To understand emerging and reemerging diseases, you must understand the interconnectedness between human health and the environment and have a grasp on epidemiology.
Human Health
Epidemiology, the study of determinates and distribution of disease in populations, is essential in protecting public health and controlling health problems. Before moving into the specifics of epidemiology, you need to understand some of the basics of human anatomy and physiology; specifically, how the immune system protects us from disease.
Your body’s first line of defense against a foreign invader is keeping the invader out. The skin is part of that defense, as it creates a barrier over most of the body. This defense continues with the mucous membranes lining your nasal pathway, and the hairs help catch particles and keep them from entering your lungs. Tears and saliva both contain lysozymes, which can break down foreign invaders. Bleeding from an open wound helps to rinse away dirt and other particles, and clotting helps keep anything from entering the body through that wound. Your body contains many different types of white blood cells that can fight off a variety of pathogens.
If an invader gets past the first line of the defense, the body’s second line of defense is the immune system. We can acquire natural immunity in two different ways: naturally acquired active immunity occurs when we are exposed to a disease-causing agent (for example, getting chicken pox as a child), and naturally acquired passive immunity occurs when antibodies are received through the placenta or breast milk. We can also attain immunity through vaccinations; this is called artificially acquired active immunity. Persons with severe immunodeficiency may be given antibody-containing serums or immunoglobins from a person or animal.
Many cells and chemicals that are part of the immune system work to destroy foreign substances as they enter the body. Macrophages circulate throughout the body and digest any foreign substances they run into. Interferons are chemicals released when a cell is attacked by a virus. These and other chemicals signal surrounding cells to shut down and prevent the virus from spreading. Lymphocytes are a type of white blood cell that produces antigens that respond to specific viruses. So, if you had chicken pox as a child, then your body will produce antibodies to protect you if the chicken pox virus enters your body again.
The state of the environment also plays a role in disease transmission. For example, the changing weather patterns associated with global warming affect disease patterns. The increased rainfall and flooding in some areas has increased the populations of a major carrier of disease—mosquitoes. The warm winters and hot dry summers in many areas are also affecting the transmission of vector-borne diseases; for example, ticks spread Lyme disease and bacteria spread cholera. There is significant evidence that outbreaks of Ebola are related to unusual patterns in the wet or dry cycle. Increases in international travel have also increased the spread of diseases worldwide. In the United States, emerging diseases such as West Nile Virus cause severe illness and sometimes death (World Health Organization, 2011). As diseases spread, or new diseases are recognized, fear of a major epidemic has caused public health agencies to prepare plans for mass epidemics or bioterrorism events.
Disease Transmission Routes
- Airborne (coughing, sneezing).
- Fecal-oral transmission (improper hand washing contaminating food, untreated sewage contaminating water supply).
- Waterborne (drinking, swimming, eating, improper hand washing).
- Direct contact (athlete’s foot, warts, STDs).
- Zoonoses (animal bites, scratches, meat, hides, feces).
- Vector-transmitted (insects, rodents).
- Soil contamination (landfill leaching).
- Fomite (transferred from inanimate objects like handrails, doorknobs, grocery carts, clothing, toys).
- Nosocomial (transferred from health workers). (Hilgenkamp, 2006, p. 54).
Environmental Health
As the human population and technology have grown, our impact on the environment—and subsequently, on our own health—has also grown. The World Health Organization (2014) defines environmental health as “all the physical, chemical, and biological factors external to a person, and all the related factors impacting behaviors. It encompasses the assessment and control of those environmental factors that can potentially affect health. It is targeted towards preventing disease and creating health-supportive environments. This definition excludes behavior not related to environment, as well as behavior related to the social and cultural environment, and genetics.”
To understand environmental health, we must first understand the environment and its many interrelated systems. We do not often think about the Earth beyond what we see around us every day, but the environment spans from the core of the Earth to the outer reaches of the troposphere. The four main divisions of the Earth system are the lithosphere (crust and mantle), hydrosphere (water), atmosphere (gases surrounding earth), and biosphere (area supporting life). Life on Earth depends on the biogeochemical cycles that occur within each of these regions. Biogeochemical cycles recycle energy and chemicals through the lithosphere, hydrosphere, atmosphere, and biosphere. Within the biosphere there are specific divisions called biomes. Biomes are characterized by similar climate, soil, plants, and animals. Because humans dominate most ecosystems on Earth, we have a large impact on the environment. Overpopulation and demands on natural resources can degrade the environment. Since the environment provides us with so many resources such as clean air, clean water, and nutrients, environmental degradation directly influences human health.
Environmental scientists and government officials look for ways to preserve the environment and conserve environmental resources. By monitoring human demand on the environment, laws such as the Endangered Species Act, Clean Air Act, and Clean Water Act have worked to protect the environment for future generations. While technology has created many problems for the environment, it is also being used to benefit the environment and human health. New farming techniques, waste management methods, and pollution control devices all help to keep the environment healthy and protect human health. Environmental health is everyone’s responsibility. Public health officials and governmental leaders are on the front lines, but the decisions made daily by businesses and individuals directly affect our health and the health of the environment.
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