Lassa haemorrhagic fever

Lassa haemorrhagic fever is a zoonotic disease and known to be endemic in Benin, Ghana, Guinea, Liberia, Mali, Sierra Leone, Togo and Nigeria, but probably exists in other West African countries. 80 per cent of people who become infected with Lassa virus have no symptoms. The overall case fatality rate is one per cent. The observed case fatality rate among patients hospitalized with severe cases of Lassa fever is 15—20 per cent, but can reach 50 per cent of hospitalized patients during epidemics. Because the clinical course of the disease is so variable, detection of the disease in affected patients has been difficult. When presence of the disease is confirmed in a community, prompt isolation of affected patients, good infection prevention and control practices and rigorous contact tracing can stop outbreaks.

The following are standard case definitions to allow national health authorities to interpret data in an international context. However, during an outbreak case definitions may be adapted to the local context and the Red Cross Red Crescent should use those agreed/established by national health authorities. NB: Consider that during community-based surveillance, volunteers should use broad (simplified) case definitions (referred to as community case definitions) to recognize most or all possible cases, provide relevant risk communication and appropriate actions and encourage them to seek care. Other actors such as healthcare workers or investigators studying the cause of a disease, on the other hand, can use more specific case definitions that may require laboratory confirmation.

Suspected case: Known exposure to a person suspected to have Lassa haemorrhagic fever AND fever greater than 38°C for less than three weeks PLUS absence of signs of local inflammation AND two major signs or one major and two minor signs.

Major signs: bleeding, swollen neck or face, conjunctiva or subconjunctival haemorrhage, spontaneous abortion, petechial or haemorrhagic rash, new onset of tinnitus or altered hearing, persistent hypotension, absence of clinical response after 48 hrs to antimalarial and/or broad-spectrum antibiotic therapy.

Minor signs: headache, sore throat, vomiting, diffuse abdominal pain /tenderness, chest/retrosternal pain, cough, diarrhoea, generalized muscle or joint pain, profuse weakness.

WHO case definition source of information:

https://www.who.int/news-room/fact-sheets/detail/lassa-fever

• People who live in or visit endemic regions (primarily in West Africa) and have exposure to the Mastomys rat, or food or household items that are contaminated with urine or faeces of these rats.
• Persons living in rural areas where Mastomys rats are usually found, especially in communities with poor sanitation or crowded living conditions.
• Unsafe domestic food storage.
• Unprotected sexual intercourse with infected people during outbreaks.
• Lack of personal protective equipment, infection prevention and control practices (barrier nursing) for healthcare workers in endemic areas and during outbreaks.

The secondary attack rate for Lassa fever in healthcare facilities varies depending on the quality of IPC practices.

• Women in the third trimester of pregnancy (over 80 per cent of all Lassa fever cases are fatal in this period).
• Immunosuppressed persons such as those receiving chemotherapy, transplant recipients or HIV carriers.
• People with chronic diseases such as renal disease, cancer, chronic liver and lung disease and diabetes.

Lassa virus.

Zoonotic disease: Multimammate rat (Mastomys). Rats carrying Lassa virus do not become ill, but they can shed the virus in their urine and faeces.

Vehicle-borne transmission:

• Lassa virus is transmitted to humans via contact with food or household items contaminated with rodent urine or faeces.
• People can become infected with the virus by inhaling tiny particles in the air contaminated with infected rodent excretions. This can occur during cleaning activities, such as sweeping.
• Lassa virus may be spread in contaminated medical equipment, such as reused needles.

Contact transmission:

• Person-to-person infections and laboratory transmission can occur, particularly in hospitals lacking adequate infection prevention and control.
• Lassa virus can spread between humans through direct contact with the tissues, blood, urine, faeces, vaginal and seminal fluids, or other bodily secretions or excretions of a person infected with Lassa fever.

Sexual transmission:

• Unprotected sexual intercourse with a man who has recovered from Lassa fever in the first year after recovery, as the virus may remain in semen for some months.

Casual contact (including skin-to-skin contact without exchange of body fluids) does not spread Lassa virus.

6—21 days.

People remain infectious as long as their blood contains the virus. It is believed that sperm may still contain virus for a period of up to a year after the patient’s recovery.

• About 80 per cent of people who become infected with Lassa virus have no or mild symptoms (e.g. slight fever, headache) and go undiagnosed.
• One in five infections progresses to severe disease, where the virus affects several organs such as the liver, spleen and kidneys.
• The onset of the disease, when it is symptomatic, is usually gradual, starting with fever, general weakness and malaise.
• After a few days, headache, sore throat, muscle pain, chest pain, nausea, vomiting, diarrhoea, cough, respiratory distress and abdominal pain may 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 develop.
• Neurological problems are possible, including hearing loss, tremors and encephalitis
• Shock, seizures, tremor, disorientation and coma may be seen in the later stages.
• Death may occur within two weeks after symptom onset, due to multi-organ failure.
• 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. Deafness may develop in mild as well as severe cases.
• Transient hair loss and gait disturbance may occur during recovery.

Other haemorrhagic fevers (Marburg haemorrhagic fever, Rift Valley fever, Crimean-Congo, dengue fever), malaria, typhoid fever, measles, shigellosis and other infections.

Laboratory specimens may be hazardous and must be handled with extreme care. Lassa virus infections can only be diagnosed definitively in the laboratory using any of the following tests:

• Antibody enzyme-linked immunosorbent assay (ELISA).
• Reverse transcriptase polymerase chain reaction (RT-PCR) assay (during the early stage of the disease).
• Virus isolation by cell culture (in 7 to 10 days, only in a high containment laboratory).

Please refer to the appropriate local or international guidelines for clinical management. All clinical management including the administration of a treatment or vaccine should be conducted by a health professional.

• Prompt isolation of affected patients.
• Supportive care and treatment of complications. Non-specific antivirals, if recommended by local protocols.
• There is currently no vaccine that protects against Lassa fever.

Immunity against reinfection does occur after recovery from the illness but it is not known how long this immunity lasts.