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Activity 5.1.2: Infectious Disease Agents

Terms in this set (12)

Disease Examples: Common Cold, Flu, and Rotavirus.

Modes of Transmission:
1. Direct/Indirect Contact:
Direct Contact - occurs through activities such as touching, hugging and kissing. Some viruses are sexually transmitted, such as herpes, HIV, and gonorrhea. An individual might get a virus from a tick or mosquito bite. Even a rabid animal can infect a human through its saliva or a bite.

Indirect Contact - occurs through touching surfaces or objects that have germs on them, such as door handles, respiratory equipment, toys, and computers.

2. By Droplet Transmission
Occurs when small droplets exit the mouth or nose of a person when he/she coughs or sneezes. These droplets are projected a distance of up to 2 meters (or 6 feet) and these droplets containing bacteria can enter the eyes, nose, or mouth of another individual or fall onto surfaces such as tables.

Reproduction: Viruses are unable to reproduce outside of a host cell.

Treatment: Antibiotics are not effective against viruses. Antiviral drugs are a class of medication used specifically for treating viral infections. Like antibiotics and broad-spectrum antibiotics for bacteria, most antivirals are used for specific viral infections, while a broad-spectrum antiviral is effective against a wide range of viruses. Unlike most antibiotics, antiviral drugs do not destroy their target pathogen; instead they inhibit their development. The body will fight off most viruses over the course of time. Vaccines do not cure viruses, but they are preventative measures against viral agents because they familiarize the immune system with the virus.
Disease Examples: Ascariasis, Trichinosis, Helminth, and Tapeworm.

Modes of Transmission: Helminth infections are mainly transmitted through the soil and occur mainly in areas with warm and moist climates where sanitation and hygiene are poor, including in temperate zones during warmer months. Soil-transmitted helminths are transmitted to humans by eggs that are passed in the feces of infected people. Adult worms live in the intestine where they produce thousands of eggs each day. If an infected individual defecates outside, these eggs contaminate the soil. Transmission of the infection to humans from the soil can happen in several ways:

1. Eggs that are attached to vegetables are ingested when the vegetables are not carefully cooked, washed or peeled.

2. Eggs are ingested from contaminated water sources.

3. Eggs are ingested by children who play in the contaminated soil and then put their hands in their mouths without washing them.

The eggs of one type of helminth infection, called hookworm, are not infectious. Instead, hookworm eggs hatch in the soil, releasing larvae that mature into a form that can actively penetrate the skin. People become infected with hookworm primarily by walking barefoot on the contaminated soil. However, there is no direct person-to-person transmission, or infection from fresh feces, because eggs passed in feces need about 3 weeks to mature in the soil before they become infectious. Since these worms do not multiply in the human host, re-infection occurs only as a result of contact with more contaminated soil in the environment.

Reproduction: Like protozoa, helminths can be either free-living or parasitic in nature. In their adult form, helminths are unable to reproduce inside the human host.

Treatment: Deworming through the administration of anthelmintic medications.
Disease Examples: Creutzfeldt-Jakob Disease (CJD) and Kuru.

Modes of Transmission: Several disorders caused by prions are inherited, so a family history of prion disease puts an individual at substantial risk. Prions can also be transmitted to humans through consumption of infected meat products, from reception of transplanted corneas that are contagious, or from contaminated medical equipment. Sporadic prion diseases develop suddenly without any known risk factors.

Reproduction: Lacking nucleic acid, prions cannot reproduce, but they replicate by stimulating normal cellular prion protein to refold into an abnormal form. The conversion of normal prion protein into abnormal prion protein and replication of prions in the brain causes degeneration of neural tissue and, ultimately, death. The process by which the prion recruits normal prion protein to convert to the disease-causing form remains unknown. In other words, prions depend on host cells in order to propagate.

Treatment: Prion diseases occur when normal prion protein, found on the surface of many cells, becomes abnormal and clump in the brain, causing brain damage. This abnormal accumulation of protein in the brain can cause memory impairment, personality changes, and difficulties with movement. Experts still don't know a lot about prion diseases, but unfortunately, these disorders are generally fatal. Prions are unique pathogens in that they appear to have no nucleic acid and thereby differ from viruses, bacteria, fungi and other pathogens. Prions are resistant to procedures that break down nucleic acid and destroy biological forms of pathogens. Also, because prions are an abnormal form of a normal protein that is genetically encoded, they do not produce an immune response in the host as would a foreign infectious agent. Prion diseases can't be cured, but certain medications may help slow their progress. Medical management focuses on keeping people with these diseases as safe and comfortable as possible, despite progressive and debilitating symptoms.
In the previous activity, each student was given a test tube containing a small volume of "bodily fluid." They were then instructed to walk around the room and exchange three or four drops of their "bodily fluid" with each of the numerous peers they "came into contact with." This contact represented shaking hands with someone and coughing or sneezing near someone. After the transfer process was completed, the majority of the participants tested positive for being "infected." This was the expected result, since diseases that are transmissible by respiratory droplets and casual physical contact such as briefly shaking hands are highly contagious. Unlike a cold or the flu, syphilis cannot be spread from person to person by shaking hands with, or inhaling the respiratory droplets of, a syphilis-infected individual. Syphilis is exclusively a sexually transmitted disease, though it can sometimes also be passed from an infected mother to her unborn child. Therefore, if the procedure from the previous activity were to be repeated - with Patient Zero being infected with syphilis and contact still representing shaking hands with someone and coughing or sneezing near someone - the infection would not spread beyond Patient Zero. Likewise, if Patient Zero had malaria and the only possible modes of transmission were by respiratory droplets or casual physical contact, the infection would again not spread beyond Patient Zero. Malaria is only transmitted to humans through mosquito bites, blood transfusions, and occasionally from an infected mother to her unborn child.
Bacteria: Properly and frequently washing hands with warm water and soap is a crucial protective measure towards preventing infection from bacterial agents. Another protective measure that prevents bacterial infection involves the sterilization of certain high-traffic objects and surfaces that are regularly handled or touched. Immunization is also an effective strategy for either eliminating an infectious disease or reducing and controlling the transmission of an infectious disease. Immunization is the process whereby a person is made immune or resistant to an infectious disease, typically by the administration of a vaccine. Vaccines stimulate the body's own immune system to protect the person against subsequent infection or disease. If an individual is already sick and contagious, they can prevent transmission to others by isolating themselves from those who are not infected. If contact with healthy individuals is unavoidable, someone who is infected can reduce the risk of infecting others by covering their mouth and/or nose whenever they cough or sneeze.

Viruses: Properly and frequently washing hands with warm water and soap is a crucial protective measure towards preventing infection from viral agents. Another protective measure that prevents viral infection involves the sterilization of certain high-traffic objects and surfaces that are regularly handled or touched. Immunization is also an effective strategy for either eliminating an infectious disease or reducing and controlling the transmission of an infectious disease. Immunization is the process whereby a person is made immune or resistant to an infectious disease, typically by the administration of a vaccine. Vaccines stimulate the body's own immune system to protect the person against subsequent infection or disease. If an individual is already sick and contagious, they can prevent transmission to others by isolating themselves from those who are not infected. If contact with healthy individuals is unavoidable, someone who is infected can reduce the risk of infecting others by covering their mouth and/or nose whenever they cough or sneeze.

Fungus: Properly and frequently washing hands with warm water and soap is a crucial protective measure towards preventing infection from fungal agents. Since fungal infections of any kind are spread through contact, individuals can prevent infection by refusing to share personal items with others and also by limiting their skin exposure in public spaces such as pools or locker rooms. To reduce transmission to others, individuals who have fungal infections should consistently wear shoes instead of walking around barefoot and avoid public places that make it more likely for their infection to spread.

Protozoa: Transmission of protozoa that live in a human's intestine to another human typically occurs either through ingesting feces-contaminated food or water or coming into close contact with an individual who is infected. Individuals can reduce their risk of becoming infected by focusing on improving their personal hygiene (hand-washing, food handling and preparation, water sanitation, etc.). To reduce the transmission of their infection, those who are ill should avoid others until they have recovered. Some protozoa live in the blood and tissue of humans instead of the intestinal tract, as is the case with malaria. Because the malaria parasite is found in the red blood cells of an infected person, malaria can be transmitted through blood transfusions, organ transplants, or the shared use of needles or syringes contaminated with malaria-infected blood. Human to human transmission of protozoa diseases like malaria can therefore be reduced by screening donated blood and tissues for the infection and inhibiting individuals with the disease from donating their blood and tissues.

Helminthes: Transmission of helminth infections can be reduced by implementing regulations on food and water quality and by improving sanitary conditions in affected regions.

Prions: Properly sterilizing medical equipment may prevent the spread of contagious prion diseases. If an individual is infected with a prion disease, whether a contagious or hereditary form, they are advised not donate organs or tissue, including corneal tissue. Newer regulations that govern the handling and feeding of cows may also help prevent the spread of prion diseases.