WHO | Lassa Fever – Nigeria

Between January 1 and February 9, 2020, 472 laboratory confirmed cases were reported in 26 of the 36 states of Nigeria and the Federal Capital Territory, including 70 deaths (death rate = 14.8%). Of the 472 confirmed cases, 75% were reported from three countries: Edo (167 cases), Ondo (156 cases) and Ebonyi (30 cases). Other states that have reported cases include: Taraba (25), Bauchi (14), plateau (13), Kogi (13), Delta (12), Nasarawa (4), Kano (4), Rivers (4), Enugu ( 4), Borno (3), Kaduna (3), Katsina (3), Benue (2), Adamawa (2), Sokoto (2), Osun (2), Abia (2), Kebbi (2), Gombe ( 1), Oyo (1), Anambra (1), FCT (1) and Ogun (1).

Fifteen confirmed cases were recorded among healthcare professionals and one death was confirmed and one probable case.

Lassa fever is endemic in Nigeria and the annual peak in human cases is usually observed during the dry season (December-April) after the Mastromy rat reproduction cycle in the wet season (May-June). Since 90-95% of human infections are due to indirect exposure (through food or household items contaminated with urine and faeces of infected rats) or direct contact with infected Mastomys rats, very high density and high circulation of Lassa fever virus in young non-immune rat populations during the season humidity creates the potential for further infection of humans, so the number of infections is expected to continue to increase until the end of the dry season.

Public health response

• The Nigerian Center for Disease Control (NCDC) has activated the National Emergency Operations Center (EOC) with an interdisciplinary, multi-party technical team to provide a well-coordinated response and rapid control of the outbreak of Lassa in all affected countries.
• Confirmed cases are being treated at designated treatment centers in the affected countries following optimized standards of care protocols. Guidelines for appropriate case management and infection prevention and control (IPC) measures are being extended to different countries.
• Surveillance activities have been intensified in the affected countries with enhanced active case finding in the affected local government area (LGA). An updated tool for in-depth case investigation was also provided to the investigation teams to ensure that all relevant information was recorded.
• Five laboratories with the capacity to test for Lassa Fever infection in serum samples are currently operating nationwide. Recently, a laboratory for Lassa fever testing facilities was established at the Federal Medical Center in Owo, Ondo State.
• Health care workers were urged to maintain a high index of suspected cases of suspected Lassa fever and to take appropriate prevention and control (IPC) measures while treating all patients in healthcare settings.

WHO risk assessment

Lassa fever is a viral hemorrhagic fever that is transmitted to humans through contact with food or household items contaminated with rodent urine or faeces. Secondary human-to-human transmission can also occur through direct contact with the blood, secretions, organs, or other body fluids of infected persons, especially in healthcare settings.

About 80% of people infected with the Lassa virus have asymptomatic disease, but in the remaining 20% ​​the disease manifests as febrile illness of varying severity that is associated with multiple organ dysfunctions with or without bleeding. The overall case fatality rate is usually between 1% and 15% in patients hospitalized with severe illness. Early supportive care with rehydration and symptomatic treatment improves survival. Lassa fever is known to be endemic in Benin, Guinea, Ghana, Liberia, Mali, Sierra Leone and Nigeria, but it may also exist in other West African countries.

Although Nigeria is an endemic fever country and has developed capacity to manage Lasse fever outbreaks, the current overall risk is considered to be moderate nationally. Capacities at the sub-national level remain sub-optimal. Fifteen confirmed cases have been reported among healthcare professionals in this epidemic and highlights the urgent need to strengthen IPC measures. Furthermore, the capacity of the state to detect and respond to lasso fever outbreaks (surveillance, laboratory, case management, coordination and IPC measures) needs to be improved.

Overall regional and global risk is considered to be low due to the minimum number of suspected cross-border transfers from Nigeria to neighboring countries.

Tip of WHO

Lasse Fever Prevention relies on promoting good “community hygiene” to discourage rodents from entering their homes. Effective measures include storing grain and other foodstuffs in rodent containers, dumping garbage away from home, and keeping the household clean. Mastomas, an African rodent genus, are so abundant in endemic areas that they cannot be completely removed from the environment. 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 prevention measures and control precautions when caring for patients, regardless of their presumed diagnosis. These include basic hand hygiene, breathing hygiene, the use of personal protective equipment (to prevent splashing or other contact with contaminated materials) and safe injection procedures.

Health care providers who care for suspected or confirmed Lassa fever should apply additional infection control measures to prevent contact with the patient’s blood and body fluids and contaminated surfaces or materials such as clothing and bedding. When in close contact (within one meter) of patients with Lassa fever, healthcare professionals should wear face protection (face shield or medical mask and goggles), clean non-sterile long-sleeved bathrobe and gloves (sterile gloves for some procedures).

The WHO continues to advise all countries endemic to Lassa fever on the need to improve early detection and treatment of cases to reduce the case fatality rate.

WHO advises against any restrictions on travel or trade in or from Nigeria and the affected areas based on currently available information.

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