LASSA FEVER: WHAT YOU NEED TO KNOW

Lassa fever is a zoonotic disease, meaning that humans become infected from contact with infected animals. The animal reservoir or host of Lassa virus (LASV) is a rodent of the genus Mastomys, commonly known as the multimammate rat. Mastomys rats infected with LASV do not become ill, but they can shed the virus in their urine and faeces.

SYMPTOMS

The incubation period of Lassa fever ranges from six to 21 days. The onset of the disease, when it is symptomatic, is usually gradual

It starts with fever, then general weakness and malaise. After a few days, headache, sore throat, muscle pain, chest pain, nausea, vomiting, diarrhoea, cough and abdominal pain may follow. In severe cases, there is facial swelling, fluid in the lung cavity, bleeding from the mouth, nose, vagina or gastrointestinal tract and low blood pressure may develop. Shock, seizures, tremor, disorientation and coma may be seen in later stages. Deafness occurs in 25 per cent of patients who survive the disease. In half of these cases, hearing returns partially after one to three months. Transient hair loss and gait disturbance may occur during recovery. Death usually occurs within 14 days of onset in fatal cases. The disease is especially severe late in pregnancy, with maternal death and or foetal loss occurring in more than 80 per cent of cases during the third trimester.

TRANSMISSION

Humans usually become infected with Lassa virus from exposure to urine or faeces of infected Mastomys rats. Lassa virus may also be spread between humans through direct contact with the blood, urine, faeces or other bodily secretions of a person infected with Lassa fever. Person-to-person transmission occurs in both community and healthcare settings where the virus may be spread by contaminated medical equipment such as re-used needles.

WHO IS AT RISK?

Lassa fever occurs in all age groups and both sexes.Persons at greatest risk are those living in rural areas where Mastomys are usually found, especially in communities with poor sanitation or crowded living conditions. Health workers are at risk if caring for Lassa fever patients in the absence of proper barrier nursing and infection prevention and control practices.

DIAGNOSIS

Because the symptoms of Lassa fever are so varied and non-specific, clinical diagnosis is often difficult, especially early in the course of the disease. Lassa fever is difficult to distinguish from other viral haemorrhagic fevers such as Ebola virus disease, as well as other diseases that cause fever, including malaria, shigellosis, typhoid and yellow fever.Definitive diagnosis requires testing that is available only in reference laboratories.

TREATMENT

The antiviral drug, Ribavirin, seems to be an effective treatment for Lassa fever if given early on in the course of clinical illness. There is no evidence to support the role of Ribavirin as post-exposure prophylactic treatment for Lassa fever. There is currently no vaccine that protects against Lassa fever.

PREVENTION / CONTROL

Prevention of Lassa fever relies on promoting good community hygiene to discourage rodents from entering homes. Effective measures include storing grains and other foodstuff in rodent-proof containers, disposing of garbage far from the home, maintaining clean households and keeping cats. 

Family members should always be careful to avoid contact with blood and body fluids while caring for sick persons. In healthcare settings, staff should always apply standard infection prevention and control precautions when caring for patients regardless of their presumed diagnosis. 

These include basic hand hygiene, respiratory hygiene and use of personal protective equipment. Laboratory workers are also at risk. Samples taken from humans and animals for investigation of Lassa virus infection should be handled by trained staff. 

Regular hand washing with disinfectants should always be encouraged.