E.Cuniculi

Encephalitozoon cuniculi (E. cuniculi)

Encephalitozoon cuniculi (EC) is a eukaryotic, unicellular, spore-forming, obligate intracellular microorganism of the phylum Microsporidia. Domestic rabbits (Oryctolagus cuniculus) are its primary host, though the parasite is also zoonotic and can infect other mammals, including immunocompromised humans. The organism is shed primarily in urine and infects the kidneys, central nervous system (CNS), and eyes.

Etiology (cause)

E. cuniculi is transmitted through ingestion or inhalation of infective spores shed in urine. Vertical (transplacental) transmission has also been documented. Once ingested, the spores invade host cells, where they replicate and form new spores.

The infection outcome depends largely on host immunity. Immunocompetent rabbits often remain subclinical or show only mild signs, whereas immunocompromised or stressed individuals may develop severe, sometimes fatal, disease.

• Source: Doboși AA, Bel L, Paștiu AI, Pusta DL. *A Review of Encephalitozoon cuniculi in Domestic Rabbits (Oryctolagus cuniculus)—Biology, Clinical Signs, Diagnostic Techniques, Treatment, and Prevention.* Pathogens. 2022;11(12):1486. doi:[10.3390/pathogens11121486](https://doi.org/10.3390/pathogens11121486)

Clinical Signs

The clinical presentation is highly variable and depends on which organ systems are most affected.

• **Neurological signs (most common):** torticollis (head tilt), ataxia, nystagmus, paresis or hemiparesis, tremors, seizures, longitudinal rolling.
• **Renal signs:** polyuria, polydipsia, weight loss, azotemia, chronic renal insufficiency, cystitis.
• **Ocular signs:** phacoclastic uveitis (from rupture of the anterior lens capsule), cataracts, secondary glaucoma.

Many rabbits remain asymptomatic or develop chronic subclinical infections, making ante-mortem diagnosis challenging.

• Sources:

 - Doboși AA, et al. *Pathogens.* 2022;11(12):1486. doi:[10.3390/pathogens11121486](https://doi.org/10.3390/pathogens11121486)  
 - Škrbec M, et al. *Encephalitozoon cuniculi Infection of Domestic Rabbits (Oryctolagus cuniculus) in Slovenia between 2017 and 2021.* Pathogens. 2023;12(4):516. doi:[10.3390/pathogens12040516](https://doi.org/10.3390/pathogens12040516)

Treatment, Prevention, and Control

• **Treatment:**

 - Fenbendazole (Safeguard®) at 20 mg/kg orally once daily for 28 days is the most widely used treatment. This reduces clinical signs and spore shedding but does not always reverse existing damage.  
 - Clinical signs (neurological or renal damage) are often irreversible. Severely affected rabbits may not recover, and culling is considered in breeding programs.  
 - Supportive care (NSAIDs, fluids, assisted feeding) may be indicated for symptomatic animals.  

• **Prevention and Control:**

 - Prevent exposure to urine from infected rabbits.  
 - Do not use infected animals in breeding colonies.  
 - Routine testing of breeding stock is recommended in rabbitries.  
 - Good sanitation and husbandry practices reduce transmission risk.  

• Sources:

 - Doboși AA, et al. *Pathogens.* 2022;11(12):1486. doi:[10.3390/pathogens11121486](https://doi.org/10.3390/pathogens11121486)  
 - Škrbec M, et al. *Pathogens.* 2023;12(4):516. doi:[10.3390/pathogens12040516](https://doi.org/10.3390/pathogens12040516)  
 - [Encephalitozoon cuniculi – ScienceDirect Topic](https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/encephalitozoon-cuniculi)  

References

• Doboși AA, Bel L, Paștiu AI, Pusta DL. *A Review of Encephalitozoon cuniculi in Domestic Rabbits (Oryctolagus cuniculus)—Biology, Clinical Signs, Diagnostic Techniques, Treatment, and Prevention.* Pathogens. 2022;11(12):1486. doi:10.3390/pathogens11121486. PMID: [36558820](https://pubmed.ncbi.nlm.nih.gov/36558820)
• Škrbec M, Dovč A, Hrženjak NM, Slavec B, Žlabravec Z, Kočar N, Rojs OZ, Račnik J. *Encephalitozoon cuniculi Infection of Domestic Rabbits (Oryctolagus cuniculus) in Slovenia between 2017 and 2021.* Pathogens. 2023;12(4):516. doi:10.3390/pathogens12040516. PMID: [37111402](https://pubmed.ncbi.nlm.nih.gov/37111402)
• Encephalitozoon cuniculi. In: **The Evolution of the Genome.** 2005. ScienceDirect. [Link](https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/encephalitozoon-cuniculi)