15.7: Review

Summary 

After completing this chapter you should be able to...

• Compare traditional and modern environmental hazards.
• Provide examples of biological, chemical, and physical hazards.
• Distinguish between morbidity and mortality.
• Distinguish between disease prevalence and incidence.
• Compare sporadic, endemic, epidemic, and pandemic patterns of incidence.
• Compare contact, vector, and vehicle modes of transmission and provide examples of how environmental degradation has increased transmission.
• Identify examples of emerging and reemerging infectious diseases.
• Briefly explain how vaccines work and their role in eradicating infectious diseases.
• Describe how antibiotic resistance evolves. 
• Identify the three main routes of exposure to chemicals. 
• Identify and define five factors that impact a chemical's safety. 
• Compare additive, antagonistic, and synergistic toxicological interactions.
• Explain how the lethal dose-50% is determined from a dose-response curve.
• Provide examples of strategies for reducing environmental hazards. 

Environmental health focuses on how the natural and human-built surroundings as well as behaviors affect human well-being. Traditional hazards are related to poverty and mostly affect low-income people and those in developing countries whereas modern hazards result from technological development and prevail in industrialized countries. Environmental health hazards are classified as biological (infectious diseases), chemical (exposure to toxins), or physical.

Epidemiology is the science underlying public health. Morbidity means being in a state of illness, whereas mortality refers to death; both morbidity rates and mortality rates are of interest to epidemiologists. Incidence is the number of new cases (morbidity or mortality), usually expressed as a proportion, during a specified time period; prevalence is the total number affected in the population, again usually expressed as a proportion. Sporadic diseases only occur rarely and largely without a geographic focus. Endemic diseases occur at a constant (and often low) level within a population. Epidemic diseases and pandemic diseases occur when an outbreak occurs on a significantly larger than expected level, either locally or globally, respectively. Diseases may be spread through contact transmission (direct physical interaction or indirect interaction through shared objects), vehicle transmission (through water, food, or air), or vector transmission (by an animal). Ecosystem degradation can exacerbate disease spread through creating conditions where vectors, pathogens, or reserviors thrive. 

Emerging and reemerging diseases have been defined as infectious diseases of humans whose occurrence during the past two decades has substantially increased or threatens to increase in the near future relative to populations affected, geographic distribution, or magnitude of impacts. Vaccination has been used to successfully eradicate several infectious diseases by stimulating a specific immune response. For remaining diseases that are commonly treated with medications, antibiotic resistance continues to be a global problem. New forms of antibiotic resistance can cross international boundaries and spread between continents.

Environmental toxicology is the scientific study of the health effects associated with exposure to toxins. The three mains routes of exposure to toxins are inhalation, ingestion, and skin or eye contact. Potency, persistence, solubility, bioaccumulation, and biomagnification all affect a chemical's safety. Bioaccumulation refers to the buildup of a toxin over an individual's lifetime whereas biomagnification occurs to increasing concentrations of a toxin as it moves up the food chain. Toxins may interact with each other in an additive, antagonistic, or synergistic way. The potency of a toxin is measure by the lethal dose-50% (LD₅₀), the concentration that is fatal to 50% of the test population. This is determined through a dose-response curve, which shows the percent of individuals affected as a function of concentration. 

The World Health Organization (WHO) is an agency of the United Nations that collects and analyzes data on disease occurrence from member nations. WHO also coordinates public health programs and responses to international health emergencies. In the United States, the Centers for Disease Control and Prevention monitors notifiable diseases and publishes weekly updates in the Morbidity and Mortality Weekly Report. Strategies for reducing environmental hazards include providing access to clean water, improving sanitation and hygiene, and limiting exposure to disease vectors. The public serves an important role by engaging in behaviors that limit disease spread or exposure to toxins and supporting policies that limit environmental hazards.

Attributions

Modified by Melissa Ha from the following sources:

• Disease and Epidemiology from Microbiology by OpenStax (licensed under CC-BY)
• Environmental Hazards & Human Health and Pests and Pesticides from Environmental Biology by Matthew R. Fisher (licensed under CC-BY)