Lymphocytic Choriomeningitis or LCM is an acute viral infection caused by an RNA virus classified as arenavirus, usually appearing as an influenza-like illness or aseptic meningitis, which may be associated with rash, arthritis, orchitis, or parotitis. This type of infection is endemic in rodents, and human infection results most commonly from exposure to dust or food contaminated by the gray house mouse or hamsters, which harbor the virus for life and excrete it in the urine, feces, semen, and nasal secretions. When transmitted by mice, the disease occurs primarily in adults, in the winter. The incubation period ranges from 5 to 10 days after exposure. Fever usually reaching 40 degrees centigrade. Other symptoms include: malaise, weakness, myalgia, especially in the lumbar area, retro-orbital headache, photophobia, anorexia, nausea, and light-headedness. Less common symptoms include sore throat and dysthesia. In the first week of illness, physical findings are few; there may be relative bradycardia and pharyngeal injection without exudates. After 5 days to 3 weeks, the patient may improve for 1 or 2 days. Many patients have a relapse with recurrent fever, headache, skin rashes, swelling of metacarpophalangeal and proximal interphalangeal joints, meningeal signs, orchitis, parotitis, and alopecia of the scalp. Patients with aseptic meningitis almost always recover without sequelae. With encephalitis, up to 33% of the patients have neurologic residua. Laboratory findings include: leukopenia, with white blood cells ranging from 2000 to 3000; thrombocytopenia, with platelets numbering from 50,000 to 100,000, and these findings appear during the first week of illness.
Chest x-rays may show basilar pneumonitis. In patients with meningeal signs, the cerebrospinal fluid usually contains several hundred cells/cu mm, but occasionally greater than 1000. Lymphocytes predominate, more than 80 %. There will be a decrease in cerebrospinal fluid glucose, with concentrations as low as 15 mg/100 ml. This has been reported in 25% of patients. The clinical manifestations are difficult to differentiate from other viral infections and the treatment is supportive. Arbovirus encephalitides caused by arthropod-borne viruses number more than 250, and 80% cause diseases in humans. Arboviruses are transmitted among vertebrates by biting insects, chiefly mosquitoes and ticks. Birds are often important sources of infection for mosquitoes which then transmit the infection to animals and humans. Man is a dead-end host for most of the agents, but is a definitive host. The agents or arboviruses are widely distributed worldwide. This infection may cause central nervous system syndromes, including aseptic meningitis and encephalitis, minor non-specific febrile illnesses, and, most commonly, inapparent infection. Headache, nausea, and vomiting, drowsiness, fever, and stiff neck are the usual presenting symptoms. Tremors, mental confusion, convulsions, and coma may develop rapidly. Paralysis of the extremities may occasionally occur. Treatment is supportive, as with other viral encephalitides. In
