Vaccines of the future: using live parasites to protect against malaria
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Picture this: It’s the last guaranteed good-weather weekend of the year. After glancing at your busy calendar, you decide to clear everything to make time for a hike. You pack all the necessary equipment: a water bottle, an extra pair of socks, and your favorite Trader Joe’s snacks. Halfway through your hike, you realized you forgot one essential item – mosquito repellent! You figure it’s no big deal, finish the beautiful hike, and go home feeling accomplished and ready to face the next four months of less-than-ideal weather.
The next day, you notice that you have a few mosquito bites, but you don’t think much of them beyond feeling itchy. But about a week later, you start to feel really sick, with headaches, fever, and chills. You go to the emergency room and after several tests, your doctor informs you that the mosquitos that bit you during your spontaneous hike have given you malaria.
The good news if you live in the United States is that mosquitos here don’t carry malaria, so this imaginary scenario is just that - imaginary. But, for the over 3 billion people who live in areas with malaria, mosquito bites are more than just an itchy annoyance – they can be a death sentence.
Malaria is one of the leading causes of infectious disease-related deaths, killing over 600,000 people every year. The disease is caused by a parasite that gets into your body after a mosquito bite. The parasite first invades your liver, but this stage of its lifecycle causes no symptoms and is unnoticeable. However, about a week after entering your liver, the parasite moves into your blood, where it causes nasty symptoms and sometimes even death.
The high burden of this disease, plus the fact that climate change is causing mosquitos that carry malaria to travel to more and more areas, means that we need new ways to prevent the spread of malaria. Researchers have discovered a way to do just that through vaccines that use live malaria parasites.
That might sound outlandish – how could giving you a parasite infection help prevent malaria? These new vaccines, called whole parasite vaccines, use malaria parasites that have been modified so that they get stuck in the liver and die off before they can enter the blood, where they would cause harm. While the modified parasites are in the liver, they cause an immune response in the body that leads to protection from future malaria infections.
Let’s dive deeper into how that works. Sitting in your liver are immune cells that act like sentinels, constantly on watch for anything that might be a threat to your body. When the modified parasites in the vaccine enter your liver, these immune cells see them and raise the alarm. This alarm calls in a new set of protective, killer immune cells who are then briefed on the parasite threat. These killer immune cells will then station themselves in your liver and stand watch, constantly looking for malaria parasites. The next time you get a mosquito bite from a malaria-carrying mosquito, these killer immune cells will spot the parasites as soon as they enter the liver and kill them before they can escape into the blood.
These potentially life-saving whole parasite vaccines aren’t available yet, as they are still in development. But when combined with other malaria prevention efforts, they provide hope that we can significantly reduce the number of people who die each year from the disease.
Until then, make sure to always remember your mosquito repellent!
References
1. Malaria’s Impact Worldwide. CDC (2024).
2. Malaria. CDC DPDx – Laboratory Identification of Parasites of Public Health Concern (2024).
3. Symptoms of Malaria. CDC (2024).
4. Jackson, A. Explainer: How climate change is amplifying mosquito=borne diseases. World Mosquito Program.
5. Goswami, D. et al. Designer Parasites: Genetically Engineered Plasmodium as Vaccines To Prevent Malaria Infection. J Immunol 202 (1): 20–28 (2019).