LASSA FEVER: WHAT YOU NEED TO KNOW
Lassa fever is an acute illness caused by the Lassa virus, named after the Nigerian town where the first cases (two missionary nurses) were detected in 1969. Lassa virus is a member of the virus family Arenaviridae and is zoonotic (i.e. animal-borne). It causes a severe and often fatal haemorrhagic illness which can occur with occasional epidemics, during which case-fatality rate can reach 50%. Since its discovery in Lassa, Borno state, Nigeria, there have been countless outbreaks of Lassa fever across West Africa. Lassa fever is endemic in portions of West Africa-Nigeria, Guinea, Liberia, Sierra Leone, however, the rodent species which carries the virus are found throughout West Africa.
The number of Lassa virus infections per year in West Africa ranges between 100,000 and 300,000 with approximately 5,000 deaths.
The present outbreak in Nigeria started with the first case recorded in Bauchi state in November 2015. Since then, cases have been reported in Kano, Nasarawa, Niger, Taraba, Rivers, Edo, Oyo states and most recently, in Abuja. There have been a total of 43 deaths from Lassa fever since the outbreak began.
Mode of transmission
The reservoir of Lassa virus is a rodent known as the ‘multimammate rat’ (due to its numerous mammary glands) of the genus Mastomys. The rat breeds frequently, producing large numbers of offspring and are numerous in the savannas and forests of West Africa. In addition, Mastomys readily colonize human homes, shedding the Lassa virus in their urine and droppings and transit same when humans come in direct contact with these materials, through touching objects or eating food contaminated with these materials. Transmission of the virus can also be air-borne or via inhalation of aerosols contaminated with rodent excretions. Infection with Lassa virus may occur through direct consumption of the rodent as food.
Person-to-person spread of Lassa fever occurs when a person comes in contact with the blood, tissue, secretions or excretions of an individual already infected with the Lassa virus. This type of transmission is common in villages and hospitals. However, the virus cannot be spread through casual skin-to-skin contact without exchange of body fluids.
Symptoms and signs
Symptoms and signs of Lassa fever typically occur 1-3 weeks after the patient comes in contact with the virus (incubation period). They include fever, pain behind the chest wall, sore throat, back pain, cough, abdominal pain, vomiting, diarrhea, conjunctivitis, facial swelling, protein in urine and bleeding from mucous membranes. Hearing loss, tremors and encephalitis have also been associated with Lassa fever.
The symptoms of Lassa fever are varied and non-specific and so clinical diagnosis is often difficult and may be mistaken for typhoid fever or malaria. It is most often diagnosed by using enzyme-linked immunosorbent serologic assays (ELISA) which detect antibodies and the Lassa antigen. The virus may be cultured in 7 to 10 days. It can also be detected by reverse transcription-polymerase chain reaction (RT-PCR).
Ribavirin is an antiviral drug which has been used with success in Lassa fever patients, especially when given early in the course of the illness (within the first 6 days). Other supportive care such as maintenance of appropriate fluid and electrolyte balance, oxygenation, blood pressure and treatment of other complicating infections.
Approximately 15-20% of patients hospitalized for Lassa fever die from the illness.
The most common complication of Lassa fever after recovery is deafness and in many cases, it is permanent. Spontaneous abortion is another serious complication.
- Avoid contact with Mastomys rodents
- Store food in rodent-proof containers
- Keep the home clean to prevent rodents from entering
- Eating these rodents is not recommended
- Make rodent traps available in and around homes to reduce their population
- Wear protective clothing such as masks, gloves, gowns, gloves to avoid contact with secretions when caring for patients with Lassa fever
- Institute infection control measures such as complete equipment sterilization and isolation of infected patients
- Educating people in high risk areas about ways to decrease rodent populations in and around their homes will aid in the control and prevention of Lassa fever
- CDC Lassa Fever Factsheet. Available online at http://www.cdc.gov/ncidod/dvrd/spb/mnpages/dispages/Fact_Sheets/Lassa_Fever_Fact_Sheet.pdf. Accessed 15th January 2016.
- Viral Haemarrhagic Fever Consortium. Lassa Fever. Available online at http://vhfc.org/lassa_fever. Accessed 15th January 2016