The Immune System: The Immune System Disease Transmission and Prevention Objectives: Objectives List the five ways diseases can be transmitted to humans. Summarize Koch’s postulates for indentifying pathogens. Analyze how the body produces immunity to pathogens. Describe how vaccines produce immunity to pathogens. Disease Transmission: Disease Transmission There are five ways of transferring disease from person to person Air: Particles of pathogens travel in the air from a sick person’s cough or sneeze. Person to Person Contact: Pathogens travel from the body surface of one person to the body surface of another. Food: Pathogens are eaten with food and are able to survive the environment of the stomach to infect the body. Water: Pathogens are drunk with water and can survive the stomach. Water borne pathogens may also enter the body through other available orifices while swimming or bathing. Animal Bites: Pathogens can be transmitted through the saliva of an animal bite. Detecting Disease: Detecting Disease The German physician, Robert Koch (1834-1910) established a procedure for diagnosing causes of infection. Koch determined that bacteria caused the disease Anthrax in cattle, sheep, goats, and humans. This disease is NOT passed from person to person. Koch performed an experiment where he isolated bacteria from a cow with anthrax and then infected a healthy cow with the bacteria. The healthy cow developed the same strain of anthrax as the sick cow. Koch’s Postulates: Koch’s Postulates 1. The pathogen must be found in an animal with the disease and not a healthy animal. 2. The pathogen must be isolated from the sick animal and grown in a laboratory culture. 3. When the isolated pathogen is injected into the healthy animal, the animal must develop the exact disease as the original sick animal. 4. The pathogen must be isolated from the second animal and grown in a laboratory culture. The cultured pathogen must be exactly the same as the original bacteria from the original animal. Long Term Defense: Long Term Defense During the immune response, some B and T cells become memory cells that maintain a copy of the infecting pathogen’s antigen. They continue to reproduce and patrol the body searching for the original pathogen. If they encounter the pathogen again they are able to mount a quick assault and destroy the pathogen even before it has a chance to multiply in the body. In short, the body is now immune. Immunology: Immunology Resistance to disease is called immunity. Edward Jenner became the father of immunology when he observed the common (in his day) and deadly disease small pox. Jenner noted that while Small Pox was common in all people and all walks of life, Milkmaids never caught it. Milkmaids, girls employed to milk cows, frequently caught a milder form of pox called Cow Pox, but they never caught Small Pox. Jenner theorized that the Cow Pox somehow granted the girls immunity to the more severe Small Pox. He isolated the Cow Pox bacteria and infected healthy people with it. They contracted the disease. He then tried to infect them with Small Pox and they were all disease free. The Small Pox and Cow Pox virus are very similar. One develops antibodies in the body that are effective in identifying the other. Vaccination: Vaccination Vaccination: A medical procedure used to produce immunity by introducing some stimulus in the body to produce antibodies against a certain pathogen. Antigen Shift: Some pathogens are capable of re-infecting a host because they constantly mutate and change. The changing antigens keep the body’s memory cells from recognizing the pathogen even though they have seen it before. Autoimmune Diseases: Objectives: Autoimmune Diseases: Objectives The ability of the immune system to distinguish cells and antigens in the body from foreign invaders is crucial to the fight against disease. In some people, the body cannot distinguish the difference. This condition is called autoimmune disease. The body attacks it’s own cells as if they were pathogens. Multiple Sclerosis (MS) Is thought to be an autoimmune disease. The immune system destroys the insulating material around the nerve cells in the brain, spinal cord, and the nerves leading from the eyes to the brain. These nerves eventually stop functioning leading to blindness, paralysis, and death. Autoimmune Diseases: Autoimmune Diseases HIV Infection: HIV Infection Before 1981, HIV was unknown. Between 1981 and 2001 more than 460,000 people in the US alone were infected with HIV. Since then, the total number of cases in the US has increased to 810,000. HIV evolved from a virus in primates in Africa. Scientists believe that the virus, by way of mutation, became able to bind to immune cells through a receptor protein called CD4. HIV usually invades Helper T-cells via the receptor CD4. These T-cells begin manufacturing the HIV virus shortly after infection. As they begin to die, the body’s immune system is no longer capable of sounding the alarm on invading pathogens. The body becomes susceptible to other opportunistic disease that would not ordinarily cause an illness. Testing For HIV: Testing For HIV Antibodies for the HIV virus, if present in the blood, are a sign that the person has been infected by the HIV virus. For a diagnosis of AIDs to occur other criteria must be met. A Helper T-cell count of less than 200 cells/ml of blood is an indication that the immune system is failing. The time from infection until the onset of the AIDS syndrome can be as long as 10 years. During this time, the patient feels fine and yet they are infectious. Transmission of HIV: Transmission of HIV The most common method of transmission is sexual contact. Use of a latex condom can reduce but not prevent spread of the HIV virus. The only positive way to avoid HIV infection is through abstinence (the concious decision to refrain from sexual contact.) HIV can pass through drug users who share needles. HIV infected blood often remains in the needle after the initial injection to be injected into the next user. HIV could once be contracted through transfused blood. At this time, rigorous blood testing on all donated blood makes this sort of transmission next to impossible. AIDS is NOT transmitted via toilet seats, kissing, hand holding, or other behaviors that do not involve blood or mucus membrane contact. Mosquitoes do not carry infected white blood cells and so it is impossible for them to vector the HIV virus.