Fears that the recent outbreak of the deadly Ebola virus in West Africa could go global has health officials around the world on increased alert. Airline passengers from the region who have shown symptoms of the disease have even been quarantined in some cases.

The outbreak -- the largest in history -- has spread across Guinea, Liberia, Nigeria and Sierra Leone and killed at least 672 people, according to the World Health Organization. The disease has no vaccine and no specific treatment. It has a fatality rate of at least 60%.

In the United Kingdom, the Department of Health confirmed Wednesday that a man who flew into Birmingham airport recently from Nigeria via Paris was clear of the virus despite saying he felt feverish. Newly appointed British Foreign Secretary Philip Hammond planned to chair an emergency meeting later Wednesday on how to stop the spread of the virus.

Two American medical missionaries working with Ebola patients in Liberia have been diagnosed with the virus. Dr. Kent Brantly, 33, is medical director of the Ebola care center run by Samaritan's Purse on the outskirts of the Liberian capital of Monrovia, and Nancy Writebol had been disinfecting doctors and nurses working with Ebola patients. A statement by the North Carolina-based group said both showed "slight improvement" in the past 24 hours but remain in serious condition.