House Mouse Blamed for Meningitis Outbreak

A common house mouse turned out to be the culprit in an outbreak of viral meningitis in Minnesota.

When a Minnesota teenager was admitted to a hospital last April with a fever of 102.9 degrees, and tested negative for flu or a bacterial infection, investigators were temporarily stumped. The patient also had photophobia, a stiff neck, and headache, signs of meningitis.

Fewer than half of meningitis cases in the US are diagnosed as to what infectious agent caused them.

Doctors treated the patient for possible bacterial or herpes simplex virus meningitis but neither turned out to be the agent causing her illness. Nor was it tuberculosis, HIV, Lyme disease, or a long list of other microbes that could have caused the meningitis.

Then on the fourth day of the patient's hospitalization laboratory results were positive for lymphocytic choriomeningitis virus (LCMV) antibody.

At that point the local physicians called in the US Centers for Disease Control and Prevention (CDC)s special pathogens branch, because of the uncommon diagnosis.

The CDC's testing confirmed LCMV was the culprit. Then it was up to the local officials in Minnesota to figure out where it had come from, and whether others were at risk.

The family had earlier reported a rodent problem in their duplex apartment. A state health department inspection found it was ongoing, with mouse droppings in a pantry.

The droppings turned out to have come from a Mus Musculus (photo), the common house mouse. According to the CDC, about 5% of US house mice carry LCMV and human infection occurs by inhaling aerosolized urine or droppings of infected rodents.

In addition to causing meningitis, the virus causes birth defects in fetuses exposed in utero. It can also cause infections in immunosuppressed recipients in organ transplant cases.

But in the past, testing mice for LCMV has meant trapping and killing them.

In the Minnesota case, the fecal pellets from the mouse (or mice) were tested and found positive for LCMV.

"This is the first report to identify LCMV-infected mice through fecal pellet testing," the CDC's Pamela Talley, MD and colleagues wrote in this week's edition of the CDC's Morbidity and Mortality Weekly Review