Lymphocytic Choriomeningitis (LCM)

Lymphocytic choriomeningitis, or LCM, is a rodent-borne viral infectious disease caused by lymphocyte choriomeningitis virus (LCM), a member of the family Adrenaline, that was initially isolated in 1933.

The primary host of LCM is the common house mouse, Mus musculus. Infection in house mouse populations may vary by geographic location, though it is estimated that 5% of house mice throughout the United States carry LCM and are able to transmit virus for the duration of their lives without showing any sign of illness. Other types of rodents, such as hamsters, are not the natural reservoirs but can become infected with LCM from wild mice at the breeder, in the pet store, or home environment. Humans are more likely to contract LCM from house mice, but infections from pet rodents have also been reported.

LCM infections have been reported in Europe, the Americas, Australia, and Japan, and may occur wherever infected rodent hosts of the virus are found. The disease has historically been under reported, often making it difficult to determine incidence rates or estimates of prevalence by geographic region. Several seismologic studies conducted in urban areas have shown that the prevalence of LCM antibodies in human populations range from 2% to 5%.

Signs and Symptoms

LCM is most commonly recognized as causing neurological disease, as its name implies, though infection without symptoms or mild febrile illnesses are more common clinical manifestations.

For infected persons who do become ill, onset of symptoms usually occurs 8-13 days after exposure to the virus as part of a aphasic febrile illness. This initial phase, which may last as long as a week, typically begins with any or all of the following symptoms: fever, malaise, lack of appetite, muscle aches, headache, nausea, and vomiting. Other symptoms appearing less frequently include sore throat, cough, joint pain, chest pain, testicular pain, and parotid (salivary gland) pain.

Following a few days of recovery, a second phase of illness may occur. Symptoms may consist of meningitis (fever, headache, stiff neck, etc.), encephalitis (drowsiness, confusion, sensory disturbances, and/or motor abnormalities, such as paralysis), or electroencephalograms (inflammation of both the brain and meninges). LCM has also been known to cause acute hydrocephalus (increased fluid on the brain), which often requires surgical shunting to relieve increased intracranial pressure. In rare instances, infection results in myelitis (inflammation of the spinal cord) and presents with symptoms such as muscle weakness, paralysis, or changes in body sensation. An association between LCM infection and myocardium (inflammation of the heart muscles) has been suggested.

Previous observations show that most patients who develop aseptic meningitis or encephalitis due to LCM survive. No chronic infection has been described in humans, and after the acute phase of illness, the virus is cleared from the body. However, as in all infections of the central nervous system, particularly encephalitis, temporary or permanent neurological damage is possible. Nerve deafness and arthritis have been reported.

Women who become infected with LCM during pregnancy may pass the infection on to the fetus. Infections occurring during the first trimester may result in fetal death and pregnancy termination, while in the second and third trimesters, birth defects can develop. Infants infected In utero can have many serious and permanent birth defects, including vision problems, mental retardation, and hydrocephalus (water on the brain). Pregnant women may recall a flu-like illness during pregnancy, or may not recall any illness.

History

Clinical manifestations of lymphocyte choriomeningitis virus (LCM) infection in incompetent individuals range from a flu like illness to severe CNS involvement with electroencephalograms. Phase 1 of LCM typically manifests as fever and headache, often with nephropathy and a corpuscular rash, resolving after 3-5 days. In many patients, a more severe headache returns within 2-4 days, associated with typical signs of aseptic meningitis.

Patients with LCM infection may report a history of exposure to rodents, hamsters, or the excreta of these animals 1-3 weeks before the onset of symptoms. Infection is most common in the autumn