Amoebas and dysentery
Just down the hall from Dr. Schryvers, Dr. Kris Chadee is working on a vaccine for a different kind of pathogen: an amoeba (a type of parasite) called Entamoeba histolytica that can contaminate food or drink. Once it enters the body, it takes up residence in the intestine and causes a severe form of diarrhea called amoebic dysentery. If the condition is left untreated, the amoebas can burrow through the intestinal wall, spread through the bloodstream, and form abscesses in organs such as the liver, lungs, and brain. At least 100,000 people die and millions are made ill by amoebic dysentery every year, mainly in developing countries.
Dr. Chadee has been studying this amoeba for the past 20 years. His first breakthrough came very early on, when he identified the protein on the surface of the parasite that allows it to attach to the intestine. It's called a galactose-binding lectin: lectin is a type of sugar-binding protein, and galactose is the name of the sugar it binds to. Galactose is found on the receptors in both the mucous layer and the epithelial cells that line the intestines.
"Pathogens that infect the gut must be able to anchor themselves; otherwise they'll be swept away," explains Dr. Chadee. "This amoeba is very tenacious. Because the lectin can bind to both the mucous and epithelial cells, the amoeba can deliver a double whammy to an infected person."
Dr. Chadee knew that if he could find a way to stop the lectin from binding, he would have the basis of a vaccine. His team worked for years to determine which parts of the lectin are necessary for sugar binding. They then packaged the antigen in an intranasal vaccine (delivered by squirting it up the nose) and tested it on gerbils-with some exciting results.
"The vaccine was 100% effective," says Dr. Chadee. "We found antibodies not only at the mucosal surface in the intestines but also in the blood and liver. This is really important because it shows that the vaccine can target both phases of the disease-when it's in the gut and when it spreads to other organs. We were ecstatic."
The next steps will be a pre-clinical trial followed by clinical trials in humans. A basic researcher like Dr. Chadee would normally enter into an agreement with a drug company to complete these stages, which can cost hundreds of millions of dollars. But here's where money, politics, and logistics all clash with science. A vaccine for a disease like amoebic dysentery that affects mainly people in the developing world is not going to be a big money-maker. Dr. Chadee has had a difficult time attracting serious interest from drug companies.
"We've hit a brick wall, and it's very disheartening. I knew this could happen-I just didn't think it would affect me personally."
Dr. Chadee may be down but he is not out. He has had preliminary talks with the Bill and Melinda Gates Foundation. The Foundation's Global Health Program supports research on vaccines to fight diseases in developing countries.
"As North Americans, we tend to think that diseases like dysentery are not our problem. Yet we are a nation of immigrants, and we are also global tourists. All these ‘developing world' diseases are importable or acquirable. And with climate change, they could be in our backyard. Any potential cure or intervention needs to be looked at seriously."