The crippling shortage of doctors, nurses and other caregivers has been exacerbated by a brain-drain of talent to richer countries but also by death among health workers from AIDS itself, the WHO report said.
Sub-Saharan Africa, home to around two-thirds of the nearly 39 million people living with AIDS or the virus that causes it, faces the severest shortage.
Skilled workers shortfall
In a blueprint presented at the 16th International AIDS Conference, the WHO said that tackling the personnel shortfall would cost a minimum of US$7.2 billion over the next five years in the 60 countries with the highest burden of HIV.
At the top end of the scale, the bill would be as high as US$14 billion.
"The shortage of health workers is devastating public health systems, particularly in the developing world, and it is one of the most significant challenges we face in preventing and treating HIV," said the WHO's assistant director-general, Anarfi Asamoa-Baah.
The WHO report, "Treat, Train, Retain," puts the spotlight on skilled medical workers in Africa who have been lured abroad - ironically, most often to the United States and Europe, which have donated most to combating AIDS.
In South Africa, for example, 37 percent of locally-trained doctors are working outside the country, while the figure for nurses who trained in
Zimbabwe is 34 percent.
NGOs lure staff
But health workers can also be lured to non-governmental organisations (NGOs) that operate within their countries, thus contributing to the public-health service crisis.
"For example, within one year, the Masaka region of Uganda lost 10 of its 21 doctors, newly trained in HIV skills, to programs run by NGOs in the region," the report said.
Key personnel can be encouraged to stay through salary increases and fringe benefits, such as help with housing costs, travel, credit, school fees and child care, it suggested.
AIDS itself is a major risk for health workers, who are exposed to infection by needle-stick injuries and contaminated blood and other body fluids.
Each year, around 1,000 infections of this kind occur among health workers, mostly in low- and middle-income countries where hospitals often lack safety equipment such as gloves and special boxes to dispose of used syringes.