As the World Health Organization (WHO) and other organizations struggle to contain Ebola in West Africa, the virus is continuing to spread. The current outbreak is the largest Ebola outbreak in history. More than 4,800 people have died of Ebola since the outbreak began in March.

Most of the nearly 10,000 Ebola cases diagnosed during the current outbreak have come in three West African countries: Guinea, Liberia, and Sierra Leone. Liberia has been particularly hard-hit, as over half of Ebola deaths have occurred in that country.

Now, just as the world was celebrating the end of Ebola in Nigeria the virus has spread to another West African nation. According to a BBC News report the first case of Ebola in Mali has now been confirmed. A two-year-old girl who was brought by relatives from Guinea to Mali has been diagnosed with the virus. The girl’s mother reportedly died weeks ago in Guinea.

The Malian health ministry stated that the young girl was brought into a hospital on Wednesday and diagnosed with Ebola through a blood sample. She is being treated in the town of Kayes and her condition is reportedly improving. Mali has quarantined 43 people who have come into contact with the girl, including several healthcare workers.

The WHO has announced that it will be sending extra personnel to Mali to help with containment. According to the BBC the WHO and the Malian government have been preparing the country for a possible Ebola outbreak for months now.

On the other side of the world, a fourth person has now been diagnosed with Ebola in the U.S. A doctor who was working with Doctors Without Borders in Guinea arrived in New York City in on October 17. On October 23 he developed serious symptoms of Ebola and was taken to Bellevue Hospital.

The first person to be diagnosed with the virus in the U.S., a Liberian named Thomas Duncan, died in Dallas, Texas on October 8. Two healthcare workers who cared for Duncan have since been diagnosed with Ebola.

This latest case could fuel fears in the U.S. over Ebola. Earlier this week New Jersey Governor Chris Christie rolled out a comprehensive Ebola preparedness plan for his state.