Tropical Diseases

Nowhere is the prevalence of certain illnesses more striking than in areas where tropical diseases flourish. In many parts of Africa, South America, and Asia, diseases exist that are rarely seen in the United States. These include malaria, which infects from 300 to 500 million people annually and kills up to 2.7 million people every year, and leishmaniasis, which affects some 12 million people internationally. Other ailments, such as measles and diarrhea, are well-known in developed areas such as the United States but are rarely fatal.

Young people are highly susceptible to death from disease in these areas. Children under five account for 40-60% of all deaths in Africa, Asia, and South America, although they make up only about 15% of the population. Such high death rates reflect the fact that tropical diseases are most prevalent in poor areas where health care is limited. Efforts to improve community health in areas where tropical diseases thrive include the establishment of health clinics and the development of new vaccines.

Ascariasis and hookworm

A common disease in tropical countries is ascariasis. The annual death rate due to ascariasis is about 20,000, most due to complications within the intestine, where the worms settle as adults. An estimated 700 million individuals are affected at any given time by the disease.

Ascariasis is spread through dirt. The worm which grows in the intestine, the roundworm Ascaris lumbricoides, is the largest such parasite, growing to a length of 19.3 in (49 cm). It can live about a year in the human body.

The disease can cause difficulties, such as bronchial asthma, in the lungs, when the parasite settles in that part of the body. The greatest threat to the human host is the loss of food nutrients which go to the worm instead of the host. Individuals whose diet is already sparse may suffer from malnutrition after infection with ascariasis.

The life cycle of the creature is similar to the life cycle of the blood fluke, though there are some differences. The disease is spread when Ascaris eggs leave the human host in feces. The new host ingests the eggs through soil or by soil-contaminated hands or food. The eggs then travel through the liver, lungs, and throat, before ending up in the intestine. Once they are in the intestine, more eggs are laid, clearing the way for further spread of the disease.

Another parasite that is spread through dirt and grows in the human body is hookworm, which affects approximately 800 million individuals in the developing world and kills about 50,000 annually. Hookworm was at one point common in the American South, but is now seldom reported in the area.

The hookworm, which grows up to 0.5 in (13 mm) in size, sucks blood and normally lives in the small intestine. Establishment of the worm in the host generally results in iron-deficiency anemia because of blood loss, and may cause bronchitis, peptic ulcers, or even heart problems.

Hookworms enter the body as larvae through the skin, taking advantage of hair follicles or other openings to help the creature pierce through the skin with its boring movement. The parasite enters the circulatory system, moving first to the lungs then to the pharynx, where it is swallowed. The final larvae stage typically occurs in the small intestine, where adult worms emerge and ultimately lay eggs. Adult worms normally live from one to 5 years if the host is not treated. They cannot multiply in the body.

Successful control of the hookworm depends on improvements in plumbing and the use of footwear, a challenge in countries where shoes are a luxury. Medication is available to destroy hookworm, but providing it in areas where hookworm infestation is severe does little to alter the problem, as those who are medicated can easily be reinfected.