Will two flus mix in Indonesia? Experts worry

* H5N1 circulates freely in Indonesia

* Flu viruses cause more deaths in poorer countries

By Olivia Rondonuwu

JAKARTA (Reuters) - Indonesia's first cases of the new H1N1 flu have raised concerns that if the virus spreads it could combine with the entrenched and deadly H5N1 avian influenza to create a more lethal strain of flu.

Even if this worst-case scenario did not occur, experts say populous, developing countries such as Indonesia, India or Egypt, where healthcare systems can be rudimentary, will suffer more deaths from the new virus.

Indonesian Health Minister Siti Fadillah Supari, who confirmed six new H1N1 cases on Sunday, said she was concerned about H1N1, widely known as swine flu, "marrying" with H5N1 avian flu.

Influenza viruses not only mutate quickly and unpredictably, but they can swap genes, especially if a person or animal becomes infected with two strains at once. The new H1N1 strain is itself a mixture of various strains, genetic tests show.

H5N1 bird flu has been circulating in Asia for years and has hit Indonesia harder than any other country. Although it only rarely infects people, it has killed 262 out of 433 infected globally since 2003, with 141 of those cases in Indonesia.

"We are scared because we are the warehouse of the world's most virulent H5N1," Supari said.

"I am worried if the viruses encounter each other in the field," C.A. Nidom, the head of the Avian Influenza lab at Airlangga University in Surabaya, said.

The World Health Organization declared a pandemic of H1N1 swine flu earlier this month and said the virus causes a moderately severe flu, spreading very easily from person to person. H5N1 spreads mostly from a bird to a person and stops there, but is far deadlier.

The mortality rate for H1N1 is 0.2 percent, according to a study in the New England Journal of Medicine, while for H5N1 it is just over 60 percent.

SERIOUS THREAT

Scientists say usually as a virus becomes more transmissible from one human to another it also becomes less deadly, although this is not guaranteed.

But Kamaruddin Zarkasie of Indonesia's Bogor Agriculture University said he felt the risk the two viruses might combine was only a random possibility.

Even if they do not, H1N1 may be a serious threat, other experts said.