Lassa Virus- An Overview


Lassa virus (LASV) is a single-stranded RNA virus that belongs to the family Arenaviridae, genus Mammarenavirus. It is one of the causative agents of viral hemorrhagic fever (VHF), a severe and often fatal disease that affects multiple organs and systems in humans. Lassa virus was first isolated and identified in 1969, after an outbreak of VHF among nurses in a hospital in Lassa, a town in northeastern Nigeria. Since then, Lassa virus has been recognized as an emerging and re-emerging pathogen that poses a significant public health threat in West Africa, where it is endemic in several countries, including Sierra Leone, Liberia, Guinea, and Nigeria. It is estimated that Lassa virus infects 100,000 to 300,000 people annually in this region, resulting in about 5,000 deaths. Lassa virus can also cause sporadic cases or outbreaks in travelers or health care workers who have been exposed to the virus in endemic areas or in laboratory settings.

Lassa virus is a zoonotic virus, meaning that it is transmitted to humans from animals. The natural reservoir of Lassa virus is a rodent of the genus Mastomys, commonly known as the multimammate rat. These rodents are widely distributed and abundant in West Africa, and can shed the virus in their urine and feces without showing any signs of illness. Humans can become infected with Lassa virus by direct or indirect contact with contaminated rodent excreta or materials, such as food or household items. Human-to-human transmission can also occur through contact with infected blood or body fluids of symptomatic patients or deceased persons. Nosocomial transmission, or transmission within health care facilities, is a major concern for Lassa virus infection, especially in resource-limited settings where infection prevention and control measures are inadequate.

The incubation period of Lassa virus infection ranges from 6 to 21 days. The clinical manifestations of Lassa virus infection are variable and nonspecific, making diagnosis challenging. About 80% of infected individuals have mild or no symptoms. However, about 20% of infected individuals develop severe disease that can affect multiple organs, such as the liver, spleen, kidneys, lungs, heart, and central nervous system. The common signs and symptoms of Lassa virus infection include fever, headache, malaise, sore throat, cough, chest pain, nausea, vomiting, diarrhea, abdominal pain, and facial swelling. In severe cases, patients may develop bleeding from various sites, such as the mouth, nose, gums, eyes, ears, vagina, or gastrointestinal tract. Other complications include shock, seizures, tremor, disorientation, coma, deafness (which may be permanent), hair loss (which may be temporary), and gait disturbance (which may be temporary). The case fatality rate of Lassa virus infection is about 1% overall but can reach up to 15% among hospitalized patients with severe disease.

The diagnosis of Lassa virus infection is based on laboratory testing of blood or tissue samples. Several methods are available for detecting the presence of the virus or its components (such as RNA or antigens) or the host immune response (such as antibodies) to the virus. These methods include reverse transcription polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA), immunofluorescence assay (IFA), immunohistochemistry (IHC), and virus isolation by cell culture. However, these methods require specialized equipment and biosafety level 4 (BSL-4) laboratories that are not widely available in endemic areas. Therefore, rapid diagnostic tests (RDTs) that can be performed at the point of care with minimal resources are needed for timely diagnosis and management of Lassa virus infection.

The treatment of Lassa virus infection consists of supportive care and antiviral therapy. Supportive care includes hydration, electrolyte balance correction,