Plagued by parasites

As I lie in my hospital bed recovering from malaria, I have time to think. Several things amaze me. First, how clever the single-celled Plasmodium parasite is. Despite my best efforts (antimalarial drugs, insecticide-treated bednets, mosquito repellents) the parasite still managed to get to me. Second, people have to live for decades feeling like this. In many parts of the world malaria is a part of life. It’s astonishing to think that over 40 per cent of the world’s population still live under threat of the disease. In the worst affected areas, if malaria doesn’t kill people in the first few years of life, they just learn to live with the debilitating fevers. And finally, how easily it can be treated. Given the right drugs I begin to feel better within a few hours.

Fevers are the most obvious symptom of the disease. They come on hard, fast and with absolute precision. I go from 100 per cent to as ill as I have ever felt, in the space of 15 minutes. This happens at 8.45 p.m. precisely every other day. There is a good reason for the tell-tale accuracy of the fevers. In humans the parasites live inside the red blood cells. The cell provides both nourishment for the rapidly multiplying parasites and a refuge from the human immune system. Once all the food in a single red blood cell has been used up (after 48 hours), the parasites must move and find a new cell to exploit. But outside the red blood cell the parasites are vulnerable to attack by the human immune system. If all the parasites in the body break out of the red blood cells at the same time, they can overwhelm the bodies defences through sheer force of numbers and make it to the safety of a new cell. So millions of parasites plus toxins from the used up red blood cells are synchronously released into my blood as the parasites rupture from the cells. The fever is my body’s shock reaction. It lasts for about six hours until all the parasites are hiding again, and then I’m back to normal until two days later.

I caught malaria in Tanzania. Ironically I was collecting mosquito samples for my PhD on the disease. I study the genetic diversity of Plasmodium in different mosquito species. I had to collect thousands of mosquitoes from the inside of people’s houses and extract the parasites from them. It was astonishing just how many blood-gorged mosquitoes I could find dangling from the ceilings of the simple mud huts. People must receive hundreds of bites per night. The villagers found it curious that I was so fascinated by the mosquitoes in their houses, but they were only too happy for me to remove a few!

In Tanzania people suffer from malaria throughout their lives. The worldwide effects of malaria are not known with any accuracy. In the West we spend more on forecasting the weather than most African nations can afford to spend on monitoring malaria. It is known that malaria kills millions of children in Africa every year, usually from anaemia – they simply run out of red blood cells to carry oxygen. If a child survives, the fevers continue throughout adulthood causing sickness and reducing the ability to work.

Globally the problem of malaria is growing due to drug-resistant parasites and insecticide-resistant mosquitoes. But these are exciting times in malaria research. The entire genome of the parasite is currently being sequenced, as are the genomes of humans and the most important mosquito species. This huge resource is helping us to unravel the interactions between the three components of this complex, co-evolving system, pointing to new ways of beating the disease. I use information generated by the sequencing project to monitor populations of Plasmodium and see whether they differ between mosquito species. Intriguingly, it looks as if they do.

Next time I carry out fieldwork I shall, of course, be doing my best not to become re-infected. But I count myself lucky that this time I had access to the treatment that is denied to so many millions.

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