Nigeria: Rising cases of Lassa fever

An upward trend in the number of Lassa fever cases is reported in Nigeria

The Nigeria Centre for Disease Control and Prevention (NCDC) reports an unprecedented upward trend in the number of confirmed cases of Lassa fever being reported, with an increased number of states reporting cases, compared to previous years. The risk of healthcare worker infections and deaths due to Lassa fever infection has also increased. In response to the current situation in Nigeria, the NCDC is strengthening existing response activities to the outbreak; a coordinated national drive with the aim of interrupting disease transmission is underway [1].

The number of Lassa fever cases in the country began to rise towards the end of November 2022 [1]. As of 29 January 2023, the cumulative total of cases since the start of the year reached 361 (confirmed) with 53 deaths, reported from 17 (of 36) states (Adamawa, Anambra, Bauchi, Benue, Delta, Ebonyi, Edo, Enugu, Gombe, Imo, Kano, Kogi, Nasarawa, Ondo, Oyo, Plateau and Taraba) and the Federal Capital Territory (FCT). The states reporting the most cases to date are Ondo (130), Edo (113) and Taraba (26) [2].

Lassa fever is an acute viral haemorrhagic illness caused by Lassa virus. It is known to be endemic in Nigeria (and other West African countries) where the natural reservoir host, the multimammate rat (Mastomys species) is prevalent. Humans can become infected from exposure to urine or faeces of infected rats, or direct contact with infected bodily fluids including blood, urine, faeces, or semen of a person infected with Lassa virus. Person-to-person transmission may occur in both the community and in healthcare settings [3]. The incubation period is usually between seven and ten days with a maximum of 21 days [4].

Since 1980, a total of eight confirmed cases have been reported in UK travellers who visited endemic countries. In February 2022, there was one case imported into the UK from Mali which resulted in a small family cluster of Lassa infection in England. These were the first reported cases in England since 2019 [5].

Advice for travellers

Before you go

Check and follow the advice from the Foreign, Commonwealth & Development Office on safety, security, and any travel restrictions at your destination.

Check our Country Information pages to research general health risks, prevention advice and any vaccine recommendations or malaria advice for your destination.

There is currently no licensed vaccine to protect against Lassa fever [3].

While you are there

The risk of exposure to Lassa virus for the majority of those travelling to West Africa is very low. Those in high-risk occupations such as healthcare and aid workers are at greater risk [3].

You can reduce your risk of infection during travel by taking the following precautions [3]:

• Practise good general hygiene measures e.g. hand washing.
• Avoid exposure to faeces or urine of Mastomys rats (e.g., contaminated food, water or surfaces).
• Do not eat, cook, or prepare bush meat (wild animals hunted for food).
• Practise safe sex using barrier contraception.
• Healthcare workers involved in the care of those with viral haemorrhagic fever (including Lassa fever) should maintain strict principles of infection control.

Symptoms of Lassa fever may include:

• fever and shivering
• malaise
• headache
• generalised aching
• sore throat
• nausea
• vomiting
• diarrhoea, or
• cough

You should seek advice from a health professional if you develop symptoms whilst you are overseas.

When you return

If you think you, or anyone in your family has symptoms within 21 days of your return to the UK you should seek medical advice. It is important to tell your healthcare provider about any recent travel to Nigeria or other countries in West Africa.

Advice for health professionals

Health professionals should remain alert for travellers returning from West Africa who develop symptoms compatible with Lassa fever.

Health professionals should practise strict universal precautions when caring for patients when Lassa fever is suspected [3].

Guidance and information about high consequence infectious disease and their management in England and further information about Lassa fever is available from UK Health Security Agency.