Malaria, Mozzies and a Mzungu (Part 1)
Christmas is coming, the bazungu are getting fat, and all the new arrivals will be off to the game parks with visitors from Europe and America escaping the cold and rain. Or snow. And all asking the same question: what about malaria?
The next few articles will be the latest information we have on malaria in Rwanda, what is malaria, how do you get it and why is there so much confusion over what is essentially an easy disease to prevent, diagnose and treat.
Even the question “what is malaria” is actually complicated and difficult to answer! If malaria means someone who is infected with malaria parasites, then in seriously endemic areas that means an awful lot of perfectly healthy people. The latest research has shown that in some areas of Rwanda, and apparently Pakwatch is the worst found so far, the average child is bitten by an infected mosquito 1,500 times a year. That is 4 or 5 bites a night. So why is the average school child up country perfectly well most of the time? (Other than being noisy, snotty, running around playing football and getting into trouble like any child from Bristol, Berlin or Boston?) He either has “malaria” all the time, or he is always on treatment, or dead in 2 weeks or something else is happening.
So what is malaria? How can a child up country be infected with malaria every day yet is perfectly well most of the time, and why is a Mzungu bitten once in the airport on the way home in intensive care for a week? We have to start from the beginning. With a mosquito
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Mosquitoes They prefer shallow temporary puddles such as car tracks and |
footprints. How they survive I do not know, but maybe that is why there are no anophylenes on Makindye, it is too steep. What is more, some prefer goats to people, do not like coming indoors, and only bite between dusk and dawn. SO most mosquitoes you catch in your bedroom in Kampala are not anophylene. Have a good look at them. Most will be Aedes, delicate rather pretty little mosquitoes with black and white markings. They go for your feet, and at least for me itch like crazy: other species I don’t even feel. The Culex are big brown hairy ones with the worst bites. And the nosiest. Anophylenes are rather nondescript, medium size with salt and pepper wings. They land on the wall, or you, with their bums up in the air like all the pictures on the malaria drug packets. The others bend in the middle and land flat to the wall, so easily identified as not anophylene. They all make a big red splodge when squashed so you cannot tell what they are that way. So in many parts of Kampala malaria is hardly ever seen as there are no Anophylenes about to give it to you.
The Parasite
But let us assume you do not live on Makindye and are bitten by a female anophylene. What will happen? Probably nothing. Even most anophylenes do not carry malaria. Or it may inject about 15 to 20 sporozoites into your blood. These are invisible, and are carried around your blood until they get to the liver. There they are actively taken up into liver cells. Each one quickly divides until they are about 40,000 little parasites called merozoites. What happens next depends on which species of malaria the mosquito had.
I will consider only falciparum, the most common and the only one that can kill. After 5 days most of the infected liver cell burst, releasing around 600,000 merozoites into your blood. A few may wait a day or two and in rare cases up to another 2 weeks. However most of them come out in the first wave after 5 days. Some of them fail to find a suitable red cell, but the ones that do change their names to trophozoites, and spend the next 2 days growing. They still are causing no harm to us at all. After almost exactly 2 days they become sticky and “sequestrate” i.e. they stick in the narrow capillaries in the deeper warmer organs such as brain, kidneys, liver, lungs. They spend just a few hours stuck, and each divides into 32 new babies, then the red cell bursts and releases the next generation of merozoites into the blood. About 10 to 15 will find a suitable red cell and become trophozoites and start over.
When the cell bursts a lot of toxins from the excreta of the trophozoites and digested hemoglobin is released into the blood, and this is what causes the fever, headache and other symptoms of malaria. If you are an adult and have 1 bite then a bit of maths shows that to begin with, on days 5 to 7 you will have about 1 parasite in 30 million red cells, too few to cause any trouble at all. Every 2 days they sequestrate, burst and release toxins and start over with 10 times as many as before. That is why malaria symptoms come in waves every 2 days getting worse each time. On day 9 there may be enough toxins to cause a bit of a fever for a few hours. On day 11 the toxins will be enough to make you pretty ill, with fever, vomiting, headache lasting half the day.
A lucky microscopist will find one parasite in 15 fields on a thick film but most would still miss them. The malaria rapid test would just be tripped, and will be a faint positive. Day 13 and with 10 times as many again, you are very ill, probably too sick to walk much further than the bathroom, and with 1 parasite in 3,000 cells that is almost 1 parasite per field on a slide and the Malaria rapid will be a strong positive. You may feel as sick as the sickest parrot that was ever sick, but this is still classified as a mild attack of malaria! It would take another 4 days of no treatment before the real trouble starts. The sticky red cells are now enough for there to be an odds on chance of the cells sticking together and blocking the capillaries when they sequestrate, so every deep organ goes into sudden failure due to blocked capillaries. This is “multi-organ failure”, affecting the kidneys, lungs, brain, and often called “cerebral malaria”. It is not a separate disease it is simply ordinary malaria that has not been treated, with the number of parasites increasing by 10 times every 2 days eventually the number of parasites reaches the critical mass of around 5%. We will consider treatment in the next Eye.
