Chapter 15 & 16

Antigenic drift vs Antigenic shift

*Antigenic Drift* point mutations over time *Antigenic Shift* overnight; reassortment and jump Influenza viruses use both antigenic drift and antigenic shift to avoid being recognized by the immune system.

Describe the mechanisms viruses use for adhesion and antigenic variation

*Antigenic Variation* changes in surface antigens that occur in a microbial population

Explain the difference between a communicable disease and a noncommunicable disease

*Communicable Disease* A disease that can be spread from one person or species to another. *Noncommunicable Disease* A disease that is not transmitted by another person, a vector, or the environment

Compare contact, vector, and vehicle modes of transmission

*Contact Transmission* Contact transmission can be direct or indirect through physical contact with either an infected host (direct) or contact with a fomite that an infected host has made contact with previously (indirect). *Vector Transmission* Vector transmission occurs when a living organism carries an infectious agent on its body (mechanical) or as an infection host itself (biological), to a new host. *Vehicle Transmission* Vehicle transmission occurs when a substance, such as soil, water, or air, carries an infectious agent to a new host.

Explain how descriptive, analytical, and experimental epidemiological studies go about determining the cause of morbidity and mortality

*Descriptive Epidemiology* collection and analysis of data *Analytical Epidemiology* -Comparison of a diseased group and a healthy group -Analytical epidemiology studies are observational studies that are carefully designed to compare groups and uncover associations between environmental or genetic factors and disease. *Experimental Epidemiology* -Involves a hypothesis and controlled experiments -Experimental epidemiology studies generate strong evidence of causation in disease or treatment by manipulating subjects and comparing them with control subjects. *Retrospective Epidemiology* Retrospective epidemiology studies use historical data to identify associations with the disease state of present cases. Prospective epidemiology studies gather data and follow cases to find associations with future disease states.

Types of epidemiological studies

*Descriptive epidemiology* -Carefully tabulate data concerning a disease -Record location and time of the cases of disease -Collect patient information -Try to identify the index case of the disease -Usually results in developing a hypothesis of causation that could be tested by more rigorous observational and experimental studies. *Analytical Epidemiology* -Seeks to determine the probable cause, mode of transmission, and methods of prevention -Useful in situations when Koch's postulates can't be applied -Often retrospective -Investigation occurs after an outbreak has occurred *Experimental epidemiology* -Test a hypothesis concerning the cause of a disease -Apply Koch's postulates

Identify and differentiate between emerging and reemerging infectious diseases

*Emerging* Infectious diseases that are new, increasing in incidence, or showing a potential to increase in the near future Emerging diseases are those that are new to human populations or that have been increasing in the past two decades. Reemerging diseases are those that are making a resurgence in susceptible populations after previously having been controlled in some geographic areas. *Reemerging* Infectious diseases that existed in the past but for a variety of reasons are increasing in incidence or in geographic range

Differentiate between endotoxins and exotoxins

*Endotoxins* released only when bacteria die and their cell walls break down *Exotoxins* toxic substances that bacteria secrete into their environment Bacterial toxins include endotoxin and exotoxins. Endotoxin is the lipid A component of the LPS of the gram-negative cell envelope. Exotoxins are proteins secreted mainly by gram-positive bacteria, but also are secreted by gram-negative bacteria.

Study of Diseases

*Etiology* Study of the cause of disease *Epidemiology* Branch of medical science concerned with the incidence, distribution, and control of diseases that affect large numbers of people. -When studying an epidemic, an epidemiologist's first task is to determinate the cause of the disease, called the etiologic agent or causative agent. -Connecting a disease to a specific pathogen can be challenging because of the extra effort typically required to demonstrate direct causation as opposed to a simple association. -We utilize the Koch postulates and Molecular Koch postulates

Compare different types of infectious diseases, including iatrogenic, nosocomial, and zoonotic diseases

*Iatrogenic Disease* A condition that is caused by a medical treatment *Nosocomial Disease* A disease acquired in a healthcare facility. *Zoonotic Disease* A disease communicable from animals to humans under natural conditions; also know as zoonosis

Explain the difference between prevalence and incidence of disease

*Prevalence* the percentage of people within a population who have a specific illness *Incidence* the number of *new* cases of a disease in a given area or population during a given period of time

Explain the difference between protozoan parasites and helminths

*Protozoan Parasites* Unicellular, or single-cell, organisms that may be flagellates, amoebae, sporozoans, apicomplexans, or ciliates. *Helminths* multicellular parasitic organisms commonly called worms or flukes

Distinguish between signs and symptoms of disease

*Signs* Objective information; can be seen, measured, heard, or felt -Color, pulse, edema *Symptoms* Subjective information -Dyspnea, pain, nausea

Emerging and reemerging

-Both WHO and some national public health agencies such as the CDC monitor and prepare for emerging infectious diseases. -An emerging infectious disease is either new to the human population or has shown an increase in prevalence in the previous twenty years

Nosocomial infections

-Hospital Epidemiology: Healthcare Associated (Nosocomial) Infections -Types of healthcare associated infections (HAIs): -Healthcare-associated infections (HAI), or nosocomial infections, are acquired in a clinical setting. Transmission is facilitated by medical interventions and the high concentration of susceptible, immunocompromised individuals in clinical settings. -Nosocomial diseases are contracted in hospital settings, whereas iatrogenic disease are the direct result of a medical procedure *Exogenous* Pathogen acquired from the health care environment *Endogenous* Pathogen arises from normal microbiota as a result of factors within the health care setting *Latrogenic* Results from modern medical procedures *Superinfections* Use of antimicrobial drugs reduces competition from some resident microbiota, allowing other microbes to thrive

Quarantining

-Individuals suspected or known to have been exposed to certain contagious pathogens may be quarantined, or isolated to prevent transmission of the disease to others. -Hospitals and other health-care facilities generally set up special wards to isolate patients with particularly hazardous diseases such as tuberculosis or Ebola -These wards may be equipped with special air-handling methods, and personnel may implement special protocols to limit the risk of transmission

Acute, Chronic, Latent

An acute disease is short in duration, whereas a chronic disease lasts for months or years. Latent diseases last for years, but are distinguished from chronic diseases by the lack of active replication during extended dormant periods.

Exoenzymes

Dissolve extracellular barriers and penetrate through or between cells Exoenzymes and toxins allow pathogens to invade host tissue and cause tissue damage. Exoenzymes are classified according to the macromolecule they target and exotoxins are classified based on their mechanism of action.

Frequency of Disease

Epidemiologists track occurrence of diseases using two measures *Incidence* Number of new cases of a disease in a given area during a given period of time -Incidence is the number of new cases (morbidity or mortality), usually expressed as a proportion, during a specified time period; prevalence is the total number affected in the population, again usually expressed as a proportion. *Prevalence* Number of total cases of a disease in a given area during a given period of time -Occurrence also evaluated in terms of frequency and geographic distribution -They also evaluate mobidity and mortality rates

Public Health Organizations

Epidemiology and Public Health Agencies at the local, state, national, and global level share information concerning disease: The United States Public Health Service -National public health agency -CDC World Health Organization (WHO) -Coordinates public health efforts worldwide -The World Health Organization (WHO) is an agency of the United Nations that collects and analyzes data on disease occurrence from member nations. WHO also coordinates public health programs and responses to international health emergencies. The Centers for Disease Control and Prevention monitors notifiable diseases and publishes weekly updates in the Morbidity and Mortality Weekly Report -Public health agencies work to limit disease transmission -Enforce standards of water and food safety -Work to reduce disease vectors and reservoirs -Establish and enforce immunization schedules -Locate and treat individuals exposed to contagious pathogens -Establish isolation and quarantine measures

Epidemology

Epidemiology is the science underlying public health. The branch of medical science concerned with the incidence, distribution, and control of diseases that are prevalent among a population at a special time and are produced by some special causes not generally present in the affected locality.

How do helminths avoid the immune system

Helminthic worms are able to avoid the immune system by coating their exteriors with glycan molecules that make them look like host cells or by suppressing the immune system.

Infections

Invasions and multiplications of microorganisms in body tissues Diseases can either be noninfectious (due to genetics and environment) or infectious (due to pathogens). Some infectious diseases are communicable (transmissible between individuals) or contagious (easily transmissible between individuals); others are noncommunicable, but may be contracted via contact with environmental reservoirs or animals (zoonoses) Infections and disease can be caused by pathogens in the environment or microbes in an individual's resident microbiota. Infections can be classified as local, focal, or systemic depending on the extent to which the pathogen spreads in the body. Viral pathogens use adhesins for initiating infections and antigenic variation to avoid immune defenses. Fungi initiate infections through the interaction of adhesins with receptors on host cells. Some fungi produce toxins and exoenzymes involved in disease production and capsules that provide protection of phagocytosis.

Morbidity

Morbidity means being in a state of illness, whereas mortality refers to death; both morbidity rates and mortality rates are of interest to epidemiologists.

Explain the roles of portals of entry and exit in the transmission of disease and identify specific examples of these portals

Pathogenic microbes have definite routes of entry and exit from infected hosts Mucous membranes (mucosa) that line Respiratory, Gastrointestinal, Genitourinary tracts Skin (usually damaged in some way: nicks, abrasions, punctures, insect bites, etc.)

Periods of Disease

The periods of disease include the incubation period, the prodromal period, the period of illness, the period of decline, and the period of convalescence. These periods are marked by changes in the number of infectious agents and the severity of signs and symptoms.

Modes of disease transmission

Transmission is from a reservoir or a portal of exit to another host's portal of entry Reservoirs of human disease can include the human and animal populations, soil, water, and inanimate objects or materials. *Contact Transmission* -Direct contact transmission: Usually involves body contact between hosts. Transmission within a single individual can also occur. -Indirect contact transmission: Pathogens are spread from host to host by fomites. -Droplet transmission: Spread of pathogens in droplets of mucus by exhaling, coughing, and sneezing. *Vehicle Transmission* -Airborne transmission: When pathogens travel more than 1 meter via an aerosol. Aerosols can occur from various activities. Sneezing, coughing, air-conditioning systems, sweeping. -Waterborne transmission: Important in the spread of many gastrointestinal diseases. Fecal-oral infection. -Foodborne transmission: Spread of pathogens in and on foods. Inadequately processed, cooked, or refrigerated foods. Foods may become contaminated with feces . -Bodily fluid transmission: Bodily fluids such as blood, urine, saliva can carry pathogens. Prevent contact with conjunctiva or breaks in the skin or mucous membranes. *Vector Transmission* -Vectors: animals that transmit disease among hosts -Biological vectors: Transmit pathogens and serve as host for some stage of the pathogen's life cycle. Biting arthropods transmit many diseases to humans. -Mechanical vectors: Passively transmit pathogens present on their body to new hosts.

Virulence

Virulence, the degree to which a pathogen can cause disease, can be quantified by calculating either the ID50 or LD50 of a pathogen on a given population. "Virulence factors" contribute to a pathogen's ability to cause disease. Fungal and parasitic pathogens use pathogenic mechanisms and virulence factors that are similar to those of bacterial pathogens Bacterial pathogens may evade the host immune response by producing capsules to avoid phagocytosis, surviving the intracellular environment of phagocytes, degrading antibodies, or through antigenic variation.

Virulence factors

traits of a microbe that promote pathogenicity

Patterns of Incidence (Occurrence)

*Endemic Disease* constantly present in a population *Sporadic Disease* occurs occasionally in a population *Epidemic* widespread outbreak of an infectious disease *Pandemic* an epidemic that is geographically widespread

Pathogenesis

"Development of disease" Pathogens enter the body through portals of entry and leave through portals of exit. *Stages of Pathogenesis:* -Exposure -Adhesion -Invasion -Infection -Transmission. Protozoa adhere to target cells through complex mechanisms and can cause cellular damage through release of cytopathic substances. Some protozoa avoid the immune system through antigenic variation and production of capsules.