Habitat Modification and the Impact on Public Health
Through habitat modification, emergence and re-emergence of infectious diseases have occurred. In order to understand habitat modification, however, one must first understand the epidemiologic triad, which is a traditional model that is used to look at the causation of infectious diseases. The model consists of a host, an agent, a vector, and the environment where the host and agent coincide. The vector transmits the infection by conveying the pathogen from one host to another without contracting the disease itself. One example of a vector is the Anopheles mosquito that carries malaria. Humans can be infected from malaria through the mosquito bites, but the mosquito is not affected by the disease, making it a vector. The transmission of the infection could be direct or indirect (1.2-Epidemiologic Triad, 2017).
This model can be used for any infection. A perfect example of this, as shown through the website, is smoking-related illnesses. Those, in this case, that make the tobacco and carcinogens found within the products of the smoke, like cigarettes, are the vectors because they bring the disease to the host. The host in this example would be those that use the products that cause the smoke-those who smoke cigarettes. The environment for this case could be an area with the smoke particles in the air, which could not only affect those that smoke, but also those that do not smoke. The agent would be the disease that is caused from the smoke, such as lung cancer. Things that could take place in the environment to help eliminate the agent could be advertisements of the harm of the products, or not allowing smoking in close, refined areas. Agents that could be used to help the public with their health could be filtered or safe cigarettes. Different hosts might be more infected through cigarettes then others based on their residence, income, and genetic susceptibility (1.2-Epidemiologic Triad, 2017).
Given this information, understanding of how habitat modification has led to emergence and re-emergence of infectious diseases can be discussed. Habitat modification is defined as the change, made by humans, of large-scale additions or subtractions to plants, animals, or man-made products to the ecosystem. These changes to the ecosystem can result in flood control, ecological imbalance, spread of disease, and loss of biologically active substances. It is through this process that humans have become the leading cause of emerging zoonoses, which are diseases that originated from animal hosts. In fact, around 75% of emerging infectious diseases worldwide occurs as a result of zoonoses. Examples of zoonoses are seen in Lyme disease, West Nile fever, Ebola virus, SARS, HIV/AIDS, and Avian influenza (Battle, 2009). Part of the reason these illness have occurred is because the human population is rising, meaning more people live closer to wildlife animals, and domesticated animals, thus, live closer to wild animals.
Air pollution is one of the many how habitat modification has led to an emergence and re-emergence of several infectious diseases. Polluted air affects the triad on a global level; to help the problem, many companies built new, taller smokestakes away from the city. However, even though this helped the local population it still devastated the total population through acid rainfalls. Through the acid rainfalls destructions of forests and lakes occurred, resulting in an increase in fish that were killed in particular areas of the world. This, as a result, had a major impact on human health (Battle, 2009). It is through air pollution that an increase risk of lung cancer and chronic respiratory disease can occur as well. Therefore, through air pollution, a change in the epidemiologic triad occurred by disturbing the environment. Through this event alone the biodiversity of the fish decreased. As a result, there are now fewer types of fish that can use bacteria to perform bioremediation to get rid of toxicants that are found within the environment.
Another example of habitat modification that has resulted in the rise of infectious disease is seen through water, which is another environmental component. All life on earth needs water, and water can easily be infected through natural and anthropogenic contaminants. Long exposures to contaminated water can lead to increase risks of certain cancers for humans. These contaminations can range from pesticides, VOCs, and heavy metals. These, if found in drinking water, can lead to a damaged immune system in an individual, liver or kidney disease, birth defects, and several disorders within the nervous system (Battle, 2009). Therefore, it is though contaminated water that diseases can appear.
Yellow Fever has had several re-emergencies within several parts of the world, like with South American forest and agricultural workers, as a result of habitat modification. Mosquitoes are the vector, while it is transmitted from primates to humans. Yellow Fever enters urban developments, then, when a traveler or worker from an area where the infectious is found travels to major cities. As a result, the increase in workers entering forests for deforestation provides an increase chance of contracting Yellow Fever. HIV is another virus that has made several re-emergences recently due to changes in the triad. By increasing the kills of a sub-group of chimpanzees humans became infected with the virus (Battle, 2009). The disease is now spread through bodily fluids of the human, and has become a major epidemic across the world today. Therefore, because there was a shift in animal deaths, the triad lost its grip and HIV was transmitted to humans.
A final disease that has re-emerged as a result of disturbing the triad is tuberculosis. During the 1930’s in Great Britain a large portion of dairy cows were infected with the bacteria that causes tuberculosis. Humans contracted the disease by drinking infected milk from the cows. The disease was easily spread among the cows because they were closely confined with one another in large numbers. There were also poorly ventilated cowsheds, which became an ideal environment for the airborne disease. It was because of this that a major shift in the environment of the animal changed, thus giving opportunity for an infectious disease to re-emerge (Battle, 2009). Even to this day there has been a rise of tuberculosis cases due to farming practices. As one can see from these three infections and environmental changes, if any major change is done to the triad, infectious disease can emerge or re-emerge.
References
Battle, C. U. (2009). Essentials of public health biology: a guide for the study of pathophysiology. Sudbury, MA: Jones and Bartlett .
1.2 - Epidemiologic Triad. (2017). Retrieved March 06, 2017, from https://onlinecourses.science.psu.edu/stat507/node/25