(CNN) - The worst outbreak of Ebola, which has killed 961 people and triggered an international public health emergency, may have started with a 2-year-old patient in a village in Guinea.
About eight months ago, the toddler, whom researchers believe may have been Patient Zero, suffered fever, black stool and vomiting. Just four days after showing the painful symptoms, the child died on December 6, 2013, according to a report published in The New England Journal of Medicine.
Scientists don't know exactly how the toddler contracted the virus. Ebola is spread from animals to humans through infected fluids or tissue, according to the World Health Organization.
"In Africa, infection has been documented through the handling of infected chimpanzees, gorillas, fruit bats, monkeys, forest antelope and porcupines," WHO says, though researchers think fruit bats are what they call the virus's "natural host."
Researchers who published the paper this year found a chain of illnesses in the toddler's family.
After the child's death, the mother suffered bleeding symptoms and died on December 13, according to the report. Then, the toddler's 3-year-old sister died on December 29, with symptoms including fever, vomiting and black diarrhea. The illness subsequently affected the toddler's grandmother, who died on January 1, in the family's village of Meliandou in Guéckédou.
The area in southern Guinea is close to the Sierra Leone and Liberia borders.
The illness spread outside their village after several people attended the grandmother's funeral.
Funerals tend to bring people in close contact with the body. Ebola spreads from person to person through contact with organs and bodily fluids such as blood, saliva, urine and other secretions of infected people. It has no known cure.
Two of the funeral attendees appeared to bring back the virus to their village, and it spread to health care workers and other family members who took care of infected patients.
"A health care worker from Guéckédou with suspected disease, seems to have triggered the spread of the virus to Macenta, Nzérékoré, and Kissidougou in February 2014," stated the report, noting that more Guinea towns were affected.
Clusters of the disease popped up in early 2014 in these areas, with the initial patients suffering fever, vomiting and severe diarrhea, according to the report. Hemorrhaging was less frequent, the report noted.
In early March, the Ministry of Health in Guinea and Doctors Without Borders in Guinea were notified about the disease clusters.
Health investigators arrived that month and began tracing the disease by examining hospital documents and conducting interviews with affected families and villagers.
Ebola has now spread to Liberia, Sierra Leone and Nigeria, prompting global concerns.
The report about the emergence of Ebola in Guinea was authored by dozens of international doctors and researchers from institutions in France, Germany, Guinea, WHO and Doctors Without Borders.