Malaria is one of the world’s worst public health problems.

The disease is caused by parasites that infected mosquitos spread, and it triggers a slate of nasty ailments, including high fever, sweating, shaking and chills. The World Health Organization estimates that 655,000 people died from malaria in 2010.

Medicine has made great strides in controlling malaria. One of the most effective weapons in use is artemisinin (ar-te-MIS-i-nin), a pharmaceutical ingredient taken from an herb used in traditional Chinese medicine. The herb also grows in the U.S. and many other parts of the world.

Artemisinin is the most effective medication for killing the parasites that cause malaria. But there’s a problem: Some parasites are becoming resistant to it. Resistant malaria strains are spreading in parts of Asia.

An article published in the journal The Lancet Infectious Diseases explores one cause of resistance: the increasing prevalence of low-quality medications containing artemisinin. Manufacturing errors by drug companies, poor or damaged packaging, and improper storage all can lead to medications that are not fully effective and sometimes even harmful.

Many experts believe taking such antimalarial drugs allows parasites to become resistant, perhaps because they are exposed to artemisinin but not killed quickly by it. Malaria-causing parasites already are resistant to many other drugs. If strains resistant to artemisinin become dominant, it would be very difficult — perhaps impossible — to contain them. Experts say malaria deaths would increase significantly.

The study authors say reports of substandard or fake antimalarial medications have increased in the past decade. They also say medical regulatory bodies should have authority to protect the supply of good-quality drugs. That could be one crucial step to helping prevent a major public health problem.