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Fifteen million people worldwide die from insect and water-borne diseases each year.  Among the killers: malaria, dengue fever, diarrhea, and cholera.  Most of their victims live in the developing countries of Africa, Asia, and Latin America; most of the diseases afflicting them are preventable.  Clean, potable drinking water, vaccines, mosquito control programs, and adequate health care are required, but too frequently developing countries lack the means to provide them.  To confront these diseases, people also need to consider the ways they contribute to the problem.  Urbanization, with its associated wells, trash, and drainage ditches, provides ideal breeding places for the mosquitoes that transmit malaria and dengue fever.  Drinking and bathing in water contaminated with human wastes can lead to diarrhea and cholera.  While many people in developed countries believe they are safe from these diseases so typical of poor, tropical countries, it is true that these diseases present a risk to us all.  In the age of air travel, people, animals and insects, which are infected with disease-causing organisms such as the malaria blood parasite, can, and do, travel around the developed world.  A recent example: the appearance in 1999 of West Nile Virus in New York City.  Possibly carried by mosquitoes hitchhiking on planes flying from Africa, this potentially lethal disease has since infected thousands of people throughout the United States. 

Learning Objectives

Students will be able to:

  1. Trace the presence of insect and water-borne diseases to environmental conditions created by human activity.
  2. Describe how these diseases, typical of poor, tropical countries, can affect the health, security, and economic well-being of people in the developed world.
  3. Discuss the role that the developed world should play in helping combat these diseases.

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Pre-Viewing Activities

  1. Introduce the following key terms to the students:

    Malaria — a serious disease caused by several species of one-celled organisms that infect red blood cells in humans and other animals and that are transmitted by mosquitoes.  Malaria kills hundreds of thousands of people worldwide each year.

    Dengue Fever — a serious disease caused by a virus that is transmitted by Aedes mosquitoes and that causes severe headache, fever, and pain in the joints.  May be fatal.

    Diarrhea — a condition, caused by a host of microorganisms, which causes uncontrolled bowel movements.  Victims become weak and dehydrated if not treated.  Millions of people worldwide, mostly from developing countries, die from diarrhea each year.

    Cholera — a serious disease, caused by a bacterium and transmitted by ingestion of contaminated water, that causes severe diarrhea and fever.  Unless treated, patients may become seriously dehydrated and die.

    bacterium — a one-celled organism, belonging to the kingdom Monera.  Bacteria live everywhere on Earth; some of them cause disease in humans.

    virus — a nucleic acid, either DNA or RNA, wrapped inside a protein that reproduces only inside cells of living creatures.  Difficult to define as either living or non-living.  Some viruses cause disease in humans.

    Aedes and Anopheles mosquitoes — two genera of mosquitoes.  The Aedes mosquito transmits dengue fever; the Anopheles mosquito transmits malaria.

    Pfisteria — a strange aquatic protozoan that apparently lives in several different forms, one of which attacks fish.  This form is thought to thrive in water contaminated with animal wastes and has been implicated as the culprit in some recent major fish kills, notably in North Carolina and the Chesapeake Bay.

    epidemic — the rapid spreading of a disease through a population

    contagion — a contagious disease

    ecotourist — a tourist that travels to experience natural wonders, such as forests and wildlife, often in exotic locales

    effluent — a discharge of liquid waste, as from a factory or nuclear plant

  2. To familiarize students with the areas in the program segments, use a wall map, desk map or an atlas and have students locate:

    • Iquitos, Peru
    • Lake Victoria
    • Nairobi, Kenya
    • Lima, Peru
    • Bangladesh
    • New York City
    • Chesapeake Bay

    After the students have found each of these locations, begin a discussion to discover what they already know about these regions.  Have the discussion center on environmental problems that they are familiar with.


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Post-Viewing Discussion

Malaria in Kenya

  1. How many people in Kombewa, at any one time, are infected with malaria?  How many Kombewa children will die from the disease before they turn five?  (Answers: 80% and 20%, respectively.)
  2. What is the role of mosquitoes in spreading the disease?  (Answer: Malaria is caused by a microscopic parasite that lives inside red blood cells.  Mosquitoes spread the parasite by biting an infected person, taking in the parasites with their blood meal, biting another person, and injecting the parasites in the process.)
  3. Why is malaria becoming more prevalent in Nairobi?  (Answer: People infected with the malaria parasite are migrating to the city where they infect others, and human-caused alteration to the local environment is creating ideal mosquito breeding conditions.)

Dengue Fever in Peru

  1. How are humans creating ideal conditions for the dengue-carrying Aedes mosquitoes to breed?  (Answer: They are leaving wells and basins uncovered and trash on the ground, all of which can hold stagnant water.)
  2. How might malaria and dengue in Nairobi and Iquitos arrive quickly in the United States?  (Answer: People can easily fly directly to these cities from the United States.  Many who do so are tourists.  While in Peru and Kenya, they can become infected and bring the diseases back to the United States in their bloodstreams.  )

West Nile Virus in New York

  1. How did people think West Nile virus arrived in the United States?  (Answer: An infected mosquito on a plane traveling from Africa to New York.)
  2. Why are people investigating dead crows and other birds?  (Answer: The West Nile Virus also infects and kills birds.  The virus was first discovered in birds.  Now, by investigating dead birds, scientists can determine how common the virus is and where it has spread.)

Water-borne Diseases in Peru

  1. How many people worldwide are estimated not to have access to clean drinking water?  (Answer: 1.1 billion.)  How many people are thought not to have access to basic sanitation services?  (Answer: 2 billion.)
  2. Compare your living conditions with those people residing in Lima's slums.  Consider the following: Sources of drinking water, Presence of electricity, Means of disposal of human waste, Means of garbage disposal, Safe housing regulations, Roads and transportation, Health services.  (Perhaps move this question to follow-up.)
  3. Diarrhea and cholera are spread through contact with dirty water.  Where might Peruvians come into contact with these diseases?  (Answer: Water used for drinking, bathing, washing clothes, preparing food.)

Water-borne Diseases in Bangladesh

  1. Why is cholera more prevalent in Bangladesh than in Peru?  (Answer: The climate, the country's fresh water, and the ocean water offshore are all warmer, encouraging the growth of plankton in which the cholera bacterium lives.  Massive annual floods, brought about by the monsoons, deposit contaminated water throughout the ponds and streams that people use for drinking water.  Thus, Bangladesh's population density, poverty, climate, and geography all conspire to give the country the highest rate of cholera infection in the world.)
  2. Why is finding a solution to the shortage of safe drinking water in Bangladesh so difficult?  (Answer: Ground water tapped by over five million wells in the country contains dangerous amounts of arsenic.  Another source of water needs to be found, but this is very difficult in such a poor, crowded country.)

Diseases Afflicting Aquatic Life in the Chesapeake Bay

  1. What pollutants entering Chesapeake Bay are thought to be harming aquatic life?  (Answer: Poorly treated sewage, pesticides, eroded soil, fertilizers, and industrial effluent.)
  2. What is the connection between these pollutants and the diseases attacking oysters and fish?  (Answer: The connection is not yet clear, but pollutants are suspected of weakening oysters so that they are susceptible to diseases, and they are thought to be altering water conditions in Chesapeake Bay so that the toxic algae, Pfiesteria, and certain species of fungi can thrive.  Both of these organisms are believed to attack fish, but the relationship between them is not yet clear.)

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Special Projects

  1. Have the students research the life cycle of the malaria-carrying Anopheles mosquito.  Based upon their findings, have them develop a malaria eradication program for Nairobi, Kenya, that employs more than the spraying of insecticides.  They should consider the following:

    • Mosquitoes can be prevalent in urban areas because uncovered wells, ditches, and trash provide abundant breeding areas for them.  To discover how mosquitoes can take advantage of such human-provided opportunities, have your students scatter a variety of receptacles filled with water around the school grounds.  Receptacles may include bowls, tin cans, trashcans, or tires.  Have the students check the receptacles daily and record how long it takes in each one for mosquito larvae, called wrigglers, to appear.  Have them note the environmental conditions for each receptacle, such as size, shape, and material of the receptacle, the amount of shade each receptacle is lying under, and the amount of fallen leaves and other organic material to be found in each.  Have your students write up their results and compare their findings.
    • Several tropical parasites that infect humans have complicated life cycles.  Have students research the life cycles of the following: schistosomiasis or bilharzia, tapeworm, hookworm, onchocerciasis or river blindness, filiariasis, and guinea worm.  The Carter Center web site ( contains much useful information on some of these parasites.  Have the students diagram the parasites' life cycles on posters.  Then discuss what measures people can take to reduce the incidence of infection of these parasites.

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