Emerging Disease Agents

Murine Norovirus Information

Murine Norovirus 1 (MNV-1) was initially reported in 2003 and currently there seem to be more questions than answers regarding its potential effects, if any, on research. Overt disease apparently only occurs in very few strains of immunoincompetent mice, e.g. mice lacking interferon receptors. The authors reported that mice lacking both interferon aß and interferon γ receptors were very susceptible to lethal infection demonstrating that interferons are needed for resistance to MNV-1. STAT1 is involved in signaling through both IFN aß and IFNγ receptors. RAG/STAT-/- mice inoculated with gradient purified virus showed encephalitis, cerebral vasculitis, pneumonia, meningitis and hepatitis (2).

Development of a serologic test was reported in 2005 by the RADIL laboratory at the University of Missouri, Columbia. Additional tests have been developed by other companies/institutions. See Links Below. The agent has probably been around for many years, but not recognized. Comparative Medicine tests for Murine Norovirus and we are aware of its presence in some mouse colonies at UNMC but no adverse effects have been observed or documented. It is noteworthy that other members of the Calicivirdae family are pathogenic in humans (gastroenteritis) and are highly resistant to inactivation. Further research and clinical observations on the agent should be productive.


  1. ACLAM Newsletter March 2006.
  2. Karst, MK, et al.: STAT1-Dependent Innate Immunity to a Norwalk-Like Virus.
  3. Science 299: 1575-1578, 2003.Hsu, CC, et al. Development of a Microsphere-Based Serologic Multiplexed Fluorescent Immunoassay and a Reverse Transcriptase PCR Assay to Detect Murine Norovirus 1 Infection in Mice. Clin and Diag Lab Immunol. 12:1145-1151, 2005.

The following links provide additional information about Murine Norovirus. If you have concerns regarding Murine Norovirus, please contact Dr. Steve Dixon, Dr. Noel Johnson or Dr. Tami Wells at 559-4034.

Rodent Helicobacter spp. Information

Many new rodent helicobacter species have been discovered as emerging disease agents within the last 5-10 years.

Detection, eradication, and research implications of Helicobacter infections in laboratory rodents Whary, MT , Fox, JG.  

Abstract from Lab Animal (NY). Vol 35, No7, July/August 2006

"Researchers first isolated and characterized Helicobacter hepaticus in 1994 as a cause of hepatitis that progressed to hepatocellular carcinoma in A/JCr mice. During the past decade, isolation and characterization of additional novel helicobacters from rodents has continued. In addition to causing overt disease, rodent helicobacter infections are important because intercurrent disease in select models will confound research data. Emerging evidence suggests that inflammatory responses to enterohepatic helicobacter infections may alter host responses to other experimental stimuli in unanticipated ways. Additionally, scientists have experimentally infected a variety of inbred mouse strains and genetically engineered mice with a variety of Helicobacter spp. isolated from rodents, birds, and higher mammals (including humans) to develop animal models of gastrointestinal diseases as well as idiopathic human disease syndromes. This review highlights current information about helicobacter infections in laboratory rodents and provides recommendations for the detection and eradication of these infections. The authors discuss the impact of subclinical and clinical disease and offer recommendations for managing helicobacter-free rodent colonies."

Various helicobacter species have been detected in rodents at UNMC and apparently have been endemic in the colonies for many years. Helicobacter free rats and mice are available from commercial vendors. Strict husbandry practices are required to maintain rodents free of helicobacter. However, with caging systems and husbandry practices in use at UNMC, helicobacter free animals can be maintained. Currently infected colonies can be re-derived, at some cost, to be free of helicobacter. If you require helicobacter-free rodents for your research, please contact Dr. Noel Johnson or Dr. Tami Wells at 559-4034.

Update: Charles River Pinpoints Pneumocystis carinii as the Causative Agent for "RRV"

September 2, 2010 - Charles River continually performs research studies on many aspects of laboratory animal science. One such study has led to the conclusion that Pneumocystis carinii (Pc) is the causative agent for interstitial pneumonia in laboratory rats, previously known by the working name "rat respiratory virus" or "RRV". This work has been submitted for publication and will be presented at the 61st AALAS National Meeting. The presentation, "Determination of Optimal Sample Types and Time Points for the Detection of Pneumocystis carinii in Rats by Real-Time PCR", is part of the Laboratory Investigations 2 platform session, and is scheduled for Wednesday, October 13th at 3:15 PM (Program Number PS75).

History of Pc/"RRV" interstitial pneumonia in laboratory rats

First appearing in literature in the mid-1990s, reports described an apparently novel and prevalent pulmonary disease which compromised inhalation toxicology studies in immunocompetent laboratory rats. This entity was characterized by lymphohistiocytic interstitial pneumonia and perivascular lymphocytic cuffing throughout the lung. More recently, researchers at Charles River published histopathologic criteria for diagnosis and described the consistent progression of lesions over time [Albers et al., Vet. Pathol. 46 (5), 992-9 (2009)]. This and other observations have led many to conclude that the causative agent is transmissible.

Charles River research study overview

In order to investigate the etiological agent, Charles River researchers first established two consistent sources of infected rats within isolators. At predetermined times after exposure, specimens were collected from exposed rats and analyzed using molecular-based techniques to screen for novel viral sequences. As no viral sequences were detected, attention turned to non-viral etiologies.

When examining the lungs of athymic nude rats exposed to rats in the "RRV"-positive isolators, high levels of Pc were noted. Although Pc had not been found by PCR in affected tissues by other researchers, it was considered as a candidate in this study because it is a pulmonary agent present in the study isolators and absent from Charles River rat colonies, all of which are negative for "RRV".

A quantitative PCR study of Pc in "RRV" lesion-positive rat lungs demonstrated a strong association between Pc and the interstitial pneumonia; findings were confirmed by the detection of Pc in archived "RRV"-positive paraffin-embedded lung tissue. This study also found that the antibody response to Pc coincided with the appearance of the characteristic interstitial pneumonia and the decline of Pc populations. Based on the evidence, we propose that the causative agent of the histologic lesions lumped into the disease entity "RRV" is Pneumocystis carinii.

Health status and testing of Charles River rat colonies

All Charles River rat colonies worldwide are negative for Pc. These colonies have been negative for interstitial pneumonia lesions for more than two years, and are currently screened quarterly by histopathology for the presence of lung lesions. Elucidation of Pc as the causative agent of "RRV" does not change the colony status of Charles River animals or the frequency of screening, but only the name of the disease and the method by which the animals are screened. Histopathologic screening for "RRV" will be phased out in lieu of a combination of PCR and serology for Pc.

Diagnostic testing available for screening laboratory rat colonies

Charles River offers multiple diagnostic tools to screen for Pc:

  • NEW: Serology via Indirect Fluorescent Antibody (IFA) test*
  • TaqMan® PCR, both as an individual agent test and as part of the Charles River Prevalent Rodent Infectious Agent (PRIA) PCR Panel
  • Histology of lung tissue (if necessary)

*Note: Tests on additional serology platforms are in development.

Contact CRL

Your research has never been more important, which is why Charles River is committed to providing the critical resources that you need. If you have any questions or require further information, please contact us by Email or by phone at 1-877-274-8371 (US and Canada) or +800-3195-3430 (International) - our professional staff members are available to discuss your specific needs.

Related Information

* Infectious Agent Technical Sheet: Pneumocystis

Idiopathic Interstitial Pneumonia in Immunocompetent Mice - 2011
From the University of Missouri Research Animal Diagnostic Laboratory (IDEXX RADIL)

Idiopathic interstitial pneumonia has been identified in laboratory mice; now RADIL research suggests Pneumocystis murina may be a cause.

In 2010 RADIL scientists proved that Pneumocystis carinii is the etiologic agent for idiopathic interstitial pneumonia in immunocompetent rats(6), a disease previously thought to be caused by a putative viral agent referred to as rat respiratory virus (RRV)(1; 7; 8). Recent studies by RADIL scientists show that a similar parallel exists in immune competent mice between Pneumocystis murina and idiopathic interstitial pneumonia.

To investigate whether P. murina causes interstitial pneumonia in immunocompetent mice, C57BL/6 mice were dosed intranasally with P. murina or a 0.22 µm filtrate of the inoculum that excluded Pneumocystis and bacteria, but not viruses. Five weeks after inoculation, lungs from inoculated mice were evaluated for interstitial pneumonia using established criteria (1). Mild to severe interstitial pneumonia was seen only in P. murina-dosed mice (Figure 1). In addition, five weeks after inoculation, all P. murina-dosed mice were positive for Pneumocystis by PCR. (Table 1). These data show that lesions of idiopathic interstitial pneumonia are induced in C57BL/6 mice inoculated intranasally with P. murina and suggest that P. murina may be a cause of idiopathic interstitial pneumonia seen in clinical diagnostic samples.

Pneumocystis are single-celled fungal respiratory pathogens of mammals that are host species-specific (2-5) with Pneumocystis murina infecting mice and Pneumocystis carinii infecting rats.(9) Historically, Pneumocystis infections in rodents have been thought only to induce disease in immunodeficient hosts.(9)

RADIL currently provides PCR testing for P. murina and P. carinii and serologic testing for P. carinii. For more information or to discuss testing recommendations, please contact RADIL at 1-800-669-0825.


  1. Albers TM, Simon MA, Clifford CB. 2009. Histopathology of naturally transmitted "rat respiratory virus": progression of lesions and proposed diagnostic criteria. Vet Pathol 46:992-999.
  2. Aliouat EM, Mazars E, Dei-Cas E, Delcourt P, Billaut P, Camus D. 1994. Pneumocystis cross infection experiments using SCID mice and nude rats as recipient host, showed strong host-species specificity. J Eukaryot Microbiol 41:71S.
  3. Durand-Joly I, Aliouat el M, Recourt C, Guyot K, Francois N, Wauquier M, Camus D, Dei-Cas E. 2002. Pneumocystis carinii f. sp. hominis is not infectious for SCID mice. J Clin Microbiol 40:1862-1865.
  4. Gigliotti F, Haidaris PJ, Haidaris CG, Wright TW, Van der Meid KR. 1993. Further evidence of host species-specific variation in antigens of Pneumocystis carinii using the polymerase chain reaction. J Infect Dis 168:191-194.
  5. Gigliotti F, Harmsen AG, Haidaris CG, Haidaris PJ. 1993. Pneumocystis carinii is not universally transmissible between mammalian species. Infect Immun 61:2886-2890.
  6. Livingston RS, Besch-Williford CL, Myles MH, Franklin CL, Crim MJ, Riley LK. 2011. Pneumocystis carinii infection causes lung lesions historically attributed to rat respiratory virus. Comp Med 61:45-52.
  7. Riley LK, Purdy G, Dodds J, Franklin C, Besch-Williford C, Hook RR, Wagner JE. 1997. Idiopathic lung lesions in rats: Search for an etiologic agent. Contemp Top Lab Anim Sci 36:46.
  8. Riley LK, Simmons JH, Purdy G, Livingston R, Franklin C, Besch-Williford C. 1999. Research update: Idiopathic lung lesions in rats. ACLAD Newsletter 20:9-11.
  9. Weisbroth SH. 2006. Pneumocystis: newer knowledge about the biology of this group of organisms in laboratory rats and mice. Lab Anim (NY) 35:55-61.