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    in this activity, you will identify portals of entry and exit found in a human host. sort each item based on whether it represents a portal of entry, portal of exit, or both portal types.

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    In this activity, you will identify portals of entry and exit found in a human host.

    Sort each item based on whether it represents a portal of entry, portal of exit, or both portal types.

    Parental route, skin, mucous membrane

    Click card to see definition 👆

    All represent both portal types:

    Parental route, skin, mucous membrane

    Click again to see term 👆

    In this activity, you will classify portals of entry as mucous membrane, skin, or parenteral route.

    Sort each item based on which one of the following portals of entry it best represents: mucous membrane, skin, or parenteral route.

    Click card to see definition 👆

    Mucous membrane: genitourinary tract respiratory tract conjunctiva

    gastrointestinal tract

    Skin: sweat gland ducts hair follicles Parenteral route: injections surgery deep wounds

    Click again to see term 👆

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    In this activity, you will identify portals of entry and exit found in a human host.

    Sort each item based on whether it represents a portal of entry, portal of exit, or both portal types.

    Parental route, skin, mucous membrane

    All represent both portal types:

    Parental route, skin, mucous membrane

    In this activity, you will classify portals of entry as mucous membrane, skin, or parenteral route.

    Sort each item based on which one of the following portals of entry it best represents: mucous membrane, skin, or parenteral route.

    Mucous membrane: genitourinary tract respiratory tract conjunctiva

    gastrointestinal tract

    Skin: sweat gland ducts hair follicles Parenteral route: injections surgery deep wounds

    In this activity, you will view scenarios for the initiation of an infection and determine whether they relate to the number of invading microbes or adherence to the host tissue.

    Each of the following scenarios describes factors that influence infection at the portal of entry. For each scenario, determine whether the pathogen’s ability to cause infection relates to the number of invading microbes or adherence to the host tissue.

    Number of invading microbes:

    - For cutaneous anthrax, the infectious dose is 10 to 50 endospores, whereas for inhalation anthrax, the infectious doses are 10,000 to 20,000 and 250,000 to 1,000,000 endospores, respectively.

    - For Vibrio cholerae, the infectious does is 10^8 cells, but if stomach acid is neutralized with bicarbonate, this number decreases significantly

    Adherence to the host tissue:

    - Neisseria gonorrhoeae uses fimbriae to attach to cells in the genitourinary tract, eyes, and pharynx

    - Staphylococcus aureus binds and infects skin by a mechanism that resembles viral attachment.

    - Treponema pallidum uses its tapered end as a hook to attach to host cells during a syphilis infection.

    - Enteropathogenic strains of Escherichia coli have fimbriae that bind to specific regions of the small intestine.

    In this activity, you will view data related to infectious doses for a specific microorganism and identify the best conclusion based on this data.

    Bacillus anthracis can cause infection via three different portals of entry. The ID50 of cutaneous anthrax is 10 to 50 endospores, whereas inhalation anthrax requires 10,000 to 20,000 endospores, and gastrointestinal anthrax requires 250,000 to 1,000,000 endospores. Which statement best describes a conclusion that can be drawn based on this information?

    It is significantly easier to be infected with cutaneous anthrax as compared to other forms of anthrax.

    Match each item related to the penetration or evasion of host defenses with its best description.

    Capsules: This viscous outer covering found in certain microorganisms helps pathogens evade the host's defenses by impairing phagocytosis

    Cell wall components: These structures contain substances that contribute to a pathogen's virulence; for example, M protein mediates microbial attachment to epithelial cells.

    Enzymes: These proteins contribute to a pathogen's virulence by, for example, forming and breaking down fibrin clots, breaking down connective proteins, and countering certain types of antibodies.

    Antigenic variation: This process allows pathogens to alter their surface antigens to avoid attack by antibodies produced by the immune system.

    Invasins: These microbial surface proteins rearrange the host cell's actin filaments, allowing pathogens to enter and move in and between cells.

    In this activity, you will match each factor that damages host cells with its description.

    Match each item related to damage to host cells with its description.

    siderophores: These proteins bind up iron obtained from the host cell's iron-transport proteins and transport this iron to bacteria through interactions with cell surface receptors.

    Direct damage: This occurs as a result of nutrient depletion, accumulation of waste products, pathogen entry and exit, and ruptured host cells.

    Toxins: These poisonous substances cause most of the damage to host cells; they can be transported by the blood or lymph and may produce far-reaching effects.

    Source : quizlet.com

    Principles of Infectious Diseases: Transmission, Diagnosis, Prevention, and Control

    Infectious disease control and prevention relies on a thorough understanding of the factors determining transmission. This article summarizes the fundamental principles of infectious disease transmission while highlighting many of the agent, host, and ...

    International Encyclopedia of Public Health. 2017 : 22–39.

    Published online 2016 Oct 24. doi: 10.1016/B978-0-12-803678-5.00516-6

    PMCID: PMC7150340

    Principles of Infectious Diseases: Transmission, Diagnosis, Prevention, and Control

    Jean Maguire van Seventer

    Boston University School of Public Health, Boston, MA, USA

    Natasha S. Hochberg

    Guest Editor (s): Stella R. Quah

    Copyright and License information Disclaimer

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    Abstract

    Infectious disease control and prevention relies on a thorough understanding of the factors determining transmission. This article summarizes the fundamental principles of infectious disease transmission while highlighting many of the agent, host, and environmental determinants of these diseases that are of particular import to public health professionals. Basic principles of infectious disease diagnosis, control, and prevention are also reviewed.

    Keywords: Control, Environment, Epidemic, Epidemiology, Host, Infection, Infectious disease, One health, Outbreak, Prevention, Public health, Reservoir, Transmission, Vector, Zoonosis

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    Introduction

    An infectious disease can be defined as an illness due to a pathogen or its toxic product, which arises through transmission from an infected person, an infected animal, or a contaminated inanimate object to a susceptible host. Infectious diseases are responsible for an immense global burden of disease that impacts public health systems and economies worldwide, disproportionately affecting vulnerable populations. In 2013, infectious diseases resulted in over 45 million years lost due to disability and over 9 million deaths (Naghavi et al., 2015). Lower respiratory tract infections, diarrheal diseases, HIV/AIDS, malaria, and tuberculosis (TB) are among the top causes of overall global mortality (Vos et al., 2015). Infectious diseases also include emerging infectious diseases; diseases that have newly appeared (e.g., Middle East Respiratory Syndrome) or have existed but are rapidly increasing in incidence or geographic range (e.g., extensively drug-resistant tuberculosis (XDR TB) and Zika virus (Morse, 1995). Infectious disease control and prevention relies on a thorough understanding of the factors determining transmission. This article summarizes some of the fundamental principles of infectious disease transmission while highlighting many of the agent, host, and environmental determinants of these diseases that are of particular import to public health professionals.

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    The Epidemiological Triad: Agent–Host–Environment

    A classic model of infectious disease causation, the epidemiological triad (Snieszko, 1974), envisions that an infectious disease results from a combination of agent (pathogen), host, and environmental factors (Figure 1 ). Infectious agents may be living parasites (helminths or protozoa), fungi, or bacteria, or nonliving viruses or prions. Environmental factors determine if a host will become exposed to one of these agents, and subsequent interactions between the agent and host will determine the exposure outcome. Agent and host interactions occur in a cascade of stages that include infection, disease, and recovery or death (Figure 2(a) ). Following exposure, the first step is often colonization, the adherence and initial multiplication of a disease agent at a portal of entry such as the skin or the mucous membranes of the respiratory, digestive, or urogenital tract. Colonization, for example, with methicillin-resistant Staphylococcus aureus in the nasal mucosa, does not cause disease in itself. For disease to occur, a pathogen must infect (invade and establish within) host tissues. Infection will always cause some disruption within a host, but it does not always result in disease. Disease indicates a level of disruption and damage to a host that results in subjective symptoms and objective signs of illness. For example, latent TB infection is only infection – evidenced by a positive tuberculin skin test or interferon gamma release assay – but with a lack of symptoms (e.g., cough or night sweats) or signs (e.g., rales on auscultation of the chest) of disease. This is in contrast to active pulmonary TB (disease), which is accompanied by disease symptoms and signs.

    Figure 1

    The epidemiological triad model of infectious disease causation. The triad consists of an agent (pathogen), a susceptible host, and an environment (physical, social, behavioral, cultural, political, and economic factors) that brings the agent and host together, causing infection and disease to occur in the host.

    Figure 2

    Potential outcomes of host exposure to an infectious agent. (a) Following an exposure, the agent and host interact in a cascade of stages the can result in infection, disease, and recovery or death. (b) Progression from one stage to the next is dependent upon both agent properties of infectivity, pathogenicity, and virulence, and host susceptibility to infection and disease, which is in large part due to both protective and adverse effects of the host immune response.

    Credit: Modification of original by Barbara Mahon, MD, MPH.

    Source : www.ncbi.nlm.nih.gov

    Chain of Infection: Definition & Example

    The chain of infection refers to how diseases begin and how they spread in a particular environment. Learn the definition of the chain of...

    Chain of Infection: Definition & Example

    Instructor John Koshuta Expert Contributor Anna Szymanski View bio

    The chain of infection refers to how diseases begin and how they spread in a particular environment. Learn the definition of the chain of infection, the six links in the chain, and an example of a chain of infection. Updated: 09/22/2021

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    Definition: The Chain of Infection

    How do viruses pass from one person to the next? When one child has a cold at school, why is the rest of the class likely to come down with one the next week? Let's explore how infection gets from one place to another, or the chain of infection.

    The chain of infection, if we think of it as an actual chain, is made up of six different links: pathogen (infectious agent), reservoir, portal of exit, means of transmission, portal of entry, and the new host. Each link has a unique role in the chain, and each can be interrupted, or broken, through various means.

    Quiz Course 278K views

    The Six Links

    The first link is the pathogen itself. This is the disease-causing organism. For many illnesses and diseases this is a virus or bacterium. In order to break this link, various methods can be used, including the pasteurization of milk, the chlorination of drinking water, or the use of disinfectants.

    The second link is the reservoir. This is the natural environment that the pathogen requires for survival. Reservoirs can be a person, an animal, or an environmental component, such as soil or water. This link can be broken through medical treatment and testing, insect and rodent eradication, or quarantine.

    The third link is the portal of exit. This link is needed for the pathogen to leave the reservoir. If the reservoir is a human, then the portal of exit may be saliva, mucous membranes, feces, blood, or nose or throat discharges. By using barrier methods, such as condoms or masks, or covering the mouth while coughing, this link can be broken.

    The fourth link is the means of transmission. The pathogen can be transmitted either directly or indirectly. Direct transmission requires close association with the infected host, but not necessarily physical contact. Indirect transmission requires a vector, such as an animal or insect. The link can be broken through hand washing, safe sex practices, or avoiding contact with infected individuals.

    Link number five is the portal of entry. Entry of the pathogen can take place in one of three ways: penetration, inhalation, or ingestion. The level and severity of an infection may depend on the depth of penetration. Similar to the portal of exit, barrier methods, such as condoms or masks, can be used to break this link along with other methods, such as insect repellants.

    The final link is the new host. Once in the new host, various factors influence the severity of infection, including the strength of the immune system and the reproductive rate of the pathogen. Immunization, health promotion, and medical treatment can be used to break this link in the chain.

    Example of a Chain of Infection

    An example of illness resulting from the chain of infection is the common cold. In this case, the pathogen is often referred to as rhinovirus. The reservoir is another person carrying this virus, who then propels the virus into the air via a portal of exit, such as a cough or sneeze. The route of transmission is direct to the new host, which takes place through inhalation (the portal of entry) of the virus.

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    Additional Activities

    Chain of Infection Follow-Up Discussion:

    In light of the COVID-19 pandemic, match the following actions into the appropriate steps of where they can break the chain.

    Wearing a mask Washing your hands

    Keeping a 6-foot distance from others

    Are there some actions that could fall into breaking more than one of the six links of the chain? Why or why not?

    How might the chain of infection look different if COVID-19 was caused by bacteria instead of a virus?

    (Example answers to the above):

    Wearing a mask best fits into the portal of exit, as it contains saliva droplets that could be spread by coughing or sneezing, greatly reducing the risk of others coming in contact with them.

    Washing your hands best fits into the means of transmission. Washing hands means that the virus is less likely to make its way to a surface or environment where it can infect others.

    Keeping a 6-foot distance could fall into the reservoir. Distancing makes someone less likely to become a hospitable environment for the pathogen. It could also fall into the means of transmission. An infected person who stays away from others is reducing the chance that they will transmit the virus.

    Yes, some actions could fall into breaking more than one of the six links of the chain, as evidenced in the example answer for keeping a 6-foot distance. Another example of an action that could fall into breaking more than one link of the chain is the wearing of condoms to prevent sexually transmitted infections. This would help prevent the wearer from transmitting any infection they have, and would reduce the risk of their sexual partner contracting the pathogen since the barrier method of the condom makes a portal of entry less susceptible.

    Source : study.com

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