Infectious Disease and Microbiology – Lymphocytic Choriomeningitis Virus

Overview

Lymphocytic choriomeningitis virus (LCMV) is an enveloped RNA virus belonging to the family Arenaviridae. It is a rodent-associated zoonotic virus that usually causes either an asymptomatic or mild febrile illness but can occasionally produce aseptic meningitis, meningoencephalitis, or other neurologic disease.

A characteristic diagnostic clue is marked lymphocytic pleocytosis in the cerebrospinal fluid (CSF).

Classification

Virus: Lymphocytic choriomeningitis virus

Abbreviation: LCMV

Family: Arenaviridae

Genus: Mammarenavirus

Major reservoir: House mouse

LCMV is related to other mammarenaviruses, including Lassa virus, but the clinical syndromes are substantially different.

Microbiologic Characteristics

LCMV is:

• Enveloped

• A single-stranded RNA virus

• Characterized by two RNA genome segments

• Helical in nucleocapsid organization

• An arenavirus

The two genome segments are conventionally called:

L segment

and

S segment

Genome

The source describes the genome as:

Two single-stranded, circular RNA segments

More precisely, arenaviruses possess two single-stranded RNA genome segments with an ambisense coding strategy. The genome is segmented but is not generally described as two conventional circular RNA molecules.

Incubation Period

The incubation period is generally approximately:

1–2 weeks

The exact interval can vary depending on the nature and intensity of exposure.

Epidemiology

Human LCMV infection is:

Uncommon

but the virus has a broad geographic distribution because its principal reservoir, the house mouse, is widespread.

Rodent Reservoir

House Mouse

The classic natural reservoir is:

Mus musculus

the:

Common house mouse

Chronically infected mice may shed virus in:

• Urine

• Feces

• Saliva

• Other secretions

Other Rodent Exposures

Human infection has also been associated with exposure to infected:

• Pet rodents

• Laboratory rodents

• Rodent-contaminated environments

Thus, a history of mouse or other rodent exposure is an important epidemiologic clue.

Transmission

Humans may acquire LCMV through exposure to:

Rodent urine, feces, saliva, or contaminated material

Transmission may occur through:

• Inhalation of contaminated particles

• Direct contact with rodent excreta

• Contaminated food or surfaces

• Contact of contaminated material with damaged skin or mucous membranes

Person-to-Person Transmission

Routine person-to-person transmission is not typical.

Important exceptions include:

Mother-to-fetus transmission

and rare transmission through:

Organ transplantation

These routes are particularly important because they can result in severe disease.

Clinical Infection

Many LCMV infections are:

Asymptomatic

or produce a nonspecific influenza-like illness.

When symptomatic, disease can have a biphasic pattern.

Initial Febrile Illness

The first phase may include:

• Fever

• Malaise

• Myalgia

• Headache

• Nausea or vomiting

• Loss of appetite

The source also lists:

• Adenitis

• Skin rash

These manifestations can occur but are less characteristic than the febrile and neurologic syndromes.

Neurologic Disease

Aseptic Meningitis

LCMV is a classic viral cause of:

Aseptic meningitis

Neurologic manifestations can include:

• Severe headache

• Fever

• Neck stiffness

• Photophobia

• Nausea and vomiting

Meningoencephalitis

More extensive CNS involvement can produce:

Meningoencephalitis

with manifestations such as:

• Altered mental status

• Confusion

• Neurologic abnormalities

• Seizures in severe cases

CSF Findings

Lymphocytic Pleocytosis

A particularly characteristic finding is:

Significant lymphocytic pleocytosis

in the CSF.

This means that CSF contains an increased number of white blood cells with a predominance of:

Lymphocytes

Typical CSF Pattern

LCMV meningitis may demonstrate:

Elevated CSF white blood cells

• ●

Lymphocyte predominance

• ●

Elevated protein

• ●

Glucose that may be reduced

The possibility of low CSF glucose is notable because it can complicate differentiation from bacterial, fungal, or tuberculous meningitis.

High-Yield Meningitis Pattern

Rodent exposure

• ●

Febrile illness

• ●

Aseptic meningitis

• ●

Marked lymphocytic CSF pleocytosis

→ Think LCMV

Congenital LCMV Infection

Important Clinical Association

Maternal infection during pregnancy can result in:

Congenital LCMV infection

The virus can cross the placenta and cause severe fetal CNS and ocular abnormalities.

Congenital Manifestations

Important abnormalities can include:

• Hydrocephalus

• Microcephaly

• Intracranial calcifications

• Chorioretinitis

• Visual impairment

• Neurodevelopmental abnormalities

Congenital infection is an important but often underrecognized manifestation of LCMV.

High-Yield Congenital Pattern

Maternal rodent exposure

• ●

Congenital hydrocephalus

• ●

Chorioretinitis

• ●

Intracranial abnormalities

→ Consider congenital LCMV infection

Transplant-Associated Infection

LCMV has rarely been transmitted through:

Solid-organ transplantation

In immunosuppressed transplant recipients, infection can be severe and potentially fatal.

This is a very different clinical setting from the usually self-limited infection occurring in immunocompetent individuals.

Diagnosis

The source lists:

• Cell culture

• Serology

Serology

Detection of LCMV-specific antibodies can support the diagnosis.

Serologic testing is particularly useful when interpreted together with:

Compatible neurologic disease + rodent exposure

Molecular Diagnosis

Molecular testing using:

RT-PCR

may detect viral RNA in appropriate clinical specimens, particularly in specialized/reference laboratory settings.

Cell Culture

LCMV can be isolated in cell culture, but routine clinical diagnosis generally does not depend on viral culture because specialized laboratory procedures and biosafety precautions are required.

Treatment

The source recommends:

Symptomatic treatment

For most immunocompetent patients:

Supportive care

is the mainstay of management.

Supportive Management

Treatment may include:

• Hydration

• Analgesia

• Antipyretic therapy

• Management of nausea and vomiting

• Neurologic monitoring in meningitis or encephalitis

• Seizure management when necessary

There is no established routine antiviral treatment for uncomplicated LCMV infection.

Prevention

Prevention primarily involves reducing exposure to:

Rodents and rodent excreta

Important measures include:

• Rodent control in homes

• Safe food storage

• Avoiding direct contact with wild mice

• Appropriate cleaning of rodent-contaminated environments

• Careful handling of pet and laboratory rodents

Pregnant individuals should be particularly cautious about exposure to potentially infected rodents because of the risk of congenital infection.

LCMV vs. Lassa Virus

Lymphocytic choriomeningitis virus

→ Arenavirus

→ House mouse reservoir

→ Usually mild febrile illness or aseptic meningitis

→ Marked lymphocytic CSF pleocytosis

→ Congenital CNS/ocular disease possible

→ Treatment primarily supportive

Lassa virus

→ Arenavirus

→ Mastomys multimammate rat reservoir

→ West Africa

→ Lassa hemorrhagic fever

→ Sensorineural hearing loss is an important complication

→ Ribavirin has historically been used in treatment

High-Yield Clinical Pattern

Mouse/rodent exposure

• ●

Biphasic febrile illness

• ●

Meningitis or meningoencephalitis

• ●

Marked lymphocytic pleocytosis in CSF

→ Think Lymphocytic choriomeningitis virus

Exam Essentials

Virus: Lymphocytic choriomeningitis virus (LCMV)

Family: Arenaviridae

Genus: Mammarenavirus

Genome: Two single-stranded RNA segments

Coding strategy: Ambisense

Envelope: Present

Nucleocapsid: Helical

Major reservoir: House mouse (Mus musculus)

Transmission: Exposure to infected rodent excreta/secretions

Frequency: Rare human infection

Major neurologic disease: Aseptic meningitis/meningoencephalitis

Classic CSF finding: Marked lymphocytic pleocytosis

Congenital disease: Hydrocephalus, chorioretinitis and other CNS abnormalities

Diagnosis: Serology, molecular testing such as RT-PCR, specialized viral culture

Treatment: Supportive/symptomatic

Prevention: Rodent control and avoidance of rodent excreta

Key clinical pearl: Think of LCMV when a patient with mouse or rodent exposure develops a febrile illness followed by aseptic meningitis with prominent lymphocytic CSF pleocytosis. Also remember LCMV as an important congenital infection associated particularly with hydrocephalus and chorioretinitis.