Solving the Rabbit Neurology Puzzle: Genomic Detection of Encephalitozoon cuniculi

Solving the Rabbit Neurology Puzzle: Genomic Detection of Encephalitozoon cuniculi

By Mark Yacoub, PhD

At MiDOG Animal Diagnostics, we recently identified the microsporidian pathogen Encephalitozoon cuniculi from a rabbit urine sample using next-generation sequencing (NGS). The finding highlights both the diagnostic challenges posed by this organism and the growing role of genomic technologies in detecting pathogens that can be difficult to confirm using conventional testing methods.

In this post, we review the clinical significance of E. cuniculi, recommended diagnostic samples, and how metagenomic sequencing can improve detection.

What is Encephalitozoon cuniculi?

Encephalitozoon cuniculi is an obligate intracellular microsporidian fungal pathogen that infects a wide range of mammals, most notably domestic rabbits. While historically considered a protozoan parasite, recent genetic discoveries have revealed that this strange organism is in fact a fungal pathogen. Many rabbits remain asymptomatic carriers, however, infection can lead to significant disease affecting the neurologic, renal, and ocular systems.

Transmission typically occurs via ingestion or inhalation of spores shed in urine. Following infection, spores disseminate through the bloodstream and establish infection in target tissues.

Clinically important sites of infection include:

• Central nervous system – encephalitis and vestibular disease
• Kidneys – granulomatous interstitial nephritis
• Eyes – phacoclastic uveitis and cataracts

Because clinical signs overlap with other conditions, confirming infection can be challenging.

Clinical Presentation in Rabbits

Infected rabbits may present with a range of signs, including:

Neurologic signs

• Head tilt
• Ataxia
• Rolling or vestibular dysfunction
• Seizures in severe cases

Renal disease

• Polyuria/polydipsia
• Weight loss
• Chronic renal insufficiency

Ocular disease

• Lens rupture
• Cataracts
• Severe uveitis

Importantly, seropositivity is common in healthy rabbits, meaning that antibody testing alone does not confirm active disease.

Diagnostic Challenges

Diagnosing E. cuniculi infection often requires integrating clinical findings with laboratory data.

Common diagnostic methods include:

Serology

• Detects antibodies
• Indicates exposure but not necessarily active infection

PCR

• Detects pathogen DNA
• Sensitivity depends heavily on sample type and timing

Histopathology

• Demonstrates characteristic granulomatous lesions
• Requires tissue sampling

However, intermittent shedding and low organism burden can limit the sensitivity of targeted assays.

Best Sample Types for Detecting Encephalitozoon cuniculi

Selecting the appropriate specimen can improve diagnostic yield.

Recommended sample types include:

Urine

• One of the most useful samples
• Spores are shed via the kidneys
• Shedding may be intermittent

Lens material / ocular samples

• Particularly valuable in rabbits with phacoclastic uveitis

Brain or kidney tissue

• Useful for definitive diagnosis in postmortem cases

Whole blood

• May detect systemic infection but sensitivity is variable

Because shedding patterns vary, combining sample types can improve detection.

Rabbit neurologic cases often present with overlapping clinical signs—comprehensive microbial screening helps uncover underlying infectious contributors

Next-generation sequencing (NGS) offers a powerful complementary approach for detecting pathogens such as E. cuniculi.

Unlike targeted PCR assays, genomic sequencing does not require prior suspicion of a specific pathogen. Instead, it analyzes all nucleic acids present in the sample, enabling simultaneous detection of bacteria, viruses, fungi, and parasites.

For pathogens like E. cuniculi, NGS offers several advantages:

Broad detection capability
Can identify rare or unexpected organisms that may not be included in targeted panels.

Improved detection in complex samples
Can detect pathogen DNA even when organism load is low.

Comprehensive pathogen screening
Helps rule in or rule out coinfections that may contribute to clinical disease.

In the recent MiDOG case, genomic sequencing detected E. cuniculi DNA directly from a rabbit urine sample, demonstrating the utility of metagenomic diagnostics for identifying microsporidian infections.

Integrating Genomic Diagnostics into Clinical Practice

For veterinarians managing rabbits with neurologic, renal, or ocular disease, genomic diagnostics can provide an additional layer of information when traditional testing is inconclusive.

Situations where NGS may be particularly helpful include:

• Unexplained neurologic disease
• Chronic renal disease with unclear etiology
• Ocular disease suggestive of E. cuniculi
• Cases with negative or conflicting PCR and serology results

By enabling unbiased pathogen detection, genomics can help clinicians reach a diagnosis more quickly and guide appropriate treatment and management.

Learn More

You can view the full MiDOG Animal Diagnostics report for this case here:
Click Here to View Example Report

If you have questions about submitting samples or using genomic testing in exotic animal cases, the MiDOG team is always happy to help.

References:

1. Harcourt‐Brown, F. M., & Holloway, H. K. R. (2003). Encephalitozoon cuniculi in pet rabbits.Veterinary Record, 152(14), 427-431.
2. Khan, I. A., Moretto, M., & Weiss, L. M. (2001). Immune response to Encephalitozoon cuniculi infection. Microbes and infection, 3(5), 401-405.
3. Latney, L. T. V., Bradley, C. W., & Wyre, N. R. (2014). Encephalitozoon cuniculi in pet rabbits: diagnosis and optimal management. Veterinary medicine: research and reports, 169-180.
4. Magalhães, T. R., Pinto, F. F., & Queiroga, F. L. (2022). A multidisciplinary review about Encephalitozoon cuniculi in a One Health perspective. Parasitology research, 121(9), 2463-2479.