The most fatal Ebola outbreak in history continues to grow in three West African countries — Guinea, Sierra Leone and Liberia.

As of July 28, most of Liberia's borders were closed, and Nigeria halted Liberia and Sierra Leone-bound flights after one infected man came into the country last week.

The outbreak began in February before moving beyond its containment in Guinea’s rural towns and into the capital city. Senegal shut its borders in hopes of isolating the disease. When the World Health Organization announced the outbreak, 83 people had died. Today, the death toll has increased to 660 people. More than 1,000 have contracted the disease. In Koundony, Guinea, one in eight residents are dead.

Ebola is an unpreventable and very contagious viral disease that spreads through bodily fluids. Currently, there is no known cure. The disease is fatal for 9 out of 10 people who contract it.

The New York Times reported that some residents in areas experiencing the outbreak are wary of foreign health workers trying to treat symptoms and contain the disease, worsening the epidemic. The virus has killed one Liberian doctor and infected several foreign aid workers.