Two Indonesian children have died from bird flu, taking the confirmed death toll in the country worst hit by the virus to 107, a health ministry official said on Monday.

One of the victims was a 15-year-old boy from Subang, in West Java, who died on Wednesday. The second victims was an 11-year-old girl from Bekasi, east of Jakarta. She died Friday and also tested positive for the virus.

“There were dead chickens in the boy’s neighboring, but in the girl’s case it is still unclear,” said Nyoman Kandun, director general of communicable disease control at the ministry, according to Reuters.

The source of the infections was being investigated, but contact with sick fowl is the most common way of contracting the H5N1 virus, health officials say.

Meanwhile, a 22-month girl from West Sumatra province was being treated in a hospital after it was confirmed she had bird flu, ministry official Lily Sulistyowati said.

“Her condition is improving, and she is being treated at a Padang hospital.”

Including the latest two deaths, Indonesia has 132 confirmed cases of the virus.

Health experts fear that the virus, which is usually spread through human-bird contact, could mutate into a form easily passed from human to human and millions of people could die because they would have no immunity to the new strain. So far, most human cases have been linked to contact with infected birds.

Health experts fear that Indonesia, which has millions of backyard chickens and poor medical facilities, could become a potential hot spot for a global bird flu pandemic.