Unit 5, Section 2 Final Version Summer 2024 PDF

Unit 5 Section 2: Disease and Epidemiology(ch 16.1, 16.3, 16.4) Skip 16.2 16.1 The language of epidemiologists Epidemiology Scientific study of Causes( causative/ etiological agent): what is the source of the outbreak? Transmission: How is it being transmitted...

Unit 5 Section 2: Disease and Epidemiology(ch 16.1, 16.3, 16.4) Skip 16.2 16.1 The language of epidemiologists Epidemiology Scientific study of Causes( causative/ etiological agent): what is the source of the outbreak? Transmission: How is it being transmitted? and prevention: How does one prevent further spread? of disease within a population Trace back to John Snow, Joseph Lister, Louis Pasteur Infectious disease epidemiology Infection disease epidemiology- concerned with how infectious diseases are distributed in a population and the factors influencing or determining that distribution. Analyzing disease in a population Morbidity- state of being diseased Morbidity rate- number of diseased individuals out of a standard number of individuals in a population Prevalence- number of individuals with a particular illness in a given population at a point in time Incidence- number or proportion of new cases in a period of time Figure 16.2 This graph compares the incidence of HIV (the number of new cases reported each year) with the prevalence (the total number of cases each year). Prevalence and incidence can also be expressed as a rate or proportion for a given population. Patterns of Incidence sporadic diseases- Diseases that are seen only occasionally, and usually without geographic concentration Examples: tetanus(most individuals vaccinated), rabies, and plague endemic diseases-disease constantly present at a low level in a certain geographic area. Ex: Plague in American Southwest, malaria in some regions of Brazil epidemic diseases- Diseases for which a larger than expected number of cases occurs in a short time within a geographic region Ex: Influenza Outbreak- small, localized epidemic Ex: abnormally high number of measles cases in one American city pandemic disease-An epidemic that occurs on a worldwide scale. For example, HIV/AIDS, H1N1 flu Figure 16.3 The 2007–2008 influenza season in the United States saw much higher than normal numbers of visits to emergency departments for influenza-like symptoms as compared to the previous and the following years. (credit: modification of work by Centers for Disease Control and Prevention) Figure 16.4 The seasonal epidemic threshold (blue curve) is set by the CDC-based data from the previous five years. When actual mortality rates exceed this threshold, a disease is considered to be epidemic. As this graph shows, pneumonia- and influenza-related mortality saw pronounced epidemics during the winters of 2003–2004, 2005, and 2008. (credit: modification of work by Centers for Disease Control and Prevention) 16.3 modes of Disease Transmission Reservoirs and carriers Reservoirs are places in the environment where a pathogen can be found. Can include human and animal populations, soil, water, inanimate objects, or materials Animals: domestic cat-Toxoplasma gondii- no symptoms in cat Water, soil: Vibrio cholera, Giardia, Clostridium tetani Humans Carrier-An individual who has recovered from a disease but retains the infectious agents in the body and continues to shed them. capable of transmitting a pathogen without displaying symptoms Ex: a person recovering from typhoid fever Passive vs active carrier Asymptomatic carrier Reservoirs and carriers definitive host- In parasitic infections, the parasite’s preferred host. In parasites with complex life cycles, the definitive host is the host in which the parasite reaches sexual maturity. intermediate hosts -Some parasites may also infect one or more intermediate hosts in which the parasite goes through several immature life cycle stages or reproduces asexually. Disease transmission Direct Contact- 1)Horizontal transmission: person to person Hand-shaking, kissing, sexual intercourse Droplet transmission: from the respiratory tract to the air (Respiratory droplets) Involves sputum or mucus Recipient must be close; travels short distance Particles over 10um 2) Vertical transmission: from mother to fetus or newborn. Ex: HIV, toxoplasmosis, gonorrhea Figure 16.9 Direct contact transmission of pathogens can occur through physical contact. Many pathogens require contact with a mucous membrane to enter the body, but the host may transfer the pathogen from another point of contact (e.g., hand) to a mucous membrane (e.g., mouth or eye). (credit left: modification of work by Lisa Doehnert) Transmission Indirect Contact- 1) Fomites- inanimate objects which are capable of carrying infectious organisms Ex: table, bed linens 2) Vehicle transmission- spread of disease through a medium like food, water, or air Poultry-Salmonella, pork- Trichinella Aerosols( airborne transmission) -a small particle transmitted through the air moved long distance by air currents Smaller particles vs droplet transmission: less than 10um Ex: SARS, ANTHRAX Transmission Indirect Contact- 3) Vector transmission- living organisms carrying disease Mechanical vectors- living organisms, usually arthropod, that passively transports disease causing organisms on its body Biological vectors- infected arthropod that transmits disease causing organisms , usually by injection or bite Ex: Malaria and West Nile virus are carried in salivary glands of mosquitoes Figure 16.10 Fomites Fomites are nonliving objects that facilitate the indirect transmission of pathogens. Contaminated doorknobs, towels, and syringes are all common examples of fomites. (credit left: modification of work by Kate Ter Haar; credit middle: modification of work by Vernon Swanepoel; credit right: modification of work by “Zaldylmg”/Flickr) Figure 16.11 Vehicle transmission Food is an important vehicle of transmission for pathogens, especially of the gastrointestinal and upper respiratory systems. Notice the glass shield above the food trays, designed to prevent pathogens ejected in coughs and sneezes from entering the food. (credit: Fort George G. Meade Public Affairs Office) Figure 16.12 (a) A mechanical vector carries a pathogen on its body from one host to another, not as an infection. (b) A biological vector carries a pathogen from one host to another after becoming infected itself. Figure 16.13 (credit “Black fly”, “Tick”, “Tsetse fly”: modification of work by USDA; credit: “Flea”: modification of work by Centers for Disease Control and Prevention; credit: “Louse”, “Mosquito”, “Sand fly”: modification of work by James Gathany, Centers for Disease Control and Prevention; credit “Kissing bug”: modification of work by Glenn Seplak; credit “Mite”: modification of work by Michael Wunderli) Transmission of Microorganisms and Viruses. Healthcare-Associated( nosocomial infections) Infection acquired during an individual’s stay at a hospital or chronic care facility Account for an estimated 1.7 million infections 99,000 deaths a year  Sites of Nosocomial Infections. Source: CDC. Division of Healthcare Quality Promotion (DHQP).  Top 10 Infectious Agents Involved in Nosocomial Infections CDC. National Healthcare Safety Network Annual Update (2008). 16.4 Global and public health Emerging and reemerging infectious diseases Infectious diseases continue to challenge public health organizations  The Global Occurrence of Emerging and Re-Emerging Diseases Modified from American College of Microbiology. Clinical Microbiology in the 21st Century: Keeping the Pace. ASM Press, 2008, Washington, D.C., Reprinted with permission of the Figure 16.16 Even before the Ebola epidemic of 2014–15, Ebola was considered an emerging disease because of several smaller outbreaks between the mid-1990s and 2000s. Reasons for emergence and resurgence of infectious diseases Changes in land use or agriculture practices: urbanization, deforestation, water projects Dengue Fever Changes in human demographics: migration of people from agrarian to urban lifestyles malaria Poor population heath: malnutrition, poor public health infrastructure cholera Pathogen evolution: resistance to drugs tuberculosis Contamination of food sources and water: substandard sanitation practices cryptosporidiosis International travel: spread diseases quickly SARS, West Nile, H1N1 Failure of public health systems: failure immunization programs diphtheria International trade : global movement produce hepatitis A, cyclosporiasis Wildlife trade: new mechanisms for disease transmission monkeypox Climate change: global changes in weather bring new diseases to new latitudes and elevations hantavirus pulmonary syndrome