USA , Download references. You can also search for this author in PubMed Google Scholar. Reprints and Permissions. Wadman, M. Sickle-cell mystery solved. Nature Download citation. Published : 10 November Anyone you share the following link with will be able to read this content:. Sorry, a shareable link is not currently available for this article. Provided by the Springer Nature SharedIt content-sharing initiative. But there is likely to be more to the development of malaria than simply controlling haem levels in the blood.
It is already known that an inflammatory response also plays a part in the onset of malaria, Soares says, which suggests the disease is triggered by a two-pronged attack. The overactive immune response leads to the accumulation of toxic T-cells. In another experiment, Soares and his team showed that build-up of these pathogenic cells after infection with malaria is inhibited in mice with one sickle cell gene — although the protective mechanism at work has yet to be established.
By Catherine de Lange The elusive mechanism by which people carrying the gene for sickle-cell disease are protected from malaria has finally been identified. Trending Latest Video Free. New mineral davemaoite discovered inside a diamond from Earth's mantle Paralysed mice walk again after gel is injected into spinal cord Will a scramble to mine metals undermine the clean energy revolution?
On the contrary, individuals who are carriers for the sickle cell disease with one sickle gene and one normal hemoglobin gene, also known as sickle cell trait have some protective advantage against malaria.
As a result, the frequencies of sickle cell carriers are high in malaria-endemic areas. Most of this protection occurs between months of life, before the onset of clinical immunity in areas with intense transmission of malaria. Those who had the sickle cell trait HbAS had a slight survival advantage over those without any sickle cell genes HbAA , with children with sickle cell disease HbSS faring the worst.
Lancet ; Malaria is transmitted to humans by female mosquitoes of the genus Anopheles. Female mosquitoes take blood meals for egg production, and these blood meals are the link between the human and the mosquito hosts in the parasite life cycle. In contrast to the human host, the mosquito host does not suffer noticeably from the presence of the parasites. Map of the world showing the distribution of predominant malaria vectors. Anopheles freeborni mosquito pumping blood Larger Picture.
Sequential images of the mosquito taking its blood meal. There are approximately 3, species of mosquitoes grouped into 41 genera.
Human malaria is transmitted only by females of the genus Anopheles. Of the approximately Anopheles species, only transmit malaria i. The rest either bite humans infrequently or cannot sustain development of malaria parasites. Anophelines are found worldwide except Antarctica. Malaria is transmitted by different Anopheles species in different geographic regions.
Within geographic regions, different environments support a different species. Anophelines that can transmit malaria are found not only in malaria-endemic areas, but also in areas where malaria has been eliminated. These areas are thus at risk of re-introduction of the disease. Like all mosquitoes, anopheles mosquitoes go through four stages in their life cycle: egg, larva, pupa, and adult. The first three stages are aquatic and last days, depending on the species and the ambient temperature.
The biting female Anopheles mosquito may carry malaria. Male mosquitoes do not bite so cannot transmit malaria or other diseases. The adult females are generally short-lived, with only a small proportion living long enough more than 10 days in tropical regions to transmit malaria. Adult females lay eggs per oviposition. Eggs are laid singly directly on water and are unique in having floats on either side.
Eggs are not resistant to drying and hatch within days, although hatching may take up to weeks in colder climates. Mosquito larvae have a well-developed head with mouth brushes used for feeding, a large thorax, and a segmented abdomen.
They have no legs. In contrast to other mosquitoes, Anopheles larvae lack a respiratory siphon and for this reason position themselves so that their body is parallel to the surface of the water.
Top: Anopheles Egg; note the lateral floats. Bottom: Anopheles eggs are laid singly. Larvae breathe through spiracles located on the 8th abdominal segment and therefore must come to the surface frequently. The larvae spend most of their time feeding on algae, bacteria, and other microorganisms in the surface microlayer. They do so by rotating their head degrees and feeding from below the microlayer.
Larvae dive below the surface only when disturbed. Larvae swim either by jerky movements of the entire body or through propulsion with the mouth brushes. Larvae develop through 4 stages, or instars, after which they metamorphose into pupae.
At the end of each instar, the larvae molt, shedding their exoskeleton, or skin, to allow for further growth. Anopheles Larva. Note the position, parallel to the water surface. The larvae occur in a wide range of habitats but most species prefer clean, unpolluted water. Larvae of Anopheles mosquitoes have been found in fresh- or salt-water marshes, mangrove swamps, rice fields, grassy ditches, the edges of streams and rivers, and small, temporary rain pools.
Many species prefer habitats with vegetation. Others prefer habitats that have none. Some breed in open, sun-lit pools while others are found only in shaded breeding sites in forests. A few species breed in tree holes or the leaf axils of some plants. The pupa is comma-shaped when viewed from the side. This is a transitional stage between larva and adult. The pupae does not feed, but undergoes radical metamorphosis.
The head and thorax are merged into a cephalothorax with the abdomen curving around underneath. As with the larvae, pupae must come to the surface frequently to breathe, which they do through a pair of respiratory trumpets on the cephalothorax. After a few days as a pupa, the dorsal surface of the cephalothorax splits and the adult mosquito emerges onto the surface of the water. The duration from egg to adult varies considerably among species and is strongly influenced by ambient temperature.
Mosquitoes can develop from egg to adult in as little as 7 days but usually take days in tropical conditions. Anopheles Adults. Note bottom row the typical resting position. Like all mosquitoes, adult anopheles have slender bodies with 3 sections: head, thorax and abdomen. Despite several decades of research, the mechanism underlying this protective effect remained elusive. Until now. Several studies suggested that, in one way or another, sickle hemoglobin might get in the way of the Plasmodium parasite infecting red blood cells, reducing the number of parasites that actually infect the host and thus conferring some protection against the disease.
The IGC team's results challenge this explanation. In painstakingly detailed work, Ana Ferreira, a post-doctoral researcher in Miguel Soares' laboratory, demonstrated that mice obtained from Prof.
Yves Beuzard's laboratory, that had been genetically engineered to produce one copy of sickle hemoglobin similar to sickle cell trait, do not succumb to cerebral malaria, thus reproducing what happens in humans. When Prof. Ingo Bechman observed the brains of these mice he confirmed that the lesions associated with the development of cerebral malaria where absent, despite the presence of the parasite.
Ana Ferreira went on to show that the protection afforded by sickle hemoglobin in these mice, acts without interfering directly with the parasite's ability to infect the host red blood cells. As Miguel Soares describes it, "sickle hemoglobin makes the host tolerant to the parasite.
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