Sundar, T. J. Harikrishnan, Bhaskaran Ravi Latha, S. Gomathinayagam, M. R. Srinivasan, and S. Ramesh. Incidence of fur mite infestation in laboratory rodents. Journal of Parasitic Diseases, 2017, 41(2): 383–386
  • Rodolfo J. Ricart Arbona, Neil S. Lipman, Elyn R. Riedel, and Felix R. Wolf. Treatment and Eradication of Murine Fur Mites: I. Toxicologic Evaluation of Ivermectin-Compounded Feed. Journal of the American Association for Laboratory Animal Science, 2010, 49(5): 564–570
  • Rodolfo J. Ricart Arbona, Neil S. Lipman, and Felix R. Wolf. Treatment and Eradication of Murine Fur Mites: II. Diagnostic Considerations. Journal of the American Association for Laboratory Animal Science, 2010, 49(5): 583–587
  • Dean H. Percy & Stephen W. Barthold. Pathology of Laboratory Rodents and Rabbits (Third Edition), 2007
  • Infectious Diseases of Mice and Rats. National Research Council, 1991