ABSTRACT
As socioeconomic development proceeds, most countries pass through what has been called a "health transition" or an "epidemiological transition". At low levels of development, rates of sickness and death are high. Most of this ill-health is due to infectious disease, caused by viruses, bacteria, parasites and other organisms. Schistosomiasis is a parasitic disease spread by water snails. Since the snails can thrive in the conditions created by irrigation projects, it is in extensively irrigated areas of the Middle East that the disease has been most important. The prevalence of human immunodeficiency virus (HIV) is more likely to be kept low if the population has a good understanding of the ways in which the disease is transmitted, and of the methods for controlling it. Along with hepatitis A, B, D and E, hepatitis C is one of a family of viral diseases causing liver disorders.
