Lassa mammarenavirus

Lassa mammarenavirus is a single-stranded RNA virus belonging to the Arenaviridae family, responsible for causing Lassa fever, a type of viral hemorrhagic fever. The virus is primarily found in West Africa and is named after the town of Lassa in Nigeria, where it was first identified in 1969. Transmission to humans occurs through exposure to the urine or feces of infected Mastomys natalensis rats, which serve as the natural reservoir. Human-to-human transmission can also occur via direct contact with the blood, urine, feces, or other bodily fluids of an infected person.

Transmission and Epidemiology

Lassa mammarenavirus is endemic in parts of West Africa, including Nigeria, Liberia, Sierra Leone, and Guinea. The virus is transmitted to humans through contact with food or household items contaminated with rodent excreta. Secondary transmission between humans can occur through direct contact with bodily fluids of an infected person, posing a significant risk in healthcare settings without proper infection control measures.

Clinical Presentation

The incubation period of Lassa fever ranges from 6 to 21 days. The onset of the disease is typically gradual, starting with fever, general weakness, and malaise. After a few days, headache, sore throat, muscle pain, chest pain, nausea, vomiting, diarrhea, cough, and abdominal pain can follow. In severe cases, facial swelling, fluid in the lung cavity, bleeding from the mouth, nose, vagina, or gastrointestinal tract, and low blood pressure may be seen. Severe cases can progress to hearing loss, tremors, encephalitis, and coma, which can be fatal.

Diagnosis

Diagnosis of Lassa fever is challenging, especially in the early stages, due to its nonspecific symptoms that mimic other febrile illnesses such as malaria and typhoid fever. Laboratory diagnosis is typically performed by testing for viral RNA by RT-PCR, detecting virus-specific antigens, or isolating the virus from blood or tissue samples. Serological tests to detect antibodies may be useful for epidemiological studies but are not effective for diagnosing acute infections.

Treatment and Prevention

The antiviral drug Ribavirin has been shown to be effective in treating Lassa fever if administered early in the course of the disease. Supportive care, including rehydration and treatment of specific symptoms, improves survival. There is no vaccine currently available for Lassa fever, making prevention focused on avoiding contact with the virus's natural reservoir and limiting person-to-person transmission. Measures include storing food in rodent-proof containers, disposing of garbage far from the home to discourage rodents, and maintaining clean households.

Public Health Impact

Lassa fever is a significant public health challenge in endemic areas, affecting tens of thousands of people annually. The disease is particularly burdensome for healthcare systems in West Africa, where resources are limited, and the risk of nosocomial transmission is high. International efforts are focused on improving diagnostic capabilities, treatment protocols, and developing vaccines to prevent the disease.