Credit: Susan Buck Ms/Public Domain

Countries must halt the rise of AIDS drug resistance to prevent a swell in new infections and deaths and spiralling treatment cost, the UN's health agency warned Thursday.

In six of 11 countries studied in Africa, Asia and Latin America, more than one in 10 people who started anti-retroviral treatment had a strain of the AIDS-causing virus that did not respond to some of the most widely-used drugs, the World Health Organization (WHO) cautioned.

Viruses can become resistant to drugs when people take incorrect doses of their prescribed medication.

Resistant strains can also be contracted directly from other people.

"Antimicrobial is a growing challenge to global health and sustainable development," the agency's director-general, Tedros Adhanom Ghebreyesus, said in a statement.

"We need to proactively address the rising levels of resistance to HIV drugs if we are to achieve the global target of ending AIDS by 2030."

The WHO recommends that when drug resistance becomes too high, countries must shift to an alternative drug of first resort.

When the most common medicines fail to work, more expensive types that can be harder to find, must be tried.

Mathematical modelling shows that an additional 135,000 deaths and 105,000 new infections could happen in the next five years unless action is taken, with treatment costs increased by $650 million (560 million euros) over the same period, said the WHO.

Unchecked, drug resistance "will be a major risk" to anti-AIDS efforts, said Marijke Wijnroks of the Global Fund to Fight AIDS, Tuberculosis and Malaria.