Interim Guidance for Minimizing Risk for Human
Lymphocytic Choriomeningitis Virus Infection Associated with Rodents
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
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
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
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:
- The public should be apprised of the risk for LCMV infection
from rodents purchased from any pet store.
- Destruction or return of recently purchased pet rodents is
not recommended. The probability of any one animal harboring
LCMV infection is low. All pets are potential carriers of
infectious diseases and should always be handled by using
- Pet rodents must not be released into the wild to prevent
introduction of nonnative species to North America.
- Persons with specific concerns regarding the health of their
pets should seek guidance from a veterinarian.
Purchasing a Healthy Pet
Information on purchasing a healthy pet and general steps to
prevent pet rodents from bringing diseases into the home is
Care of Pet Rodents
Anyone handling or keeping pet rodents should take the following
precautions to reduce the risk for LCMV infection:
- Wash hands with soap and water (or alcohol-based hand
sanitizers when soap is unavailable and hands are not visibly
soiled) after handling pet rodents or cleaning up pet droppings,
cages, or areas where pets have been.
- Keep rodent cages clean and free of soiled bedding.
- Clean cages outdoors or in a well-ventilated area.
- Closely supervise young children when cleaning cages or
handling rodents and supervise or assist children in washing
their hands immediately after handling rodents and rodent cages
- Never kiss or hold pet rodents close to the face.
- Never allow pet rodents to come into contact with wild
rodents or their droppings or nests. Cover pet rodent cages and
food supplies and always supervise pet rodents when they are not
in their cages.
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:
- Avoid contact with wild rodents. Pregnant women who reside
in a household with a wild rodent infestation should have the
infestation addressed promptly by a professional pest control
company or another member of the household.
- Keep pet rodents in a separate part of the home. Pregnant
women should ask another family member or friend to clean the
cage and care for the pet or arrange for temporary adoption of
the pet by a responsible person. Pregnant women should avoid
prolonged stays in any room where a rodent resides.
Precautions for Persons with Weakened Immune
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
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.