There are 460 recognized species of mosquitoes, of which only about 100 transmit the malaria parasite to the human being and only 30 – 40 transmit the most dangerous and deadly of parasites, the Plasmodium falciparum. The Anopheles gambiae mosquito is known as a vector for its role in transmitting malaria to the human being by feeding on it and simultaneously injecting the Plasmodium f. parasite. It is also the most dangerous because it carries the exceptionally virulent Plasmodium parasite which infects the host with malaria. It is existent worldwide, infects millions with malaria and kills more than one million African children each year.
Malaria was first described as far back as 2700 BCE in China, fourth century Greece, and in India and Rome. Chinese physicians used the herb Quinghao in the treatment of malaria, and in 1971 Chinese scientists isolated the anti-malaria agent artemisinin (known as sweet wormwood in the US) as the anti-malarial agent in it. When Spanish priests came to the New World in the 17th century, they learned of a medicinal bark, quinine, which the Indians used to treat tropical fever due to mosquito bites. Quinine is a common medicine used in the treatment of malaria. In 1880 Charles Louis Alphonse Laveran, a French army surgeon first discovered parasites in a patient’s blood, and was later awarded the Nobel Prize for his discovery.
The Anopheles gambiae mosquito flourishes in a warm, wet tropical climate although it is also found in colder climates, as far north as Canada (sometimes jokingly referred to as Canada’s national bird) but without the Plasmodium parasite. Water is essential for the female that lays aquatic larvae. These go through four life stages: egg, larva, pupa, and imago. The first three stages of development take place within water. The imago is the mature flying creature which lives on land and must feed on mammals by sucking their blood and, if carrying the parasite, simultaneously injects the parasite into the bloodstream.
Four main qualifiers for malaria contagion are (1) the abundance of vectors, (mosquitoes); (2) the prevalence of disease-causing pathogens (parasites) suitable to both the vectors, and the human or animal hosts; (3) local environmental conditions, especially the temperature and humidity; (4) the immunological status of the human population. Over a period of time some members of a locale develop a resistance to malaria which is passed on to the next generation.
Vector-borne diseases are prevalent in the tropics and subtropics and are relatively rare in temperate zones. A study was done which compared forested versus deforested sites, and deforested sites were found to have an increased infection rate compared with the forested sites because deforested sites have higher temperatures and relative humidities than forested. Emerging Infectious Diseases (April 2011): “Deforestation changes microclimates, leading to more rapid sporogonic development of Plasmodium falciparum and to a marked increase of malaria.” .
Two hundred sixty million years ago the ancestors of the modern day Drosophila and the Anopheles mosquitoes diverged in the Permian period. The Old and New World Anopheles clades continued to evolve and diverge again 80 mya. Its genome is diploid with six chromosomes. Fossils have been found in amber dating back to the Eocene period and German amber from the Oligocene period.
The study of the genome of the Anopheles g. mosquito is essential to tracing how it is itself infected by the Plasmodium f. parasite and then infects another creature when it feeds on it. In order to develop anti-malarial drugs, it is necessary to study the genome of the host mosquito and the sporogony (reproduction by multiple fission) of the parasite to test the sporontocidal effectiveness of the drug. When the parasite reproduces by sexual reproduction, it produces a large number of fully formed infectious sporozoites inside the mosquito which migrate to its salivary glands. Compared to genomes of non parasitical eukaryotes (microbes with a nucleus which carries genetic material), the malaria sporozoan has a complex life cycle but a less complex genome, a large part of it devoted to its immune evasion within the host, and its complex parasitical interactions.
The mosquito inoculates the parasite into the host when it bites it and takes a blood meal. Upon entering the body, the sporozoites circulate through the blood to infect the liver. Mosquitoes usually alight softly on their victim and have finished feeding before noticed. This occurs most often while the person is still rather than in motion. Quinine sulfate is the most commonly prescribed drug prescribed for treatment, but artemisinin is preferred by some doctors in severe cases. A hybrid of quinine and artemisinin have been used with much success according to some studies.
Preventing malaria requires environmental planning. Mosquitoes lay their eggs in water, so draining swamps and covering up pools of standing water is a first line of defense. Spraying the larvae with anti-mosquito poison is done in grassy fields and wherever water collects. Mosquito repellant sprayed or rubbed on the skin is often very effective, although it does not always work for some people. Protective clothing, long sleeves, high socks and long pants worn with the mosquito repellant can prevent mosquito bites. The sleeping area should have window screens to keep the mosquitoes out, and if not sleeping in a closed room, mosquito netting should be covered over the resting or sleeping area.
Prevention is the best way to avoid infection, since there is no effective vaccine against malaria.
