Above: Image © istockphoto.com/iJacky
Did you Know? The World Health Organization estimates that there were 219,000,000 new cases of malaria worldwide in 2010. These infections led to 660,000 deaths.These days, Canadians don’t often worry about contracting malaria—unlike in the 1800s, when the disease was widespread in North America. However, in places like sub-Saharan Africa the threat of malarial infection remains constant and dangerous. Scientists, who have been studying the disease for years, recently made a significant breakthrough: a vaccine that prevents malaria infection!
Malaria is caused by the Plasmodiidae family of parasites, the most deadly of which is the Plasmodium falciparum species. The parasite gains entry into a human host with the help of one of nature’s biggest nuisances: the mosquito! Infected female mosquitoes harbour the parasite in their saliva in the form of sporozoites, which are like microscopic worms. When a mosquito bites, these sporozoites are injected into the bloodstream.
After the parasite has made thousands of copies of itself, it infects red blood cells, causing an immune response that produces the flu-like symptoms associated with malaria: mild to severe dizziness, vomiting, and malaise are especially common. However, the telltale sign of malaria is a recurring fever, which can be deadly.
Did You Know? In 2012, the international community spent approximately $2.5 billion on malaria prevention and treatment.Efforts to control malaria have traditionally been focused on preventing mosquito bites and treating infections. Families in hard-hit regions are given insecticide-treated mosquito nets to sleep under, or have their homes sprayed with insecticides to keep mosquitoes out. If someone does contract the disease, they receive artemisinin-based combination therapy (ACT) drugs that destroy the parasite.
Although these methods have been successful in reducing the number of cases and deaths in recent decades, they are extremely expensive to keep up over the long term. What’s more, Plasmodium-carrying mosquitoes are becoming resistant to insecticides, and two species of the parasite itself are becoming resistant to ACT treatments!
A research group in the US has developed a more permanent solution: a vaccine. Usually, a vaccine contains a “killed” form of the pathogen it protects against. For example, if the pathogen is a virus, the vaccine will contain a weakened form of the virus. The immune system quietly reacts to this relatively harmless invader while storing memory immune cells that will attack and destroy the active form of the virus if it ever appears in the body.
Did You Know? Canada has been declared “malaria-free” by the World Health Organization.In the case of the malaria vaccine, researchers based at the US National Institutes of Health irradiated a portion of the falciparum parasite to kill it. The microscopic parasite was then frozen and given to volunteers intravenously, meaning the vaccine was injected directly into a vein. Afterward, these volunteers did not develop malaria when they were bitten by Plasmodium falciparum-carrying mosquitoes. In fact, blood drawn from the volunteers indicated that their immune systems were effectively destroying the parasite!
Despite these promising results, the new vaccine still has its flaws. Five doses of vaccine were required to achieve 100% immunity from infection. Having to give the vaccine intravenously makes the process long and inefficient, especially for large numbers of people. In those parts of the world that require the vaccine the most–places like Nigeria or India–a low-maintenance delivery method is essential.
Did You Know? In 2010, Nigeria accounted for roughly 25% of all malaria cases worldwide–that’s about 55 million new cases in one year.Furthermore, it's not clear whether the vaccine can be tolerated by people with compromised immune systems, such as those infected with HIV or suffering from AIDS. This is an important question because some of the regions with a high incidence of malaria, especially sub-Saharan Africa, also happen to have high rates of HIV/AIDS.
Nevertheless, the vaccine is an exciting first step that will hopefully lead to the development of a more practical tool for fighting malaria.
Malaria on the Rideau (Rideau Canal World Heritage Site) World Malaria Report 2013 (World Health Organization)
Bartoloni A, Zammarchi L. 2012. Clinical aspects of uncomplicated and severe malaria. Mediterranean Journal of Hematology and Infectious Diseases. 4(1):e2012026. Schlagenhauf-Lawlor P (ed.). 2008. Travellers’ Malaria, 2nd ed. BC Decker, Hamilton, ON. Seder RA, et al. 2013. Protection against malaria by intravenous immunization with a nonreplicating sporozoite vaccine. Science 341(6152):1359-1365.