* Myanmar wiped out polio in 2000, but reinfections occur * Immunity levels need to be raised to avoid new spread
GENEVA, Feb 23 (Reuters) - Myanmar is stepping up its polio vaccinations after the crippling virus emerged for the first time in more than three years, infecting an infant, the World Health Organisation said on Wednesday.
A seven-month-old girl caught a rare strain of polio that can spread when some people in a community are immunised with oral polio vaccine (OPV) and others are not, WHO spokesman Oliver Rosenbauer said. She had not been vaccinated against the disease.
“On very rare occasions, when replicating in the human gut, OPV strains genetically change and may spread in communities that are not fully vaccinated, especially in areas where there is poor hygiene, poor sanitation or overcrowding,” he said.
Polio is transmitted in human excrement. Communities that lack clean water, toilets and sewer systems are particularly vulnerable to infections when not enough people are immunised against the virus.
There are no other known cases of paralysis from the strain in Myanmar, which was found in December, according to the WHO. More than 10,000 children have been immunised in response to the discovery and more vaccinations are planned.
“It seems to have occurred in an area with population immunity gaps, so the key is to rapidly raise immunity levels,” Rosenbauer said.
Polio attacks the nervous system and can cause irreversible paralysis within hours, with young children most vulnerable.
There has been a 99 percent drop in the number of infections worldwide since 1988, when the WHO, Rotary International, UNICEF and the U.S. Centers for Disease Control and Prevention launched an effort to eradicate the virus as was done for smallpox.
Polio is now endemic in only four countries -- India, Pakistan, Nigeria and Afghanistan -- compared to 125 when the eradication drive began. At the time, polio caused paralysis in nearly 1,000 children every day.
Myanmar was declared polio-free in 2000 but had a brief outbreak in 2007 when the virus was imported from elsewhere. The military-ruled country is also battling drug-resistant malaria along its border with Thailand. (Reporting by Laura MacInnis; Editing by Elizabeth Fullerton)