THH - Types of Environmental Risks (Lesson)
Types of Environmental Risks
Infectious Disease
Infectious disease is a normal part of our exposure to the environment. Bacteria, viruses, fungi, and protists are normally present in all environments and some can cause infectious disease directly and others can produce deadly toxins. Viruses can infect every type of living organism and tend to be very specific, yet are responsible for the largest number of zoonoses, diseases able to spread between different species of animals, like rabies.
Viruses and Human Disease
Viruses cause many human diseases. In addition to the flu and HIV, viruses cause rabies, measles, diarrheal diseases, hepatitis, polio, cold sores, and other diseases. Viral diseases range from mild to fatal. One way viruses cause disease is by causing host cells to burst open and die. Viruses may also cause disease without killing host cells. They may cause illness by disrupting homeostasis in host cells.
Cold sores are caused by a herpes virus.
Some viruses live in a dormant state inside the body. This is called latency. For example, the virus that causes chickenpox may infect a young child and cause the short-term disease chickenpox. Then the virus may remain latent in nerve cells within the body for decades. The virus may re-emerge later in life as the disease called shingles. In shingles, the virus causes painful skin rashes with blisters (see image below ).
Shingles is a disease caused by the same virus that causes chickenpox.
Some viruses can cause cancer. For example, human papillomavirus (HPV) causes cancer of the cervix in females. Hepatitis B virus causes cancer of the liver. A viral cancer is likely to develop only after a person has been infected with a virus for many years.
The Flu
Influenza, or flu, is a contagious respiratory illness caused by influenza viruses. Influenza spreads around the world in seasonal epidemics. An epidemic is an outbreak of a disease within a population of people during a specific time. Every year in the United States, about 200,000 people are hospitalized and 36,000 people die from the flu. Flu pandemics can kill millions of people. A pandemic is an epidemic that spreads through human populations across a large region (for example a continent), or even worldwide. Three influenza pandemics occurred in the 20th century and killed tens of millions of people, with each of these pandemics being caused by the appearance of a new strain of the virus. Most influenza strains can be inactivated easily by disinfectants and detergents.
Emerging Viral Diseases
Modern modes of transportation allow more people and products to travel around the world at a faster pace. They also open the airways to the transcontinental movement of infectious disease vectors. One example of this occurring is West Nile Virus, which scientists believe was introduced to the United States by an infected air traveler. With the use of air travel, people can go to foreign lands, contract a disease and not have any symptoms of illness until they get home, possibly exposing others to the disease along the way. Be sure to watch this video Links to an external site. to learn more about the Virus Crisis.
Often, new diseases result from the spread of an existing disease from animals to humans. A disease that can be spread from animals to humans is called zoonosis (pronounced zo-o-nosis). When a disease breaks out, scientists called epidemiologists to investigate the outbreak, looking for its cause. Epidemiologists are like detectives trying to solve a crime. The information epidemiologists learn is important to understand the pathogen, and help prevent future outbreaks of disease.
A deadly strain of avian flu virus named H5N1 has posed the greatest risk for a new influenza pandemic since it first killed humans in Asia in the 1990s. The virus is passed from infected birds to humans. Fortunately, the virus has not mutated to a form that spreads easily between people. Several lethal viruses that cause viral hemorrhagic fever have been discovered, two of which are shown below. Ebola outbreaks have been limited mainly to remote areas of the world. However, they have gained extensive media attention because of the high mortality rate—23 percent to 90 percent—depending on the strain. The primary hosts of the viruses are thought to be apes in west-central Africa, but the virus has also been isolated from bats in the same region.
The Ebola virus (left), and Marburg virus (right), are viruses that cause hemorrhagic fevers that can cause multiple organ failures and death.
People get exposed to new and rare zoonoses when they move into new areas and encounter wild animals. For example, severe acute respiratory syndrome (SARS) is a respiratory disease which is caused by the SARS coronavirus. An outbreak in China in 2003 was linked to the handling and consumption of wild civet cats sold as food in a market. In 2005, two studies identified several SARS-like coronaviruses in Chinese bats. It is likely that the virus spread from bats to civets, and then to humans. Be sure to watch the video on Zoonotic (pronounced zo-o-notic) diseases in the sidebar.
Noninfectious Diseases
Noninfectious Diseases are diseases that are not caused by a pathogenic agent, and cannot be transferred from one person to another. There are many types and are caused by many different environmental factors and or genetics. These diseases can be due to nutritional deficiency or lifestyle. These diseases are not transmissible, but genetic diseases are often passed down from parents to their children.
Environmental Toxins
The following are major groups of toxins. Research and know the impact, sources and examples of all of them by using your text and any additional resources, including the ones in the sidebar. After your research, complete the assignment below.
- Heavy metals
- Carcinogens
- Teratogens
- Neurotoxins
- Mutagens
- Irritants
- Hormonally Active Agents {(HAA) Endocrine or Hormone disruptors}
- Sensitizers (allergens)
- Persistent Organic Pollutants (POPs)
- Volatile Organic Compounds (VOCs)
RESOURCES IN THIS MODULE ARE OPEN EDUCATIONAL RESOURCES (OER) OR CREATED BY GAVS UNLESS OTHERWISE NOTED. SOME IMAGES USED UNDER SUBSCRIPTION.