Date: November 17, 2000
UVic Research Aims to Slay the Dragon of African Sleeping Sickness
UVic biochemistry professor Dr. Terry Pearson calls African sleeping sickness a sleeping dragon -- it sleeps for long periods of time, only to wake up and flare into an epidemic. Pearson and his research team are fighting to slay the dragon.
There have been two sleeping sickness epidemics in the past 120 years, each of which killed nearly a million people. And recently, the beast has awoken to create another epidemic. As of October 2000, more than 500,000 people are infected, and another 60 million are at risk.
"Can you imagine what would happen if 500,000 North Americans were infected?" asks Pearson. "We just wouldn't tolerate it."
Although scientists have known for more than a century that African sleeping sickness is caused by a deadly parasite called the African trypanosome, there is still no vaccine. But Pearson and his research group are working to develop just such a vaccine.
The African trypanosome is carried in the tsetse fly, which looks much like a small horsefly. The fly carries the parasite and passes it on to new victims when it bites, similar to the way mosquitoes spread malaria.
African trypanosomes are unique microorganisms because they are so hardy. Through a process called "antigenic variation," they can alter their surface molecules, or coat, to resist the body's immune response.
"The parasites have evolved to avoid immune response," says Pearson. "They're very clever that way. They've got a good head start on us, having survived in mammals for millions of years."
The immune system can't recognize the parasites until their numbers in the blood are extremely high. It fights most of them off, but the remaining few adapt, or create new coats, and multiply again. This continues with wave after wave of parasites.
"Eventually the immune system wears out, and the parasite numbers keep getting higher and higher until they invade the central nervous system, ultimately causing death," says Pearson.
The parasites can create more than a thousand different surface coats to protect themselves against the body's immune response. This makes it virtually impossible to develop a normal vaccine, which would be useless as soon as the parasite adapted.
However, the parasites don't adapt or change coats when inside the tsetse fly. So the research team has been studying molecules on the surface of parasites taken from inside flies, instead of from inside human bodies. This may enable them to develop an "altruistic" vaccine to prevent tsetse flies from spreading the disease to more than one victim.
This altruistic vaccine would allow a person's body to create antibodies against the fly form of the parasite. After a bite, the parasites would still enter the bloodstream and adapt, causing infection, but the fly would carry away antibodies in the blood meal that could interact with the parasite in the fly, preventing it from infecting someone else.
"It wouldn't help the immunized person but the vaccination might prevent transmission," he says.
Pearson's team has also been working on creating inexpensive, durable and easy-to-use diagnostic tests to improve the chances of early diagnosis of African sleeping sickness. If the diagnosis is made early enough there is a greater chance that patients will take measures to combat the disease before the parasites make their way from the bloodstream into the cerebo-spinal fluid and the brain.
"Only a small number of people are currently tested on an annual basis -- fewer than five per cent of those at risk," says Pearson.
Misdiagnosis remains a pervasive problem because of the nature of the disease. A patient infected with the disease will often feel sick in waves, which correspond to the buildup and decline of parasites in the blood.
Patients tend to seek help when they feel well enough to walk and talk -- times when parasite numbers are low in their blood. At that stage, the disease can't be detected, and patients go home with an incorrect diagnosis. When they fall sick again, they may go to a different doctor because the last one didn't help, and the process repeats itself.
"It can persist like this for several years. The person just gets sicker and sicker and then dies," says Pearson. "The disease can take from months to years to kill."
If tests were more easily available and simpler, enabling more people to administer them from more locations, the number of early diagnoses would increase and many more people would survive.
Pearson and his research team receive most of their funding from the Natural Sciences and Engineering Research Council of Canada.
Dr. Terry Pearson (Biochemistry) at (250) 721-7080.
UVic media releases and other resources for journalists are available on the World Wide Web at http://communications.uvic.ca/media