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Interim Guidance for Minimizing Risk for Human Lymphocytic Choriomeningitis Virus Infection Associated with Rodents
On July 29, this report was posted as an MMWR Dispatch on the MMWR website (http://www.cdc.gov/mmwr).
In May 2005, CDC received reports of four organ-transplant recipients with unknown illness. All were discovered to have been infected with lymphocytic choriomeningitis virus (LCMV) via a common organ donor (1). Epidemiologic investigation traced the source of the virus to a pet hamster purchased by the donor from a local pet store. LCMV testing of other rodents at the pet store revealed three other LCMV-infected rodents (two hamsters and a guinea pig), supplied by a single distributor (distributor A). Preliminary laboratory testing of hamsters from distributor A has identified an infection rate of approximately 3% among the animals sampled. The facility of distributor A is under quarantine until it can be documented as free of LCMV infection. This report provides background information on LCMV and interim guidance* for the public on reducing risk for LCMV infection from pet rodents.
LCMV is a rodent-borne arenavirus endemic in house mouse (Mus musculus) populations worldwide (3--5). Pet rodents (e.g., hamsters and guinea pigs) can become infected with LCMV after contact with wild rodents at a breeding facility, pet store, or home. The prevalence of LCMV in pet rodents is not known. Although other animals could possibly become infected with the virus, documented infections in humans have occurred only after exposure to infected mice, guinea pigs, and hamsters (6,7).
LCMV infection in humans with normal immune systems usually causes either asymptomatic or mild, self-limited illness, characterized by any or all of the following symptoms: fever, malaise, lack of appetite, muscle aches, headache, nausea, and vomiting. Aseptic meningitis also can occur in some patients, but the infection is rarely fatal (6). LCMV infection during the first or second trimester of pregnancy can cause severe illness or developmental defects in the fetus, including hydrocephalus, psychomotor retardation, and blindness (8); the proportion of developmental defects caused by LCMV is not known. Serologic studies of previous infection in humans in urban areas of the United States have demonstrated a prevalence of previous LCMV in those populations of approximately 5% (3).
Person-to-person transmission has not been associated with LCMV, except for transmission from mother to fetus or through organ transplantation (1). Human infection occurs most commonly through exposure (by direct contact or aerosol) to secretions or excretions of infected animals (9). LCMV infection is a well-known occupational risk for laboratory workers who work with LCMV-infected laboratory rodents (9).
An outbreak associated with pet hamsters sold by a single distributor was reported in 1974, when 181 symptomatic cases in persons with hamster contact were identified in 12 states; no deaths occurred (10). The outbreak was brought under control by voluntary cessation of sale and destruction of the infected breeding stock.
Control of Wild Rodents
Environmental modifications and hygiene practices that deter rodents from colonizing the home and work environment are the best means of reducing risk for exposure to infectious rodents. In addition, if rodents are found in work or living areas, safe practices for cleaning rodent waste and nesting materials are recommended. Preventing wild rodent entry also reduces opportunity for infection of pet rodents.
Detailed instructions on rodent-proofing, safe cleaning practices, and trapping wild rodents are available at http://www.cdc.gov/ncidod/dvrd/spb/mnpages/dispages/lcmv.htm.
General Recommendations for Preventing LCMV Infection from Pet Rodents
Hamsters and other rodents are common pets, and the number of documented human LCMV infections from pet hamsters and other rodents is low. Basic precautions can reduce the risk for acquiring LCMV and other infections from pet rodents. Because rodents might not always exhibit signs of ill health resulting from LCMV infection, CDC recommends taking appropriate precautions with any rodent:
Purchasing a Healthy Pet
Information on purchasing a healthy pet and general steps to prevent pet rodents from bringing diseases into the home is available at http://www.cdc.gov/healthypets/lcmv_rodents.htm.
Care of Pet Rodents
Anyone handling or keeping pet rodents should take the following precautions to reduce the risk for LCMV infection:
Precautions for Pregnant Women
Although the risk for LCMV infection from pet rodents is low, pregnant women or women who think they might become pregnant should be aware of the risks associated with LCMV infection during pregnancy. The following precautions can be taken to reduce the risk for acquiring LCMV infection during pregnancy:
Precautions for Persons with Weakened Immune Systems
For the organ recipients described in this report, transplantation of LCMV-infected organs into persons with medically induced immunosuppression likely increased disease severity. Persons with impaired immune-system function should avoid contact with all rodents.
Testing for LCMV in Pet Rodents
CDC does not recommend testing pet rodents. Serologic testing on rodents can be inaccurate and misleading. All pet animals should be assumed capable of transmitting certain infectious diseases.
Testing for LCMV in Humans
Testing for LCMV infection in asymptomatic persons is not necessary. Similarly, testing persons with previous history of LCMV-compatible illness generally is not useful. Persons with active disease suggestive of LCMV should seek medical care and report any exposures to wild or pet rodents. A physician should determine whether testing for LCMV is indicated. Physicians should work closely with their respective state health departments to discuss forwarding of samples to state laboratories or CDC for testing.
Reported by: Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; EIS officer, CDC.
* These recommendations were assembled by a CDC working group to provide interim guidelines for protection of public health. Guidelines for care of laboratory animals have been published previously (2). In addition, the National Association of State Public Health Veterinarians, in conjunction with partners, is developing a set of comprehensive veterinary infection-control guidelines.
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Date last reviewed: 8/3/2005