Lecture 15: URTI Infections

(URTI Infections) Lecture 15 Flora of the Upper Respiratory Tract · alpha streptococci (like acidic mucosal surfaces) URT Infections · viral infections ↳ common cold ↳ infectious mononucleosis (kissing disease) · bacterial infections ↳ Strep throat & complications ↳ diphtheria ↳ otitis media ↳ epiglottitis Causes of Pharyngitis (sore throat) ↳ whooping cough Organism: Disease: Percentage: Virus Common cold, pharyngitis, croup, mono 40% Bacteria Pharyngitis, tonsillitis 15-30% Chlamydia/Mycoplasma (pneumoniae) Unknown Pharyngitis Epidemics and outbreaks Pharyngitis Up to 30% The "Common Cold" · >100-200 different viruses can cause a cold, so immunity not usually a protective factor, no vaccines · ~30-50% of colds caused by rhinoviruses (hosts are primates) ↳ usually just upper respiratory tract · 15-20% caused by coronaviruses ↳ easily spreads to sinuses, lower respiratory tract, and middle ear Rhinovirus · >50% common colds caused by rhinovirus · small virus, RNA genome, non-enveloped · >100 subtypes, classed into three classes based on the receptor they bind to: ↳ 90% bind to ICAM-1 (intracellular adhesion molecule) · transmission: direct contact, some by droplet · does not grow at 37C, optimal at 33C, therefore only grows in upper respiratory tract (not rest of body b/c not body temp) · 10-12 hours incubation period (symptoms show) · self-limiting infection: no antivirals or vaccine Infectious Mono "Kissing Disease" · HHV-4 (EBV) Epstein Barr Virus EBV related Cancer · associated with Burkitt's lymphoma and other B cell lymphomas · DNA virus, Herpesviridae, enveloped, latent in B cells · Infectious Mononucleosis (IM)("kissing disease") ↳ most common childhood cancer in Africa ↳ associated with malaria endemic areas · most people have the infection when young and have mild or sub-clinical infection · more severe disease when older (teenagers, college students) · systemic effects on cardiovascular and lymphatic systems · virus shed intermittently from saliva through life · symptoms: fever, sore throat, swollen lymph glands in neck, general weakness, fatigue, enlarged spleen · production of heterophile antibodies (weird antibodies that agglutinate other mammals RBC) ↳ no function for antibodies except lab tests · Ampicillin rash: a complication not just a rash ↳ happens when you have mono and are given beta-lactams (super antigen effect) Streptococcal pharyngitis (Strep throat) · streptococcus pyogenes (Strep group A) - beta hemolytic · on inspection, strep throat cannot be differentiated from any other type of infection so laboratory tests are necessary! · need to treat all cases of streptococcus pyogenes pharyngitis with antibiotics to prevent sequelae (complications coming after an infection) Scarlett Fever · S. pyogenes can produce an erythrogenic toxin ↳ you can get scarlett fever when first getting strep throat if it has this superantigen toxin · pinkish-red sandpaper-like skin rash · high fever · Strawberry tongue (loses upper membrane and becomes inflamed) · Scarlett fever varies in severity, may progress to glomerulonephritis or rheumatic fever Rheumatic Fever · non-infectious complication of a S. pyogenes infection occuring after an infection has disappeared · cross reactivity of bacterial antigens with tissue antigens · some evidence for T lymphocyte invasion in addition to neutrophil damage · most often mitral value damage (in heart) gets smaller Diphtheria · caused by Corynebacterium diphtheria, an aerobic G+ bacillus (non-spore forming) · bacteria do not invade tissues, they produce an exotoxin ↳ inhibits protein synthesis in host cells - tropism for nerve cells ↳ death of epithelial cells leads to inflammation and accumulation of phagocytes · toxoid vaccine · symptoms: sore throat, fever, malaise, neck swelling "bull neck", nerve paralysis, white-gray membrane across back of throat (pseudomembrane) ↳ pseudomembrane: covers back of throat and can prevent breathing, hard to remove, will bleed if you try to dislodge it · C. Diphtheriae: apathogenic unless lysogenized (transduced) by a bacteriophage with exotoxin gene ↳ all isolates of this bacteria must be tested for toxin production · Effects of toxin: myocarditis, cardiac failure, polyneuritis, death (toxin has affinity for nerve cells) · treatment: antibiotics AND antitoxin · vaccine: effective but requires boosters in older populations Most Common Causes of Bacterial URTI's Pathogens in Otitis Media · Haemophilus influenzae · Streptococcus pneumoniae close to 100% of children in daycares have · Moraxella catarhalis · Streptococcus pneumoniae · (middle ear infection) · Moraxella catarrhalis · Haemophilus influenzae all three of these in nasopharynx · Staphylococcus aureus · Streptococcus pyogenes · "cold viruses" Less often Whooping Cough (Bordatella pertusis) · small aerobic G- coccobacillus (bacilli) · produces many exotoxins · does not invade tissues, colonizes ciliated respiratory epithelium and kills cells with tracheal cytotoxin · transmission: droplet · Three stages of disease: ↳ catarrhal: cold-like ↳ paroxysmal: gasping cough ↳ convalescence: healing · infants most at risk for: broken ribs, pertussis pneumonia, oxygen deprivation · pathogenicity: ↳ FTA filamentous hemagglutinin (for adherence) ↳ pertusis toxin (systemic effects) ↳ tracheal cytotoxin: damages ciliated cells ↳ lethal toxin: tissue necrosis ↳ adenylate cyclase: reduces phagocytic activity ↳ LPS · treatment: antibiotic not usually effective for disease but reduces infectivity eg. erythromycin · Vaccine: new acellular vaccine (against toxins) combined with tetanus and diphtheria DTaP