New pathogenic virus discovered by IDEXX BioAnalytics - 32% of rat models affected*

New virus discovered – what does it mean for your facility?

The newly discovered Rat polyomavirus 2 (RPyV2) can cause severe disease and mortality in immunodeficient rats. No clinical signs have been observed in immunocompetent rats but a possible impact on research data in apparently healthy animals is not excluded. Population surveys found antibodies to this novel virus in 32% of immunocompetent rats used in biomedical research in North America.

These high prevalence rates are common for newly discovered viruses. This of course happens because there was no exclusion possible before. The same happened with the discovery of Murine Norovirus (MNV). As a facility manager, you might think that prevalence would not be a sufficient reason to test but the main reason to check for this new virus is because of its possible impact on research data.

This post is to tell you all about the newly discovered Rat polyomavirus 2, what the clinical signs are, how to make sure your facility has not been exposed and what the possible impact is on research data.


Quick overview:

RPyV2 is an epitheliotropic polyomavirus

Diagnosis of RPyV2 infection can be made by serology for immunocompetent rats and faecal PCR for immunodeficient rats.

Virus is shed primarily in respiratory and salivary secretions. Shedding is prolonged in immunodeficient rats and transient in immunocompetent rats.

Virus transmission occurs by direct contact. Fecal-oral and sexual transmission may also occur.

Prevalence of RPyV2 infection in rat research colonies in North America is 32%

Test available
IDEXX BioResearch is the only company that can offer health monitoring specifically to detect Rat polyoma virus 2, both by serology (serum or Opti-Spot(tm)) and Real-PCR. The only thing you need is 2 fecal pellets (immunodeficient rats) or an Opti-Spot(tm) strip (immunocompetent rats) and we can do the test for you.


How was the virus discovered?

Due to increasing signs of disease and death among their females and pups in a SCID rat colony, a university asked us to diagnose some of their models.

We ran our full diagnostic profiles and used the most advanced technologies, but initial results came back negative. We than assembled a multidisciplinary team of IDEXX experts to investigate. The vivarium staff, together with experts from the microbiology, PCR, Serology and the Pathology department, combined their expertise and found the cause.

Our histological examination demonstrated viral inclusions in multiple tissues; most notably, within epithelial cells of the respiratory tract and salivary glands.

Finally, deep sequencing identified a novel virus that is unrelated to any known virus that infects rats, mice, or other animals. The novel virus is of the family Polyomaviridae and was provisionally named Rattus norvegicus polyomavirus 2 (RPyV2).

After this discovery it was a top priority for us to develop accurate assays to detect this specific virus. The research teams developed and validated these new PCR and serology assays for the novel Rat polyomavirus 2 (RatPyV2).


What is the disease expression?

What are the clinical signs to look out for regarding Rat polyomavirus 2?

The clinical signs can range from mild to severe as described below but can be also aspecific. Therefore, for an accurate diagnosis and for screening purposes it is essential to perform a serological or PCR test.

Clinical signs in immunodeficient rats included:

  • Emaciation
  • Hunched posture
  • Dyspnea
  • Mortality of dams and pups

Evaluation of tissues revealed:

  • Severe degeneration of the salivary glands
  • Severe degeneration of the exorbital lacrimal glands
  • Severe degeneration of Harderian glands
  • Viral inclusion in the epithelium of the respiratory and reproductive tracts

Histological examination

Histological examination revealed severe atrophy of the salivary glands, the exorbital lacrimal glands and Harderian glands.


May this virus impact your research?

The virus is capable of causing severe clinical signs in immunodeficient rats. No clinical signs have been observed in immunocompetent rats but we do not know yet if it may have a secondary impact on research data because of immunological response or being oncogenic as many viruses of the same family.


Does it affect mice?

Currently there are no signs that the Rat polyomavirus 2 is capable of infecting mice. 


How to find out if this virus is present in your facility?

To date, population surveys in North America labs, found antibodies to this virus in 32% of rats.

  • A serological test on immunocompetent animals or faecal PCR in immunodeficient animals is available at IDEXX BioResearch.
  • PCR on immunocompetent rats is not recommended because of the transient shedding.



* in our US laboratory setting

The IDEXX BioResearch team