Lymphocytic Choriomengitis Virus (LCMV) is a highly significant zoonotic infection of research personnel who work with transplantable rodent tumors (especially in hamsters) and rodent cell lines as well as for owners of pet hamsters. LCMV is an arenarius (an RNA virus).

Wild mice are considered the principal reservoir hosts but laboratory mice and Syrian hamsters also serve as important natural hosts. Humans, nonhuman primates, dogs, rabbits, guinea pigs, rats, and chickens are also susceptible. Both infected mice and hamsters can have chronic infections with high concentrations of virus shed in urine, saliva, and milk. Transmission is probably via mucus membranes and broken skin. Vertical (transovarian and/or transuterine) transmission has been confirmed in mice.

Clinical signs in mice vary depending on the strain of virus, strain of mouse and age of mouse. Two primary forms are recognized in natural LCMV infections:

• Persistent tolerant infection: This form results when infection is acquired in utero or within a few days after birth. There is lifelong viremia and shedding of virus. Transient runting can occur during the first 3 weeks of life which is sometimes followed by modest growth retardation. At 7-10 months of age, immune complex glomerulonephritis occurs and is characterized by emaciation, rough haircoat, hunched posture, ascites, and possible death. The manifestation of glomerulonephritis is due to circulating viral-immunoglobulin (IgG)-complement complexes that accumulate in renal glomeruli, choroid plexus, synovial membranes, blood vessel walls, and epidermis. In addition, there is generalized lymphoid hyperplasia and perivascular accumulation of lymphocytes and plasma cells in all visceral organs.

• Nontolerant (acute) infection: This form occurs when infection is acquired after the first week of life (i.e. after immunocompetence develops). Viremia occurs without any viral shedding. The outcome is either death within a few days to weeks, or recovery with virus elimination. In experimentally-induced nontolerant infections, the primary pathological lesions are hepatic necrosis, generalized lymphocytolysis of T and B cells, and fibrinoid necrosis of lymphoid organs.

Natural infections in hamsters are generally considered subclinical. In humans, the usual clinical manifestations are those of a flu-like illness and include fever, headache, myalgia, nausea, vomiting sore throat, and phobophobia. Occasionally, rash, diarrhea, cough, lymphadenopathy, orchitis, delirium or amnesia occurs.

Serological testing is the most practical procedure for routine diagnosis. The tests of choice are the IFA, micro plaque-reduction assay for neutralizing antibody, and the enzyme-linked immunosorbent assay. The mouse antibody production (MAP) test can be used to test transplantable tumors and other biologic materials for viral contamination.

The most practical method of control of LCMV is to obtain mice and hamsters only from colonies shown to be free of the disease and to maintain them in a facility that excludes wild rodents. In addition, all biologic materials (such as transplantable tumors) coming into the facility should be pretested and shown to be free of virus prior to experimental use. If LCMV is identified in a rodent population, the entire stock should be eliminated. All virus-contaminated animal caging/equipment must be sterilized and contaminated animal rooms must be disinfected. Cesarean derivation or embryo transfer (of infected rodents) is of no value because of transovarian or transuterine transmission of the virus.