The developing world

The term ‘developing world’ is used to describe the majority of tropical countries which are ‘hot, humid and poor’. An alternative term is the ‘less economically sound’ nations, as these countries are often advanced in human and cultural resources. Haematological practice is different to that in most developed countries. Genetic diseases such as the haemoglobinopathies and red cell enzymopathies are frequent in many tropical regions. Deficiency anaemia and haemolytic anaemia are often secondary to infections such as ancylostomiasis (hookworm) and malaria. Medical treatment regarded as routine in the developed countries is commonly unavailable. For instance, only about 20% of the world’s haemophiliac population has access to factor VIII replacement therapy.

With the ever-increasing availability of ‘exotic’ holidays and regular foreign travel within immigrant populations, doctors in the developed world are seeing more tropical diseases. In the patient with unexplained symptoms such as malaise and fever, or signs such as splenomegaly, a history of travel should not be overlooked.

Malaria

Malaria is a protozoal disease, the infectious agent being Plasmodium falciparum, P. vivax, P. ovale or P. malariae. Mortality from the disease has fallen over the last decade but it remains a serious health risk throughout the tropics and subtropics where insecticide resistance of anopheline mosquitoes and multiple drug resistance of malarial parasites make control and treatment challenging. According to the World Health Organization, there were 216 million cases of malaria and an estimated 655 000 deaths in 2010. Most deaths occur in children living in Africa where the disease accounts for 20% of all childhood mortality.

The life cycle of the malaria parasite is illustrated in Figure 49.1. When taking a meal of blood an infected mosquito initiates human infection by the inoculation of malarial sporozoites. These rapidly pass to the liver where they enter hepatocytes and divide. After several days, enormously increased numbers of parasites (merozoites) depart the liver and invade red cells. Here the merozoites develop via ring forms and trophozoites into schizonts. Rupture of the schizont releases 12–20 merozoites back into the blood, thus perpetuating the cycle. The duration of the blood cycle varies between malarial species, explaining the different periodicity of fever in each type. A further mosquito becomes infected when it feeds on blood containing gametocytes, the sexual form of the parasite.