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Methods of Disease Transmission
There are three major methods of disease transmission: contact transmission, vehicle transmission, and vector transmission. Contact transmission is defined as the spread of pathogens by direct contact, indirect contact, or droplets. Direct contact means coming into physical contact, such as touching, licking, or copulating. This category also includes the transmission from a woman to a fetus in her uterus and the transmission from one part of the body of an individual to another part. Indirect transmission is spreading pathogens by means of inanimate objects such as utensils, medical equipment, and tissues. Objects that can carry infections in this case are called fomites. Droplets transmission occurs via mucus droplets within a relatively short distance, e.g. through sneezing. Vehicle transmission mainly occurs via air, water, or food. Particularly, airborne transmission occurs via dust or droplets that travel long distances (longer than one meter). Waterborne transmission is the main method of transmission for many intestinal diseases, such as cholera. Foodborne transmission is also characteristic of many intestinal diseases: pathogens are transmitted through food that may be improperly cooked or contaminated with fecal materials.
In the case of vector transmission, what is referred to as “vectors” are usually insects that cause diseases as they are part of pathogens’ lifecycles, e.g. mosquitoes can cause malaria and fleas can cause bubonic plague. Vectors are arthropods that transmit diseases from one host to another (Whitfield, Falk, & Rotenberg, 2015). Also, insects can carry pathogens, e.g. flies can carry typhoid or dysentery from a host to food eventually consumed by a person.
Pathogens listed in the videos on penetrating host tissues and inactivating and hiding from host defenses are streptococcus (including group A streptococci, Streptococcus pneumoniae), Clostridium perfringens, pseudomonas, Leishmania, Legionella, staphylococci, Neisseria meningitidis, Neisseria gonorrhoeae, HIV, the measles virus, tuberculosis bacteria, Shigella, Listeria, the influenza virus, and Trypanosoma.
There are surveillance mechanisms in a body that participate in the detection of pathogens thus ensuring protection from diseases. However, many pathogens may demonstrate various methods of hiding from surveillance or inactivating defenses, which makes such pathogens more likely to survive and reproduce within a body (Bauman, Machunis-Masuoka, & Cosby, 2012). One of the methods is encapsulation. Pathogens are detected according to the presence of certain molecules on their surface that are not normally found on the surface of host cells. However, if an invader is in a capsule composed of polysaccharides similar to those of the host organism, it will not be recognized as foreign and will be ignored by defenses (Hiding from Host Defenses). This method is used by Streptococcus pneumoniae, which causes bacterial pneumonia. Some bacteria even manage to survive and reproduce inside phagocytes. Other microorganisms display the ability to hide from host defenses by changing their surface antigens frequently, either as a result of mutations or genetic recombination. Those microorganisms whose antigens are undetectable are less likely to be eliminated by host defenses and more likely to reproduce. These features are present in RNA viruses, such as the influenza virus and HIV.
The way these pathogens enter a body should also be addressed, as there are mechanisms in host organisms that protect them from foreign microorganisms, but some bacteria or viruses manage to break through the protection. Traits that help microorganisms enter a body are called virulence factors (Penetrating Host Tissues). A particular group of virulence factors are enzymes secreted to help pathogens penetrate host tissues. Some streptococci produce an enzyme that breaks apart the “glue” formed by substances such as hyaluronic acid to fill in the gaps between cells. Therefore, these streptococci are able to penetrate deeper within the host tissues. However, there is another barrier under the superficial layer, and it is formed by collagen fibers. Streptococci secrete another enzyme called collagenase that helps them digest fibers and move deeper. RNA viruses, as well as streptococci, may enter the body by dissolving blood clots on injured skin.
Safety and Statistics
Streptococcus and HIV are often mentioned in the context of workplace safety. The goal of reports on infectious diseases in the workplace is to control the spread of diseases by means of education and prevention measures (“Infectious diseases in the workplace,” 2007). For streptococcus, a major recommended measure is committing to proper hygiene practices. The workplace should be kept clean, and such a simple practice as washing hands regularly can help avoid contacting the pathogen and prevent its spread. HIV is transmitted through body fluids, which lowers the risk of contacting it in the workplace, but the risk still exists. One of the suggested recommendations is to avoid contacting object that may carry body fluids of other people, e.g. toothpicks. The risk to be infected in the workplace is higher for those who have wounds on their body, which is why it is necessary to take care of wounds and injuries to prevent infections.
According to the Centers for Disease Control, more than 1.2 million people in the United States are living with HIV; concerning the mortality rate, “the rate of deaths of persons with diagnosed HIV infection was 4.7. Deaths of persons with diagnosed HIV infection may be due to any cause” (“Diagnoses of HIV infection in the United States and dependent areas,” 2015, p. 7). Concerning streptococcus pneumoniae, approximately 900,000 Americans are infected every year, and 3,700 deaths in the United States were caused by pneumococcal meningitis and bacteremia in 2013 (“Streptococcus pneumoniae,” 2015).
Bauman, R. W., Machunis-Masuoka, E., & Cosby, C. D. (2012). Microbiology: With diseases by body system. New York, NY: Benjamin Cummings.
Hiding from Host Defenses [Video file]. Web.
Infectious diseases in the workplace. (2007). Web.
Penetrating Host Tissues [Video file]. Web.
Streptococcus pneumoniae. (2015). Web.
Whitfield, A. E., Falk, B. W., & Rotenberg, D. (2015). Insect vector-mediated transmission of plant viruses. Virology, 479(1), 278-289.