Malaria is still one of the most important killers in tropical regions, and it has proved to be very difficult to combat. However, a glimmer of hope has appeared thanks to a promising new vaccine.
Malaria is a deadly disease. In the West, it is mostly known by name only as it is essentially a tropical disease. Malaria is caused by a parasite of which four species can infect people. Of these,
Plasmodium falciparum is the most dangerous as it causes an estimated 700,000 to 2.7 million deaths annually, the majority of them young children in Africa.
Malaria is transmitted by female mosquitoes of the
Anopheles genus. The mosquitoes suck blood from humans in order to let their eggs develop. At that moment, the human can be infected. The life cycle of
Plasmodium falciparum is complex and quite interesting. I added some more information below.
The New England Journal of Medicine has two articles regarding research into a new vaccine against malaria (published December 8, 2008). The vaccine targets the stage of
Plasmodium falciparum before it enters the red blood cells (see below).
One trial was held in Bagamoyo, Tanzania. It was a phase 2b trial, which means that it was a trial on a fairly large population. It was a trial involving 340 infants. They either received the trial vaccine or a hepatitis B vaccine at 8, 12 and 16 weeks of age. The vaccine turned out to be very safe, and it led to a significant reduction of malaria infections, approximately 65% protection against malaria infections.
The
second trial was held in Kenya, involving 894 children of which 809 finished the study according to the protocol. 402 of these children received the actual vaccine at 5 to 17 months of age. Here, the vaccine had about 53% efficacy.
These results are extremely promising, and will most likely lead to a Phase 3 trial in which the vaccine will be tested in larger populations.
These vaccines are being developed by GlaxoSmithKline, a Belgo-British pharmaceutical company. There are other companies that are actively developing vaccines for malaria, but this company seems the furthest ahead. It is interesting to note that the Bill and Melinda Gates Foundation is paying for this research, and according to
de Volkskrant, a leading Dutch newspaper, the foundation has already invested more than 100 million USD in this development.
Pharmaceutical companies are often blamed for the high prices they charge, but what is usually forgotten are the enormous investments the development of new pharmaceuticals require. Research like this is prohibitively expensive, and most trials stop without ever being developed into a commercial product. Compare that with the billions of dollars unproven and untested alternative "medicines" such as homeopathic products bring in for companies that have essentially no research expenses whatsoever.
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Life cycle of Plasmodium falciparum
The mosquito bites the human. During this bite, sporozoites are released from the salivary glands of the mosquito in the bloodstream of the human victim. These sporozoites are carried by the blood to the liver, where they invade liver cells (hepatocytes). This process is so fast that there are no more sporozoites in the bloodstream, approximately 30 minutes after infection.
During a period of around two weeks, the sporozoites multiply asexually into thousands of merozoites. Their growth is so enormous that they literally burst from the liver cells. These merozoites enter the bloodstream where they invade red blood cells (erythrocytes). In the red blood cells, each merozoite forms a dozen or so new merozoites within a schizont, a process that takes about 48 hours. These make the red blood cells rupture, and it is at the time of this rupture that the clinical symptoms of malaria such as fever and chills are felt.
Some of the merozoites do not become schizonts but they change into male and female gametocytes that reproduce sexually. These gametocytes are ingested by the mosquito during her blood meal. In the midgut of the mosquito, the male gametocytes rapidly divide, producing 8 flagellated microgametes (small sex cells). The female gametocytes become macrogametes which are fertilized by the microgametes. This leads to ookinetes that go through the intestinal wall of the mosquito where they encyst as oocysts. When the oocysts rupture, they release hundreds of sporozoites into the body cavity of the mosquito. Finally, they migrate to the salivary glands of the mosquito and the cycle can start over.
Remarkable about this is that the mosquito doesn't seem to be bothered by the process, only the human is. This life cycle also explains why there are so many black people with sickle-cell anaemia. These people are protected against the plasmodium parasite. Sickle-cell anemia is a genetic disorder that manifests itself in the production of abnormal haemoglobin. This leads to sickle (C) shaped red blood cells that are stiff and sticky and have difficulty passing through blood vessels where they often form clumps, leading to excruciating pain, infections, organ damage. Malaria can't reproduce well in these abnormal red blood cells, and sickle-cell anaemia is thus a protector against this deadly disease, even though it is in itself not exactly a desirable condition.
This is but one example of natural evolution at work and of the blind and cruel way it comes about.
