Infectious Disease and Microbiology – Lassa Virus

Overview

Lassa virus is an enveloped RNA virus in the family Arenaviridae that causes Lassa fever, a viral hemorrhagic fever endemic in West Africa.

Humans usually acquire infection through exposure to urine or feces from the multimammate rat, Mastomys natalensis, although person-to-person transmission can also occur through contact with infected body fluids.

Classification

Virus: Lassa virus

Family: Arenaviridae

Genus: Mammarenavirus

Disease: Lassa fever

The source groups it under the arenaviruses.

Microbiologic Characteristics

Lassa virus is:

• Enveloped

• An RNA virus

• Characterized by two single-stranded RNA genome segments

• Helical in nucleocapsid organization

• An arenavirus

The genome segments are conventionally called:

L segment

and

S segment

Genome Organization

The viral genome is:

Segmented single-stranded RNA

with two major segments.

Arenaviruses have an ambisense coding strategy, meaning that portions of the genome encode proteins in opposite orientations.

Epidemiology

Lassa fever occurs primarily in:

West Africa

Countries with recognized endemic transmission include several areas of the region where the rodent reservoir is common.

Reservoir

The major reservoir is:

Mastomys natalensis

commonly called the:

Multimammate rat

These rodents can carry and shed the virus without necessarily becoming severely ill.

Transmission

Human infection commonly occurs after exposure to:

Rodent urine or feces

Transmission may occur through:

• Contaminated food

• Contaminated household surfaces

• Inhalation of aerosolized contaminated particles

• Direct contact with rodent excreta

Person-to-Person Transmission

Lassa virus can also spread between humans through:

Direct contact with infected blood or body fluids

This is particularly important in:

• Household settings

• Healthcare environments

• Situations with inadequate infection-control precautions

Incubation Period

The typical incubation period is approximately:

6–21 days

Symptoms may initially be nonspecific, which can make early recognition difficult.

Lassa Fever

Clinical Manifestations

Lassa fever may range from mild illness to severe systemic disease.

Early manifestations may include:

• Fever

• Weakness

• Malaise

• Headache

• Myalgia

• Sore throat

Severe Disease

More severe infection can produce:

• Vomiting

• Diarrhea

• Abdominal or chest pain

• Facial swelling

• Hypotension

• Bleeding manifestations

• Shock

• Multiorgan dysfunction

Although classified as a viral hemorrhagic fever, major bleeding is not present in every case.

Hearing Loss

A particularly important complication of Lassa fever is:

Sensorineural hearing loss

Hearing impairment may develop during or after the acute illness and can persist after recovery.

This is one of the most characteristic complications associated with Lassa fever.

Pregnancy

Lassa fever can be especially severe during:

Pregnancy

Maternal and fetal outcomes may be poor, particularly with severe infection.

High-Yield Clinical Pattern

West Africa

• ●

Rodent exposure

• ●

Acute febrile systemic illness

• ●

Possible hemorrhagic manifestations

• ●

Sensorineural hearing loss

→ Think Lassa fever

Diagnosis

The source lists:

• Cell culture

• Serology

Modern diagnosis may also include molecular detection such as:

RT-PCR

especially during acute illness.

Serology

Serologic testing can detect:

Lassa virus-specific antibodies

and may help establish the diagnosis depending on the stage of infection.

Viral Culture

Virus isolation is possible but requires:

High-containment laboratory facilities

because of the infectious risk.

It is therefore not a routine diagnostic method in most clinical laboratories.

Treatment

The source lists:

Ribavirin

Ribavirin has historically been used for severe Lassa fever, particularly when administered early in the course of illness.

Supportive Care

Management also depends heavily on:

• Fluid and electrolyte management

• Hemodynamic support

• Oxygenation and respiratory support when necessary

• Management of bleeding

• Treatment of secondary complications

Supportive care is essential even when antiviral therapy is considered.

Prevention

The source recommends:

Strict isolation for the duration of illness

Modern infection prevention focuses on appropriate isolation and meticulous precautions against exposure to:

Blood and body fluids

Infection-Control Measures

Important measures include:

• Appropriate personal protective equipment

• Safe handling of blood and body fluids

• Safe injection practices

• Proper disposal of contaminated materials

• Appropriate laboratory precautions

• Avoiding unprotected contact with infected patients

Rodent Control

Prevention also requires limiting exposure to the reservoir.

Useful measures include:

• Keeping food in rodent-proof containers

• Maintaining clean household environments

• Reducing rodent access to homes

• Avoiding consumption of food contaminated with rodent excreta

• Safe handling of rodents

Lassa Virus vs. Ebola Virus

Lassa virus

→ Arenavirus

→ Rodent reservoir

→ West Africa

→ Ribavirin historically used

→ Hearing loss is a characteristic complication

Ebola virus

→ Filovirus

→ Primarily spread through infected body fluids during outbreaks

→ Severe hemorrhagic/systemic illness

→ Specific monoclonal antibody therapies are available for some Ebola virus disease

High-Yield Reservoir Pattern

Mastomys natalensis

• ●

Rodent urine/feces exposure

• ●

West Africa

→ Lassa virus

Exam Essentials

Virus: Lassa virus

Family: Arenaviridae

Genus: Mammarenavirus

Genome: Two segmented single-stranded RNA segments

Envelope: Present

Nucleocapsid symmetry: Helical

Geography: West Africa

Reservoir: Mastomys natalensis

Transmission: Rodent excreta; infected human blood/body fluids

Disease: Lassa fever

Incubation: Approximately 6–21 days

Major complication: Sensorineural hearing loss

Diagnosis: Serology, RT-PCR; culture in specialized laboratories

Treatment in source: Ribavirin

Supportive care: Essential

Prevention: Rodent control and strict blood/body-fluid infection precautions

Key clinical pearl: Think of Lassa fever in a patient from or exposed in West Africa who develops an acute febrile illness after rodent exposure, particularly when sensorineural hearing loss occurs. The classic reservoir is the multimammate rat, Mastomys natalensis.