Clinical picture, the natural course of malaria

Children are very susceptible to infection. The highest mortality is found in children below the age of 5 years. Gradually, after repeated infections, a partial immunity develops in those who survive. There is a high degree of tolerance to the infection in adults, provided that they live in a stable malaria region. This semi-immunity (premunition) is maintained by repeated infections and mild latent infections. It disappears after approximately 6 to 24 months if there is no further infection (e.g. a stay in a non-malaria region). This partial immunity is reduced during pregnancy. A pregnant woman is at increased risk of hypoglycaemia and cerebral malaria. Malaria is an important cause of severe (sometimes spectacular) anaemia in the mother, low birth weight, premature birth, abortion and increased perinatal death. Chondroitin sulphate and hyaluronic acid, both present in abundance around the syncytiotrophoblasts of the placenta, are mucopolysaccharides (glycosamine glycanes) which act as receptors for red blood cells infected with P. falciparum. Infected cells accumulate in the placenta, resulting in reduced placental function. Probably there are also other receptor molecules. The placental barrier is very seldom passed. Congenital malaria is not common and occurs chiefly in neonates of non-immune women. Neonates of semi-immune women receive transplacental anti-Plasmodium antibodies. Due to this passive resistance in the first 3-6 months they are at a lower risk of malaria. AIDS has no direct influence on malaria, although if routine blood transfusions are given for severe anaemia, there is a risk of infection by this route.

Several observations of humans infected with both malaria and helminths suggest that co-infection provides a benefit to either parasite. The evidence indicates that malaria patients co-infected with helminths are protected from severe malaria, possibly through skewering of the immune response towards T helper (Th)2 immunity.

Category: Medicine Notes