Overview

• Encephalitozoonosis is now called microsporidiosis.
• Obligate intracellular spore forming parasite found in a wide array of domestic mammals.
• Infection with the parasites Encephalitozoon cuniculi and other species.
• Encephalitozoon cuniculi has been divided into three strains-I rabbit type, also detected in man, II mouse type, and III dog type.
• Affects brain, kidney, liver, intestine, eye, lungs.
• Uncommon in the United States but may be more prevalent in other countries.
• Organ systems affected:
  • Neurologic
  • Renal/Urologic
  • Hepatobiliary
  • Gastointestinal
  • Ocular
  • Hemic/lymphatic/immune

Signalment

• Dogs and cats
• No sex or breed predilection
• Young animals

Signs

• Appears a few weeks postpartum
• Stunted growth
• Ill-thrift
• Depression
• Inappetance and weight loss
• Nephritis progressing to renal failure
• Neurologic abnormalities-convulsions, viciousness, biting, vocalization, ataxia, circling, hypermetria
• Ocular abnormalities-including cataracts, uveitis, and blindness

Causes & Risk Factors

• Transmitted through ingestion, inhalation, transplacentally or rarely through epithelium after trauma.
• Infectious spores are excreted in urine, feces, and mucus.
• Can be ingested from tissues of infected rabbits or mice.
• Kennel housing is a risk factor.

Differential Diagnosis

• Rabies
• Canine distemper
• Canine herpesvirus
• Neosporosis
• Toxoplasmosis
• Hydrocephalus
• Feline panleukopenia
• Septicemia

CBC/Biochemistry/Urinalysis

• Normochromic, normocytic anemia
• Lymphocytosis and monocytosis
• High serum ALT and ALP expected
• Azotemia-variable
• Hyperproteinemia
• Urinanalysis-haematuria and proteinuria

Other Laboratory Tests

• Serology (immunofluorescent antibody staining, complement fixation, ELISA, and Western immunoblot assays)-blood and CSF (IFA >100 or ELISA >800).
• PCR-highly specific and sensitive but not routinely available in veterinary diagnostic labs.
• Histopathology-brain, lung, kidney, placenta, eye. Difficult to identify parasites by light microscopy with H&E stains. Trichrome stain, Calcofluor white fluorescent stain or Fungi-Fluor stain can be used to identify organisms.
• Cytology-aqueous humor and lens material (low sensitivity).
• Urine sediment-special stains may identify parasite spores.

Imaging

May be contributory but not diagnostic.

Diagnostic Procedures

CSF-pleocytosis, increased protein. May see organisms with special stains.

Pathologic Findings

• Urogenital-lymphocytic–plasmacytic interstitial nephritis, hemorrhagic cystitis, renal cortical cysts, or infarcts.
• Neurologic-lymphocytic-plasmacytic meningoencephalitits, thrombosis and encephalomalacia, perivascula cuffing with occasional intracellular parasitic cysts containing Gram-positive spores.
• Hepatic-multifocal microgranulomatous hepatitis.
• Respiratory-interstitial pneumonia.
• Cardiac-fibronous pericarditis.
• Gastrointestinal-regional enteritis.
• Other-reticuloendothelial hyperplasia of the spleen and hyperplasia of the bone marrow. Necrotic, tortuous medium-sized to small arteries (polyarteritis nodosa).

Drug(s)

• No treatment has been reported. Try benzimidazoles, particularly albendazole (400 mg q12h for >3 weeks), because they work in mice and humans.
• Trimethoprim or pyrimethamine and sulphonamides, alone or in combination, with albendazole have been effective in humans with disseminated infections.

Contraindications/Possible Interactions

N/A

Prevention/Avoidance

• Sanitation-important; accomplish with 70% ethanol, hydrogen peroxide, 10% formalin and 10% bleach.
• Spores survive in humid environments at ambient temperatures.

Expected Course and Prognosis

A number of patients recover without further signs if neither the renal nor the cerebral manifestation becomes severe.

Zoonotic Potential

• Potential risks to humans, especially the immunosuppressed and children.
• Single report of possible direct transmission between dog and child.

Abbreviations

• ALP = alkaline phosphatase
• ALT = alanine aminotransferase
• CSF = cerebrospinal fluid
• PCR = Polymerase chain reaction