LONDON (Reuters) - Nearly a million people die from malaria each year because they cannot afford the most effective treatment and instead often buy old drugs to which the malaria parasite has become resistant, researchers said on Monday.

Artemisinin combination therapy, or ACT, drugs made by firms such as Novartis and Sanofi-Aventis can cost as much as 65 times the daily minimum wage in some African countries, according to a study of 6 high-risk nations by Populations Services International Malaria.

ACTs can cost up to $11 to patients buying over the counter, while older drugs to less effective drugs cost just $0.30 cents.

"With most people accessing anti-malarial medication through the private sector, price becomes a critically important barrier," said Desmond Chavasse, director of PSI.

"A full course of an adult treatment of ACT can be up to 65 times the minimum daily wage. This provides an overpowering incentive (for patients) to make the wrong anti-malarial choice."

Malaria is a potentially deadly disease transmitted via mosquito bites. Children account for about 90 percent of the deaths in the sub-Saharan Africa and parts of Asia -- the worst affected areas.

Chavasse was speaking to reporters from Nairobi, where he was at an international malaria conference to present a study called ACTwatch -- a research project by PSI and the London School of Hygiene and Tropical Medicine on the malaria drugs market across 6 sub-Saharan African countries and Cambodia.

The study -- designed to provide baseline data to allow experts to judge a planned drug subsidy scheme being offered in 11 nations -- looked at availability, pricing and volumes for 23,000 malaria treatments sourced from 20,000 outlets.