The Human Immune System and Infectious Disease

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| Essay on Immunizations|
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| Immunization is a procedure routinely used to improve the body's ability to overcome infection and protect against diseases caused by infectious agents. It works against a specific disease by training the immune system to rapidly recognize and eliminate the infectious agent that causes that disease, thus resulting in immunity. Protection can be acquired either by passive or by active immunization.Passive immunization involves transfer of antibodies obtained from an immune donor to a nonimmune individual and results in temporary immunity. Currently, antibody-based therapies represent a form of treatment for disorders induced by venoms or toxins and for viral infections. Injections of antibody preparations derived from immunized human donors are used for the prophylaxis and treatment of tetanus, rabies, and pneumonia caused by respiratory syncytial virus (RSV), as well as infections caused by hepatitis A virus, hepatitis B virus, and varicellazoster virus. Monoclonal antibodies are expected to replace preparations derived from human donors. However, at this time, only one monoclonal antibody has been licensed for an infectious disease (RSV infection). Active immunization induces an adaptive, longlasting immune response to a pathogen by introducing the killed or attenuated pathogens or antigens derived from the pathogens into the body. These nonpathogenic forms of the pathogen are the major component of a vaccine. Therefore, active immunization is routinely achieved by administering different types of vaccines. In the past 100 years, the use of vaccines (along with sanitation practices) has dramatically reduced the number of deaths caused by infectious diseases. Administration of vaccines results in the induction of a vigorous immune response, similar to the one that would be induced by natural infection. Vaccine administration may result in antibody responses, cellular responses, or both. A major feature of effective vaccines is the ability to induce memory immunity, which allows the immune system to respond quickly and strongly to infections even several years after immunization. However, in order to maintain sustained, long-term responses, it is necessary to give multiple doses of a vaccine.Due to the dangers associated with administering a live, infectious agent, attenuated or killed pathogens are routinely used as vaccines. Attenuated pathogens lose their ability to cause disease while maintaining their capacity to transiently grow within the immunized individual. Killed or inactivated vaccines are produced by killing pathogens with chemical or heat treatments. Certain other types of vaccines dispense with the whole organism and use just the important parts that will stimulate an immune response. Such vaccines are called subunit vaccines and consist of inactivated toxins (toxoids), capsular polysaccharides, or recombinant protein antigens.In 1798, Edward Jenner developed the first live vaccine for smallpox from the cowpox virus. Jenner observed that a person who contracted cowpox, a much milder disease, would not get smallpox. He inoculated a farm boy with fluid from cowpox lesions of a milkmaid. Six weeks later, Jenner injected the boy with fluid from a smallpox sore. As expected, the boy did not develop the infection. Jenner's discovery established the general principles of safe and effective vaccination and resulted in a sharp decline in the death rate from smallpox in Europe and North America. The use of improved smallpox vaccines eventually led to the eradication of this disease in 1980. However, doses of smallpox vaccine are once again being stockpiled around the world because of concerns related to bioterrorism. Jenner's success with the smallpox vaccine set the foundation for future vaccine development. In 1881, Louis Pasteur developed the first heatkilled anthrax bacilli vaccine. He also proposed that attenuated forms of a virus could be used for immunizations against more...
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