More than 240 doctors and nurses working in West Africa to try to contain the Ebola epidemic have become infected with the illness, and more than 120 have died, the World Health Organization says.

The health agency issued a statement Tuesday detailing the "unprecedented" toll that Ebola is taking on health workers who have been treating infected patients in Guinea, Liberia, Nigeria, and Sierra Leone.

"Ebola has taken the lives of prominent doctors in Sierra Leone and Liberia, depriving these countries not only of experienced and dedicated medical care but also of inspiring national heroes," the WHO said.

The health agency says a high proportion of medical staff have become infected in this epidemic and says there are several reasons why.

Firstly, there far too few medical staff for an outbreak of this size – the largest ever. The WHO estimates that in the three hardest-hit countries, only one to two doctors are available to treat 100,000 people, and most are in urban areas.

What's more, there have been shortages of the gloves, masks and other personal protective equipment that can protect medical staff from becoming infected with the virus.

"Even in dedicated Ebola wards, personal protective equipment is often scarce or not being properly used," the agency said.

As well, the current outbreak has not been contained to remote villages the way other outbreaks have been. Instead, it's hitting cities and areas where the public is unfamiliar with the disease, which has increased opportunities for undiagnosed patients to come into contact with hospital staff.

There is also the problem that several other infectious diseases that mimic Ebola, such as malaria, typhoid fever, and Lassa fever, are endemic in these areas. Doctors and nurses have often not suspected Ebola in ill patients and not taken protective measures until it's been too late.

"Some documented infections have occurred when unprotected doctors rushed to aid a waiting patient who was visibly very ill. This is the first instinct of most doctors and nurses: aid the ailing," the agency explained.

The Ebola virus can spread to health care workers when the blood or bodily fluids of infected people comes into contact with the workers' broken skin or mucous membranes. It can also be spread through contact with surfaces contaminated with infected fluids.

The heavy toll on health care workers in this outbreak has led some staff to refuse to come to work. In other cases, patients are shunning hospitals, worried by how many health care workers are becoming ill. That's led to the closure of hospitals, putting patients with other medical needs at risk.

This Ebola epidemic began in December 2013 and has infected at least 2,600 people and led to the deaths of more than 1,400.

Study finds insufficient protective equipment

A study published this month in Tropical Medicine and International Health, found that even before this outbreak, health care workers in some of the world’s poorest countries consistently lack basic protective equipment.

The study, based on data compiled between 2008 and 2013, found that in Liberia, only 56 per cent of hospitals had protective eyewear for doctors and nurses, and only 63 per cent had sterile gloves. In Sierra Leone, just 30 per cent of hospitals had protective eyewear, while 70 per cent had sterile gloves.

Study leader Dr. Adam L. Kushner, with the Johns Hopkins Bloomberg School of Public Health’s Department of International Health, says that one of the only benefits of the current Ebola crisis is that it's highlighted the lack of personal protective equipment for health workers in many countries.

“We can all learn from this new epidemic and be better prepared for the next one by remembering that inexpensive protective equipment can keep doctors and nurses safe from infection – and better able to care for patients who need them,” Kushner said in a statement.

“It is imperative that we make this a priority.”