What is Lassa fever?

Three British citizens have been brought back to the UK from Sierra Leone for medical tests after coming into close contact with two Dutch doctors diagnosed with a potentially fatal virus described as a cousin of Ebola.

According to The Guardian, one of the doctors who contracted Lassa disease while working in the West African country has died - prompting Public Health England (PHE) to bring home the British trio and to begin monitoring a further 15 Brits who may have been exposed. 

What is Lassa fever?

Lassa fever is a hemorrhagic fever caused by the Lassa virus and is carried by wild rats, which spread the virus through their urine and droppings, says the UK Foreign and Commonwealth Office (FCO) website.

The type of rats that carry the disease is most common in tropical West Africa and once infected, will shed the virus throughout their life.

The FCO notes that transmission of Lassa virus to humans “normally occurs through contamination of broken skin or mucous membranes via direct or indirect contact with infected rodent excreta, on floors, home surfaces, in food or water”.

It can also pass from person to person through bodily fluids, meaning healthcare workers are particularly at risk.

What are the symptoms?

Most people who contract Lassa will have “only mild symptoms such as fever, headache and general weakness”, and some may not experience any symptoms at all, the BBC reports.

There is no vaccine for the condition and it is extremely hard to diagnose, because about 80% of infected people show no or only mild symptoms. In addition, the symptoms are extremely similar to those of other a number of other diseases.

In severe cases, Lassa fever closely resembles Ebola, causing “bleeding through the nose, mouth and other parts of the body”, and significant damage to internal organs, says the broadcaster.

Lassa fever has a fatality rate of about 1% overall, but women who contract the disease late in pregnancy face an 80% chance of losing their child, or dying themselves.

Has the disease reached the UK? 

Dr Jake Dunning, head of emerging infections at PHE, says that despite the repatriations from Sierra Lione, there are currently “no confirmed cases of Lassa fever in the UK”.

“It is important to emphasise that Lassa fever does not spread easily between people and the overall risk to the public is very low,” he added.

By contrast, Nigeria has been gripped by an outbreak of the deadly disease since the beginning of the year, with at least 90 confirmed deaths. The BBC reports that the epidemic has around a 22% fatality rate among confirmed and probable cases.