Awaiting Disaster: Ebola crisis over shadow Lassa fever cases

The peak season for Lassa fever in West Africa is about to begin. The viral haemorrhagic fever has been largely forgotten in the Ebola crisis, and health workers are warning that they may not have the resources to deal with the disease if cases increase.

At first sight the symptoms of Lassa are identical to Ebola. There can be bleeding, vomiting and fever. But whereas Ebola is a new outbreak, Lassa is a constant presence. Every year it infects from 300,000 to 500,000 people, killing up to 20,000.

All of the countries worst hit by Ebola are home to Lassa fever. On Friday, Dr Geraldine O'Hara from Doctors Without Borders (MSF) told the BBC that one of her colleagues had died of Lassa despite all efforts to save her.

Nigeria may also be seeing its first outbreak of the season. Only weeks after successfully containing Ebola, Nigerian media have reported an outbreak of Lassa in Oyo State.

There is one main difference between an outbreak of Ebola and Lassa. A Lassa outbreak is caused by rats. The rodents carry the disease into homes and food stores, especially in the dry season running from November to April.

"We have had literally dozens of cases of Lassa fever already in the eastern part of Sierra Leone," said Prof Robert Garry of Tulane University which has researched Lassa in West Africa for a decade.

Once infected, Lassa can spread from person-to-person. Not everyone who catches it becomes seriously ill, but fatality rates have been known to be as high as 70%. It is less easily transmitted than Ebola, but nonetheless patients must still be treated in complete isolation.

The containment of Lassa fever was a major focus in West Africa until Ebola arrived. It was in a Lassa laboratory that Sierra Leone's first Ebola case was identified.

Dr Sheik Umar Khan, head of the Lassa fever programme at Kenema Government Hospital, had spent a decade building a specialised treatment centre. He died of Ebola in September.

"We lost our head physician and six of our nurses and a lab technician," said Dr John Schieffelin from Tulane University, who worked at the hospital.

Kenema's Lassa ward had been overwhelmed with Ebola patients. "It is essentially abandoned except for the Ebola treatment area," said Dr Schieffelin.

The remaining health workers in West Africa are already overstretched with Ebola. As cases of a second haemorrhagic fever begin to rise, some are worried that Lassa may go undiagnosed and untreated.

"Attention has completely shifted now from Lassa to Ebola. There are cases of Lassa fever being actually considered to be Ebola cases in many places," said Prof Christian Happi of Redeemer's University in Nigeria. "In that regard it is a very complicated situation for us, especially in Liberia and in Sierra Leone."

"This is a hidden disaster," said Dr Matthias Borchert in Liberia from the Charite University of Medicine in Berlin and the London School of Hygiene and Tropical Medicine. "The health system in Liberia has virtually come to a halt for anything but Ebola. Whether it is Lassa, malaria or complicated deliveries - it is difficult to find any treatment."