Malaria, Mozzies and a Mzungu (Part 2)
What happens when we take treatment?
Remember the symptoms are due to the toxins released by the ruptured red cells. With a really fast acting drug like artemether, the parasites are almost all dead in about 4 hours. The red cell then gets eaten in the spleen and releases the toxins. So about 4 hours after treatment there is a new wave of symptoms and you will feel a lot worse.
And there are now 10 times more parasites then in the last wave, so after treatment you will be feel far worse then you did before. People who say they have had malaria many times and take their favourite remedy and are better the next day have not had malaria. The next day you are not better you are worse. A lot worse. We will consider treatment in the next Eye.
What has been described is what happens in a complete non-immune adult bitten by one infected mosquito. 2 or more mosquitoes and the whole picture is brought forward 2 or 4 days, with you getting pretty sick in 9 days, and multi-organ failure and death if not treated by day 14. A new born baby, bitten by 5 mosquitoes and with 1 tenth the volume of blood could go from perfectly well on day 7 to dead in just 2 or 3 days without treatment.
Or perhaps not. Life is not easy for a malaria parasite in Africa. At every stage danger lurks. The immune system. Without it, most of Africa would be uninhabitable.
Immunity
Once you have had malaria, and have been treated, the immune system produces antibodies to the different stages of the parasite. Organs such as the spleen develop special cells that eat and destroy the cells with parasites in them, and enzyme pathways develop that clear away the toxins.
The immunity is only partial and gets slowly more efficient each time it is stimulated by a new infection. So the Pakwatch schoolboy is perfectly well most of the time. When he gets malaria the toxins don’t make him so ill, he has a large spleen that eats the parasitized red cells before they sequestrate and release new parasites, and antibodies that kill the merozoites in the blood and possibly the sporozoites too. For him malaria is now a self-limiting disease, that most of the time he doesn’t even notice.
However he is the source of the epidemic! Because we have left out one part of the cycle. The Mzungu, with no immunity either gets treated or dies. He cannot infect a mosquito, because the trophozoites in his blood are not infectious to the mosquito. However when the parasites realize that the immune system is giving them a hard time, they stop developing more trophozoites, but instead develop into male and female gametocytes, these are infectious to the mosquito.
Mating in the Mozzy
The male and female actually “hatch“ in the mosquito’s stomach, mate and produce the sporozoites. Trophozoites in the stomach of a mosquito simply get digested. So mosquitoes can only carry malaria if they are biting semi-immune people who have had malaria for a few days and are getting better without treatment. No immunes, no gametozyte carriers, means no transmission of malaria.
You can only become immune by getting malaria many times. Babies born to immune mothers and breast-fed have some immunity, and develop their own each time they get infected. So in most rural areas by the time they are 5 they are either immune, or dead.
They are now carriers, infectious to mosquitoes and keeping the epidemic going. They may get sick every now and again when the number of parasites overwhelm the immune system, but will recover quickly with treatment. But not the Mzungu or a Rwandan who has lived all his life in Kampala. He may not have had malaria more than a few times, his immunity is weak or nonexistent, and without prompt and full treatment he is going to die.
So what use is this knowledge of the life cycle of parasites and the role of the immune system?
Practical application
First of all, you cannot possibly have a diagnosis of malaria until you have been in the country at least 7 days. A diagnosis of malaria in the first week is wrong
Secondly, visitors of less than 5 years are not going to develop immunity without being very ill every few weeks for many years. SO the excuse I often hear that I am here for 2 years so do not want to take prophylaxis because I can become immune is just plain daft. The reason none of my family have had malaria for 20 years is not because we are immune, it is because we don’t get bitten,
Next, in some areas of Kampala malaria is so rare most of us do not take any precautions at all and never get malaria. But in most areas up country malaria is common. If you go to a game park or even a campsite in Jinja and don’t take prophylaxis you are probably going to get malaria. And even the mildest of faint positives is going to make you as sick as a dog for a week.
Next, if a non-immune expat walks into a doctor with a slight headache and a bit of vomiting and has a slide and is told he has malaria that is very unlikely. Non-immunes with malaria are very sick indeed even with very few parasites. Those who think they have had malaria “lots of times” and just had a fever and a bit of a headache for a few days and get better after treatment have almost certainly not had malaria.
Lastly immunes are immune because they get a lot of malaria. So if they think they are getting malaria all the time, how come? Either they really do get malaria all the time and are immune and therefore don’t get sick any more, or they don’t get malaria very often and when they do they are sick. If you are sick every few months and always being treated for malaria, it is most unlikely to be malaria, because if it was, you would be immune and so malaria wouldn’t make you sick, would it? Catch 22.
In the next article I will write in detail about diagnosis and treatment
Summary
Malaria is a disease with 2 distinct extremes and a gray area in between. On one extreme the semi immune who gets infected every day but isn’t sick. He is the carrier who keeps the epidemic going by infecting mosquitoes. On the other extreme, the non-immune. Just one bite and about 10 to 12 days later he is very ill, despite just a few parasites. Without proper treatment the number of parasites will increase 10 times every 2 days and he will die of multi organ failure.
One disease, 2 extreme outcomes.
