Common Rodent Pathogens That Can Compromise Your Research

(Taken from The Companion Guide To Infectious Diseases of Mice and Rats

National Academy Press 1991)

Ectromelia ( Mouse Pox) - DNA virus, family Poxviridae. Affects mice only Clinical signs: Often latent. Variable signs include dermal papules or pustules, necrosis and sloughing of digits or limbs; sudden death. Pathology: Gross - Minimal changes to pale or red spots on liver; enlarge spleen initially (shrunken spleen in later stages); reddening of intestines. Microscopic - Minimal to severe necrosis of liver, pancreas and spleen; intestinal hemorrhage; lymphoid necrosis; cytoplasmic inclusion bodies may occur in skin and elsewhere. Control: Quarantine and testing of in mice and mouse tissues from sources other than commercial barrier facilities. Cesarean derivation of infected mouse stocks is not acceptable because intrauterine infection is known to occur in mice infected during pregnancy. Interference with research: Up to 100% of the animals in an experiment can die in an explosive outbreak. Manipulations that exacerbate ectromelia virus infections or promote epizootics include experimental infection with tubercle bacilli, x-irradiation, administration of various toxic chemicals, shipping, tissue transplantation, castration, and tumors. Ectromelia virus infection can alter phagocytic response. Conversely, procedures that decrease phagocytosis can increase susceptibility to ectromelia virus, e.g., large doses of endotoxin or splenectomy. More information.

Epizootic Diarrhea of Infant Mice (EDIM) - Unclassified. Affects mice and rats - Clinical signs: High morbidity; soiling about the tail from about 5 - 15 days of age. Soiling may last longer in severe cases and may be ephemeral in mild ones. Death occurs only late in the disease and is due to constipation and/or secondary bacteremia. Animals may be stunted through weaning and postweaning period. Pathology: Gross - distention of colon with light mustard-colored feces. Stomach is often distended. Microscopic - vacuolation of epithelial cells at tips of villi of small intestine, particularly in ileum. With proper stains, small acidophilic intracytoplasmic inclusions can be seen. More information.

H-1 Virus - Single-stranded DNA virus, family Parvoviridae, genus Parvovirus. Affects rats and hamsters - Clinical signs: Natural infections are inapparent. Pathology: There are no pathologic changes noted with natural infections. Interference with research: It might possible for H-1 virus to alter studies of fetal development or teratogenesis, but this has not been reported to occur as a result of natural infections. H-1 virus has been reported to cause hepatocellular necrosis when rats are subjected to liver injury by hepatotoxic chemicals, parasitism, or partial hepatectomy. H-1 virus has been reported to inhibit experimental tumor induction by adenovirus 12 and dimethylbenzanthracene in hamsters. More information.

Kilham Rat Virus - Single-stranded DNA virus, family Parvoviridae, genus Parvovirus. Affects rats only - Clinical signs: KRV infections rarely cause clinical disease. Pathology: Parvoviruses attack rapidly dividing cells. In newborn and young rats, KRV can couse jaundice, hemorrhagic infarction with thrombosis in multiple organs, and cerebellar hypoplasia. Interference with research: KRV can contaminate transplantable tumors and rat cell cultures, interfere with in vitro lymphocyte responses, suppress the development of Moloney virus- induced leukemia, and alter in vitro lymphocyte responses and cytotoxic lymphocyte activity. KRV has been known to induce interferon production. Immunosupression can cause clinical disease in inapparently infected rats. More information.

Lethal Intestinal Virus of Infant Mice (LIVIM) - Unclassified. Affects mice only - Clinical signs: High mortality; emaciation and death in animals usually before 10 days old. Some soiling may occur about the tail. Pathology: Gross - Small intestine greatly distended by gas and fluid; colon usually empty but may contain small amount of colorless watery to mucoid material. Microscopic - blunting of villi; epithelial multinucleate giant cells in intestine; intracytoplasmic inclusions. More information.

Lymphocitic Choriomeningitis (LCM) - RNA virus, family Arenaviridae, genus Arenavirus. Affects mice only - Clinical signs: Usually none. Characterized by immunologic tolerance and absence of symptoms; photophobia, conjunctivitis, spasticity and convulsions may be seen. Congenital or transplancental infections are most frequent and result in retarded growth and shortened life-span. Pathology: Gross - Clear fluid in pleural cavity; enlarged spleen. Microscopic - Variable; lesions may include lymphocytic infiltration of meninges, necrosis of liver and lymphoid tissue; glomerulonephritis occurs in aged animals. Interference with research: LCMV infection is an important zoonotic infection that can cause serious disease and sometimse fatality in personnel. LCMV is a frequent contaminant of biologic materials, including transplantable tumors of mice, hamsters, and guinea pigs; tissue culture cell lines; virus stocks, including leukemia viruses, distemper virus, rabies virus, and mouse poliomyelitis virus; and Toxoplasma gondii sublines. LCMV infection has an inhibitory effect on tumor induction by polyomavirus, Rauscher virus, and mammary tumor virus. More information.

Mouse Adenovirus (MAD) - DNA virus, two strains - MAd1 and MAd2. Affects mice and rats - Clinical signs: Natural infection does not cause clinical disease. Pathology: There are no pathologic lesions associated with infections of MAD-1, viral inclusions in intestinal mucosa are associated with MAD-2 infections. Interference with research: MAD-1 can produce extensive persistent lesions in the kidneys of adult mice and render them more susceptible to experimental Escherichia coli-induced pyelonephritis. More information.

Mouse Hepatitis Virus (MHV) - Single-straded RNA virus, family Coronaviridae, genus Coronavirus. Affects mice only - Clinical signs: In immunocompetent mice, MHV infections are usually subclinical. Infan mice of naive breeding populations can show diarrhea and high mortality when infected with the more virulent enterotropic MHV strains. Athymic (nu/nu) mice show progressive emaciation leading to debility and death. Pathology: Gross - Strains of MHV differ greatly in virulence and tissue tropism, and mouse strains differ greatly in susceptibility to MHV. These factors interact with host age and route and dose of virus inoculation to determine the outcome of infection. Mechanisms of host resistance to MHV infection are poorly understood. Mice are fully susceptible to the virus as neonates, but some strains acquire resistance at 2 - 3 weeks of age as lymphoreticular function matures. Cell-mediated immunity is important in the development of resistance. There are two major disease patterns: the respiratory pattern and the enteric pattern. In the respiratory pattern, infection involves the nasal passages and lungs; intestinal involvement is minimal. In the enteric pattern, infection is primarily restricted to the bowel. Interference with research: MHV has been reported to alter many experimental results. Examples are alterations in immune function and hepatic enzyme activities; inhibition of lymphocyte proliferative responses in mixed lymphocyte cultures and mitogen-stimulated cells; alteration of phagocytic and tumorcidal activity; increase of hepatic uptake of injected iron; and increase of susceptibility to other indigenous pathogens. More information.

Mouse Parvo Virus (MPV) - DNA virus, family Parvoviridae, genus Parvovirus. Affects mice only - Clinical signs: Usually latent infection; asymptomatic. Interference with research: Can inhibit tumor growth. Has been thought to be associated with intestinal hemorrhages and accelerated involution of hepatic hematopoiesis in the DBA/2 stain. More information.

Minute Virus of Mice (MVM) - DNA virus, family Parvoviridae, genus Parvovirus. Affects mice only - Clinical signs: Usually latent infection; runting may occur in neonatal animals following experimental inoculation. Pathology: Gross - none. Microscopic - In experimental infections, necrosis of the external germinal layer of the cerebellum reported in mice; necrosis of ependyma and choroid plexus may be seen in rats; intranuclear inclusions may be present in affected areas. Interference with research: MVM is a frequent contaminant of mouse leukemia virus preparations, transplantable tumors, hybridomas, and cell lines. More information

Mycoplasma Pulmonis (Infectious Catarrh) - Gram negative bacterium, family Mycoplasmataceae. Affects mice and rats - Clinical signs: Chattering in mice; snuffling and rales in rats; labored respiration; rarely head tilt, incordination, and circling; sporadic deaths. Pathology: Gross - Red to grey consolidation of lungs, often with abscesses; mucopurulent nasal exudate; purulent to caseous exudate in middle ears. Microscopic: Suppurative bronchitis and bronchopneumonia; peribronchiolar lymphoid cuffs and nodules; suppurative otitis media and sometimes labyrinthitis; mucopurulent rhinitis; occasional oophoritis and salpingitis in the rat. Interference with research: Morbidity and mortality caused by Mycoplasma Pulmonis can disrupt long-term studies. It alters ciliary function, cell kinetics, and immunity in the respiratory tract and changes the response to carcinogens. More information.

Pasteurella pneumotropica - Gram negative coccobacillus, family Pasteurellaceae. Affects most laboratory animal species - Infections are usually sub-clinical. When clinical infections do occur, signs in mice include conjunctivitis, panopthalmitis, dacryoadenitis, subcutaneous and cervical abscesses, bulbourethral gland infections, uterine infections, and otitis media, while signs in rats include opthalmitis, conjunctivitis, subcutaneous abscesses, and mastitis. Interference with research - There have been no reports of interference with research. More information

Pneumonia Virus of Mice (PVM) - RNA virus, family Paramyxoviridae, genus Pneumovirus. Affects mice and rats - Clinical signs: Natural infections are subclinical, except in immunocompromised hosts. Chronic illness, emaciation, and death have been reported in infected athymic mice. Pathology: No pathologic lesions have been associated with natural infections in immunocompetent hosts. Chronic pneumonia has been reported to occur in naturally infected athymic mice. Control: Cesarean derivation and barrier maintenance. Interference with research: There have been no reports of interference with research results. More information.

Polyoma Virus - Double-stranded DNA virus, family Papovaviridae, genus Polyomavirus. Affects mice only - Clinical signs: Usually inapparent; natural or experimental infection of neonatal mice causes stunted growth and tumor development after 1 - 6 months. Pathology: Gross - Usually none. Neonatal infections cause tumors in various sites, particularly parotid salivary gland. Microscopic - Variable. Tumors are most often pleomorphic sarcomas. Control: Cesarean derivation and barrier maintenance are usually effective in eliminating the virus because transplacental transmission does not occur. Interference with research: Polyomavirus can complicate research by contaminating tumor lines, stocks of other viruses, and other biologic materials that are passaged in mice. More information.

Reovirus - 3 - RNA virus, family Reoviridae, genus Reovirus. Affects mice and rats - Clinical signs: Natural infections are subclinical. Pathology: There are no pathologic changes associated with natural infections. Control: Cesarean derivation and barrier maintenance. Interference with research: Reovirus-3 is an occasional contaminant of and may interfere with research involving transplantable tumors and cell lines. More information.

Sialodacryoadenitis Virus (SDA) - RNA virus, family Coronaviridae, genus Coronavirus. Affects rats only - Clinical signs: Mice not affected. In rats, may be inapparent. Neck may be swollen and appear shortened; eyes may be bulging and red. Pathology: Gross - Enlarged submaxillary salivary glands; exopthalmos. Microscopic - Necrosis of ductular epithelium and inflammation of submaxillary and parotid salivary glands. Harderian glands undergo severe necrosis of tubuloalveolar epithelium followed by squamous metaplasia and inflammation. Interference with research: The virus can seriously complicate studies involving the eyes, salivary glands, lacrimal glands, or respiratory tract. More Information

Sendai Virus - RNA virus, family Paramyxoviridae, genus Paramyxovirus. Affects mice and rats - Clinical signs: Usually none; a latent infection which may be activated by intranasal instillations; labored respiration, chattering and variable mortality. Pathology: Gross - Partial or complete consolidation of lungs with red color. Microscopic - Interstitial pneumonia reported. Interference with research: Experimental Sendai Virus infection alters the phagocytic function of pulmonary macrophages. Concurrent SV and M. Pulmonis infections are synergistic in mice, causing disease of far greater severity than that caused by either agent alone. It has been reported (but not confirmed) that infected mice have deficiencies in T - and B - cell function that persist thourghout life, but most of the evidence indicates that such deficiencies are transient, lasting only a few weeks. SV infection inhibits in vitro mitogenesis of lymphocytes, increases natural killer cell mediated cytotoxicity, and increases cytotoxic lymphocyte responses after in vivo stimulation with SV - coated syngeneic cells. Isograft rejection is altered and the neoplastic response to respiratory carcinogens can be increased or decreased. Wound healing is delayed. Cyclophospamide increases in the clinical and pathologic severity of SV infection. SV infection in rats alters the mitogenic responses of T cells, reduces the severity of adjuvant arthritis, and decreases antibody response to sheep erythrocytes. SV infection alters host responses to transplantable tumors. More Information