Malaria kills 1-3 million people a year, mainly among children under 5. This is about 500 every hour, and it tends to come back in recurrent bouts throughout life.
It has been known since the 1890s that mosquitoes transmit malaria by protozoa such as Plasmodium falciparum. P. falciparum is the main transmitter in humans, causing 90% of modern cases.
There are eventually 3 outcomes of malaria:
- Infected blood cells are recognised by the immune system and killed
- Drug treatments kill the infected cells
- The patient dies
Symptoms become less serious as a person becomes older, as their immune system becomes stronger. This is why the majority of deaths are from young children. Malaria does have a tendency, however, of returning and reinfecting a person multiple times; each time the protozoa uses a different set of genes and the person has to be reinfected several times before they gain immunity to all of the responsible genes.
These symptoms are seen as being caused due to the release of toxins by the protozoa. Symptoms increase as the new merozites- the sort of cell produced by the protozoa- are released.
The invasion of a red blood cell can be seen by some obvious changes. The normal disc shape turns highly uneven and lumpy. As the P. falciparum is released from host cells, the lumps move further to the outside of the cell, creating the bumps on the outside of the cell. The knobs also produce a sort of protein which takes the red blood cell out of commission and away from the other red blood cells. Normally mis-shapen cells are taken to the spleen and destroyed, but the cells are no longer reach the spleen, so are not destroyed, allowing the merozites to be freely produced.
More serious physical symptoms:
- Infected blood cells bind with uninfected cells, that can block blood capillaries
- Infected blood cells bind to blood vessel linings in the brain, which can cause cerebral malaria, which is the biggest cause of death.
Mosquito saliva contains anticoagulants, which allow them to suck up blood through their probosces, but the anticoagulants are irritant and thus cause itching. The saliva also contains the Plasmodium parasites, which enter directly into the blood.
Within a few minutes, a certain type of cell, known as sporozites, have reached the host’s liver.
Once inside the host’s liver cells, the Plasmodium falciparum cell nucleus divides rapidly, creating a cell with many nucleus. Then each new nucleus buds off from the original parent cell, with a little cytoplasm, forming a new type of cell called a merozite. The liver cell bursts, releasing the merozites.
Merozites then infect red blood cells and digest the haemoglobin in them as a food source. The merozites each undergo nuclear division several times, and produce up to 32 new offspring each. The blood cell bursts and within just a few minutes, merozites are released and each one then enters a new red blood cell.
The cycle of release of the merozites occcur every 3-4 days.
Injection is normally a quite effective method of prevention . If the insect involved can be removed, the transmission is far less effective than even with the injection, however.
Vaccines must be suitable for use among small children, as they have the highest fatality rates. The variety of malarial forms and antigens makes finding a single vaccine very challenging. Researchers are working on finding a vaccine that recognises antigens present in the most severe forms of malaria first. The idea behind this is to reduce acute symptoms and keep the infant alive long enough for them to fight an infection naturally.
When in the past marshland has been drained for farming, this has reduced the number of mosquitoes, and thus the rate of incidence of malaria. However, this does have a large environmental cost, due to species which have then lost their habitats. A method of separation without environmental damage is even easier- installing glass into windows. Mosquito nets are another very easy, very effective method.
Insecticides are a popular method of eradication of malaria. However, this is not a sensible method in most areas, because the effected areas are massive, and thus the insecticide needed would be massively expensive and infeasible to deliver. Delivery to small, localised waters is feasible, and could be done easily.
Drugs to prevent malaria can be taken before and throughout visiting a country where malaria is endemic. The best known sorts are based of quinine. Quinine has been used by native American peoples in Bolivaria and Peru using natural bark from a Cinchona tree to treat malaria before scientists researched its use properly. The bark of the tree was then transferred back to imperialist powers which found the native peoples from the sixteenth century on-wards.
Quinine derivatives have since had to be added, thanks to the increasing incidence of strains resistant to quinine. Some are even more effective than quinine was originally. Chloroquinine is one of these. In a red blood cell, the merozite digests the haemoglobin, and uses amino acids from it in order to grow. The haem group left is normally toxic, but Plasmodium neutralise it by converting it into another chemical, haemozoin. Chloroquinine interferes with this conversion.The haem then builds up and kills of the merozites itself.
Other drugs target enzymes involved in Plasmodium DNA replication and growth. Artemisinins are a new class of drugs discovered from research based on Chinese traditional medicine for malaria. It is unknown how artmesinins work, but they have been used for over 2,000 years to cure malaria.
These methods could help save many lives from the disease in the tropics. The main limiting factors seem to be extreme poverty, a lack of infrastructure for distribution, poor governance, and disturbances, as well as any other number of human failures to develop nations evenly worldwide.