To avoid this fate, the P. falciparum parasite displays adhesive proteins on the surface of the infected blood cells, causing the blood cells to stick to the walls of small blood vessels, thereby sequestering the parasite from passage through the general circulation and the spleen. The blockage of the microvasculature causes symptoms such as those in placental malaria. Sequestered red blood cells can breach the blood–brain barrier and cause cerebral malaria. Genetic resistance
According to a 2005 review, due to the high levels of mortality and morbidity caused by malaria—especially the P. falciparum species—it has placed the greatest selective pressure on the human genome in recent history. Several genetic factors provide some resistance to it including sickle cell trait, thalassaemia traits, glucose-6-phosphate dehydrogenase deficiency, and the absence of Duffy antigens on red blood cells.The impact of sickle cell trait on malaria immunity illustrates some evolutionary trade-offs that have occurred because of endemic malaria. Sickle cell trait causes a change in the haemoglobin molecule in the blood. Normally, red blood cells have a very flexible, biconcave shape that allows them to move through narrow capillaries; however, when the modified haemoglobin S molecules are exposed to low amounts of oxygen, or crowd together due to dehydration, they can stick together forming strands that cause the cell to distort into a curved sickle shape. In these strands, the molecule is not as effective in taking or releasing oxygen, and the cell is not flexible enough to circulate freely.
Preauricular sinuses and preauricular cysts are two common congenital malformations. Each involves the external ear. The difference between them is that a cyst does not connect with the skin, but a sinus does. Frequency of preauricular sinus differs depending the population: 0.1–0.9% in the US, 0.9% in the UK, and 4–10% in Asia and parts of Africa.Preauricular sinuses are inherited features, and frequently appear next to both ears. Preauricular sinuses can be associated with other defects that are not visible, one example being branchio-oto-renal syndrome. Presentation
Complications
Occasionally a preauricular sinus or cyst can become infected. Most preauricular sinuses are asymptomatic, and remain untreated unless they become infected too often. Preauricular sinuses can be excised surgically, but often present a high risk of recurrence. Causes
Preauricular sinuses and cysts result from developmental defects of the first and second pharyngeal arches. This and other ear malformations are sometimes associated with renal anomalies. In rare circumstances these pits may be seen in genetic conditions such as branchio-oto-renal syndrome; however these conditions are always concurrent with other health concerns. Treatment
Courses of treatment typically include the following:
Surgical excision is indicated with recurrent fistular infections, preferably after significant healing of the infection. In case of a persistent infection, infection drainage is performed during the excision operation. The operation is generally performed by an appropriately trained specialist surgeon e.g. an otolaryngologist or a pediatric Surgeon. The fistula can be excised as a cosmetic operation even though no infection appeared. The procedure is considered an elective operation in the absence of any associated complications.