UK officials are checking for any possible cases of Lassa fever after a traveller to England, who has since returned to Nigeria, is known to have been infected.
The virus does not spread easily between people, and the overall risk to the public is very low, experts advise.
Anyone yet to be contacted by the UK Health Security Agency (UKHSA) is very unlikely to have had any exposure, they say.
In some West African countries, where the disease is endemic, people usually become infected through exposure to food, or household items contaminated with urine or faeces of rats.