UPDATE 1 - Egyptian woman dies of bird flu - MENA

* Egypt's 25th bird flu death

* Six-year-old's death from bird flu reported on Tuesday

* A 4-yr-old boy has contracted bird flu

(Adds details, background)

CAIRO, April 22 (Reuters) - A 25-year-old Egyptian woman has died of the H5N1 bird flu virus, the 25th human fatality of the disease in Egypt, state news agency MENA said on Wednesday.

The woman, from Cairo, died of respiratory failure, MENA reported.

On Tuesday MENA reported a six-year-old boy had died from the disease. Ali Mohamed Ali Somaa from Qalyubia was Egypt's first bird flu fatality of 2009, MENA quoted a health ministry spokesman as saying.

Somaa had been admitted to hospital in late March.

Ahmed Ramadan Kamal el-Din, a 4-year-old boy from Sohag province, has contracted bird flu and was in hospital. The boy was being treated with the antiviral drug Tamiflu.

His infection brought to 67 the number of bird flu cases in humans in the most populous Arab country, which has been hit harder by bird flu than any other country outside Asia.

Egypt has seen a surge in human cases in recent months, with 16 confirmed since the start of the year, compared to seven cases between Jan. 1 and April 17 last year.

While the H5N1 avian influenza virus rarely infects people, experts say they fear it could mutate into a form that people could easily pass to one another, sparking a pandemic that could kill millions.

Most infected Egyptians had come into contact with infected domestic birds in a country where roughly 5 million households depend on domestically raised poultry as a significant source of food and income.

The World Health Organisation said this month it was concerned some Egyptians may carry the bird flu virus without showing symptoms and this could give the virus more of a chance to mutate to a strain that spreads easily among humans.