Lymphocytic choriomeningitis (LCM) is a viral disease carried by rodents that can affect humans. It is caused by the lymphocytic choriomeningitis virus (LCMV), a member of the Arenaviridae family, first identified in 1933. This virus is primarily associated with the common house mouse (Mus musculus). LCM can occur wherever infected rodents are found globally.
How Lymphocytic Choriomeningitis Spreads
The common house mouse is the main natural carrier of LCMV. Once infected, these mice can shed the virus throughout their lives, often without showing symptoms. Other rodents, such as hamsters and guinea pigs, can also become infected if they contact wild mice in breeding facilities, pet stores, or homes. While rare, pet rodents can become carriers if exposed to wild mice.
Humans contract LCMV by exposure to fresh rodent urine, droppings, saliva, or nesting materials. This exposure occurs through inhaling aerosolized particles, ingesting contaminated food, or direct contact with broken skin or mucous membranes. Human-to-human transmission is rare, but can occur from a pregnant person to their fetus or, in uncommon instances, through organ transplantation from an infected donor.
Recognizing the Symptoms
LCMV infection can manifest with a wide range of symptoms, or be asymptomatic, especially in healthy individuals. When symptoms do appear, they typically begin 8 to 13 days after exposure to the virus and often follow a biphasic course.
The initial phase, lasting up to a week, resembles a flu-like illness. Common symptoms include fever, fatigue, muscle aches, headache, lack of appetite, nausea, and vomiting. Some individuals may experience a sore throat, cough, joint pain, chest pain, testicular pain, or parotid gland pain.
Following a few days of recovery, a second, more severe phase of illness occurs if the infection progresses to the nervous system. This can involve meningitis (fever, headache, stiff neck) or encephalitis (drowsiness, confusion, seizures, paralysis). Sometimes, the virus causes meningoencephalomyelitis, affecting both the brain and spinal cord, or acute hydrocephalus.
Diagnosis and Management
Diagnosing LCM involves several methods, starting with clinical suspicion based on symptoms and a history of rodent exposure. Serologic testing, which detects antibodies to LCMV in blood or cerebrospinal fluid, is a diagnostic approach. Polymerase chain reaction (PCR) can also detect the virus’s genetic material, and viral culture can be performed.
There is no specific antiviral treatment approved for LCM. Management focuses on supportive care to alleviate symptoms, including pain relief, proper hydration, and hospitalization for individuals with severe neurological symptoms. Sometimes, anti-inflammatory medications like corticosteroids are considered to manage severe inflammation.
Preventing Infection
Preventing LCM infection centers on minimizing contact with rodents and their bodily fluids. Sealing entry points into homes with materials like steel wool or caulk prevents rodents from entering. Trapping mice and removing potential food sources and nesting sites are also important steps in rodent control.
When cleaning areas contaminated by rodent urine, droppings, or nesting materials, ventilate the space before starting. Wear gloves and a mask. Contaminated surfaces should be thoroughly wetted with a disinfectant solution, such as a bleach mixture, to avoid stirring up airborne viral particles. Avoiding direct contact with wild or pet rodents, especially for pregnant individuals due to congenital LCM risk, reduces infection chance.
Potential Health Outcomes
Many individuals who contract LCMV experience no symptoms or only mild, self-limiting illness and recover completely. However, severe cases, particularly those involving neurological complications like meningitis or encephalitis, can lead to more serious outcomes. Fatalities are uncommon (less than 1%), but temporary or permanent neurological damage is possible. Lasting effects can include deafness or arthritis after recovery.
Congenital LCM carries more severe risks. Infection in the first trimester can increase miscarriage risk. In the second or third trimester, it can cause severe birth defects, including hydrocephalus, chorioretinitis, and intellectual disabilities. The mortality rate for infants with congenital LCMV infection is approximately 35%, and among survivors, about two-thirds experience long-term neurological abnormalities.