Pathogenesis of Viral Disease - In-depth Notes

Pathogenesis of Viral Disease

  • Course: HUBS2601

  • Instructor: Prof Nathan Bartlett

  • Institution: University of Newcastle, Australia

Course Objectives

By the end of the course, students will:

  • Understand virus infection mechanisms and their role in diseases, particularly gastrointestinal and respiratory pathologies.

  • Focus areas include:

    • Gastroenteritis due to Rotavirus

    • Respiratory infections such as influenza

Mucosal Immune System

  • Key Differences:

    • Systemic Immune System:

    • Largely sterile environment.

    • Quick, vigorous response upon microbial recognition.

    • Mucosal Immune System:

    • Constant exposure to foreign substances and commensal microbes (up to 1imes10141 imes 10^{14}).

    • Less responsive to foreign antigens; limits inflammation from benign exposures.

Gastrointestinal Tract Defenses

  • Defensive Structures: Special adaptations of GI organs to combat infection.

  • Barrier Defenses:

    • Mechanical: Mucosal epithelial surfaces.

    • Chemical:

    • Mouth: Saliva, which contains lysozyme.

    • Stomach: Low pH (acidic environment).

    • Small Intestine: Mucus, bile acid, and antimicrobial enzymes.

    • Large Intestine: Mucus.

  • Commensal Microflora: Bacteria residing in mouth, small and large intestine contributing to defense.

Gastroenteritis Overview

  • Definition: Inflammation of the gastrointestinal tract (GI), leads to illnesses like stomach flu or infectious diarrhea.

  • Symptoms: Diarrhea (watery or with blood), vomiting, abdominal pain, fever, lethargy, dehydration.

  • Duration: Typically less than 2 weeks.

  • Causes: Commonly viral (Rotavirus, Norovirus, Campylobacter).

    • Transmission:

    • Consuming contaminated foods/drinks, or close contact with infected individuals.

    • Prevention: Handwashing, clean water consumption, waste disposal, breastfeeding.

    • Treatment: Isotonic solutions for hydration, possible IV in severe cases, antibiotics not usually needed.

Pathogens Inducing Gastroenteritis

  • Common viruses:

    1. Rotavirus (most prevalent in children).

    2. Norovirus and Campylobacter (common in adults).

    3. Other viruses include Adenovirus, Astrovirus, Sapovirus.

Rotavirus

  • Family: Reoviridae; primary cause of viral gastroenteritis in children.

  • Characteristics:

    • Non-enveloped, icosahedral structure, dsRNAdsRNA genome of size 18.5 kbp$.

    • Appearance: 60-80nm wheel shape seen under electron microscope.

  • Infection Process: Ingested via fecal/oral route, resists stomach acid, infects intestinal cells.

    • Causes cell death and villus atrophy, leading to diarrhea due to fluid secretion and impaired absorption.

Prevention and Treatment of Rotavirus

  • Preventative measures include disinfection, avoiding contaminated sources, and good hygiene practices.

  • Treatment is generally supportive (hydration, symptom management) and may include vaccines such as Rotarix for infants.

Respiratory Viral Infections in Children

  • Risk Factors: Major cause of childhood mortality; significant healthcare burden.

    • Common pathogens: Rhinovirus, RSV, Coronaviruses, Influenza.

  • Clinical Features:

    • URTI: Cough, nasal discharge.

    • LRTI: Wheeze, severe cough, possible pneumonia.

Influenza Overview

  • Characteristics: Highly contagious; seasonal spikes in cases, especially during winter.

  • Impact: Significant morbidity and mortality worldwide, directly affecting 15% of the global population with substantial healthcare costs.

Pathogenesis of Viral Disease

  • Course: HUBS2601

  • Instructor: Prof Nathan Bartlett

  • Institution: University of Newcastle, Australia

Course Objectives

By the end of the course, students will:

  • Understand virus infection mechanisms and their significant role in various diseases, particularly gastrointestinal and respiratory pathologies.

  • Focus areas include:

    • Gastroenteritis due to Rotavirus, a major cause of morbidity in young children globally.

    • Respiratory infections such as influenza, which can lead to severe complications and increased mortality rates, especially in elderly and immunocompromised populations.

Mucosal Immune System

  • Key Differences:

    • Systemic Immune System:

    • Functions in a largely sterile environment; initiates rapid and vigorous immune responses upon microbial recognition, which can sometimes lead to inflammation and tissue damage.

    • Mucosal Immune System:

    • Constantly exposed to foreign substances, pathogens, and commensal microbes (up to 1 imes 10^{14}),necessitatingamoreregulatedimmuneresponse.</p></li><li><p>Lessresponsivetoforeignantigens,therebylimitinginflammationfrombenignexposures,whichiscrucialformaintaininghomeostasisinmucosalsurfaces.</p></li></ul></li></ul><h5id="7824a545−525b−44e7−8ada−17f1477508be"data−toc−id="7824a545−525b−44e7−8ada−17f1477508be"collapsed="false"seolevelmigrated="true">GastrointestinalTractDefenses</h5><ul><li><p><strong>DefensiveStructures</strong>:<br>Specialadaptationsofgastrointestinalorgans,suchasthepresenceofmucosalbarriersandspecificimmunecells,helpcombatinfectionefficiently.</p></li><li><p><strong>BarrierDefenses</strong>:</p><ul><li><p><strong>Mechanical</strong>:</p></li><li><p>Mucosalepithelialsurfacesserveasphysicalbarriersagainstpathogens.</p></li><li><p><strong>Chemical</strong>:</p></li><li><p><strong>Mouth</strong>:Saliva,richinlysozyme,providesbothlubricationandenzymestobreakdownbacteria.</p></li><li><p><strong>Stomach</strong>:ThelowpHandacidicenvironmenteffectivelykillmanyingestedpathogens.</p></li><li><p><strong>SmallIntestine</strong>:Producesmucus,bileacids,andantimicrobialenzymesthatinhibitpathogensurvival.</p></li><li><p><strong>LargeIntestine</strong>:Continuestoproducemucus,whichprotectstheepithelialcellsandfacilitatestheeliminationofpathogens.</p></li></ul></li><li><p><strong>CommensalMicroflora</strong>:</p><ul><li><p>Diversepopulationsofbacteriaresidinginthemouth,smallintestine,andlargeintestinecontributetothedefenseagainstpathogensbyoutcompetingharmfulmicrobes,producingmetabolitesthatinhibitpathogens,andmodulatingimmuneresponses.</p></li></ul></li></ul><h5id="07163474−2161−4b56−a180−13271b8cb1d1"data−toc−id="07163474−2161−4b56−a180−13271b8cb1d1"collapsed="false"seolevelmigrated="true">GastroenteritisOverview</h5><ul><li><p><strong>Definition</strong>:</p><ul><li><p>Inflammationofthegastrointestinaltract(GI),leadingtoillnessessuchasstomachfluorinfectiousdiarrhea,whichcaninfluenceoverallhealthifsevere.</p></li></ul></li><li><p><strong>Symptoms</strong>:</p><ul><li><p>Symptomscanincludediarrhea(whichcanbewateryorcontainblood),vomiting,abdominalpain,fever,lethargy,anddehydration,whichmayleadtoseriouscomplicationsifnotmanagedproperly.</p></li></ul></li><li><p><strong>Duration</strong>:</p><ul><li><p>Symptomstypicallylastlessthan2weeks,althoughsomecasesmaypersistlonger,especiallyinvulnerablepopulations.</p></li></ul></li><li><p><strong>Causes</strong>:</p><ul><li><p>Commonlyviral(withpathogenssuchasRotavirus,Norovirus,andCampylobacter).</p></li></ul></li><li><p><strong>Transmission</strong>:</p><ul><li><p>Viaconsumingcontaminatedfoodsordrinksorthroughclosecontactwithinfectedindividuals,highlightingtheimportanceofhygienepractices.</p></li></ul></li><li><p><strong>Prevention</strong>:</p><ul><li><p>Keypreventivemeasuresincluderigoroushandwashing,cleanwaterconsumption,properwastedisposal,andbreastfeedinginfantstoenhanceimmunity.</p></li></ul></li><li><p><strong>Treatment</strong>:</p><ul><li><p>Treatmentprimarilyfocusesonhydrationthroughisotonicsolutions.Inseverecases,intravenousfluidsmaybenecessary;antibioticsaretypicallynotindicatedastheconditionisoftenviral.</p></li></ul></li></ul><h5id="129d827a−7a5c−4219−9629−b9c731775e0f"data−toc−id="129d827a−7a5c−4219−9629−b9c731775e0f"collapsed="false"seolevelmigrated="true">PathogensInducingGastroenteritis</h5><ul><li><p>Commonvirusesaffectinggastroenteritisinclude:</p><ol><li><p>Rotavirus(mostprevalentinchildren,causingsignificantmorbidity)</p></li><li><p>NorovirusandCampylobacter(commoninadults,associatedwithoutbreaks)</p></li><li><p>OtherviralpathogensincludeAdenovirus,Astrovirus,andSapovirus,whichmayalsocontributetogastrointestinalillnessesinvariouspopulations.</p></li></ol></li></ul><h5id="9eea33de−a6b3−439d−98c6−7d1b9d115583"data−toc−id="9eea33de−a6b3−439d−98c6−7d1b9d115583"collapsed="false"seolevelmigrated="true">Rotavirus</h5><ul><li><p><strong>Family</strong>:</p><ul><li><p>Reoviridae;itistheprimarycauseofviralgastroenteritisinchildrenunderfiveyearsofage,whichcanleadtoseveredehydrationandhospitalization.</p></li></ul></li><li><p><strong>Characteristics</strong>:</p><ul><li><p>Non−enveloped,icosahedralstructurewitha), necessitating a more regulated immune response. </p></li><li><p>Less responsive to foreign antigens, thereby limiting inflammation from benign exposures, which is crucial for maintaining homeostasis in mucosal surfaces.</p></li></ul></li></ul><h5 id="7824a545-525b-44e7-8ada-17f1477508be" data-toc-id="7824a545-525b-44e7-8ada-17f1477508be" collapsed="false" seolevelmigrated="true">Gastrointestinal Tract Defenses</h5><ul><li><p><strong>Defensive Structures</strong>: <br> Special adaptations of gastrointestinal organs, such as the presence of mucosal barriers and specific immune cells, help combat infection efficiently. </p></li><li><p><strong>Barrier Defenses</strong>: </p><ul><li><p><strong>Mechanical</strong>: </p></li><li><p>Mucosal epithelial surfaces serve as physical barriers against pathogens. </p></li><li><p><strong>Chemical</strong>: </p></li><li><p><strong>Mouth</strong>: Saliva, rich in lysozyme, provides both lubrication and enzymes to break down bacteria. </p></li><li><p><strong>Stomach</strong>: The low pH and acidic environment effectively kill many ingested pathogens. </p></li><li><p><strong>Small Intestine</strong>: Produces mucus, bile acids, and antimicrobial enzymes that inhibit pathogen survival. </p></li><li><p><strong>Large Intestine</strong>: Continues to produce mucus, which protects the epithelial cells and facilitates the elimination of pathogens. </p></li></ul></li><li><p><strong>Commensal Microflora</strong>: </p><ul><li><p>Diverse populations of bacteria residing in the mouth, small intestine, and large intestine contribute to the defense against pathogens by outcompeting harmful microbes, producing metabolites that inhibit pathogens, and modulating immune responses.</p></li></ul></li></ul><h5 id="07163474-2161-4b56-a180-13271b8cb1d1" data-toc-id="07163474-2161-4b56-a180-13271b8cb1d1" collapsed="false" seolevelmigrated="true">Gastroenteritis Overview</h5><ul><li><p><strong>Definition</strong>: </p><ul><li><p>Inflammation of the gastrointestinal tract (GI), leading to illnesses such as stomach flu or infectious diarrhea, which can influence overall health if severe. </p></li></ul></li><li><p><strong>Symptoms</strong>: </p><ul><li><p>Symptoms can include diarrhea (which can be watery or contain blood), vomiting, abdominal pain, fever, lethargy, and dehydration, which may lead to serious complications if not managed properly. </p></li></ul></li><li><p><strong>Duration</strong>: </p><ul><li><p>Symptoms typically last less than 2 weeks, although some cases may persist longer, especially in vulnerable populations. </p></li></ul></li><li><p><strong>Causes</strong>: </p><ul><li><p>Commonly viral (with pathogens such as Rotavirus, Norovirus, and Campylobacter). </p></li></ul></li><li><p><strong>Transmission</strong>: </p><ul><li><p>Via consuming contaminated foods or drinks or through close contact with infected individuals, highlighting the importance of hygiene practices. </p></li></ul></li><li><p><strong>Prevention</strong>: </p><ul><li><p>Key preventive measures include rigorous handwashing, clean water consumption, proper waste disposal, and breastfeeding infants to enhance immunity. </p></li></ul></li><li><p><strong>Treatment</strong>: </p><ul><li><p>Treatment primarily focuses on hydration through isotonic solutions. In severe cases, intravenous fluids may be necessary; antibiotics are typically not indicated as the condition is often viral. </p></li></ul></li></ul><h5 id="129d827a-7a5c-4219-9629-b9c731775e0f" data-toc-id="129d827a-7a5c-4219-9629-b9c731775e0f" collapsed="false" seolevelmigrated="true">Pathogens Inducing Gastroenteritis</h5><ul><li><p>Common viruses affecting gastroenteritis include: </p><ol><li><p>Rotavirus (most prevalent in children, causing significant morbidity) </p></li><li><p>Norovirus and Campylobacter (common in adults, associated with outbreaks) </p></li><li><p>Other viral pathogens include Adenovirus, Astrovirus, and Sapovirus, which may also contribute to gastrointestinal illnesses in various populations.</p></li></ol></li></ul><h5 id="9eea33de-a6b3-439d-98c6-7d1b9d115583" data-toc-id="9eea33de-a6b3-439d-98c6-7d1b9d115583" collapsed="false" seolevelmigrated="true">Rotavirus</h5><ul><li><p><strong>Family</strong>: </p><ul><li><p>Reoviridae; it is the primary cause of viral gastroenteritis in children under five years of age, which can lead to severe dehydration and hospitalization. </p></li></ul></li><li><p><strong>Characteristics</strong>: </p><ul><li><p>Non-enveloped, icosahedral structure with adsRNAgenomeofapproximatelygenome of approximately18.5kbp18.5 kbp$.

    • Under the electron microscope, Rotavirus appears in a characteristic wheel shape, aiding in its identification in clinical settings.

  • Infection Process:

    • The virus is typically ingested via the fecal/oral route, resists stomach acid, and subsequently infects intestinal cells.

    • This process leads to cell death and villus atrophy, which results in diarrhea due to disrupted fluid absorption and increased secretion.

Prevention and Treatment of Rotavirus

  • Preventative Measures:

    • Disinfection of surfaces, avoiding contaminated sources, and employing good hygiene practices such as vaccination (e.g., Rotarix) for infants are key to prevention.

  • Treatment:

    • Generally supportive, focusing on hydration and symptom management. Vaccination significantly reduces the incidence and severity of Rotavirus infections in children.

Respiratory Viral Infections in Children

  • Risk Factors:

    • Respiratory viral infections are a major cause of childhood mortality and represent a significant healthcare burden. Vulnerable groups include young children, the elderly, and individuals with pre-existing health conditions.

  • Common Pathogens:

    • Key viruses include Rhinovirus, Respiratory Syncytial Virus (RSV), various Coronaviruses, and Influenza, each contributing uniquely to morbidity in different age groups.

  • Clinical Features:

    • Upper Respiratory Tract Infections (URTI) typically present with symptoms like cough and nasal discharge, while Lower Respiratory Tract Infections (LRTI) can lead to wheezing, severe cough, and potential pneumonia, which may necessitate medical intervention.

Influenza Overview

  • Characteristics:

    • Influenza viruses are highly contagious, exhibiting seasonal spikes in cases, particularly during winter months.

  • Impact:

    • Influenza causes significant morbidity and mortality worldwide, with an estimated 15% of the global population affected during peak seasons, leading to substantial healthcare costs and strain on global health systems.