By Maggie Fox, Health and Science Correspondent

WASHINGTON (Reuters) - Within days of infection, the AIDS virus destroys more than half of the immune cells that might recognize and help fight it -- a finding that may force a re-evaluation of how to tackle the deadly infection, two teams of U.S. researchers report.

Two separate studies in monkeys showed that SIV, the monkey version of the human immunodeficiency virus or HIV, attacks CD4 memory T-cells right away and wipes out more than half of them.

"The findings may require a rethink of strategies to design HIV drugs and vaccines," Dr. Mario Roederer of the National Institute of Allergy and Infectious Diseases and colleagues said in one of two reports published in the journal Nature on Sunday.

The findings will be difficult to replicate in people, because most people do not know the moment they are infected with the AIDS virus, which gradually destroys the immune system, leaving patients vulnerable to numerous infections.

But SIV is a good model and works in a similar way.

Both teams worked with monkeys that they infected with SIV. They watched what happened to their immune cells.

Right away the virus attacked the CD4 T-cells that had the correct configuration for the virus. Normally during an infection such cells would recognize and latch onto an invader, helping other components of the immune system destroy it.

But HIV is different because it targets the immune system, and the two studies show how quickly it makes it impossible for its victims to launch a defence.

Roederer's team used new, sensitive tests to show just how the virus moves so quickly.

"Specifically, 30 percent to 60 percent of CD4 memory T- cells throughout the body are infected by SIV at the peak of infection, and most of these infected cells disappear within four days," they wrote.

"Furthermore, our data demonstrate that the depletion of memory CD4 T-cells occurs to a similar extent in all tissues. As a consequence, over one-half of all memory CD4 T-cells in SIV-infected macaques are destroyed directly by viral infection during the acute phase -- an insult that certainly heralds subsequent immunodeficiency."

This means any attempt to vaccinate against HIV or to provide efficient treatment must stop this process right away.

Dr. Ashley Haase of the University of Minnesota Medical School and colleagues made similar findings. Not only does the virus directly kill the CD4 cells, they found, but it also causes them to them to commit cell suicide.

There is no cure for HIV infection, which killed more than 3 million people globally last year and which infects 39 million people, according to the United Nations.

Drug cocktails can control the infection but it comes back quickly if they are stopped. More than two dozen vaccines are being tested, but experts do not expect any of them to prevent HIV infection in substantial numbers of people.

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U.S. government guidelines call for HIV-infected women to have pap smears every six months, creating a significant cost especially since AIDS-fighting drugs are allowing such patients to live longer, they said.

The new report says women who initially test negative for the papillomavirus after an HIV diagnosis can reduce the frequency of the pap smears.

Cutting the testing frequency to every three years, as with healthy women, would lessen the burden on patients and their doctors, said the report published in this week's issue of the Journal of the American Medical Association.

The conclusion needs to be confirmed in a larger study, wrote author Tiffany Harris of the Albert Einstein College of Medicine, Bronx, New York, who based her findings on 855 HIV-positive female patients and another 343 HIV-free patients.

As many as 950,000 people in the United States and 39 million people around the world are infected with HIV, and 3.1 million died of AIDS last year, according to health authorities.

Indian patent law could prove a tonic for Bangladesh drug firms DHAKA (AFP) - Pharmaceutical firms in Bangladesh are hoping a new Indian patent law banning Indian companies from manufacturing cheap generic drugs could prove a tonic for their exports. India's parliament, in line with an agreement brokered with the World Trade Organization (WTO), approved a law Wednesday that prohibits the country from copying and selling low-cost generic copies of drugs patented elsewhere after 1995, including those used to treat HIV-AIDS. The law replaces legislation which allowed India drug makers to copy patented products using a different manufacturing process. Although Bangladesh is a member of the WTO, it does not have to pass similar legislation until 2016 because it is designated as one of the 49 least developed countries. "India's law is a big advantage for us because our companies will continue to copy patented drugs whereas the Indians cannot," Nazmul Hassan, chief executive officer of Bangladesh's second biggest drug maker Beximco Pharmaceuticals, said Saturday. "It means we can now sell generic drugs including HIV-AIDS anti-retrovirals and cancer drugs much cheaper than the Indians," said Hassan who is also general secretary of Bangladesh Association of Pharmaceuticals Industries said. Global health activists and aid agencies have criticised the Indian law, which they say could threaten millions of HIV-AIDS and cancer patients who depend on cheap Indian generic drugs. France-based Medecins Sans Frontieres (Doctors Without Borders) said 50 percent of the people living with HIV-AIDS in the developing world depend on generic drugs from India, which is the world's fourth-largest producer of medicines by volume but only 13th by value -- an indication of the relative cheapness of its products. However drug firms disputed claims that millions of HIV-AIDS and cancer patients were threatened by the law. Indian Commerce Minister Kamal Nath told parliament that concerns over the rise of medicine prices locally were also baseless as only 10 out of the 195 drugs being sold in the domestic market would be covered by the new patent law. Still, Bangladesh says the passage of the law gives it the opportunity to enter the market for HIV-AIDS drugs, particularly in Africa. "We have started manufacturing five anti-retroviral drugs according to World Health Organization standards and have applied for registration of the drugs in Kenya and East African countries," Hassan said. Drug manufacturing is a 700-million-dollar industry in Bangladesh with earnings of 1.50 billion taka (25 million dollars) from exports of generic drugs last year, Hassan said.

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