Chapter 21


Infectious Diseases Affecting the Respiratory System



Upper Respiratory Tract Infections: Common Cold

  Also called Rhinitis

  Most commonly caused by rhinoviruses, coronaviruses, and adenoviruses

  There is typically no fever, but malaise, scratchy throat, runny nose, sneezing, and cough are frequently exhibited

  Involve local inflammatory reactions characterized by swelling of nasal mucosa and increased production of mucus

  Transmitted by inhalation or fomites

  Most treatments alleviate the symptoms but dont affect the virus

  Can predispose patient to secondary infections by other microorganisms





  Pain and pressure in the sinus region with drainage that may be greenish, headache, or facial tenderness

  Bacterial causes include: Haemophilus influenzae, Streptococcus pneumoniae, Streptococcus pyogenes, and Staphylococcus aureus

  Fungal causes include Aspergillis




Otitis Media (Ear Infection)

  Viral infections may lead to inflammation of the eustachian tubes and buildup of fluid in the middle ear

  Earache, fever, vomiting, loss of hearing, may lead to ruptured eardrum

  Causative agents include: Haemophilus influenzae and Streptococcus pneumoniae

  Treatments include removal of adenoids, ear tubes, and antibiotics





  Results in redness, swelling and tenderness of throat, fever, headache, nausea, and difficulty swallowing

  May also result in white pus-filled nodules on the tonsils

  Transmitted via respiratory droplets or contact with mucus secretions

  Treat with antibiotics early

  Streptococcus pyogenes (Strep Throat)

  Untreated infections can lead to several complications:

  Scarlet fever bacteriophage-encoded erythrogenic toxin causes sandpaperlike rash on the skin and high fever

  Rheumatic fever cross reaction between M protein and heart muscle can damage heart valves

  Glomerulonephritis - antigen-antibody complexes deposit in the kidneys and cause nephritis

  Fusobacterium necrophorum

  Causes serious pharyngitis infections in adolescents and adults

  Lemierres syndrome bacteria invade the bloodstream and cause neck swelling, otitis media, sinusitis, and meningitis




  Caused by the bacterium Corynebacterium diphtheriae

  Symptoms include low-grade fever, sore throat, vomiting, and lymph node enlargement

  Diptheria exotoxin - absorbed into the blood stream causing damage to the heart, nerves, and kidneys

  A characteristic pseudomembrane  usually forms on the tonsils or pharynx

  a grayish film consisting of inflammatory cells and fluid

  can block airway resulting in asphyxiation

  Prevented with DTaP toxoid vaccine

  treat with anti-toxin or antibiotics if exposed





Lower Respiratory Tract Infections: Whooping Cough

  Caused by Bordetella pertussis

  Disease has 3 distinct stages:

  Catarrhal Stage symptoms include nasal drainage, congestion, and sneezing

  Paraoxysmal stage - violent, uncontrollable coughing followed by deep inspiration which gives off a whoop sound

  Convalescent stage bacteria and symptoms are gone, but patient is susceptible to secondary infections

  Virulence factors include: filamentous hemagglutinin (FHA), pertussis toxin, and tracheal cytotoxin

  help the bacteria to attach to and destroy the respiratory epithelium resulting in a build-up of mucus

  Secondary bacterial infection is chief cause of death due to damage in respiratory tract

  Transmitted via respiratory droplets

  Acellular DTaP vaccine prevents infection

  treated with antibiotics




Respiratory Syncytial Virus

  Children under 6 months of age and premature babies are susceptible to disease

  The virus enters the respiratory tract and causes cells to fuse together creating a clump of cells known as a syncytia

  cells die and slough off causing a clogging of the bronchi; patients are often susceptible to secondary infections because of this

  Experience symptoms of croup and bronchiolitis:  runny nose, cough, fever, wheezing, difficulty breathing, and a dusky skin color from lack of oxygen

  Transmitted by droplets or fomites

  Treated with antivirals or passive antibodies




Influenza (Flu)

  Caused by Influenza viruses A, B, and C

  Antigenic drift - virus constantly mutates hemagglutinin (H) and neuraminidase (N) receptor genes to evade host immunity

  Antigenic shift two viruses exchange genetic material in the same host cell to produce a new virus

  Symptoms include fever, head and muscle aches, chills, lack of energy, and dry cough

  Virus damages respiratory epithelium and deaths are commonly attributed to secondary bacterial infections such as pneumonia

  Spread via respiratory droplets and fomites

  Prevented with subunit vaccine, attenuated nasal vaccine, or anti-virals early





  Caused by the airborne bacteria Mycobacterium tuberculosis

  the bacteria are inhaled, phagocytized by macrophages of the lung tissue, and multiply within them

  Most infections are asymptomatic, but clinical tuberculosis is divided into 3 stages:

  Primary tuberculosis - leukocytes surround the bacteria-containing macrophages resulting in the formation of a tubercle

Lesions can form when tissue-damaging enzymes are released from leukocytes

Cell-mediated immune response to the bacteria can be detected using the TB skin test

  Reactivation tuberculosis - results when tubercles expand and bacteria drain into the respiratory tract

symptoms include violent coughing, greenish or bloody sputum, low grade fever, weight loss, extreme fatigue, night sweats, and chest pain leading to body wasting called consumption

  Disseminated tuberculosis can involve kidneys, bones, genital tract, brain, and meninges and is usually fatal

  Transmitted via respiratory droplets

  Treat with a combination of antibiotics for 2-12 months

  multi-drug-resistant TB (MDRTB) are common due to noncompliance

  an attenuated BCG vaccine is available

  a new extensively drug resistant strain called   XDR-TB was identified in 2006





  Inflammatory condition where fluid fills the alveoli of the lung

  Symptoms include fever, headache, cough, painful breathing, and sputum containing blood & pus

  May be community-acquired or nosocomial



Community-Acquired Pneumonia:  Causes

  Streptococcus pneumoniae (Pneumococcal)

  Leading cause of community-acquired pneumonia in older adults

  Virulence factors include a capsule and pneumolysin (similar to streptolysin of S. pyogenes)

  Complications include:  pleurisy, septicemia, endocarditis and meningitis

  Polysaccharide conjugate vaccine is available or antibiotics early

  Mycoplasma pneumoniae

  Leading cause of pneumonia in college students and is also common among military recruits

  Generally mild disease and is often referred to as walking pneumonia

  Legionella pneumophila

  Commonly found in amoeba in warm natural waters and resists heating, cooling, and some chlorines

allows the bacteria to survive in air conditioners, poorly treated pools, showers, and vegetable sprayers in supermarkets

  Can cause lung abscesses, pneumonia and fatal respiratory failure

  Treat with combination of antibiotics

  Histoplasma capsulatum (Histoplasmosis)

  Fungal spores are widespread and mainly found in soils contaminated by bird or bat droppings

  A small inhaled dose survives in macrophages and is carried to other sites

  Usually produces mild respiratory symptoms, but a few develop more severe symptoms

  Chronic pulmonary histoplasmosis signs and symptoms similar to tuberculosis

  Infections in immunocompromised individuals can lead to lesions in the brain, intestines, heart, liver, spleen, bone marrow, and skin

  Treat with anti-fungal medications for weeks

  Pneumocystis jiroveci

  Pneumocystis pneumonia is the most frequent opportunistic infection in AIDS patients

  Most infections in immunocompetent individuals are asymptomatic

  Treat with anti-fungals


  Nosocomial Pneumonia

  Most commonly associated with mechanical ventilation and may involve multiple species of bacteria

  Elevating patients head may reduce aspiration and prevent infection

  Treat with broad spectrum antibiotics early



  Hantavirus Pulmonary Syndrome

  Caused by the Hantavirus and transmitted by inhalation of dust containing urine, feces, or saliva of infected rodents

  Prodromal phase resembles other viral infections

  Fever, chills, muscle aches, headache, nausea, vomiting, and diarrhea

  Can cause pulmonary edema and acute respiratory distress syndrome (ARDS)

severe breathing difficulties and drop in blood pressure

Treatment involves supportive care