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This 7 page Class Notes was uploaded by Gabriela Saint-Louis on Friday March 13, 2015. The Class Notes belongs to 1101 at George Washington University taught by Tamara Henry in Spring2015. Since its upload, it has received 152 views.
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Date Created: 03/13/15
Chapter 7 Communicable Diseases Infections of public health importance are primarily those that are communicable that is they can be transmitted from person to person or from animals or the physical environment to humans Communicable diseases may be caused by a wide variety of organisms ranging from bacteria to viruses to a spectrum of parasites including malaria and hookworm The Burden of Disease Caused by Communicable Diseases for many centuries Communicable diseases were the leading cause of death and disability among all ages 0 especially the young and elderly Not only the causes of great epidemics but can also become endemic and become routine causes of death 0 key role in maternal deaths associated with childbirth infant and early childhood deaths as well as deaths of malnourished infants and children 190039s 0 brief despite from deaths and disabilities caused by com diseases and other infections due to medical efforts to treat infections and public health efforts to prevent infection vaccines 0 195039s Resistance of gonorrhea and pneumococcus to a range f antibiotics became widespread 200039s 0 return of infections that were previously under control as well as emergence of new diseases TB great epidemic of the 1700s and 18005 has returned in force partially as a result of HIVAIDS o In uenza is anticipated to return again in pandemic form as has occurred repeatedly in prior centuries a pandemic of in uenza is most likely to occur when ongoing mutations produce new strains capable of persontoperson transmission 0 Pandemic an epidemic occurring worldwide or over a very wide area crossing international boundaries and affecting a large number of people How we establish that an Organism is a contributorv cause of a communicable disease traditionally relied on Koch39s postulates 0 hold that in order to de nitely establish a causeand effect relationship these four conditions must be met 1 organism must be shown to be present in every case of the disease by isolation of the organism 2 organism must not be found in cases of other disease 3 once isolated organism must be capable of replicating the disease in an experimental animal 4 organism must be recoverable from the animal 0 National Institute f Allergy and Infectious Disease developed the Modern Kochs Postulates 1 Evidence of an epidemiological association 2 isolation 3 Transmissions to establish aht an organism is a contributory cause of the disease Direct evidence of transmission 0 when researchers are able to directly isolate and transmit diseases from person to person ex Chicken Pox 0 very rare Meningococcal meningitis o epidemic in Geneva Switzerland 1805 0 Efforts to ful ll Koch39s Postulates were not successful because transmission to animals was not possible an a large number of humans were carriers without developing the disease 0 transmission from person to person ahs been documented in outbreaks of the disease and has been used to con rm the nal criteria of Modern Koch39s postulates 0 Understanding the mechanism of transmission is important for establishing etiology understanding the degree of communicability of a disease designing interventions to reduce its spread Factors that affect the ease with which a communicable disease is transmitted 1 Route of Transmission 0 the anatomical and physiological methods of transmission from person to person and from animal species to humans 0 communicable disease may be transmitted from person to person or from animal species 0 the physical environment to humans 2 Asymptomatic Transmission 0 the ability to transmit the disease while humans or animals are free of symptoms of the disease 0 diseases with potential to create human epidemics are often disease that can be transmitted from person to person while the individual is free of symptoms i ex in uenza chicken pox measles and mumps 0 Chronic carriers individuals that can transmit the disease after they have recovered from the clinical disease or after they are infected but don39t develop symptoms i examples HIV like Magic Johnson hepatitis B and hepatitis C 3 Reproduction ratio Rm 0 the number of ne cases one individual with the disease generates on average over the course if its communicable period 0 provides a measure of the inherent transmissibility of a disease 0 indicates the number of new cases one individual with the disease generates on average over the course of its communicable period 0 Provides a measure of the potential for an epidemic39s development given the patterns of transmission in a particular society i when this is less than 1 each infected individual results in less than one new infected individual thought to have low potential for becoming an epidemic disease ii if the ratio is greater than 1 the infection is likely to become endemic or epidemic in the population iii diseases with high rations have great potential fro developing into epidemics Available public Health Tools to address the burden of communicable diseases 1 Barrier protections including isolation and quarantine o barrier protection i as old as hand washing and as new as insecticide impregnated bed nets impact on the rate of malaria ii condoms most successful intervention to prevent STD iii masks reducing spread of disease in healthcare institutions 0 A special form of barrier protection consists of separating individuals with disease from the healthy population to prevent exposures 2 Immunizations designed to protect individuals as well as populations 0 Use of Immunizations i immunizations refers to the strengthening of the immune system to prevent or control disease passive immunity provide effective short term protection inactivated dead and live vaccines attenuated live can often stimulate the body s own antibody production 0 Cellmediated immunity from live vaccines produce longterm protection that more closely resemble the body s own response to infection 0 some vaccines are not effective for the very young and the elderly 0 use of vaccines require extensive investigations to de ne their effectiveness and safety as well as identify highrisk groups for whom they should be recommended 0 live vaccines have potential to cause injury to a fetus and can themselves produce disease particularly in those with reduced immunity 0 while vaccination occurs before exposure ideally but when an outbreak occurs vaccination of large numbers of potentially exposed invidiuals living the surrounding area may be key to effective control 0 Herd immunity or Population immunity some infections especially highly contagious viruses can be controlled by vaccinating a substantial proportion of the population often in the range f 7090 public health authorities are interested in the levels of protection in the community that is the level of protection of the unvaccinated as well as the vaccinated 3 screening case nding 0 screening for communicable diseases ful lls the same criteria for noncommunicable diseases ex screening for TB and syphilis has been an effective part of the control of these infections screening for STD39s are aroutine part of clinical care HIV screening has been recommended for hishrisk individuals and for populations with an estimated prevalence above 1 case nding 1 screening for communicable diseases has often been linked with the public health practice known as case nding 2 Case nding implies con dential interviewing of those diagnosed with a disease and asking for their recent close physical or sexual contacts f 3 Aims to maintain con dentiality however when following up with sexual contacts con dentiality ls dif cult to maintain 4 treatment and contact treatment 0 direct treatment treatment of symptomatic disease may in and of itself reduce the risk of transmission ex successful treatment of HIV has been shown to reduce the viral load and thereby reduce the ease of transmission 0 epidemiological treatment treatment of contacts effective in controlling a number of communicable diseases sexual partners of those with gonorrhea and chlamydia are routinely treated even when their infections cannot be detected 5 efforts to maximize effectiveness of treatments and prevent resistance to treatment 0 impact of antibiotic resistance o efforts to control resistance have been modest compared to forces encouraging resistance us as i overuse of prescribed antibiotics overthecounter sales of antibiotics in many countries and widespread use of antibiotics to stimulate modest growth in agricultural animals 0 DOT directly observed therapy i aims toensure complete adherence to TB treatment by observing individuals taking treatment at daily or at less frequent intervals ii efforts underway to reduce or eliminate use of antibiotics for animal growth and to place inceased restrictions on the prescribing of highly useful new antibiotics two basic strategies for combating complex infections Elimination amp Control only two viral diseases have been successfully targeted for eradication small pox which has been eradicated and Polio nearing completion to eradication example SMALLPOX characteristics that made eradication possible 0 No animal reservoir smallpox is an exclusively human disease does not affect other species that can then infect additional humans if eliminated from humans it has nowhere to hide and later reappear in human populations 0 short persistence in environment small pox virus requires human contact and cannot persist for more than a brief time in the environment without a human host 0 Absence of a longterm carrier state Once an individual recovers from small pox he or she no longer carries the virus and cannot transmit it to others 0 Different from HIVAIDS and hepatitis B which can maintain longterm carrier states and be infectious to others for years or decades 0 the disease produces longterm immunity once an individual recovers from smallpox very effective immunity is established preventing a second infection 0 vaccination also establishes longterm immunity As with the disease itself the live smallpox vaccine produces very successful longterm immunity has not mutated to become more infectious despite the extensive use of vaccination o Herd immunity protects those who are susceptible Longterm immunity from the disease or the vaccine makes it possible to protect large populations At least 80 of the population needs to be vaccinated to interrupt the spread of the infection to the remaining susceptible people 0 Easily identi ed disease this makes it possible to quickly diagnose the disease and protect others from being exposed 0 Effective post exposure vaccination smallpox vaccine is effective even after exposure to smallpox enables effective use of What is called ring vaccination o ring vaccination involves identi cation of a case of smallpox vaccination of the individual 5 household and close contacts followed by vaccination of all those Within a mile radius of the smallpox case Available options for the control of HIVAIDS biology of HIV virus makes it a dif cult epidemic to control 0 HIV attacks the very cell designed to control it 0 virus can avoid exposure to treatments by residing inside cells and temporarily not replicating many treatments work by interrupting the process of replication and thus are not effective when the replication stops 0 today heterosexual transmission is the most commonr out of infection higher risk of transmission rom male to female than from female to male 0 public health interventions properly used latex condoms male circumcision abstinence early diagnostic tests to detect HIV in early stages 0 transmission of HIV sex sharing contaminated needles blood mother to fetus Available options for control of In uenza ability to be rapidly transmitted through the air from person to person and its short incubation period have made it an ongoing public health problem often kills the very young the very old and those with chronic illnesses particularly those with respiratory diseases and suppressed immune systems Continues to mutate creating new types against which previous infections and previous vaccinations have little or no impact Inactivated or dead vaccines have been the mainstay of immunization against in uenza 0 current technology requires about six months lead time to produce large quantities of the vaccine Use of barrier protection such as masks isolation methods and even quarantine has been considered part of a comprehensive effort to control in uenza Available Options for Control of Rabies caused by a RNA virus that is transmitted through saliva of infected animals and slowly replicates o spreads to nerve cells and gradually invades the central nervous system over a 2060 day incubation period 0 Once central nervous system is involved disease progresses almost inevitably to death within one to two weeks 0 Any warmblooded animal can be infected with rabies some species particularly susceptible raccoons skunks and bats Cats and dogs can also be infected and transmit the virus use of post exposure vaccination success of rabies control is a result of a series of coordinated efforts to utilize vaccinations in different settings laws requiring rabies vaccination of dogs and cats have been enforced in the USgt for decades and have greatly reduced the number of reported infections in these animals 0 today only 10 of rabies infections comes from dogs and cats
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