By Umaru Fofana

FREETOWN, Aug 27 (Reuters) - A British nurse infected with Ebola may have caught the deadly virus after playing with a one-year-old boy whose mother had died in a treatment centre but who himself had initially tested negative for the disease, a medical colleague said.

William Pooley, 29, the first Briton to contract the virus, was flown back to Britain from Sierra Leone at the weekend and is receiving the experimental drug ZMapp in a London hospital in an attempt to save his life.

Close to 1,500 people have so far died across Guinea, Liberia and Sierra Leone in the worst epidemic in the disease's 38-year history. Symptoms of the highly-contagious virus include vomiting and bleeding from the eyes and ears.

During his time as a volunteer at a clinic in remote eastern Sierra Leone, Pooley developed a bond with a baby boy named Sellu Borbor thought to have caught the virus from his mother's breast milk, according to his supervisor Finda Josephine Sellu.

Like other health workers, Pooley initially took precautions handling the infant since his mother was diagnosed with the virus and later died. But he played with him freely after the baby tested negative for the disease, she said.

"Pooley and some other nurses fell in love with the boy and would play with him in their free time," Sellu told Reuters.

Borbor was tested again after he developed a fever and tested positive for Ebola the second time around. He died on August 24 -- the same day that Pooley was diagnosed.

"KIND, HELPFUL" YOUNG MAN

It is not clear why the initial test result for Borbor came out negative, although experts say the virus can sometimes go undetected and recommend several tests.

Another nurse known to have played with Borbor has also tested positive for the disease, Sellu said.

Sellu praised Pooley's dedication to his patients during his short period in Kenema.

"Some patients are very weak and messy but Pooley would attend to them with dedication and commitment," she said. "I feel very sad he tested positive and I pray this kind, helpful, hardworking young man gets well soon."

Ebola has killed over half of those infected in the current outbreak, including at least 120 healthcare workers.

The Kenema clinic in Sierra Leone is known to be understaffed and several staff there, including its head doctor Sheik Umar Khan, have succumbed to the illness. (Writing by Emma Farge; Editing by Joe Bavier and Gareth Jones)

Our Standards: The Thomson Reuters Trust Principles.