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What type of virus is LCMV?

Arenavirus, single-stranded enveloped RNA virus.


LCMV strains are closely related antigenically, but can vary in 4 properties. List these properties.

  1. Rate of replication
  2. Tissue tropism
  3. Pathogenicity
  4. Immunogenicity


What strains of the LCMV have been used extensively to develop and study mouse models of virus-induced immune injury?



Neurotropic and viscerotropic strains.




True or False. LCMV can infest both insect and mammalian cells.



True or False. Natural infection of LCMV in immunocompromised adult mice is usually self-limiting and asymptomatic.


False. Natural infection in immunocompetent adult mice is usually self-limiting and asymptomatic.



What are the four basic patterns of LCMV clinical disease that are recognized from the study of experimentally induced infection?



  1. Cerebral form - 5-6 days after intracranial inoculation in immunocompetent mice
  2. Visceral form - adult mice after inoculation with viscerotropic strains
  3. Runting and death - in neonatally infected suckling mice
  4. Late-onset disease - in previously asymptomatic carrier mice that develop immune complex glomerulonephritis.  Usually the result of prenatal or neonatal infection and occurs in PI mice around 9-12 months of age.




Which laboratory animals can be infected with LCMV?  Which of these species are known transmitters of the disease?


 Mice, hamsters, guinea pigs, and NHP can be infected.

Hamsters can transmit virus to other hamsters and mice, and are the primary source of human LCMV.



What are the BSL requirements for LCMV?

BSL-2 practices, containment equipment, and facilities are suitable for:

  • activities utilizing known or potentially infectious body fluids
  • cell culture passaged of laboratory-adapted strains
  • adult mice with mouse-brain-passaged strains

BSL-3 is required for:

  • all work with infected hamsters
  • high potential for aerosol production
  • production quantities or high concentrations of infectious materials
  • manipulation of infected transplantable tumors, field isolates, and clinical material from human cases
  • any strain shown to be lethal in NHPs

BMBL, p 216


How does LCMV usually enter an animal facility?

Infected biologicals or by feral mice, which are natural reservoirs.


How do LCMV carrier mice develop?

Carrier mice develop as a result of asymptomatic prenatal or neonatal infection.


True or False. Infection of LCVM in adult mice is acute because of the onset of effective immunity. Spread of the disease is halted.



Describe LCVM shedding in the adult hamster.

The adult hamster can remain viremic and viruic for many months.


What is the primary source of human LCVM infection?



What is LCMV the prototype for?

Virus-induced T lymphocyte-mediated immune injury and immune complex disease.


How is LCMV diagnosed?

Serologically by IFA or ELISA tests.


Why are false negative results for LCMV seen?


Carrier mice may develop poor humoral immune responses that can lead to false negative results.



Differential diagnosis for LCMV.

Neurological clinical signs rule/out: MHV, MEV, meningoencephalitis from metastatic bacterial infection, trauma, neoplasia, and toxicity.

Early-onset disease rule/out: Other causes of early mortality including MHV, ectromelia virus, Reovirus 3 infection Tyzzer’s disease or husbandry-related insults.


List ways to prevent and control LCMV in a mouse colony.


Selective testing and culling can be done because the mouse to mouse spread is slow. For mice that are replaceable, depopulation is a more reliable option. Valuable stock can be rederived, but check progeny to rule out in utero transmission.



How is LCMV controlled in hamsters?

Infected hamsters excrete a large amount of the virus in urine and saliva. Exposed hamsters should be destroyed.


List other ways humans can contract LCMV.

Humans can contract LCMV by exposure to contaminated cell cultures, transplantable tumors and vaccines.


Give the ways in which LCMV can complicate research.

  • stimulate or suppress immunological responses in vivo or in vitro and replicate in cells used in immunological studies
  • immune complex disease can complicate long-term experiments and morphological interpretations
  • illness and death in infected animals.


What type of virus is Sendai virus (SV)?


  • family Paramyxoviridae
  • subfamily Paramyxovirinae
  • genus Respirovirus.
  • antigenically related to human parainfluenza virus 1



True or False. Sendai virus is a single stranded DNA virus whose lipid solvent-resistant envelope contains glycoproteins with hemagglutinating, neuramidase and cell fusion properties.

False. Sendai virus is a single stranded RNA virus whose lipid solvent-sensitive envelope contains glycoproteins with hemagglutinating, neuramidase, and cell fusion properties.


What mammalian cell lines does SV grow best in?

Monkey kidney, Baby hamster kidney (BHK-21), and mouse fibroblast (L).


What are the clinical signs of SV in mice?

  • In adult mice, hunched position, erect hair coat, rapid weight loss, dyspnea, chattering sounds and crusting around the eyes. Highly susceptible adults may die.
  • The infection is lethal in suckling mice.
  • Athymic mice and immunosuppressed mice are at high risk and may develop wasting syndrome.


What strain is resistant to clinically apparent SV?  Which is highly susceptible?

C57BL/6 resistant

DBA/2 are highly susceptible


Does prenatal infection occur with SV?



Enzootic infection of SV is commonly detected in postweaned (_ to _ weeks old) and is associated with seroconversion within _-_days and the termination of infection.


Enzootic infection is commonly detected in postweaned (5 to 7 weeks old) and is associated with seroconversion within 7-14 days and the termination of infection.



What other species are susceptible to SV infection?

Rats, hamsters, and guinea pigs


True or False. Viral replication of SV during natural infection is restricted to the respiratory tract tract.





Explain the gross lesions seen in the lungs of mice infected with Sendai virus.

Partial to complete consolidation of the lungs. Individual lung lobes are meaty and plum-colored. The cut surface may exude a frothy serosanguinous fluid. Pleural effusions or abscesses caused by secondary bacterial infections are sometimes seen. Fluid may accumulate in the pleural and pericardial cavities.


What cell types does SV target?

Airway epithelium and type II pneumocytes.  Type I pneumocytes less severely affected.


How does mouse genotype determine the histologic pattern of pneumonia seen in SV infection?

Susceptible mice (e.g. DBA/2) usually have significant bronchopneumonia and interstitial pneumonia.

The interstitial pneumonia component may be less prominent in resistant mice (e.g. C57BL/6).


How is SV diagnosed?

Clinical signs of respiratory disease are highly suggestive of SV infection.

IFA or ELISA can be used to diagnose the disease. Antibody can be detected 7 days post infection. Histopathology, immunohistochemistry, and viral isolation can be used to confirm the infection. RT-PCR can also be used to detect the disease.


Give the differential diagnosis for SV.

PVM, though the disease is usually milder, and bacterial pneumonias.


How can SV be controlled once found in a colony of mice?

Allow the disease to “burn-out” by having a 4-6 week quarantine period, where no new animals are introduced to the colony either as adults of by breeding.


How can SV infection complicate research?

  • immunosuppression
  • inhibit growth of transplantable tumors
  • pulmonary changes can compromise interpretation of experimentally induced lesions


What type of virus is Pneumonia Virus of Mice?


  • enveloped RNA virus
  • genus Pneumovirus
  • family Paramyxoviridae
  • subfamily Pneumovirinae



True or False. Natural PVM infection in mice is asymptomatic.



What are the clinical signs associated with PVM in immunodeficient mice?

Dyspnea, listlessness, and wasting may occur.


PVM causes natural infections of  what species?

PVM causes natural infections of mice, rats, hamsters, and possibly other rodents and may be infectious for rabbits.


True or False. Intimate contact between mice is not necessary for the spread of PVM.

False. Intimate contact is probably required for effective transmission of PVM.


Where does replication of PVM take place?

Replication of PVM is exclusively in the respiratory tract and peak titers are reached in the lungs 6-8 days after infection.


What gross lesions are seen with natural PVM infection?

Gross lesions are rare with natural PVM infection. Pulmonary consolidation can be seen in experimentally infected mice.


What histological lesions are associated with PVM infection?

Mild necrotizing rhinitis, necrotizing bronchiolitis, and interstitial pneumonia


The predominant inflammatory infiltrate in PVM infection is compromised of what?

mononuclear cells, but some neutrophils are present.



How is PVM diagnosed?

Diagnosis is based primarily on serological detection that can be supplemented by histopathology, immunohistochemistry, in situ hybridization, and viral isolation.


In immunodeficient mice, PVM must be differentiated from what?

other pneumonias, especially those due to Sendai virus and Pneumocystis carinii.


How can PVM infection complicate research?

primarily by exacerbating pneumocystosis


What are the two members of the family Reoviridae that infect mice?

Reovirus and Murine rotavirus (EDIM virus)


Reovirus contains what genomic straucture?

segmented, double-stranded RNA, and is relatively heat stable.


Characterize the pathology and clinical signs of Reovirus.

Reovirus-3 severe pantropic infection in infant mice.

Reovirus-1 similar distribution of significantly milder lesions

Reovrus-2 is highly enterotropic

Acute disease affects sucklings about 2 weeks of age. Adults usually have asymptomatic infections.

  • Sucklings present with emaciation, abdominal distension, and oily, matted hair due to steatorrhea
  • Icterus may develop, most apparent on feet, tail, nose
  • alopecia, runting, and icterus may present for several weeks even though virus can no lonnger be recovered
  • Incoordination, tremors, and paralysis occur just before death
  • infants born to immune dams are protected from disease


Are infants born to immune dams protected from Reovirus?



How is Reovirus 3 transmitted?

Reovirus is highly infectious in infant mice and can be transmitted by oral-fecal or aerosol routes. Mechanical transmission by arthropods has been documented. Virus may be carried by transplantable neoplasms and transmitted inadvertently by injection.


Describe the distribution of lesions in Reovirus 3 infection.

Pantropic - Lesions are seen in the liver, intestines, heart, brain, pancreas, salivary glands, lungs and skeletal muscles.


Describe the distribution of lesions in Reovirus 1 and 2 infection.

Reovirus 1: Distribution of lesions similar to those of Reovirus 3 but significantly milder

Reovirus 2: enterotropic, inducing mild enteritis.


What are the differentials for Reovirus infection?

Reovirus 3 infection needs to be differentiated from other diseases causing diarrhea in infants including mouse coronaviruses, EDIM virus, Salmonella spp, or Clostridium piliforme.


74.        How does Reovirus 3 infection complicate research?

  • Infections in breeding colonies can result in high mortality in suckling mice.
  • Virus is suspected of being oncolytic.
  • Reovirus 3 can potential interfere with hepatic, pancreatic, neurological or cardiovascular research.


Structure of rotaviruses?

double stranded RNA viruses that have wheel-like appearance ultrastructurally.


True or False. EDIM virus is a group A rotavirus that replicates in differentiated epithelial cells if the small intestines by budding into cisternae of endoplasmic reticulum.



Describe EDIM susceptibility.

age-related susceptibility, with infant mice < 2 weeks old and immunodeficient mice being most susceptible.


What are the cardinal signs of EDIM infection?


Diarrhea with fecal soiling of the perineum, which may extend to the entire pelage in severe cases.

In EDIM infection, morbidity is high but mortality is low.



What rodent species does EDIM infect?

Mice only.


How is EDIM transmitted?

Oral –fecal route. Virus can be shed in the feces for at least 17 days in asymptomatic infected adults. Dams can contract the disease from their litters.


Describe the gross and histological lesions with EDIM.

  • Grossly, lesions are primarily in the gastrointestinal tract, but thymic atrophy can be associated with infections related stress.
  • Intestine often distended, flaccid, and filled with grey-green gaseous liquid or mucoid fecal material that soils the pelage.
  • Stomach often contains curdled milk
  • Virus preferentially infects terminally differentiated enterocytes in SI & LI, which accounts for age-related susceptibility (the number of such cells decreases as intestinal tract matures)
  • Villar epithelial cells contain vacuolization with cytoplasmic swelling, giving villi a clubbed appearance


Explain the relationship between the EDIM virus and age-related susceptibility.


The virus preferentially infects the terminally differentiated enterocytes in the small and large intestines. These cells decrease in number as the intestinal tract matures.



True or False. In EDIM, the lamina propria of the small intestine is edematous, necrotic and inflamed.


False. The lamina propria of the small intestine is edematous, but necrosis and inflammation are not prevalent.



List the differentials for EDIM infection.

Differentials include other diarrheal diseases of suckling mice including

  • MHV
  • Reovirus 3
  • Tyzzer’s disease
  • Salmonella
  • Dual infections may also be present; hence, thymic lesions may be due to MTV (mouse thymic virus) infection.


How can the spread of EDIM be controlled?

  • microbarrier caging
  • good sanitation
  • cessation of breeding for 4-6 weeks to allow immunity to build in the adults
  • culling


How can EDIM infection complicate research?

Growth retardation in suckling mice. Thymic necrosis may interfere with immunological responses.


What is MHV? 

Mouse Hepatitis Virus; Mouse Coronavirus.


Describe the structure of MHV.

Mouse coronaviruses are large, pleomorphic, enveloped RNA viruses with radially arranged peplomers.


True or False. Hepatitis is a common feature of natural MHV infection in immunocompetent mice.

False. Hepatitis is not a common feature of natural MHV infection in immunocompetent mice.


Explain another method of categorizing MHV isolates.

MHV isolates are also categorized based on its organotropism:

  • enterotropic strains primarily infect the intestinal tract
  • polytropic strains initially infect the respiratory tract, but then progresses to multisystemic dissemination
  • Isolates can contain features of both tropisms.


MHV isolates and strains share internal antigens. What are the internal antigens? How can these strains and isolates be distinguished?

M and N. They can be distinguished by neutralization tests that detect strain-specific spike (S) antigens.


True or False. MHV share antigens with the coronaviruses of rats.



What clinical signs with MHV are seen in suckling mice?


Diarrhea, inappetance, dehydration, weight loss, lassitude and ruffled pelage, often terminating in death.



How is MHV transmitted?

Natural infection is transmitted by respiratory or oral routes. Natural vertical transmission has not been demonstrated. MHV infection can also be introduced through injection of contaminated biologicals.


True or False. MHV infection in immunocompetent mice is self-limiting.





Immune-mediated clearance is associated with sero-conversion usually begins _______ after MHV infection and mice recover fully in _________.


Immune-mediated clearance is associated with sero-conversion usually begins about a week after MHV infection and mice recover fully in 3-4 weeks.



What type of immunity is associated with MHV infection?

Both cellular and humoral.


Can mice become re-infected with MHV?

Yes. Mice can develop immunity to one strain of MHV and can remain susceptible to one or more genetically and antigenically divergent strains, thus making re-infection possible.


Where do polytropic strains of MHV replicate initially? What are the subsequent outcomes?

Replication is in the nasal mucosa resulting in necrotizing rhinitis. If the virus gains assess to blood vessels and lymphatics, viremic dissemination occurs, which leads to secondary infections of many tissues and organs (white spots on liver –classic lesion). Nasal infection can also extend directly to the CNS.


What is the hallmark of MHV infection.

Syncytia at margins of necrosis


Enterotropic strains of MHV most commonly infect what sites?

Terminal ileum, cecum, and proximal colon.


True or False. Athymic and SCID mice infected with enterotropic MHV can develop chronic proliferative bowel disease with syncytia formation.



How can MHV infection be diagnosed?

Serologically with ELISA and IFA testing, PCR on fecal material or in tissue, injection of adult mice with suspect serum or tissue to elicit sero-conversion, clinical signs are suggestive, presence of syncytia, especially when combined with immunohistochemistry to detect MHV antigen. Neutralization testing can be used to differentiate between strains.


What are the differentials for MHV infection?

Other diseases that cause diarrhea, runting or death in suckling mice or wasting disease in immunodeficient mice including, EDIM, mousepox, Reovirus 3, Tyzzer’s disease and salmonella. Mouse encephalomyelitis virus infection and neoplasms should be considered when neuro signs are present.

  • inappetance (failure to suckle) is a distinguishing characteristic


What is MEV? Characterize the virus.


Mouse Encephalomyelitis Virus (Theilovirus - ThV), a small non-enveloped RNA, family Picornaviridae, genus Cardiovirus


List the established strains of MEV.

TO (Theiler’s original), FA, DA, and GD VII.


MEV is rapidly destroyed by temperatures over _____ and by ____ but not ______.

MEV is rapidly destroyed by temperatures over 50° C and by alcohol but not by ether.


What clinical signs are seen with MEV infection?

Flaccid posterior paralysis, which may be preceded by weakness in the forelimbs or hindlimbs. Mice are otherwise alert. Mice die because of the inability to obtain food and water. With recovery, a gait disturbance may be present due to a chronic demyelinating phase.


What strain of MEV infects both mice and rats?

MGH strain, after experimental inoculation.


How is MEV acquired?



In MEV infection, acute necrosis of ganglion cells, neurophagia, and perivascular inflammation occurs primarily in the ventral horn of the spinal cord grey matter, but can also involve the ______, _______, and _______.


hippocampus, thalamus and brain stem.



What causes the white-matter lesions seen in MEV infection?

Immune injury.


How can MEV infection be diagnosed?

ELISA, IFA, PCR, characteristic lesions in the CNS on histopathology and virus isolation in BHK-21 cells with intestine or CNS tissue.


List the differentials for MEV infection.

Neurotropic variants of MHV, injury or neoplasm of the spinal cord. Polyomavirus in athymic mice may result in signs similar to those of MEV.


Etiology of PVM


Murine pneumonia virus, paramyxoviridae



Murine paramyxoviruses

Sendai virus

Pneumonia virus of mice


Clinical signs of PVM

Subclinical in immunocompetent strains

dyspnea, listlessness, wasting in immunocompromised strains


Histopathology of PVM

necrotizing rhinitis and bronchiolitis, interstitial pneumonia

Mononuclear cell infiltrate


what is LIVIM

Lethal Intestinal Virus of Infant Mice

MHV (Coronavirus)