It’s amazing to think that some of the smallest organisms cause humans some of the most trouble. For example, malaria is caused by a tiny, single-celled parasite, so small that several can live within one of our blood cells. In 2010, about 219 million people in the world were infected with malaria (mostly in tropical/subtropical areas). About 1 million people died from it that year, including many children. Currently there’s not a very effective vaccine available; the best is called RTS,S (or Mosquirix) and it confers protection to only about 30% to 60% of babies tested in clinical trials.
But a more promising vaccine is on the way. In an article published in Science magazine this month, researchers reported that a new vaccine, called PfSPZ, is about 70% to 100% effective. However, the vaccine was tested in a very small-scale trial, so further tests will need to be done before it’s known just how well it works.
The malaria parasite (which belongs to the genus Plasmodium) spreads to a person from a mosquito’s bite. It travels from the mosquito’s saliva to a person’s blood stream, and eventually makes its way to the liver, where thousands of parasites are made. They then spread to the red blood cells to continue their lifecycle. The parasites can cause fever, headache, coma, and, of course, death.
The RTS,S vaccine takes a standard approach; it’s made to work against a specific protein found on the parasite. The potentially more effective new vaccine, PfSPZ, works in a different manner; mosquitoes with the malaria parasite are treated with radiation to weaken them, and then technicians manually cut out the mosquito’s salivary glands to get the parasites! That’s some detailed microsurgery. (But the technicians have finely tuned their skills; each one can now dissect out those salivary glands from about 150 mosquitoes in an hour!) These weakened, radiated parasites are used in the PfSPZ vaccine. In a trial with 15 volunteers, 12 were protected from malaria using the PfSPZ vaccine. But the vaccine clearly needs to be tried on more people, and using different malaria strains, before we know just how effective it is.
Even if you don’t live in an area with malaria, if you’re spending summer evenings outside in a mosquito-prone area you may want to consider bringing along mosquito repellant, since mosquitoes can carry other diseases too, such as the West Nile virus.
For further reading:
- Seder, R. A. et al.’s article “Protection Against Malaria by Intravenous Immunization with a Nonreplicating Sporozoite Vaccine” in Science
- Jocelyn Kaiser’s article “Unconventional Vaccine Shows Promise Against Malaria” in Science’s News & Analysis
- National Health Service, UK’s article “New Malaria Vaccine Could Save Millions of Lives”