Host-Pathogen Relationships: Infection and Disease
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Questions and Answers

Explain how colonization differs from an infection that leads to disease.

Colonization refers to the presence of microorganisms on a body surface without causing disease, whereas an infection leading to disease involves the invasion of tissues and subsequent tissue damage.

Describe two ways the host's nonspecific defense mechanisms can prevent infection.

Intact epithelial surfaces like skin and mucous membranes act as physical barriers. Additionally, secretions such as tears, saliva, and gastric juices contain antimicrobial substances.

How do exotoxins and endotoxins contribute to disease?

Exotoxins are toxins produced and secreted by bacteria, while endotoxins are bacterial toxins released when the bacterial cell dies. Both types of toxins can cause damage to the host and contribute to the severity of the disease.

Explain why the terms 'infection' and 'disease' are not synonymous.

<p>Infection refers to the invasion and growth of a pathogen within a host. Disease refers to the impairment of tissue function as a consequence of that invasion and growth. An infection does not always result in disease.</p> Signup and view all the answers

Describe how antibiotic drug therapy can diminish a host's resistance.

<p>Antibiotics can disrupt the balance of normal flora, potentially allowing opportunistic pathogens to thrive, or they can lead to antibiotic resistance in pathogens, making infections harder to treat.</p> Signup and view all the answers

How do malnutrition and cancer impair the host's resistance to infection?

<p>Malnutrition weakens the immune system due to a lack of essential nutrients required for immune cell function and antibody production. Cancer and its treatments can also suppress the immune system, making the host more susceptible to infections.</p> Signup and view all the answers

Explain how a previously damaged anatomical structure might diminish resistance to infection.

<p>A damaged anatomical structure, such as a skin wound or a compromised respiratory tract, can provide an entry point for pathogens, bypassing the body's initial barriers to infection.</p> Signup and view all the answers

Differentiate between a 'source' and a 'reservoir' in the context of the environment's role in infection.

<p>A reservoir is the natural environment where a pathogen lives and multiplies. A source is the immediate point from which the pathogen is transferred to the host.</p> Signup and view all the answers

Explain the difference between a reservoir and a source of infection, providing a specific example to illustrate the distinction.

<p>A reservoir is the long-term habitat where an infectious agent lives and multiplies (e.g., monkeys for yellow fever). The source is where the agent is immediately transmitted from (e.g., mosquitos carrying yellow fever from monkeys to humans).</p> Signup and view all the answers

Differentiate between contagiousness and virulence, providing an example of a pathogen that is highly contagious but not very virulent.

<p>Contagiousness refers to how easily a pathogen is transmitted, while virulence describes its ability to cause disease. Polio virus is an example of a pathogen that is highly contagious but not very virulent, because most people who contact it do not develop clinical disease.</p> Signup and view all the answers

Describe how pathogens typically exit a host and relate this to how they enter a new host.

<p>Pathogens often exit a host through secretions or excretions, using portals of exit that are frequently the same as portals of entry. For example, a respiratory virus exits via coughing and enters a new host via inhalation.</p> Signup and view all the answers

Explain the process by which microorganisms contaminating food or water cause disease. Name two specific bacterial examples.

<p>Microorganisms ingested through contaminated food or water enter the gastrointestinal tract, leading to infections. Examples include <em>Salmonella</em> and <em>Vibrio cholerae</em>.</p> Signup and view all the answers

Describe how pathogens can enter the urinary tract and list possible signs and symptoms of such an infection.

<p>Pathogens can ascend into the bladder through the urethra or via a catheter. Symptoms include painful urination, blood in urine, pelvic pain, and flank pain.</p> Signup and view all the answers

What are fomites, and how do they contribute to the transmission of infectious diseases? Give an example.

<p>Fomites are inanimate objects that transmit diseases by harboring pathogens on their surfaces. An example is a contaminated doorknob transmitting cold viruses.</p> Signup and view all the answers

Distinguish between mechanical and biological vector transmission, providing an example of each.

<p>Mechanical vector transmission involves the passive transport of pathogens (e.g., a fly carrying bacteria on its legs). Biological vector transmission involves the pathogen undergoing part of its life cycle within the vector (e.g., a mosquito transmitting malaria).</p> Signup and view all the answers

Describe how the crossing of mucosal surfaces can lead to infection, and provide two examples of viruses that are transmitted this way.

<p>Microorganisms can penetrate oral, anal, genital, or conjunctival linings, leading to local irritation, ulceration, pain, and redness. Examples include HIV and herpes simplex virus (HSV).</p> Signup and view all the answers

Differentiate between mechanical and biological vector transmission, providing an example of each.

<p>Mechanical transmission involves the external transfer of a pathogen by a vector without the vector being infected, like a fly carrying <em>E. coli</em> on its legs. Biological transmission involves the pathogen undergoing part of its life cycle inside the vector before being transmitted, such as the malaria parasite <em>Plasmodium</em> in Anopheles mosquitoes.</p> Signup and view all the answers

How do 'intoxication' and 'infection', as modes of food or waterborne transmission, differ in their mechanisms of causing disease?

<p>Intoxication occurs when a pre-formed toxin or chemical causes body malfunction, like botulism from improperly canned foods. Infection involves the ingestion of a pathogenic organism that then grows and multiplies in the gastrointestinal tract, such as <em>V. cholerae</em> in contaminated water.</p> Signup and view all the answers

Describe how a pathogen might utilize both the bloodstream and the lymphatic system to spread within the body.

<p>A pathogen can enter the bloodstream directly, causing septicemia and spreading rapidly. Alternatively, it can enter the lymphatic system, leading to enlarged and tender lymph nodes near the infection site before potentially entering the bloodstream from there.</p> Signup and view all the answers

Explain how the airborne transmission of a pathogen differs from vehicle-borne transmission utilizing a fomite.

<p>Airborne transmission involves pathogens suspended in droplets or dust that can remain in the air, like the cold virus. Vehicle-borne transmission involves pathogens transferred via a contaminated inanimate object (fomite) to a susceptible host, such as contaminated medical equipment.</p> Signup and view all the answers

During which stage of an infectious disease is it most likely that an infected individual could unknowingly transmit the pathogen to others, and why?

<p>The prodromal period is when transmission is most likely to occur unknowingly because the infected individual experiences initial, often mild, symptoms that they might not recognize as indicative of a serious infection, yet they are already shedding the pathogen.</p> Signup and view all the answers

What distinguishes direct contact transmission from indirect contact transmission?

<p>Direct contact transmission involves physical contact, such as skin-to-skin contact, for example STDs. Indirect contact transmission occurs when pathogens are transferred via an intermediate item or organism.</p> Signup and view all the answers

During which two stages of an infectious disease might the intensity of signs and symptoms be relatively stable, according to Figure 14.10?

<p>According to Figure 14.10, the intensity of signs and symptoms would be relatively stable during the fastigium and convalescence stages.</p> Signup and view all the answers

Describe a scenario in which a pathogen could cross the placenta to the fetus, and what potential consequence could this have?

<p>A pathogen in the mother's bloodstream can cross the placenta and infect the fetus, leading to a congenital infection. This can result in developmental abnormalities, disease, or even death of the fetus.</p> Signup and view all the answers

Flashcards

Infection

A process where a pathogen invades and grows within a host.

Disease vs. Infection

Disease results from infection when tissue function is impaired.

Colonization

Presence of organisms on a surface without causing disease.

Toxin Production

Pathogens can produce harmful toxins that affect the host.

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Host

An organism that allows a pathogen to reside and reproduce.

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Resistance

The host's ability to prevent infection and disease.

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Source of Infection

The immediate site from which a pathogen is transferred to a host.

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Chain of Infection

The sequence: infectious agent, reservoir, exit, transmission, entry, susceptible host.

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Reservoir

The habitat where infectious organisms live and multiply.

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Source

The origin of pathogens that infect hosts, often the means of transmission.

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Virulence

The ability of an organism to cause infectious disease.

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Portals of Exit

Routes through which pathogens leave the host body.

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Inhalation

Entry of pathogens into the respiratory tract through the air.

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Fomites

Inanimate objects that can transmit diseases.

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Vector

An insect or small animal that transmits disease to humans.

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Direct contact transmission

Transmission of pathogens through physical contact between individuals.

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Indirect contact transmission

Transfer of pathogens via intermediate objects or organisms.

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Airborne transmission

Pathogens suspended in droplets or dust, remaining in the air for extended periods.

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Vector-borne transmission

Pathogens transmitted through animals or insects to humans.

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Septicemia

Infection that spreads through the bloodstream.

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Prodromal Period

The initial phase where first symptoms of the disease appear.

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Convalescence

The recovery phase after an illness.

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Study Notes

Host-Pathogen Relationships

  • "Infection" and "disease" are not synonymous.
  • Infection occurs when a pathogen invades and grows within a host.
  • Disease occurs when pathogen invasion and growth impair tissue function.
  • The body has defense mechanisms to prevent infection, and disease if infection occurs.

Chain of Infection

  • Infectious agent
  • Susceptible host
  • Reservoir
  • Portal of entry
  • Portal of exit
  • Mode of transmission

Host Infection and Pathogens

  • Infection occurs when micro-organisms (pathogens) invade sterile tissues.
  • Infectious disease occurs when infection is associated with clinically manifested tissue damage.
  • Colonization is the presence of organisms on a body surface or in a lumen, without causing disease.
  • All persons have bacteria and some fungi on skin and in oral cavity.
  • Invasion of tissues occurs when pathogens avoid the immune system to cause disease.
  • Toxin production (endotoxins or exotoxins) can occur in or be ingested by the body.

Host

  • A host is a person (or animal) who permits the lodgment of an infectious disease agent under natural conditions.
  • The severity and degree of infection depend on the host's ability to fight off the infectious agent.

Defense Mechanisms

  • Resistance is the ability of a host to prevent infection and disease.
  • Resistance is aided by:
    • Barriers: intact, functional epithelial surfaces (respiratory tract, gastric acid, antibacterial action in bladder secretions and saliva).
    • Immune system: nonspecific (skin, mucosal surfaces, tears, saliva, gastric juices, immune system), and specific (immunity against a particular agent).
  • Nonspecific defense mechanisms may decrease with age.
  • Resistance can be diminished by:
    • Debilitation from malnutrition
    • Cancer
    • Poorly functioning immune system
    • Drug therapy
    • Previously damaged or abnormal anatomy

Environment: Source & Reservoir

  • Source: the immediate site from which a pathogen is transferred to a host (human, animal, inanimate objects like water, soil, food).
  • Reservoir: the place where infectious organisms live and multiply (humans, animals, food, water, and feces). -Yellow fever example: reservoir is monkeys, source are mosquitoes carrying virus.

Virulence

  • Virulence is the ability of an organism to cause infectious disease.
  • Some infectious agents are easily transmitted (contagious) but not very virulent (causing disease).
  • Conversely, other agents have high virulence (e.g. Ebola) but not high contagiousness.

The Movement of Pathogens

  • Pathogens leave the host through portals of exit similar to those of entry.
  • Pathogens are often found in secreted or excreted body materials.

Sites of Entry

  • Ingestion in gastrointestinal tract : salmonella, cholera
  • Inhalation into respiratory tract: cough, chest pain, shortness of breath
  • Ascension into urinary tract: painful urination, blood in urine, pelvic pain, flank pain
  • Ascension into biliary tree: abdominal pain, jaundice
  • Crossing mucosal surfaces: HPV, HIV, herpes, gonorrhea, experience local irritation, ulceration, pain, redness
  • Entrance through wound sites: direct inoculation leads to direct spread

Transmission

  • Three main types of transmission:
    • Contact (direct, indirect)
    • Vehicle/fomite (airborne, vehicle-borne, food or waterborne)
    • Vector (mechanical, biological)
  • Fomites: inanimate objects that transfer disease.
  • Vector: insect or small animal carrying disease.

Spread of Infectious Agents in the Body

  • Travel via bloodstream (septicemia).
  • Travel via lymphatic system (enlarged tender lymph nodes indicate infection).
  • Travel via body cavity (cerebrospinal fluid, peritoneal fluid, joint space, crossing placenta for congenital infection).

The Natural Course of Disease

  • Sequence of events in infectious disease.
  • Stages: Incubation (exposure – first signs), Prodromal(vague symptoms), Fastigium(disease at peak), Defervescence(decline), Convalescence(recovery), Defection (pathogen removed).

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Description

Explore the differences between infection and disease, emphasizing the body's defense mechanisms. Learn about the chain of infection, including infectious agents, susceptible hosts, and modes of transmission. Understand how pathogens invade tissues and cause disease through various mechanisms like toxin production.

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