Notes from the Field: Lymphocytic Choriomeningitis Virus Infections in Employees of a Rodent Breeding Facility — Indiana, May–June 2012

In late April 2012, an infectious disease physician contacted CDC regarding a patient with aseptic meningitis who worked at a rodent breeding facility in Indiana. Lymphocytic choriomeningitis virus (LCMV) infection was suspected, and LCMV-specific antibody was detected in blood and cerebrospinal fluid from the patient, confirming the diagnosis. LCMV is an arenavirus carried by the common house mouse. Persons become infected through close contact with infected rodents, through infected organ transplantation, or from mother to fetus. In immunocompetent adults, symptoms can range from mild febrile illness to meningeal symptoms (e.g., headache, stiff neck, or sensitivity to light). Congenitally infected infants can have a range of severe birth defects including hydrocephalus, chorioretinitis, blindness, and mental retardation (1). Infections in organ recipients, who are immunosuppressed, can have a case-fatality rate approaching 90% (2).

CDC notified the Indiana State Department of Health of a potential outbreak of LCMV infection at the rodent breeding facility and subsequently notified county health officials and the Indiana Board of Animal Health. A serosurvey was performed; 52 current and former employees of the facility consented to serum testing. Of the 52 tested, 13 (25%) demonstrated recent LCMV infection as evidenced by the prescence of immunoglobulin M (IgM) and IgG by enzyme-linked immunosorbent assay (ELISA). Nine employees who showed laboratory evidence of recent exposure reported experiencing a clinical illness consistent with LCMV; symptoms ranged from severe influenza-like illness to meningeal symptoms that required hospitalization. Of the persons experiencing illness, 89% were male; ages ranged from 20 to 48 years. No employees, including those not tested, were known to be pregnant at the time of the serosurvey. All employees who experienced clinical illness have since recovered. Three additional employees had evidence of a previous LCMV infection, with detectable anti-LCMV IgG and no IgM.

The rodent facility bred and raised mice and rats for sale as live and frozen feeder animals for reptiles or birds of prey. The facility housed approximately 155,000 adult mice and 14,000 adult rats. A representative sample of healthy-appearing adult rodents was tested for evidence of LCMV infection by ELISA and polymerase chain reaction. Of 1,421 mice tested, 296 (20.8%) had detectable anti-LCMV IgG, and 10 (0.7%) had detectable LCMV RNA. Of 399 rats tested, none were positive by ELISA or polymerase chain reaction. All living mice at the facility were euthanized. All rodents remaining in cold storage at the time of diagnosis also were disposed of in accordance with local environmental regulations. The buildings and equipment housing the mice were cleaned and disinfected. Used litter and contaminated feed were disposed of in accordance with local environmental regulations. Live mice distributed from the facility before the LCMV diagnosis currently are being followed to the point of purchase through an ongoing investigation.

Any persons with direct or indirect contact with these animals should be made aware of the public health risk and should seek medical evaluation if they have had any recent illness. Pregnant women or immunocompromised persons should be cautioned to avoid contact with rodents in general. Wild mice in the United States have a prevalence of LCMV estimated at 3.9%–13.4% (3). Any additional rodent populations that have come into direct contact with potentially infected mice should be depopulated.

Employers of rodent breeding facilities of all kinds should make their employees aware that working with rodents can expose them to LCMV and should educate workers regarding risks for exposure, including potential health effects. Employers also should work with their local health departments to develop guidance material on disease prevention and provide the recommended personal protective equipment for employees. Routine serologic testing of rodents can be used to detect and control LCMV infections. Evidence of LCMV infection in rodents should be dealt with promptly to prevent human illness from occurring. Purchasers of frozen rodents used to feed another pet should be reminded to always wear plastic gloves when handling the rodents and to wash their hands afterward.

Reported by

Vanderburgh County Dept of Health, Evansville; Indiana State Board of Animal Health, Indianapolis; Indiana State Dept of Health. Div of High-Consequence Pathogens and Pathology, National Center for Emerging and Zoonotic Infectious Diseases, CDC. Corresponding contributor: Viral Special Pathogens Br, dvd1spath@cdc.gov, 404-639-1115.

References

1. Bonthius DJ. Lymphocytic choriomeningitis virus: a prenatal and postnatal threat. Adv Pediatr 2009;56:75–86.
2. MacNeil A, Ströher U, Farnon E, et al. Solid organ transplant–associated lymphocytic choriomeningitis, United States, 2011. Emerg Infect Dis 2012;18:1256–62.
3. Childs JE, Glass GE, Korch GW, Ksiazek TG, Leduc JW. Lymphocytic choriomeningitis virus infection and house mouse (Mus musculus) distribution in urban Baltimore. Am J Trop Med Hyg 1992:47;27–34.