Lymphocytic Choriomeningitis Virus Infections in Employees and Mice of a Rodent Breeding Facility--Indiana, 2012

BACKGROUND: Lymphocytic Choriomeningitis Virus (LCMV) is a murine infection caused by an arenavirus.  Outbreaks of human illness have been associated with rodent production and ownership of pet rodents.  In April, 2012 a case of LCMV was confirmed in an individual who worked at a rodent breeding facility in Indiana.  An investigation was conducted to identify the exposure source and any additional cases.

METHODS: A sero-survey was performed of current and recently employed individuals of the rodent production facility where the index patient was employed.  Sixty-nine persons associated with the facility participated and provided recent medical histories.  A clinical case was defined as an individual with laboratory evidence of recent LCMV exposure, which consisted of the presence of immunoglobulin M (IgM) and G (IgG) by enzyme-linked immunosorbent assay (ELISA), and symptoms consistent with LCMV infection.  A representative sample of adult rodents was tested by ELISA and polymerase chain reaction (PCR) for evidence of LCMV.  Subsequent to testing all live mice at the facility were euthanized. All deceased rodents, including those that had been held in cold storage, were disposed of in accordance with local environmental regulations.  Live mice that had been shipped from the facility were followed to the point of consumer purchase.  Any mice remaining at retail locations or those comingled with potentially infected mice were euthanized.

RESULTS: Of the 69 individuals tested, 13 (18.8%) demonstrated evidence of recent LCMV infection.  Of those recently infected, eight (61.5%) reported clinical illness; five (38.5%) sought medical care and four (30.7%) were diagnosed with aseptic meningitis.  Of the 1,421 mice tested, 296 (20.8%) had detectable anti-LCMV IgG and 10 (0.7%) had detectable LCMV RNA.  No rats were found to be positive by either ELISA or PCR. 

CONCLUSIONS: Employees of rodent breeding facilities are at high risk of exposure to LCMV.   Employers should inform workers of this risk and educate them on the potential health effects.  Employers should also work with public health to develop best practices materials on disease prevention and provide appropriate equipment to employees for protection. Facility managers should work with animal health officials to develop a biosecurity plan to prevent the introduction of infectious diseases into breeding populations.  Managers could also purchase replacement animals from a pathogen free source and conduct routine serologic testing of breeding stock to detect and control infections.  Evidence of zoonotic infections in rodents should be handled promptly to prevent human illness from occurring.