London: No stone has been left unturned to tackle Malaria.  But all this effort goes in vain when fake and poor quality anti-malaria drugs sell in the market.  Many such fake drugs are being sold openly in African countries that are posing as a great threat to the efforts to control the killer disease in the continent.

The counterfeit medicines could not only harm patients but also promote drug resistance among malaria parasites, said the scientists from the Wellcome Trust-Mahosot Hospital Oxford University Tropical Medicine Research Collaboration.

The new study, published in the Malaria Journal, called for public authorities to take immediate action help tackle one of the world's deadliest diseases.

"Failure to take action will put at risk the lives of millions of people, particularly children and pregnant women, said Dr Paul Newton, who led the study.

"The enormous investment in the development, evaluation and deployment of anti-malarials is wasted if the medicines that patient actually takes, due to criminality or carelessness, of poor quality and do not cure," Dr Newton said.

For their study, the researchers examined fake and substandard anti-malarial drugs found on sale in 11 African countries between 2002 and 2010.

It was found that some of the fake tablets being sold in those countries have originated in China.

The researchers also discovered that some fake drugs contained a mixture of the wrong pharmaceutical ingredients that would initially alleviate the symptoms but not cure malaria, which kills about 800,000 people yearly.

Some of the ingredients in the drugs could cause serious side effects, especially if they were mixed with other drugs a patient might be taking, like anti-retrovirals to treat HIV.

The worse could be that after a period, the malariaparasite could develop resistance to the drugs being used to treat it, the researchers said.

This has happened in the past with medicines such as chloroquine and mefloquine, they said, warning that the fake drugs could lead to the same effect on artemisinin, one of the most effective drugs now being used to treat malaria.

They say small quantities of artemisinin derivatives are being put in some of the counterfeit products to ensure that they pass authenticity tests.

But at the level it is present, these drugs are unlikely to rid the body of malaria parasites, but could enable them to build up resistance to artemisinin, they warned.

The Asian origin of the fake drugs was identified using traces of pollen found in some of the tablets, they added.