Wk5: Protozoa Medical Microbiology Notes PDF

Wk5: Protozoa Created @October 21, 2024 4:01 PM Class MEDBIO BMS2036 Ciliates Apicomplexa Flagellates Amoebae Protozoas - sensitive to heat - killed off in high heat...

Wk5: Protozoa Created @October 21, 2024 4:01 PM Class MEDBIO BMS2036 Ciliates Apicomplexa Flagellates Amoebae Protozoas - sensitive to heat - killed off in high heat Transmission: Ingestion Giardia lambia Toxoplasma gondii Vectors - Plasmodium sp Anopheles sp - mosquito Sexual contact Trichomonas vaginalis Transovarial Babesia bovis Placental Toxoplasmosis gondii Wk5: Protozoa 1  Malaria: plasmodium sp. p. falciparum p. vivax Apicomplexa: Rigid more pointed - polar ring and conoid Wk5: Protozoa 2  Merozoite - infected form in humans Sporozoites undego schizogony in liver Role of circumsporozoite protein and heparin sulfate glucosaminoglycan Symptoms are mild Malarial hepatitis - rare Variation in liver involvement depends on species Malaria pathogenicity: Echinocytosis - influx of K and Cl ions - cell returns to normal shape after 10 mins Wk5: Protozoa 3  Cyclical malarial fever toxins - ROS + protoxoal hemozoin - pyrogens Conditions protective against malaria Sickle cell Thaliasemia Wk5: Protozoa 4  Lack of duffy factor Glucose - 6 - dehydrogenase deficiency Malaria quinine treatments works by preventing parasites from breaking down their own toxic byproducts. Toxoplasmosis Toxoplasma gondii Apicomplexan – obligate intracellular parasite ‘Flu like illness in most hosts Complex pathology in at-risk hosts Wk5: Protozoa 5  Trypanosoma spp Flagella Nucleus at the front African trypanosomiasis - sleeping sickness T. brucei gambiense T. brucei rhodesiene American trypanosomiasis - chagas disease Human African trypanosomiasis - sleeping sickness Tsetse fly habitats: Forests / shrub land Rivers and watering holes Animal reservoirs Concentration close to human settlements Very hard to eradicate Cytokine release - important in pathogenicity Swollen lymph nofrd, face, and hands Wk5: Protozoa 6  Skin rash Fever and severe headaches Fatigue, muscle and joint pain Fatal if not treated Progression of disease causes Weight loss Neurological impairment Drug targets for trypanosomes Glycosome - enzymes - ATP production Enzymes - synthesised in cytoplasm and transported to glycosome Suramin binds to enzymes in cytoplasm American Trypanosomiasis Spread by blood transfusions Contact with vector is less common - urban areas are increasingly impacted Two stages: Acute stage - swelling at site of infection Chronic stage - appears after asymptomatic period of several years 27% develop cardiac symptoms - fatal 3-6% develop megaviscera or peripheral nerve damage Wk5: Protozoa 7  Leishmaniasis: obligate intracellular parasite transmitted by female sandflies Occurs as cutaneous/ mucocutaneous or visceral disease Clincal presentation One or more skin sores following a bite from infected sandfly Untreated - sores lasts from weeks to years - raised edges and a central crater Mucocutaneous leishmaniasis Occurs months-years after cutaneous lesion has healed Scanty presence of parasites Nasopharangeal tissues affected Inflammation - non specific granulation tissue and histiocytes, solitary or small groups of leishmanias may be seen lining vacuoles Wk5: Protozoa 8  Visceral leishmaniasis Fever Weight loss Enlargement of spleen and liver Anaemia Untreated - fatal Wk5: Protozoa 9  Wk5: Protozoa 2 Created @October 23, 2024 11:03 AM Class MEDBIO BMS2036 Waterborne protozoan diseases: Cryptosporidium parvum - cryptosporidiosis Cyclospora cayetanesis - cyclosporiasis Giardia lamblia - Giardiasis Balantidium coli - Balantdiasis - dysentery Acanthamoeba spp. - Keratitis Protozoa: survival in the environment Bacterial spores and protozoan cysts have the same function Giardia lamblia: Occurs if there is unsafe water or poor water quality Long-term giardia conditions Diarrhoea for several weeks, abdominal cramps Can last for months or years Symptoms that replicate IBS - irritable bowel syndrome Fatigue, tiredness, weight loss Few protozoa that can persist that cannot be detected Metronidazole: Affects anaerobes Wk5: Protozoa 2 1  Exploit metabolic or anaerobic pathways Can treat protozoa diseases Activated in body in presence of POR - reduced to a nitro radical anion Diagnosing protozoal infections: Filtered Ethyl acetate - removes fatty residues Cryptosporidiosis: Immunocompetent Fluid and electrolyte replacement Some protective immunity Self limiting Immunocompromised No treatment Severe diarrhoea: dehydration and weight loss Wk5: Protozoa 2 2  Not self-limiting and no targeted treatment Vigorous rehydration; anti-diarrhoeal drugs Extraintestinal infection - fatal Cryptosporidiosis and poverty A major cause of childhood diarrhoea Associated with malnutrition Cryptosporidiosis - pathogenicity: Cryptosporidia mature in exocytoplasmic vacuoles No consensus on specific pathogenicity mechanism Impaired Na+ and H2O absorption? Increased Cl- absorption? Induction of host cell apoptosis Found in lakes and rivers contaminated with sewage and animal faeces Diagnosing gastrointestinal protozoal infections: Microscopy techniques - gold standard method for identification Acanthamoeba Keratitis: Keratitis: Inflammation of cornea Almost exclusive to contact lens wearers Risk factors: swimming pools, lakes, sea water, storing lens in home made solutions, poor lens hygiene Severe pain, redness, scant, protozoa cause granulomatous encephalitis Treatment: multiple antimicrobials like topical antiseptics Severe corneal scarring can occur - corneal transplantation may be required Wk5: Protozoa 2 3  Severe loss of vision of the eye could occur Therapy and treatment lasts for more than a year Agar plate seeded with bacteria and inoculated with swab from the infected eye Active forms of amoeba will scoot around the plate PCR may be used Wk5: Protozoa 2 4  Wk7: Clinical virology and diagnostics Created @November 10, 2024 5:11 PM Class MEDBIO BMS2036 Why are virus diagnostics needed? 1. Appropriate management of patients a. Avoids further unnecessary testing b. Avoids Unnecessary drug use c. Informs patient treatment and prognosis d. Are treatment strategies working 2. Routine public health measures a. Screening of donated blood (HIVE, HepB. HepC) b. Notifiable infections like measles, rubella, Mpox i. Activate contact tracing ii. Limit spread of outbreak iii. Put mechanisms in place to contain and eradicate 3. Surveillance a. Monitor signifcance and prevalence of viruses in a community b. Monitoring and tracking of outbreaks like COVID-19 c. Evidence of remerging or emerging viruses i. Individuals traveling from other countries e.g polio in London ii. Viruses spreading within animal communitites iii. Viruses with zoonotic potential Wk7: Clinical virology and diagnostics 1  Viral infections share many symptoms Flu like symptoms Fever Chills Generalised aches and pains Headache Poor appetite Fatigue Drowsiness ILI - influenza like illness can be caused by RSV, Malaria, acute HIV, herpes, Hep C, Rabies, Dengue fever, Pneumonia, measles, SARS, Covid- 19 5% of GPs are involved with sentinel surveilance Swabs sent to clinical virology labs Monitors rate of circulating influenza and other respiratory viruses See unusual patterns, monitoring of circulating sub-types Help identify new viruses: important for diagnosis and surveillance SARS-CoV-2, COVID Lujo virus Dependent on good sampling Type of sample will largely be determined on signs/symptoms of disease Indicates what organ systems are involved Wk7: Clinical virology and diagnostics 2  Methods of clinical virology Isolation of virus - direct method - detect infectious virus Cultivation in cell culture followed by identification Need cells from other organisms to infect and replicate For new viruses - trial and error to find out what the virus can infect the ‘host range’ Detection of virus components - indirect method - cannot detect infectious virus Of virions, viral antigens, viral nucleic acids Serology - indirect method Detection of antibodies in patient’s serum Virus can be titrated on living cells Time consuming Not suitable for all viruses Research technique but still used in diagnostics Virus sequencing Metagenomic sequencing used when target is unknown If known then use amplicon sequencing that amplifies a region of the viral genome# Sequences can be aligned to known virus sequences An unknown virus similarities and related viruses can be identified Direct detection Wk7: Clinical virology and diagnostics 3  Wk7: Intro to virology Created @November 4, 2024 2:58 PM Class MEDBIO BMS2036 Virus: Obligate intracellular parasite Comprising of genetic material Instructions for making new copies of the virus Surrounded by a protein coat - capsid Virus genetic material Sometimes a membrane - envelope Made from fatty lipids molecules taken from host cells Surface proteins Help the virus to recognise and bind to cells in the host organism All viruses have: Viral genome: DNA or RNA Viral capsid: Protein coat Some viruses have an envelope: Lipid bilayer with glycoprotein - help virus to bind with cells More fragile than viruses without one Less resistant to environmental constrain than non enveloped Capsid: Wk7: Intro to virology 1  Protect the viral genomic material DNA and RNA are fragile to things like pH, heat, drying, UV Ensuring delivery of genomic material into the cell Host cell recognition Proteins on the capsid can be recognised by host cell receptors Viral structure: Bacteriophage Tobacco mosaic virus Human immunodeficiency virus or HIV Capsid form and assembly: 3 forms: Helical Icosahedric Scaffolded icosahedric Capsid assembly: formation of the capsid shell Packaging: viral genome placement inside a capsid or an envelope Capsid: Closed 3-dimensional structure No holes - Stable Built of repeating protein structures Wk7: Intro to virology 2  CryoEM: Transmission electron cryomicroscopy Viral envelope: A lipid bilayer Involved with virus attachment to cells Envelope proteins recognised by cellular receptors Can fuse with hose cell membrane Virus can exit cells using cell machinery Can avoid cell damage Wk7: Intro to virology 3  Envelope vs non-enveloped Non enveloped More resistant to pH, heat, dryness, alcohol, soap Usually causes more damage Exiting cells - disrupts integrity of the membrane and cause cell lysis Names of structures? Capsomers - clusters of proteins that compose the capsid Peplomers - Proteins on the envelope of the virus Virion - complete virus particle Structure of viruses is important: Create treatments Develop vaccines Knows what kills viruses - soap, alcohol, bleach Wk7: Intro to virology 4  Virus classification: Classified by a taxonomic system Grouped by phenotypic characteristics Morphology Nucleic acid type Replication Host Disease caused Baltimore classification system: 7 different groups based on nucleic acid, sense, method of replication Classify viruses based on their manner of messenger RNA (mRNA) synthesis Virus names: Disease they cause Organisms they infect Place found Scientists who identified it Viruses outnumber bacteria 10:1 Estimate of 320,000 types of viruses for now… ~1.10+15 viruses 5-8% of DNA is made of virus genetic material Infectious life cycle Wk7: Intro to virology 5  A susceptible cell has a functional receptor for a given virus - the cell may or may not be able to support viral replication A resistant cell has no receptor - it may or may not be competent to support viral replication A permissive cell has the capacity to replicate virus - it may or may not be susceptible A susceptible AND permissive cell is the only cell that can take up a virus particle and replicate it Virus particles are meta stable Stable enough to protect the genome Capsid structure is symmetrical- proteins fit tightly together and provide stability Unstable enough to come apart following infection Bonds are not permanent (usually non-covalent) Following infection, the capsid comes apart to expose genomic material Infectious Cycle Very simply the viral life cycle is: 1. Attachment to cells 2. Enter & uncoating 3. mRNA 4. Translation using host ribosomes 5. Assembly 5. Egress (exit) Wk7: Intro to virology 6  Pathogenesis: Viral Pathogenesis: the process by which a virus causes a disease Effects of the viral infection and replication + Effects of host response (immune system) = DISEASE Viral Virulence Capacity of a virus to cause disease in a host Virulence can be quantitated: Virus titer Mean time to death Mean time to appearance of signs Wk7: Intro to virology 7  Measurement of fever, weight loss Many signs/symptoms of disease are caused by immune response! Symptoms = What only you can feel Signs = what others detect Virulence can be quantitated: - Virus titer (B) - Mean time to death (A) - Mean time to appearance of signs - Measurement of fever, weight loss Viral virulence is a relative property Influenced by dose, route of infection, species, age, sex, and susceptibility of host Not correct to compare virulence of different viruses For similar viruses assays must be the same Virulence depends on the route of inoculation: Plant viruses cause ~£40 billion worth of crop losses a year Wk7: Intro to virology 8  Livestock diseases result in huge losses to the farming industry Impact on wild animals or domesticated animals Felines-SARS, SARS-CoV-2 How do viruses affect us: Acute infection Long-term infections Oncogenesis Economic impact Can viruses be beneficial? Oncolytic viruses Alternatives to antibiotics Gene therapy Biological control-an alternative to pesticides? Looking for new viruses: Wk7: Intro to virology 9  Causes of human disease Potential zoonotic viruses-pandemic potential? Identifying good viruses? Phages? Virus definition: A virus is an obligate intracellular parasite comprising genetic material (DNA or RNA), often surrounded by a protein coat (capsid), sometimes a membrane (envelope). Viruses hijack the cell “factory” (cellular pathways) for their own benefits (replication + dissemination) No cell = No virus Wk7: Intro to virology 10 Wk7: Intro to virology 11  Wk8: Lab Created @December 10, 2024 7:56 PM Class MEDBIO BMS2036 Introduction Purpose of the Practical: Teach interpretation of viral diagnostic assays. Provide hands-on experience with haemagglutination (HA), haemagglutination inhibition (HI), and plaque assays. Develop diagnostic skills applicable to real-world scenarios. Preparation Requirements: Read pages 1-11 of the manual for background on techniques and influenza. Watch video tutorials for visual understanding of the assays. Familiarize with lab safety protocols, reagents, and equipment. Health and Safety Main Hazards: Potentially infectious agents. Reagents under COSHH regulations. Precautions: Wear PPE (lab coat, gloves, safety glasses). Tie back long hair, avoid food/drinks, and keep the workspace tidy. Proper disposal of materials: Gloves: Grey bins. Wk8: Lab 1  Tips and consumables: Clear bags. Large disposable items: Dedicated bins. Do not dispose of plaque assay plates; they are reused. Introduction to Viral Diagnostics Diagnostic Methods: Direct Methods: Assess infectivity via cell culture (e.g., plaque assays). Indirect Methods: Detect viral components (e.g., PCR, ELISA). Key Techniques: Plaque Assay: Measures infectivity by quantifying plaque-forming units (pfu/ml). Relies on virus-induced cytopathic effects in cell cultures. Limitations: Cannot identify virus type; not all viruses form plaques. Electron Microscopy: Visualizes virus particles but does not assess infectivity. Polymerase Chain Reaction (PCR): Amplifies specific viral genomes. High sensitivity and specificity; does not measure infectivity. ELISA: Uses antibodies to detect viral antigens. Quantitative but does not assess infectivity. HA and HI Assays: HA: Measures viral particle concentration by agglutination of red blood cells. HI: Identifies virus subtype by using specific antibodies to inhibit agglutination. Wk8: Lab 2  Experiment Summaries Experiment 1: PCR Purpose: Identify the virus in each patient's sputum sample. Concept: Specific primers amplify target viral genome sequences. Analysis: Positive bands on the agarose gel confirm the presence of the virus. Differentiation of viruses based on specific primer-target interactions. Experiment 2: Haemagglutination Assay (HA) Purpose: Quantify the viral load (total viral particles) in sputum samples. Protocol: 1. Prepare serial dilutions of sputum samples. 2. Add sheep erythrocytes to observe haemagglutination. 3. Incubate for 2 hours and determine the highest dilution showing haemagglutination (HA titre in HA units). Interpretation: HA titre = Highest dilution with visible haemagglutination. Experiment 3: Haemagglutination Inhibition Assay (HI) Purpose: Identify the influenza A subtype for each patient. Protocol: 1. Mix diluted patient samples with specific antibodies (anti-H1 or anti-H3). 2. Add sheep erythrocytes and observe inhibition of haemagglutination. Interpretation: HI titre confirms virus subtype based on antibody specificity. Experiment 4: Plaque Assay Wk8: Lab 3  Purpose: Measure the infectious viral titre in sputum samples and test susceptibility to oseltamivir. Protocol: 1. Dilute samples 1:10,000 and plate them on cell monolayers. 2. Incubate with and without oseltamivir. Analysis: Count plaques to calculate infectious titre (pfu/ml). Compare plaque numbers to evaluate drug effectiveness. Case Studies Patient Histories: 1. Patient A: Elderly, unvaccinated, exposed to infected grandchildren. 2. Patient B: Diabetic student, exposed to an infected co-worker. 3. Patient C: Student returning from a poultry farm in China, exposed to birds. Diagnosis and Results: 1. Patient A: PCR and HI indicate H1N1 influenza. High viral load; resistant to oseltamivir. 2. Patient B: PCR and HI confirm H1N1 influenza. Low viral load; susceptible to oseltamivir. 3. Patient C: PCR suggests avian influenza (H5N1 or H7N9). Requires further testing with specific antibodies for confirmation. Final Diagnosis and Treatment Plan Wk8: Lab 4  Patient A: Virus: Influenza A (H1N1). Treatment: Adamantane-class antiviral (e.g., amantadine). Patient B: Virus: Influenza A (H1N1). Treatment: Oseltamivir. Patient C: Virus: Suspected avian influenza (H5N1 or H7N9). Treatment: Oseltamivir, with caution; confirm diagnosis through additional tests. Conclusion Integration of Results: Use multiple assays for accurate diagnosis and treatment planning. Understand limitations and complementary nature of diagnostic techniques. Key Learning Outcomes: Practical knowledge of virology diagnostics. Insight into treatment strategies for viral infections. Wk8: Lab 5  Wk9: Virus life cycle Created @November 18, 2024 3:02 PM Class MEDBIO BMS2036 Virus is dependent on its host cell Must use same tools as host cell Viruses do not grow: Inoculation phase Virus undergoes the first step - attachment to host cells Eclipse - viruses now being manufactured within host cells Penetration step where virus enter the cells and uncoating of genetic material Manufacture of viral components like viral proteins and new genetic material Maturation After synthesis of capsids, enxymes and other materials, new virus particles formed during assembly step Total virus count increases before release Viruses assemble not grow Virus is dependent on host cells Viruses on normal cellular processes Endocytosis Cytoskeletal transport Nuclear import/export Wk9: Virus life cycle 1  Transcription machinery Translation machinery Secretory pathway Glycoproteins on surface of the virus - recognise attachment and entry receptors to initiate penetration of the viral particle in the cells Different viruses can bind to same receptors - adenovirus and coxsackievirus B3 Same virus can bind to multiple receptor - retroviruses can bind to 16 receptors Difficult to penetrate the cytoplasm Cytoplasm is crowded Movement of large protein complexes will not occur by diffusion Virus stops cellular translation Use the translation complex for own translation Viral genomes must make mRNA to be read by host ribosomes Seven classes of viral genomes: 1. dsDNA Wk9: Virus life cycle 2  2. gapped dsDNA 3. ssDNA 4. dsRNA 5. ss (+) RNA 6. ss (-) RNA 7. ss (+) RNA with DNA intermediate dsDNA dsDNA gapped virus: DNA dependent DNA polymerase encoded by host cells Replication of genetic material occurs in the cell nucleus ssDNA virus DNA dependent DNA polymerase encoded by host cells Wk9: Virus life cycle 3  Ss (+) RNA virus Replication is cytoplasmic only, no DNA form Ss (-) RNA virus Replication can be cytoplasmic (Bunyavirus) OR nuclear (influenza virus) Wk9: Virus life cycle 4  dsRNA virus Replication is cytoplasmic only, no DNA form Retrovirus Replication of genetic material occurs in the cell nucleus Wk9: Virus life cycle 5  mRNA is always the plus strand DNA of equivalent polarity is also the + strand RNA and DNA complements of + strands are negative strands not all + RNA is mRNA Viruses use membrane to create small viral factories Nuclear viral assembly Wk9: Virus life cycle 6  Capsid form and assembly 3 capsid forms Helical Icosahedric Scaffolded icosahedric Capsid assembly - formation of the capsid shell Packaging - viral genome placement inside a capsid or envelope Virus budding by cellular exocytosis Envelopes of viruses are derived from membrane, could be internal or plasma membrane Enveloped viruses use secretory pathway to assemble mature and egress the cell Popular because it doesn’t disturb the cell Wk9: Virus life cycle 7  HIV budding formation of lentirius nucleocapsid linked to budding process Envelope proteins are responsible for directing assembly and budding at that location Wk9: Virus life cycle 8  Wk9: Respiratory viruses Created @November 22, 2024 4:22 PM Class MEDBIO BMS2036 Learning Outcomes Understand the burden of respiratory viruses on public health. Study key respiratory viruses (e.g., RSV, Rhinovirus, Influenza). Comprehend: Virus burden and epidemiology. Virology and pathogenesis. Treatment and prevention. Respiratory Viruses Overview 1. Upper Respiratory Infections: Common conditions: Rhinitis, pharyngitis, laryngitis. Symptoms: Runny nose, cough, sore throat. Examples: Influenza virus, Respiratory Syncytial Virus (RSV). 2. Lower Respiratory Infections: Conditions: Bronchiolitis, pneumonia, croup (common in children). Severe symptoms: Stridor, respiratory failure. 3. Seasonality: Peak activity for respiratory viruses varies, typically in colder months. Key Respiratory Viruses Respiratory Syncytial Virus (RSV) Wk9: Respiratory viruses 1  History & Epidemiology: Discovered in 1956. Leading cause of respiratory infections in infants and young children. Global impact: 33 million cases annually. 3.4 million hospitalizations; up to 199,000 deaths/year. Re-infection common due to lack of long-lasting immunity. Virology: Enveloped, negative-sense single-stranded RNA (ssRNA) virus. Divided into A and B subtypes based on F and G proteins. Pathogenesis: Incubation period: 2-8 days. Causes syncytia formation, inflammation, mucous overproduction. Can result in asthma development post-infection. Diagnosis & Treatment: Diagnosed primarily via PCR. No specific treatment; prophylaxis with palivizumab for high-risk infants (costly). Rhinovirus Virology: Non-enveloped, positive-sense ssRNA virus. Belongs to Picornaviridae family. Three species: A, B, C (~160 serotypes identified). Clinical Features: Major cause of the common cold (~50% of upper respiratory infections). Wk9: Respiratory viruses 2  Symptoms: Runny nose, sneezing, coughing, sore throat, fatigue. Can exacerbate asthma due to immune response. Transmission: Via aerosols, microdroplets, and fomites. Prefers cooler temperatures (~32°C), thriving in the nasal cavity. Treatment: No vaccine; management focuses on symptom relief. Coronaviruses Virology: Enveloped, positive-sense ssRNA viruses. Largest RNA viruses known, with diverse host ranges (e.g., bats, humans). Key strains infecting humans: Common cold: 229E, OC43, NL63, HKU1. Severe: SARS-CoV (2002), MERS-CoV (2012), SARS-CoV-2 (2019). Pathogenesis: Range from mild (common cold) to severe respiratory illnesses with multi- organ dysfunction (e.g., SARS-CoV-2). Pandemic Potential: Due to zoonotic spillovers and high genetic diversity. Influenza Virology: Enveloped, segmented negative-sense RNA virus. Four subtypes: A, B, C, D. A & B are most relevant to human infections. Host Range: Wk9: Respiratory viruses 3  Influenza A has the largest host range (natural hosts: aquatic birds). Pathogenesis: Virus enters cells via hemagglutinin (HA) binding to sialic acid receptors. Replicates in the nucleus (unique among RNA viruses). Key Concepts: Antigenic Drift: Gradual accumulation of mutations in HA/NA, leading to seasonal flu. Antigenic Shift: Reassortment of genome segments, potentially causing pandemics. Symptoms: Fever, muscle aches, cough, fatigue. Key Mechanisms in Virus Pathogenesis 1. Evasion of Host Immunity: Suppression of interferon signaling (RSV, Influenza). Delayed apoptosis (RSV). 2. Innate Immunity: Toll-like receptors (TLRs) and NOD-like receptors (NLRs) recognize viral components. Production of interferons (Type I and III) and pro-inflammatory cytokines. 3. Tropism: Virus binding to specific cell surface receptors (e.g., ICAM-1 for Rhinovirus, Neu5Ac for Influenza). Prevention and Future Prospects RSV: Ongoing development of pre-fusion glycoprotein-based vaccines. Wk9: Respiratory viruses 4  High-risk infants may receive monoclonal antibodies (e.g., palivizumab). Rhinovirus: No vaccines due to high strain diversity. Influenza: Seasonal vaccination using trivalent or quadrivalent vaccines. Antiviral drugs: Oseltamivir (Tamiflu). Coronaviruses: Continued monitoring for potential zoonotic spillovers. Focus on vaccine development and genomic surveillance (e.g., Nextstrain platform). Conclusion Respiratory viruses represent a significant public health challenge. Each virus has distinct virological features, pathogenesis, and clinical implications. Diagnostics and prevention efforts (e.g., vaccines, antivirals) are crucial for managing these infections. Wk9: Respiratory viruses 5  Wk10: Gastroenteritis viruses Created @December 7, 2024 9:48 PM Class MEDBIO BMS2036 Gastroenteritis: Lower respiratory infections remained the world’s most deadly communicable disease Low income countries suffer far more from transmissible diseases Diarrhoeal diseases remain in the top 5 causes of death Wk10: Gastroenteritis viruses 1  Viral gastroenteritis - inflammation of the lining of the stomach, small and large intestine Most people recover without problems but have complications regarding dehydration Highly contagious and extremely common Many viruses infect via the GI tract but disseminate elsewhere They do not cause gastroenteritis Causes pathology elsewhere in the body eg poliomyelitis For gastroenteritis viruses, the gut has to be BOTH the portal of entry and the target tissue Replicate in the gut and remain in the gut Induce symptoms in the gut, usually diarrhoea and/or vomiting All gastroenteritis viruses transmit via the oral-faecal route but not all viruses that transmit via the oral faecal route are gastroenteritis viruses GE viruses spread via the oral-faecal route Food and water ⇒ food poisoning Excreted in faeces Poor hygiene, sanitation, clean water availability Can cause severe outbreaks Highly transmissible ⇒ fast replication and highly resistant These are not normally serious as long as fresh drinking water is available - usually not in developing countires Fluid intake needs to be higher than lost through vomiting and diarrhoea Wk10: Gastroenteritis viruses 2  Diagnostic of GE viruses Most GE viruses remain poorly characterised Don’t grow well in laboratory settings Very small amounts are sufficient to cause infection and so is highly transmissible GE viruses are rarely detectable in food Routine food screening is not feasible and most food contaminations are identified retrospectively from patients clinical samples Ways to diagnose GE viruses Electron microscopy Genomic / NAAT tests - RT-PCR on the viral genome Immunological tests - Antigenic detection, ELISA Cell culture is not available for viral types None of the available methods informs of infectivity Best approach is to prevent: HACCP guidelines for handling and safe management of food Wk10: Gastroenteritis viruses 3  Rota viruses Members of the Reoviridae family Non-enveloped dsRNA viruses protected by 3 protein capsid layers 70nm icosahedral viruses with spikes radiating from central hubs ‘Hit and run’ virus Rotavirus genome and capsid 18kB dsRNA genome divided into 11 segments 3 capsid layers protecting the genome Proteolytic cleavage of VP4 by host proteases Key determinant of virus tropism dsRNA is a potent PAMP triggering host inflammatory response Virus immune evasion mechanism Maximises transcription and replication of virus genome Virus infects the tips if the microvilli in the intestine Wk10: Gastroenteritis viruses 4  Massive change in the host ability to reabsorb water Most effective treatment is rehydration Rotavirus transmission: Reasons for high transmission High stability to inactivation Quick infection (2-4 days) High production of viral particles in stools Target Children Seasonality All year round (but annual RtV epidemic exist) Treatment i.v. fluid therapy for children Rehydration for adults Rotavirus burden: RtV are major causes of viral gastroenteritis in infants and young children worldwide 1N deaths pa (mainly in developing countries) Major cause of hospitalisations for acute gastroenteritis in developed countries 1B pa in the US alone ~75K hospitalisation pa in under 5yo in the EU Wk10: Gastroenteritis viruses 5  Noroviruses NoV are the single major cause of non-bacterial GE ~45% GE cases UK ~25% of all GE cases in US Very high transmissibility ⇒ implications for childcare settings, hospital wards, food handlers, cruise ships Highly contagious Norovirus incidence True incidence has been underestimated for long time Increase of cases until 2010 Stabilised after that Wk10: Gastroenteritis viruses 6  Norovirus incidence Marked seasonality Winter months Winter vomiting bug Human behaviour Health authorities ‘Stay at home for 48 hours after symptoms have stopped’ Norovirus classification Caliciviridae family - 4 genera - vesivirus, lagovirus, sapovirus and norovirus Infecting man lay within the sapovirus and norovirus groups and cause winter vomiting disease Non-enveloped 7.5kB +ve ssRNA genome (Baltimore’s group IV) True ‘hit and run’ viruses (~12 hours) Wk10: Gastroenteritis viruses 7  Norovirus - molecular features 3 open reading frames: Non-structural proteins ⇒ ORF1 Structural proteins ⇒ subgenomic RNA VP1 self assembly to form viral capsid Priming strategy: 5’ VPg (13-15kDA) Norovirus transmission: symptoms appear 12-48h post infection and last between 2-3 days Transmitted via oral-faecal route: Consumption of contaminated food Person-person or fomite to person contact Airborne droplets (vomit) Symptoms include nausea, vomiting, diarrhoea, abdominal cramps and pain In the UK, norovirus infections cost the NHS ~£80M pa No effective treatment available; prevention remains best treatment Drugs against protein synthesis, protease and polymerase are in the pipeline Vaccines Antigenic drift and number of serotypes circulating are a concern Transient immunity that wanes quickly Recombinant capsid protein vaccines under development Astroviruses Non-enveloped, 30nm icosahedral virus with a pelicular 5-6 pointed, star like appearance 7kB positive ssRNA ⇒ group IV Wk10: Gastroenteritis viruses 8  Worldwide distribution Transmitted through oral-faecal route (winter) Infects epithelial cells of the intestinal tract, inducing mostly diarrhoea Affects mostly 2 groups: young children and elderly, institutionalised patients Determinants of immunity not well understood, but generated immunity is long lasting >80% 5-10yo children have antibodies against AstV Diagnosis by EM, ELISA or NAAT Adenoviruses Non-enveloped, icosahedral viruses with large dsDNA genome (~36-38kB) ⇒ group I baltimore classification Very distinctive morphology that facilitates diagnostic by EM More than 50 serotypes some with strong links to respiratory and eye infections Serotypes, some with strong links to respiratory and eye infections Affects mostly children, up to 50% seroprevalence that then decreases Transmitted through oral-faecal route and found robustly and universally in water Waterborne rather than foodborne Indicators of faecal contamination Incubation Duration Virus ID (particles) Symptoms period (days) (days) Adenovirus Not known 5-7 Watery Diarrhoea 5-7 Diarrhoea & Astrovirus