The increase in cases of Ebola in west Africa is a "cause for concern", but the risk to travellers remains "very low", Public Health England (PHE) said.
Around 779 cases have been reported in Guinea, Sierra Leone and Liberia, killing an estimated 481 people in the largest ever known outbreak of the disease.
PHE confirmed it has sent a number of laboratory and health staff to the region in a bid to bring it under control.
"The increase in cases and expansion into new areas are cause for concern, as this indicates that the outbreak is not yet under control," Dr Dilys Morgan, head of gastrointestinal, emerging and zoonotic diseases at PHE, said.
"The risk to travellers and people working in these countries of contracting Ebola is very low, but we have alerted medical practitioners about the situation in West Africa and requested they remain vigilant for unexplained illness in those who have visited the affected areas."
An infectious diseases doctor who contracted the Ebola virus at work in Guinea has spoken to ITV News about beating the disease.
Could the deadly virus which has killed over 400 people in West Africa spread to Britain and the rest of Europe?
The clinic in Guinea is fully aware of the deadly nature of the virus. On one side are the patients - on the other is the morgue.