Lymphocytic choriomeningitis

Lymphocytic choriomeningitis (LCM) is a viral disease, spread by rodents, that presents as aseptic meningitis, encephalitis, or meningoencephalitis. Lymphocytic Choriomeningitis Virus (LCMV) is the causative agent and is a member of the Arenaviridae family.

The name is from the tendency of an individual to have high levels of lymphocytes during infection. It is spread by the common house mouse. Mice become chronically infected by keeping the virus in their blood. Female mice will transmit infection to their offspring.

The virus is resistant to drying and therefore humans can become infected by inhaling aerosolized particles of rodent urine, feces, or saliva. The only documented cases of transmission from animals are from mice and hamsters.

Cases have been reported in North and South America, Europe, Australia, and Japan. The virus tends to be more common among lower socio-economic groups. LCMV manifests through various clinical symptoms and can even be asymptomatic. Onset occurs between one to two weeks after exposure and is usually followed by a biphasic febrile illness. Common symptoms include fever, lack of appetite, headache, muscle aches, malaise, and nausea. The less common symptoms include sore throat, cough, as well as a joint, chest, and parotid pain. The second phase consists of meningitis or encephalitis.

LCM is a concern in obstetrics, as vertical transmission can occur. In immuno-competent mothers the virus has no effect but it can damage the fetus. Blood tests can determine whether a current or previous infection is present. Diagnosis is usually determined through symptoms and the period of time before the onset of meningitis symptoms. A PCR assay has been developed that may be used in the future for prenatal diagnosis.

There is no current treatment for humans. Ribavirin treatment is used sometimes but there is not sufficient evidence to support routine use. Mortality rate is less than one percent. In laboratory animals immunosuppressive therapy has been effective in stopping the disease. LCMV in laboratories may cause serious long-term repercussions to worker safety. In 1989, an outbreak among humans occurred in a US cancer research institute that studied the effects of various therapeutic and diagnostic agents in animal models. Hamsters in the institute came up with LCMV and later seven workers were positive for LCMV.

Reported outbreaks have decreased in recent years, perhaps due to improved biohazard management in laboratories. However, it is possible that sporadic cases have been overlooked because of the wide range of clinical presentations. Clare A. Dykewicz et al. recommend vigilant screening laboratory animals to be used in research facilities either through serum samples or cell line aliquots, as well as ensuring adequate ventilation in housing areas and use of appropriate sanitation products. Other practices to reduce cross-contamination in rodents include washing hands or changing gloves between animal care activities, thoroughly decontaminating cages before reusing them, and avoiding housing healthy rodents in the vicinity of potentially infected rodents.