'Disease X': Scientist who discovered Ebola warns about deadlier pandemics

'Disease X' ("X" stands for unexpected) is only hypothetical—a serious disease that scientists and public health experts fear could spread across the world if and when it breaks out, according to the World Health Organization.

However, 'Disease X' is a hypothesis rooted in scientific facts. Experts warn of the very real possibility of a disease as contagious as COVID-19 and as deadly as Ebola.

The chatter around 'Disease X' has grown with a case in DRC's Ingende town, where a woman exhibited the symptoms of Ebola but tested negative for the disease.

Although experiencing Ebola-like symptoms are said to be common, doctors still do not know the cause of her high fever and diarrhea, according to CNN.

Even now that she has recovered, her illness remains a mystery.

The patient's physician, Dr. Dadin Bonkole, told CNN, "We've all got to be frightened...Ebola was unknown. COVID was unknown. We have to be afraid of new diseases."

Professor Jean-Jacques Muyembe Tamfum, who helped discover the Ebola virus, told the publication that humanity faces an unknown number of new and potentially fatal viruses emerging from Africa's tropical rainforests.

Notably, since the first animal-to-human infection was identified in 1901 (the yellow fever), scientists have found at least 200 more viruses known to cause diseases in humans.

New species of viruses are being discovered at a rate of three to four a year, according to a research by Mark Woolhouse, a professor of infectious disease epidemiology at the University of Edinburgh.

Experts say the rising number of emerging viruses is a result of ecological destruction and wildlife trade.

When their habitats are cleared, animals like rats or bats survive where larger animals get annihilated.

They're able to live alongside humans, which raises the chances of vectors carrying new diseases to humans.

Scientists believe zoonotic illnesses—like Ebola and COVID-19—transfer to humans when wild animals are butchered.

The United Nations has warned that if the current trends of deforestation and population growth continue, DRC's rainforest may completely disappear by 2100, exposing humans to more viruses.

A multidisciplinary group of scientists estimates that an annual global investment of $30 billion into projects to protect rainforests, stop wildlife trade, and farming would be enough to balance out the cost of preventing future pandemics.