19-4 Biological Hazards: Disease in Developed and Developing Countries

What Are Nontransmissible and Transmissible Diseases? To Spread or Not to Spread

A nontransmissible disease is caused by something other than a living organism and does not spread from one person to another. Such diseases tend to develop slowly and have multiple causes.

A transmissible disease is caused by living organisms and can spread from one person to another. Infectious agents or pathogens cause such diseases. These agents are spread by air, water, food, and body fluids, and by some insects and other nonhuman carriers. All such pathways are called vectors.

Typically, a bacterium is a one-celled microorganism that can replicate (clone) itself by simple cell division. A virus is a microscopic, noncellular infectious agent.

A parasite is an organism that feeds off another organism. Protists are a diverse assortment of microscopic or near-microscopic organisms that live as single cells or in simple colonies.

As a country industrializes, it usually makes an epidemiological transition in which deaths from the infectious diseases of childhood decrease and those from the chronic diseases of adulthood (heart disease and stroke, cancer, and respiratory conditions) increase.

Case Study: Are We Losing Ground in Our Struggle against Infectious Bacteria? Growing Germ Resistance to Antibiotics

We may be falling behind in our efforts to prevent infectious bacterial diseases because of the astounding reproductive rate of bacteria, which can produce about 16 million offspring in 24 hours. Their high reproductive rate allows them to become genetically resistant to an increasing number of antibiotics through natural selection. They can also transfer such resistance to non-resistant bacteria

An additional factor is overuse of antibiotics. At least half of all antibiotics used to treat humans are prescribed unnecessarily. In many countries, antibiotics are available without prescriptions, which also promotes unnecessary use.

The result of these factors acting together is that every major disease-causing bacterium now has strains that resist at least one of the roughly 160 antibiotics we use to treat bacterial infections. Consequently, Canada, the United States, and other countries are reporting an increase in the number of patients who contract infectious bacterial disease while they are in a hospital or other healthcare facility.

Case Study: The Global Tuberculosis Epidemic—A Potential Threat

Since 1990, one of the world’s most underreported stories has been the spread of tuberculosis (TB).

The bacterium causing TB infection moves from person to person mainly in airborne droplets produced by coughing, sneezing, singing, or even talking. At the rate of 9 million people per year, the TB bacillus has now infected more than one of every three people in the world.

Most infected people do not appear to be sick, and about half of them do not even know they are infected. As a result, this serious health problem has been called a silent global epidemic.

Several factors account for the recent increase in TB. One is the lack of TB screening and control programs, especially in developing countries, where about 95% of the new cases occur. A second problem is that most strains of the TB bacterium have developed genetic resistance to almost all effective antibiotics.

Slowing the spread of the disease involves early identification and treatment of people with active TB, especially those with a chronic cough. Treatment with a combination of four inexpensive drugs can cure 90% of those with active TB. However, to be effective, the drugs must be taken every day for 6–8 months. Because the symptoms disappear after a few weeks, many patients think they are cured and stop taking the drugs.

How Serious Is the Threat from Viral Diseases? Watch Out for HIV, Flu, and Hepatitis B

What are some of the world’s most widespread and dangerous viruses?

  • The influenza or flu virus

  • The human immuno deficiency virus (HIV)

  • The hepatitis B virus (HBV)

In recent years, three other viruses have received widespread coverage in the media:

  • West Nile virus is transmitted by the bite of a common mosquito that has become infected by feeding on birds carrying the virus.

  • Severe acute respiratory syndrome (SARS) originated in China in 2002. Within weeks, this highly contagious disease had spread to 30 countries around the world, including Canada.

  • Avian influenza, or bird flu as it is popularly known, is a viral infection that normally affects only birds.

Case Study: How Serious Is the Global Threat from HIV and AIDS? A Rapidly Growing Health Threat

The global spread of acquired immune deficiency syndrome (AIDS), caused by HIV, is a serious and rapidly growing health threat. The virus itself is not deadly, but it kills immune cells and leaves the body defenceless against infectious bacteria and other viruses.

Within 7–10 years, at least half of those with HIV develop AIDS. This long incubation period means that infected people often spread the virus for several years without knowing they are infected. So far, there is no vaccine to prevent HIV and no cure for AIDS.

Case Study: Malaria—A Deadly Parasitic Disease That Is Making a Comeback

About one of every five people in the world—most of them living in poor African countries—is at risk of malaria. Over the course of human history, malarial protozoa probably have killed more people than all the wars ever fought.

Health experts say prevention is the best approach to slowing the spread of malaria. Methods include increasing water flow in irrigation systems to prevent mosquito larvae from developing (an expensive solution that uses much more water than required for irrigation) and fixing leaking water pipes. A problem is that poor villagers in malarial regions cannot afford screens on their homes and mosquito nets for their beds. The WHO calls for countries to do away with all taxes and tariffs on insecticide-treated bed nets, and to give such bed nets to the poor.

Other approaches include cultivating fish that feed on mosquito larvae (biological control), clearing vegetation around houses, planting trees that soak up water in low-lying marsh areas where mosquitoes thrive (a method that can degrade or destroy ecologically important wetlands), and using zinc and vitamin A supplements to boost resistance to malaria in children.

Solutions: How Can We Reduce the Incidence of Infectious Diseases? More Money and Assistance

Bad News:

  • High Death Rates: Infectious disease mortality is extremely high in developing countries.

  • Low Research Funding: Only 10% of global medical R&D funding goes to infectious diseases in developing nations, despite their significant impact.

  • Pharmaceutical Industry Shift: Major drug companies have reduced research on antibiotics and vaccines due to high costs and lower profitability compared to chronic disease medications.

  • Lack of Clean Water & Sanitation: One-third of the world's population lacks access to clean drinking water and sanitation.

  • Child Mortality: Children under five make up 10% of the global population but account for 40% of global illnesses; 11 million die annually from preventable and treatable causes.

Good News:

  • Decline in Infectious Disease Mortality: Global death rates from infectious diseases have dropped by two-thirds from 1970 to 2006 and are projected to keep falling.

  • Increased Immunization: Between 1971 and 2006, vaccine coverage for major diseases in developing countries rose from 10% to 90%, saving 10 million lives annually.

  • Oral Rehydration Therapy (ORT): A simple, low-cost solution of boiled water, salt, and sugar/rice has drastically reduced child deaths from diarrhea (from 4.6M in 1980 to 1.5M in 2010).

  • Solar Water Disinfection: WHO promotes a DIY method using sunlight and plastic bottles to disinfect water, making clean drinking water more accessible in tropical regions.