Fake and substandard drugs are responsible for tens of thousands of deaths around the globe each year, and the persistent lack of reliable medicines in poor countries threatens to roll back decades of efforts to combat malaria, tuberculosis, HIV/AIDS and other conditions, researchers said Monday.

"The pandemic of falsified and substandard medicines is pervasive and underestimated, particularly in low- and middle-income countries where drug and regulatory systems are weak or non-existent," Jim Herrington, a University of North Carolina public health professor who co-edited a collection of articles on the topic published in the American Journal of Tropical Medicine and Hygiene, said in a statement.

The articles, funded in part by the Bill and Melinda Gates Foundation, detail various aspects of the long-standing problem of substandard drugs, as well as looking at potential solutions to reducing the harm they cause each year.

One piece describes the discovery of falsified and poor quality malaria drugs that contributed to the deaths of an estimated 122,000 African children in 2013. In another study, scientists examined nearly 17,000 samples of antibiotics, antimalarial and anti-tuberculosis drugs and found that as many as 41 percent failed to meet quality specifications.

While such investigations offer clues to the scope of the problem, researchers say it remains unknown exactly how pervasive counterfeit and low-quality drugs are. Falsified medicines account for an estimated $75 billion market annually, but even that is simply an educated guess. While the problem is most pervasive in poor countries dealing with malaria and other infectious diseases, it also affects medicines for cancer, cardiovascular disease and other serious illnesses around the globe, experts said.

"We know this epidemic is occurring over a very wide area, crossing international boundaries and affecting a large number of people," Gaurvika Nayyar, a program manager for the U.S. Pharmacopeial Convention, a scientific nonprofit that sets standards for drugs, said at an event on the topic Monday in North Carolina. "This is just the tip of the iceberg."

The World Health Organization has repeatedly warned about counterfeit drugs, particularly in developing countries, and in the past has worked with international investigators in an effort "to dislodge the criminal networks raking in billions of dollars from this cynical trade."

According to the Centers for Disease Control and Prevention, drug counterfeiting is most common in countries without strong regulations governing the manufacture of medicines, and few ways to enforce existing laws. The CDC has estimated that 10 to 30 percent of medicines sold in developing countries are counterfeit, far less than than the estimated 1 percent or less in the United States, Australia and other industrialized countries.

In January, the Food and Drug Administration created a new unit, the Office of Pharmaceutical Quality, aimed at ensuring the consistency, safety and quality of drugs that reach the American public. That's a complex undertaking, given the large number of drugs that come from India, China and many other countries.

"Globalization ... has redefined the field of medical product regulation by adding layers of complexity to the supply chain and creating opportunities for the potential contamination and/or intentional adulteration," former FDA commissioner Margaret Hamburg wrote in an essay accompanying Monday's collection of articles. "Today’s medical-product landscape blurs the line between domestic and foreign production, drawing attention to the need for global quality and safety oversight to prevent patient exposure to falsified products."

Researchers said Monday that innovative ways of testing drug quality are emerging, such as simple paper-based test cards that are easily portable and can identify low-quality malaria medications. But they argue that new technologies alone will not be enough to tackle the far-reaching pandemic of fake and poor-quality drugs. That, they argue, will require more public awareness, more international coordination and leadership focused on the problem and tougher laws to prosecute criminals who profit from selling counterfeit medicines.