PRETORIA -- New research suggests that the number of fresh HIV infections in the world appears to have peaked, according to a report by leading AIDS researchers published today in the British health journal The Lancet.
They cited evidence including a study, also published today, that indicated that the number of pregnant women infected with HIV in southern India has declined by more than a third from 2000 to 2004.
The findings raise hopes that prevention programs are having a positive impact in the fight against AIDS, which has claimed an estimated 25 million lives. Rates of infection have remained high in areas including southern Africa, the epicenter of the pandemic, and the United Nations's AIDS program estimates that about 5 million people are infected globally each year.
The analysis published in The Lancet by three veteran AIDS epidemiologists -- two working for the US Agency for International Development and one for the World Bank -- said that India and much of sub-Saharan Africa are seeing decline in rates of new infections. The two areas account for three-quarters of the world's HIV cases.
Other countries showing a downward trend of infections, according to US Census Bureau data and cited in the study, are Uganda and Zambia, where infections apparently peaked in 1987; Kenya in 1993; Botswana and Lesotho in 1994; and South Africa around 1997.
James D. Shelton, lead author of the analysis on HIV incidence and senior medical scientist at USAID's bureau for global health, said in a telephone interview from Washington that the main reason for declines in new infections is rooted in the natural life cycle of disease outbreaks. He said individuals who are most susceptible to a virus tend to be infected first, and as time passes fewer people are as susceptible.
Epidemiologists believe that AIDS exploded in parts of eastern Africa and throughout southern Africa through sexual networks that included prostitution rings and men and women who had multiple partners. People with HIV, which causes AIDS, pass it on most readily soon after becoming infected and in their dying days.
But Shelton said a second reason for a reduction in new infections globally was rooted in various types of prevention. He noted that programs aimed at changing the behavior of high-risk groups in Thailand and Cambodia, mostly intravenous drug users and sex workers, were a major factor in containing those outbreaks. In West Africa, widespread male circumcision probably acted as a strong protective barrier, preventing the region from the galloping prevalence rates experienced in southern Africa, the researchers wrote.
And in areas of high rates of HIV infection, Shelton said, studies have shown some success for prevention programs -- notably those promoting reduction of partners and effective condom use -- to bring about reductions in HIV infections in Uganda, Kenya, Zimbabwe, Rwanda, Malawi, Ethiopia, and Haiti.
''It gives us hope that behavior can change on a large scale and can affect the course of the pandemic," said Shelton, who was speaking in a private capacity. ''I don't think, though, it's happening much in southern Africa yet."
Shelton and his fellow researchers seized on new HIV prevalence data from India to reexamine the global picture of new infections because India is believed to have the second-highest numbers of people infected, behind South Africa, with an estimated 5.1 million people living with HIV.
In India, researchers had predicted a major increase in HIV cases in the early part of this decade, but AIDS investigators recently found that HIV prevalence among pregnant women attending antenatal clinics in southern India fell by 35 percent, from 1.7 percent in 2000 to 1.1 percent in 2004, according to a second article in The Lancet published today. Southern India, which has about 350 million people is believed to have roughly three-quarters of India's HIV infections.
Prabhat Jha, an author of the study and director of the Centre for Global Health Research in Toronto, said in a telephone interview from New Delhi last night the reason for the decline is that sex workers report using condoms much more frequently than before. The HIV epidemic in India is largely based on sex workers and men who pay for their services and then infect their regular partners.
''Sex workers are not reporting fewer clients, but we believe that serious efforts through peer intervention programs to reach sex workers has led many more to protect themselves with condoms," Jha said.
The researchers found no significant change of HIV prevalence in northern India, where prevention programs have not been as widespread as in the south.
Jha agreed that the number of new infections globally is falling. ''There is now increasing evidence the epidemic is turning around, or it can't get any worse in some settings," he said.
But he cautioned that in the United States after the introduction of life-extending antiretroviral drugs, new infections increased as people become more lackadaisical about protecting themselves.
''In the West, with some gay men, there was an attitude of 'I have treatment, I've got a pill, so I don't need to use condoms,' and the epidemic starts creeping back up. Imagine that writ large in Africa," Jha said. ''So we don't know the future of AIDS in the antiretroviral era yet."
About 1.3 million people now are taking antiretroviral drugs in the developing world, the World Health Organization said earlier this week. That represents a tripling of those on the therapy in two years, but still far short of an estimated 6 million people who need the drugs.
Karen Stanecki, a UNAIDS senior adviser on demographics and related data, said in a telephone interview from Geneva that the researchers did not have complete estimates of new infections from around the world, and could be missing key trends from smaller African nations as well as from countries in Eastern Europe.
''Their focus on the bigger countries could mask the fact that there could be serious problems in other countries," she said.
Plus, she added, ''HIV prevalence may have stabilized, but it has stabilized at very high levels."
John Donnelly can be reached at email@example.com