Question

how are geography and malaria connected? how/why does the heterozygous condition provide additional protection? what was this additional protection lead to the increase of sickle cell anemia in certain geographic areas? Also, how may certain anthropogenic trends such as deforestation and climate change increase or decrease malaria rates?

Answer 1

Sickle cell anemia is a genetic disorder caused due to mutant hemoglobin gene .

80 percent of sickle cell disease occur in subsaharan Africa, India, Saudi Arabia and in mediterranean countries or in population whose ancestors where from this region

But having a sickle cell trait that is the heterozygous condition for sickle cell anemia provided additional protection from malaria. The percentage of people having this heterozygous trait was more in equatorial Africa compared to South Africa and central africa and later it came to know that this high incidence of heterozygous sickle cell anemia gene was to give additional protection against malaria. The reason for this protection is that in sickle cell trait the part of heamoglobin, heam is present in free form in the blood and these free heam provide protection from malaria. More over the sickle cell is deformed and stretched which makes the membrane of it porous , the nutrients required for the malarial parasite leak out.

But as the heterozygous population increases they keep on passing gene to the next generation and the number of homozygous sickle cell anemia cases has increased which led to a majority of African population born with this disease. And more over an individual with homozygous condition of sickle cell anemia has no protection and they are more severely affected than the normal individual.

Deforestation has promoted the incidence of malaria. The study was done in Amazon forest and found that deforestation increase malaria. This is because it provides favourable conditions for malarial vector anopheles mosquito to grow ,that is the breeding grounds for mosquito is increased.

Extreme conditions like increase in temperature, humidity and rainfall leads to increased incidence of malaria. This is also due to high propagation rate of the mosquito.