Encephalitozoon cuniculi (Nosema cuniculi, Nosema muris, Infectious motor paralysis)

Prevalence
  • Infects a variety of mammalian hosts
  • Extremely common in the domestic rabbit
  • Relatively rare in other lab animal species
 
Significance
  • Usually low in studies involving rats and mice
  • Significant in studies involving passage of transplantable tumours and other materials
  • May alter humoral immune responses
Disease
  • Obligate intracellular, eukaryotic fungus within the microsporidian phylum
  • Spores evident as gram-positive ovoid using tissue Gram stains (carbol fuchsin)
  • Following extrusion of sporoplasm from spore coat, sporoplasm may invade susceptible host cell
  • Target organs of high blood flow – moderate to severe lesions in lung, liver, and kidney (occasionally myocardium, heart and brain lesions also evident)
  • Lesions frequently confined to kidney – focal, irregular, depressed areas 1-100mm in diameter
  • On cut surface, indistinct, linear, pale gray-white areas may extend into underlying cortex
  • Characterized by the presence of a coiled polar filament in the mature spore stage
  • Serum antibody titers detectable by 3-4 weeks – high titers by 6-9 weeks
  • Frequently subclinical – rabbits may present:
    • neurological signs - head tilt, ataxia, vestibular signs, behavioral changes
    • uveitis and cataracts in young rabbits
Transmission
  • Mainly horizontal – orofaecal route, vertical - transplacentally
  • Through organisms excreted in urine
  • Rabbits – readily infected experimentally by oral or respiratory route
  • Iatrogenic transmission through contaminated needles
  • Known to be contaminant of transplantable tumours
  • Humans susceptible to zoonotic infection – severe disease in immunosuppressed
Diagnosis
  • Preferred - ELISA testing of serum or DBS samples – results should always be confirmed by clinical history and/or histopathology
  • Identification of characteristic lesions
  • Demonstration of organisms in tissue sections
  • Readily differentiated from protozoal infections by tissue tropisms and staining properties
  • Differential diagnosis for rabbits – otitis interna, toxoplasmosis, and Baylisascaris migration
Strains
  • Mice - strain differences in susceptibility:
    • resistant - BALB/c, A/J, SJL
    • susceptible - C57BLI6, DBA/1, 129/J
    • lethal in nude mice
Duration
  • Chronic, usually latent infection (may be present for > 1 year)
  • Spores seen in urine at 1 month – excreted in large numbers up to 2 months
  • Spore shedding terminated by 3 months
  • Spores survive less than 1 week at 4°C, viable for at least 6 weeks at 22°C
Durability
  • Spores are resistant to drying for up to 4 weeks
  • Use of sporicidal disinfectants and high temperatures thought to be effective
Screening
  • Common and potentially deadly pathogen of rabbits which has prompted growing concern and increased demand for regular screening.
Prevention and Control
  • No known effective chemotherapeutic agents
  • Serologic testing and selection of antibody free breeding stock
  • Caesarean rederivation, improved sanitation and barrier maintenance in rats and mice
  • Mice and rats should not be housed near known infected rabbit stocks
Reading
  • Stephen W. Barthold, Stephen M. Griffey, & Dean H. Percy. Pathology of Laboratory Rodents and Rabbits (Fourth Edition), 2016
  • Infectious diseases of Mice and Rats. National Academy Press: ISBN 0-309-03794-8