American Fancy Rat & Mouse Association

This article is from the Mar./Apr. 1996 AFRMA Rat & Mouse Tales news-magazine.


Raising Newborn Rats/Mice: Update; Reovirus 3

By Carmen Jane Booth, D.V.M.

Raising Newborn Rats/Mice: Update

As Karen mentioned in the July/August 1994 newsletter, hand-raising newborn rodents is very difficult. Newborn rodents have an extremely Rat Milkman high metabolic rate and need a great deal of energy (food) in order to thrive and survive without their dams. Fat yields more calories per unit than either carbohydrates or protein and this is the essential problem with hand rearing. Rat milk is higher in fat than other domestic species and specialized to meet the nutritional requirements of rats. Kitten and other milk replacers contain lower amounts of fat and the volume that would have to be fed the newborn rodents to meet their energy requirements is often greater than they can consume reasonably. There are human medical products that could be added to the formula that consists predominantly of fat that might help, but again the volume constraints will always be an issue. More frequent feeding may increase survival but all the other factors such as temperature, humidity, and stimulation of urination and defecation are equally important.

If possible, transfer the pups (kittens) to another dam. The best success occurs if pups are transferred to an experienced mother who gave birth recently. The best success is when both the abandoned pups and the foster mother’s pups are less than 24 hours old. Some success has occurred with pups as old as 4 days. In school we successfully cross-fostered mice onto rats.

Reovirus 3

Q My mice tested positive to Reovirus 3 and I would like to know all about this virus. The pathologist said it was very rare for mice to have. Karen Robbins

A Reoviruses (respiratory enteric orphan virus) cause have been isolated in humans and a wide variety of mammals, birds, reptiles, insects, and other species. In mammals they have been divided into three serotypes 1, 2, and 3. Reovirus 3 has been associated with natural infections in laboratory rodents and as pathogen in mice. A number of different reovirus 3 strains have been studied.

Seroconversion (the change of a serologic test from negative to positive, indicating the development of antibodies in response to infection or immunization) is a frequent finding in mouse colonies. Although the true prevalence of reovirus 3 in mouse colonies is unknown, it has been reported to exceed 80% in some colonies

These viruses can be transmitted by fecal-oral or aerosol (air) and by insects. Transmission among mice seems to occur primarily by direct contact among young mice. Mice of all ages are susceptible but only neonatal mice develop disease. Adults commonly have asymptomatic infection. Reovirus 3 replicates in multiple organs of neonatal mice in the absence of significant lesions, until around day 10–12, when mice may become clinically ill and develop lesions in multiple tissues, followed by recovery.

Lesions are nonspecific but may include: runted mice with matted hair from fatty feces (steatorrhea), liver and pancreatic problems such as hepatitis (inflamed liver) or acinar pancreatitis (inflamed pancreas) with jaundice (yellow tinge, most easily seen in the feet and tail), neurologic symptoms such as incoordination tremors and paralysis, or death. Animals that recover develop immunity to the virus and any pups born to immune dams (moms) do not develop the disease.

Diagnosis is made by serologic testing in the absence of obvious disease.

Karen, I would expect that your mice are probably all immune to this virus and are seropositive from acquiring natural immunity from their dams. Many pathologists are not as familiar with rodent disease as those of other species. Reoviruses are not generally significant pathogens. *

Updated February 2, 2015