March 31, 2000

World Health Week spotlights malaria’s global persistence

Featured Image

Dyann Wirth, Ph.D., delivered the World Health Week lecture. (photo by Dana Johnson)

World Health Week spotlights malaria's global persistence

Vanderbilt University School of Medicine students got a first-hand look last week at the devastating effects of a disease that, despite being simple to diagnose, is still incredibly difficult to treat.

That disease, malaria, is still reported between 300 million and 500 million times each year around the world, even with the progress made in medicine over the past century.

"Infectious diseases still make up 1/3 of the causes of death in the world despite amazing advances over the last several decades in the development of vaccines and antibiotics that treat common diseases," said Dyann Wirth, Ph.D., the keynote speaker at last week's World Health Week. "Although we've made many advances in infectious diseases, we are at about the same place that we were several centuries ago."

Wirth, professor in the Department of Immunology and Infectious Diseases at Harvard School of Public Health, is also director of the Harvard Malaria Initiative, a World Health Organization expert advisor, and 1999 President of the American Society of Tropical Medicine and Hygiene.

One of the reasons that little progress has been made is because of drug resistance, Wirth said. In fact, there are more cases of malaria in the world today than there has been at any other time, partly due to population growth.

"We haven't been very successful. If you have a scorecard, the parasite is actually winning," she said.

Wirth has focused her career on malaria for the past 15 years, since she was a post-doctoral student at Harvard University and attended a lecture on malaria.

"It just captured my interest as a biological problem as well as a world health problem. I actually have never taken a course in parasitology. I learned it on the job."

Besides the 300-500 million new cases of malaria diagnosed each year, about 2 to 3 million children die from malaria, almost exclusively in Africa. The disease, which is found only in humans and infected mosquitoes, is also a major cause of disability.

Control is very important, Wirth said. The use of insecticide to eliminate the mosquito population in some areas has been somewhat successful, Wirth said. A simple "on the ground strategy" is using pyretherin insecticides to treat bed nets in areas where malaria is prevalent.

In some areas, where treated bed nets were used, there was a 30 to 60 percent reduction in childhood mortality, Wirth said. The bed nets don't prevent infection, but reduce the number of episodes of malaria.

"We think of malaria as an acute disease. But in Africa, it's a long-term chronic disease because people receive 300 to 500 infected bites a year. That's a bite every day," Wirth said. "So even if you cure the malaria that comes out of a child's liver today, there's going to be another batch right behind it tomorrow."

Prevention is an area that must also be explored, she said. The Bill Gates Foundation recently donated $50 million to ongoing research to develop a malaria vaccine.

"The biggest challenge is can we really make a malaria vaccine? There is an issue of partial immunity that is acquired after multiple infections. Immunity does not prevent infection. Any immunity is short-lived. And there are probably hundreds of thousands of parasite types all over the world. That's another issue. We're extremely hopeful, but we shouldn't get too optimistic."

Another challenge is drug resistance. The parasite has shown resistance to all known anti-malarial drugs.

"Through the 1970s, we had a good impact in fighting malaria. But by 1997, we were back to where we were in 1900. That's a sobering thought."