Infectious Diseases of the Respiratory System

Infectious Diseases of the Respiratory System Infections of the Respiratory tract • Most common entry point for infections • Upper respiratory tract –nose, nasal cavity, sinuses, mouth, throat • Lower respiratory tract –Trachea, bronchi, bronchioles, and alveoli in the lungs Fig. 21.1a Protective Mechanisms Normal flora: Commensal organisms • Limited to the upper tract • Mostly Gram positive or anaeorbic • Microbial antagonist (competition) Protective Mechanisms Clearance of particles and organisms from the respiratory tract Cilia and microvilli move particles up to the throat  where they are swallowed. Alveolar macrophages migrate and engulf particles and bacteria in the alveoli deep in the lungs. Other Protective Mechanisms • • • • • Nasal hair, nasal turbinates Mucus Involuntary responses (coughing) Secretory IgA Immune cells Selected Bacterial Infections Pharyngitis Group A Strep - Streptococcus pyogenes (Many viruses also cause this) Pneumonia Streptococcus pneumoniae Diphtheria Corynebacterium diphtheriae Tuberculosis Mycobacterium tuberculosis Whooping cough - Bordetella pertussis Streptococcus pyogenes • Gram positive streptococci • Carried and transmitted from the throat • In Respiratory secretions Group A Strep • Capsule -resistant to phagocytosis • Enzymes damage host cells • M protein adhesin The M protein has many antigenic varieties and thus, different strain of S.pyogenes cause repeat infections Strep Throat • Fever • Tonsillitis • Enlarged lymph nodes • Middle-ear infection Infected Middle Ear (otitis media) Scarlet Fever Caused by Erythrogenic Toxin secreted by S. pyogenes Scarlet Fever • The erythrogenic toxin is coded by a gene lysogenic bacteriophage within the genome of S. pyogenes • Rash is an inflammatory reaction to the toxin Bacterial Pneumonia Bacterial, viral or fungal infection can cause Inflammation of the lung with fluid filled alveoli Streptococcus pneumoniae • Pneumococcus • Encapsulated • Often secondary infection following influenza virus Bacterial Pneumonia Streptococcus pneumoniae • 2/3 of all pneumonia • Risk Factors- old age, season, underlying viral infection, diabetes, alcohol and narcotic use • Variable capsular antigen • Purified component (capsule) vaccine Others that cause pneumonia: Mycoplasma pneumoniae Legionella pneumophila Diphtheria The Diphtheria Outbreak of Nome, Alaska, 1925 Heroic Alaska Dog Teams Nome, Alaska 1900 Nome, Alaska, Balto and Gunnar Kaasen‟s Team The 34th Annual Iditarod Race Commemorating the 1925 Emergency Delivery of Diphtheria Serum to Nome, Alaska Diphtheria • Transmitted by droplets or fomites • Infects the upper respiratory tract • Begins with severe sore throat, lowgrade fever and swollen lymph nodes or with skin rash, 1-6 days after infection Corynebacterium diphtheriae • Aerobic Gram + bacillus • Toxin inhibits protein synthesis of cells to which it binds • Destroyed cells and WBC form "pseudomembrane" which blocks airways Diphtheria An “AB” toxin • B = binding subunit • A = active subunit which binds to and inhibits a eucaryotic ribosomal translation factor • Vaccine is diphtheria toxoid Corynebacterium diphtheriae • To produce toxin, C. dithpheriae must be infected with a bacteriophage carrying the toxin gene Bordetella pertussis • Gram negative cocco-bacillus • Capsule • Adherence to ciliated cells • Pertussis toxin is AB toxin Pertussis (Whooping Cough) • Cough • Violent coughing followed by whooping sound • Vaccine – it is made of purified components • Not lifelong immunity – adult carriers Mycobacterium tuberculosis • Acid-fast bacillus – complex cell wall with “cord factor” • Causes TB: lungs bones, other organs • Airborne, (milk, v. rare) Mycobacterium tuberculosis • Thick lipid coat of “Mycolic fatty acids” • Grows very slowly • Resists killing by macrophages and grows in them Tubercule formation A tubercle in the lung is a “granuloma” consisting of a central core of TB bacteria inside an enlarged macrophage, and an outer wall of fibroblasts, lymphocytes, and neutrophils Tuberculosis • Primary – Lung tubercles, caseous, tuberculin skin reaction • Secondary (reactivation) – Consumption: Coughing and chronic weight loss • Dissemination – Extrapulmonary TB (lymph nodes, kidneys, bones, genital tract, brain, meninges) Tuberculosis Elimination requires long antibiotic treatment with “cocktail” of antibiotics because of the resistance that develops. Multi-Drug Resistant Mycobacterium tuberculosis TB Skin Test Virus infections • Respiratory syncytial virus (“RSV”) • Influenza virus Fungal Infections •Coccidiodomycosis (Valley Fever) Coccidioides immitis Respiratory Syncytial Virus • Enveloped (membrane) RNA virus • Spread by respiratory droplets • Community outbreaks in late fall to spring • Upper respiratory tract infection – epithelial cells • May be fatal in infants Influenza Virus An enveloped RNA virus Structure Influenza Virus New human strains every year • Mutations Pandemic strains  Genetic Recombinant Viruses •1957 Asian Flu H2N2 •1968 Hong Kong Flu H3N2 •1977 Russian Flu H1N1 Bird Flu Directly from birds •?? H5N1 „H‟ and „N‟ Flu Glycoproteins H – Hemagglutinin  • Specific parts bind to host cells of the respiratory mucosa • Different parts are recognized by the host antibodies • Subject to changes N - Neuraminidase • Breaks down protective mucous coating • Assist in viral release Influenza • Epidemics and pandemics, mostly in winter • Upper respiratory tract infection – epithelial cells • Multivalent killed virus vaccine with strains from the previous year (Grown in embryonated eggs) • Bird flu (H5N1) pandemic in birds Coccidioides immitis • Soil fungus in American Southwest • Cause of Valley Fever • Highly infectious Valley Fever is an Endemic Disease Coccidioides immitis Life Cycle Coccidioides immitis • Valley Fever usually a flu-like illness • Can spread to bones, skin, meninges • 100,000 new cases/yr in SW