Lassa, a cousin of the Ebola virus, has killed more than 100 people this year

IRRUA, Nigeria - A battle is being waged on two fronts against an outbreak of Lassa fever, a cousin of Ebola, that has killed 110 people in the country this year.

Even as doctors are grappling to contain the threat, health watchdogs are struggling to understand why the deadly virus has spread so dramatically.

The Nigeria Center for Disease Control, or NCDC, has confirmed 353 Lassa cases since Jan 1, compared with 143 cases for the whole of last year.

But the possible reasons for this surge are many, said NCDC director Chikwe Ihekweazu.

"The harder you look, the more you find," he said, citing a change in the virus' environment, mutation - and better reporting of cases by the public in response to awareness campaigns.

Lassa fever is an acute viral hemorrhagic disease that can be transmitted to humans from infected rat feces or urine.

Like the notorious Ebola - but thankfully somewhat less contagious - it can also be passed from one person to another via contact with infected bodily fluids.

Full protective gear for medical personnel is vital and isolation is essential.

A visit to the Lassa fever isolation ward at the Irrua Specialist Teaching Hospital in southern Edo State - the only such unit in a country of 190 million people - provides a snapshot of the practical difficulties in tackling the peril.

Before the unit was built in 2008, suspect blood samples were sent to South Africa for an accurate diagnosis - but when the results came back it was already too late, doctors say.

Despite its unique status, the Lassa facility, staffed by a dozen Nigerian employees and a handful of European tropical medicine specialists, is struggling.

In normal times, it treats just a couple of dozen patients each year. But since the start of 2018, the unit has already admitted more than 150.

Dead rats in jars of formaldehyde decorated the corridors of the small clinic. Inside the isolation ward, the temperature was stifling at above 40 C.

Kevin Ousman, who specializes in combating viral risks at the World Health Organization, spends his days reminding people of basic protection.

"Given the situation we're living here, we are going right down to the basics," Ousman said.