LONDON - Seven members of a remote Amazonian tribe in Peru have tested positive for the pandemic H1N1 flu, raising fears the virus could quickly infect communities with little immunity to outside diseases, a group lobbying for tribal peoples' rights said on Wednesday.

Survival, a London-based group, said the regional health department in Cusco had recorded the cases of the virus, commonly known as swine flu, among the Matsigenka, a tribe living along the Urubamba river in the Peruvian Amazon.

There are an estimated in 12,000 Matsigenka in the Latin American country, and some 332,000 indigenous people in the Amazon. Passengers on boats plying the Urubamba, a major tributary of the Peruvian Amazon, are thought to have been the source of the swine flu, Survival researchers say.

"Isolated tribes have no immunity to the infectious diseases that circulate though our industrial society and will be particularly susceptible to swine flu," said Dr Stafford Lightman, professor of medicine at Bristol University, in a statement.

"This could be devastating, infecting whole communities simultaneously, leaving no-one to care for the sick or bring in and prepare food."

The H1N1 flu outbreak, declared a pandemic on June 11, has spread around the world since emerging in April and could eventually affect 2 billion people, according to estimates by the U.N. World Health Organisation.

Survival researchers said they were worried the outbreak may rapidly spread if the infected Matsigenka come into contact with other isolated communities such as the Nanti. One group of 130 Nanti, which has had no contact with the outside world, live upstream from the infected Matsigenka.

The Amazon area is Peru's most underdeveloped region, where Indians tend to their crops living in wooden shacks with no access to running water or electricity.

Exposure to outsiders has historically been disastrous for them. More than half of the Murunahua tribe died of colds and other illnesses after they were contacted by development workers for the first time in 1996.

Human rights activists say unchecked logging in the Amazon is destroying its rain forest, threatening ancient tribal life, and pushing some of the world's last isolated tribes into neighbouring Brazil. They are also concerned about the Lima government's plans to open up communal lands to oil drilling and mining.

"Isolated tribes across the world already face threats from illegal loggers, ranchers, poachers, and even over-zealous tourists, encroaching on their lands and bringing diseases against which they have no immunity," said Stephen Corry, director of Survival, in a statement.

"In times of a global pandemic, it is even more important than ever that their land rights are recognised and protected before it is too late."

In defence of their land rights, a coalition of tribes in Peru's Amazon has led months of blockades that turned into clashes with police and forced their Congress to overturn two laws that indigenous leaders said would put ancestral lands in the hands of foreign mining and oil companies.

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