Lassa fever is an animal-borne, or zoonotic, acute viral illness. It is endemic in parts of West Africa including Sierra Leone, Liberia, Guinea and Nigeria. Neighboring countries are also at risk, as the animal vector for Lassa virus, the “multimammate rat” (Mastomys natalensis) is distributed throughout the region.
An estimated 100,000 to 300,000 infections of Lassa fever occur annually, with approximately 5,000 deaths. Surveillance for Lassa fever is not standardized; therefore, these estimates are crude. In some areas of Sierra Leone and Liberia, it is known that 10-16% of people admitted to hospitals annually have Lassa fever, demonstrating the serious impact the disease has on the region.
History of Lassa Fever
Lassa Fever was first discovered in 1969 and is named after the town in Nigeria where the first cases occurred; in Lassa town, in the south of what is now Borno State, Northeast Nigeria.
Signs and Symptoms of Lassa Fever
Signs and symptoms of Lassa Fever include mild symptoms such as:
Slight feverGeneral malaise and weaknessHeadache. More serious symptoms of Lassa Fever include:Hemorrhaging (in gums, eyes, or nose, as examples)Respiratory distressRepeated vomitingFacial swellingPain in the chest, back, and abdomen and,Shock. Neurological problems have also been described, including;Hearing loss or deafness.Tremors,Encephalitis
How Long Does it Take for Lassa Fever Symptoms to Occur?
Signs and symptoms of Lassa fever typically occur 1-3 weeks after the patient comes into contact with the virus. For the majority of Lassa fever virus infections (approximately 80%), symptoms are mild and are undiagnosed. In 20% of infected individuals, however, disease may progress to more serious symptoms. Death may occur within two weeks after symptom onset due to multi-organ failure.
The most common complication of Lassa fever is deafness. Various degrees of deafness occur in approximately one-third of infections, and in many cases hearing loss is permanent. As far as is known, the severity of the disease does not affect this complication: deafness may develop in mild as well as in severe cases.
Approximately 15%-20% of patients hospitalized for Lassa fever die from the illness. However, only 1% of all Lassa virus infections result in death. The death rates for women in the third trimester of pregnancy are particularly high. Spontaneous abortion is a serious complication of infection with an estimated 95% mortality in fetuses of infected pregnant mothers.
Because the symptoms of Lassa fever are so varied and nonspecific, clinical diagnosis is often difficult. Lassa fever is also associated with occasional epidemics, during which the case-fatality rate can reach 50% in hospitalized patients.
How Lassa Fever is Transmitted
Lassa Fever can be transmitted via the following ways:
Direct contact with the Lassa virus which is mostly found in Mastomys rodents.Ingestion: Mastomys rodents are sometimes consumed as a food source and infection may occur when rodents are caught and prepared. Mastomys rodents shed the virus in urine and droppings and direct contact with these materials, through touching soiled objects, eating contaminated food, or exposure to open cuts or sores, can lead to infection.Inhalation: Contact with the virus may also occur when a person inhales tiny particles in the air contaminated with infected rodent excretions. This aerosol or airborne transmission may occur during cleaning activities, such as sweeping.Person-to-person transmission may occur after exposure to the virus in the blood, tissue, secretions, or excretions of a Lassa virus-infected individual.Lassa virus may be spread in contaminated medical equipment, such as reused needles.
Lassa Fever Treatment
Ribavirin, an antiviral drug, has been used with success in Lassa fever patients. It has been shown to be most effective when given early in the course of the illness. Patients should also receive supportive care consisting of maintenance of appropriate fluid and electrolyte balance, oxygenation and blood pressure, as well as treatment of any other complicating infections.
How to Prevent Lassa Fever Infection
To prevent Lassa Fever infection, you should:
Avoid contact with Mastomys rodents, especially in the geographic regions where outbreaks occur (Nigeria, Guinea, Benin, Togo, Sierra Leone, Ghana, Cote d’Ivoire, Liberia, and Mali).Store food away in rodent-proof containers and keeping the home clean helps to discourage rodents from entering homes.Stop using these rodents as a food source.Take preventive precautions against contact with patient secretions such as wearing protective clothing, such as masks, gloves, gowns, and goggles; using infection control measures, such as complete equipment sterilization; and isolating infected patients from contact with unprotected persons until the disease has run its course.
Lassa Fever Diagnosis
Lassa fever is most often diagnosed by using enzyme-linked immunosorbent serologic assays (ELISA), which detect IgM and IgG antibodies as well as Lassa antigen. Reverse transcription-polymerase chain reaction (RT-PCR) can be used in the early stage of the disease. The virus itself may be cultured in 7 to 10 days, but this procedure should only be done in a high containment laboratory with good laboratory practices. Immunohistochemistry, performed on formalin-fixed tissue specimens, can be used to make a post-mortem diagnosis.
Risk of Exposure
Individuals at greatest risk of Lassa virus infection are those who live in or visit endemic regions, including Sierra Leone, Liberia, Guinea, and Nigeria and have exposure to the multimammate rat. The risk of exposure may also exist in other west African countries where Mastomys rodents exist. Hospital staff are not at great risk for infection as long as protective measures and proper sterilization methods are used.
