Nearly 40% of Nepali women trafficked into India to work as sex workers there have been found to be HIV positive on their return home, a study has found.
Thousands of women work in India's red light districts
Sex trafficking may be a major factor in the spread of HIV in India and the rest of South Asia, the report said.
Nepal has traditionally had low rates of HIV/Aids but thousands of Nepali women and girls are trafficked into India every year.
India has nearly 2.7 million people infected with the HIV virus.
The report published in the Journal of the American Medical Association, studied medical records of 287 Nepali women who worked for years in Indian brothels.
The authors of the study said they found that 38% of the women and girls, repatriated to Nepal from India, had tested positive for HIV.
The study said the infection rate among the girls aged 14 or less was alarmingly higher at 60%.
It attributed the higher rate of infection among younger girls to a widespread myth that sex with virgins could cure HIV/Aids.
In many of India's big red light districts - like Sonagachi in Calcutta, GB Road in Delhi and Kamathipura in Mumbai (Bombay) - thousands of women and young girls work as sex workers to earn a living.
Many of their clients continue to insist on sex without condoms and the trafficked girls, mostly from rural villages and unaware of the HIV/Aids threat, are forced to oblige.
In the eastern Indian state of West Bengal, Calcutta is the hub for the trafficking of girls where a large number of women and girls are smuggled in from Nepal, Bangladesh or Burma.
From Calcutta, they are sold to brothels in Mumbai and Delhi.
A US state department report last month said India had the world's largest human trafficking problem.
But it noted that the government had taken some steps to deal with sex trafficking.