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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, CNN reported.

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.