JAKARTA, Feb 16 (Reuters) - A 16-year-old Indonesian boy from Central Java has died from bird flu, taking the country's death toll from the virus to 104, the health ministry said on Saturday.

The ministry said on its Web site the boy had fallen sick on Feb. 3 with fever symptoms and respiratory problems after five chickens belonging to him and a neighbour died.

There has been a sudden spike in bird flu cases in Indonesia since the start of the year. Some experts say the flare-up is caused by factors such as damp weather and poor sanitation during the rainy season.

Contact with sick fowl is the most common way of contracting bird flu, endemic in bird populations in most of Indonesia.

Although bird flu remains an animal disease, experts fear the H5N1 virus could mutate into a form easily passed from human to human. Millions of people could die because they would have no immunity to the new strain. (Reporting by Muhamad Al Azhari; Editing by Catherine Evans)

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