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BACTERIAL AND VIRAL PATHOGENS OF THE URT AND EAR

1. Identify common viral and bacterial pathogens associated with URT and ear infections

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URTI

VIRUSES:

• Rhinovirus

• Parainfluenza Virus

• Influenza Virus

• RSV – Respiratory Syncytial Virus

• Human metapneumavirus

• Adenovirus

BACTERIA:

• GPC - Group A strep. – Streptococcus pyogenes,

• GNR – Hib

• GNR – Bortadella Pertussis

• Diphtheria

EAR

• Streptococcus pneumonia

• Haemophilus Influenzae

• Streptococcus pyogenes

• Staph. Aureus

• Moraxella Catarrhalis

2. Identify the typical clinical features resulting from infections with each of the major classes of pathogens

Bacterial Infection

• Green/yellow nasal discharge

• Facial pain, tenderness in teeth, peri-orbital swelling

• Headaches, fever, ear pain with discharge

• Lasts longer than viral. > 2 weeks and generally does NOT resolve on its own

Viral

• Primary episode of viral infection usually lasts several days to several weeks. [ ] of virus at sites of infection rises and then falls during this time

• Rate at which intensity of viral infection rises and falls at given sites depends on the accessibility of that organ or tissue to both the virus and systemic immune effectors, intrinsic ability of the virus to replicate at that site, endogenous non-specific and specific resistance

• Primary infections cleared by specific and non-specific immune responses

|SYMPTOM |BACTERIA |VIRUS |CLINICAL FEATURES |CLINICAL ASSESSMENT |

|URTI |Strep pneumonia |Rhinovirus |Watery/purulent nasal discharge, |Full Hx (Incl. past |

|Common cold Influenza |Strep pyogenes |Coronavirus |sneezing, sore throat &/or tonsils|episodes, |

|Sore throat |Hib |Parainfluenza – 1, -2, -3 |(+/- pus), cough, wheeze, earache,|complications, |

|Tonsillitis |Bortadella Pertussis |Influenza Virus |enlarged tender cervical LN’s, |asthma/COPD), |

|Bronchitis |Diptheria |Epstein Barr Virus (EBV) |fever, headache, malaise, |Vitals, examine ENT, |

| |H. Influenzae |Resp. Syncytial Virus (RSV) |lethargy, muscular aches and pains|listen to chest for air|

| |Staph. Aureus | | |entry, crackles and |

| | | | |wheezes |

|PHARYNGITIS |Strep. pyogenes |Parainfluenza – 1, -2, -3 |Fever, sore throat, oedema, |As per URTI, Examine |

| | |Influenza Virus |hyperaemia of tonsils and |ENT, Vitals |

| | |Epstein Barr Virus (EBV) |pharyngeal walls | |

|PNEUMONIA |Strep. Pneumonia |H. Influenzae |Cough with sputum (dry cough is |As per URTI, presence |

| |Staph. Aureus |RSV |typical of atypical pneumonia) |of rapid breathing and |

| | |Parainfluenza – 3 |fever, rapid breathing, pleuritic |fever, listen to chest |

| | |Influenza |chest pain, cyanosis, confusion, |for crackles &/or |

| | | |drowsiness, hypotension, shock |wheezes over areas of |

| | | | |lung consolidation, |

| | | | |Sa02 |

|ACUTE BACTERIAL |Strep pneumoniae | |As per URTI but with additional |As per URTI, tap |

|SINUSITIS |H. influenzae | |facial pain/tenderness |frontal sinuses (above |

| | | | |eyes) and maxillary |

| | | | |sinuses looking for |

| | | | |tenderness |

|OTITIS MEDIA |Strep pneumoniae | |Young child with irritability, |Full Hx incl. past |

| |H. Influenzae | |disturbed sleep, pulling at ears, |infections, Vitals, |

| |Strep. Pyogenes | |occ. Vomiting and diarrhea, pain |examine ENT, feel LN’s,|

| |Staph. Aureus | |in ear, fever and URTI symptoms, |listen to chest for |

| | | |red/yellow bulging ear drum |crackles and wheezing |

The most common BACTERIA assoc. with Otitis Media are:

Streptococcus pneumonia

▪ GPC

▪ Can cause sinusitis, acute Otitis media, conjunctivitis, pneumonia and meningitis.

▪ Transmitted via aerosols

▪ It possesses a thick polysaccharide capsule which is antiphagocytic

Streptococcus Pyogenes

▪ GAS – GPC

▪ Most common bacterial cause of pharyngitis (sore throat)

▪ High virulence due to capsule and cell wall which are antiphagocytic. Also contains streptokinase and DNAse

▪ Causes Otitis media, sinusitis, scarlet fever, rheumatic fever

Haemophilus Influenzae

▪ Small GPR

Encapsulated group – cause invasive diseases e.g. meningitis, epiglotitis and bacteraemia

▪ Have polysaccharide capsule

Non-encapsulated group – cause mucosal infections e.g. Otitis media, conjunctivitis, pneumonia and bronchitis

▪ They are part of the normal flora but are opportunistic pathogens

Moraxella Catarrhalis

▪ Important cause of Otitis media and maxillary sinusitis in children. Also causes bronchitis, pneumonia and conjunctivitis

▪ Present in the normal flora but becomes opportunistic in immunocompromised patients

▪ Produces β-lactamases

Staphylococcus Aureus

▪ GPC

▪ Occasional member of normal flora (esp. among hospital staff and patients)

▪ Rarely causes Otitis media but can cause osteomyelitis (bone infection and inflammation) if it colonizes in the mastoid sinuses

▪ Transmission is air-borne particles

VIRAL pathogens associated with Otitis media are:

RSV – Respiratory Syncytial Virus

▪ Paramyxovirus is the major cause of LRTI in kids (bronchiolitis, pneumonia)

▪ May cause common cold in adults

▪ 75% of children infected with the virus have the virus in the middle ear fluid and acute Otitis media

Other BACTERIAL pathogens commonly involved in URTI’s are:

Bortadella Pertussis

▪ Attaches to ciliated cells of the URT mucosa

▪ Endotoxins are the cause of whooping cough

Corynebacterium Diptheriae

▪ Toxin producing bacteria which can colonize in the pharynx, larynx, nose, genital tract and skin causing DIPTHERIA

▪ Rare in developed countries

VIRAL pathogens commonly involved in URTI’s are:

Rhinovirus and coronavirus

▪ Together cause >50% of common colds

▪ Cause a flow of virus-rich fluid from the nasopharynx, triggering the sneeze reflex and hence the spread of the virus

▪ Damage to the epithelium and inflammatory mediators (bradykinin) cause the symptoms of a cold

Influena virus – Cold, LRTI

Parainfluenza Virus – Cold, laryngitis

Adenovirus – cold, pharyngitis, conjunctivitis, bronchitis

EBV – Glandular fever

OTITIS MEDIA

Inflammation of the middle ear

▪ Acute, chronic, or with effusion

▪ Freq assoc with URTI

▪ Usually precipitated by a viral URTI that causes auditory tube oedema – resulting in accumulation of fluid and mucous → 2⁰ bacterial infection

o S. pneumonia, H. Influenzae, Moraxella catarrhalis, β-haemolytic strep

o Viral causes – RSV, adenovirus, enterovirus, rhinovirus

▪ Viruses – S. pneumonia (35%), H. Influenzae (25%), M. Catarrhalis (15%), S. pyogenes

▪ Common in infants and small children (peak incidence = 6-18 months)

o Eustachian tube shorter, wider and more horizontal

o Infant tube more flexible and inefficient at clearing secretions

o Size and gradient of tube in adults = more difficult for the infection to rise up and take residence in middle ear

3. Discuss the typical host responses to infection with the major classes of infectious agents

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Mechanism of tissue response to infection:

Micro-organism

Cell and tissue injury

Release or activation of inflammatory mediators

Inflammatory response

Infectious agents can cause damage in three ways:

• Direct damage: They contact/enter cells and directly cause cell death.

• Indirect damage: Via endotoxins, ectotoxins or degradative enzymes or by damage to blood vessels → ischaemic necrosis.

• Induce a damaging host response:

o Acute: 1. Suppurative

2. Necrotising

o Chronic: 3. Cytopathic and cytoproliferative

4. Mononuclear and granulomatous

5. Chronic inflammation and scarring

Suppurative Inflammation:

This is acute inflammation, characterised by increased vascular permeability, oedema and neutrophil infiltration. The neutrophils are attracted by the release of chemoattractants from the pyogenic bacteria: usually extracellular gram +ve cocci or gram –ve rods. Neutrophils are also attracted by bacterial endotoxins.

Suppurative inflammation usually occurs in the case of an aggressive pathogen, such as Streptococcus pneumonaie causing acute lobar pneumonia, or in the case where host defences are compromised. This could be due to:

• Stroke, brain tumor or cancer of the larynx inhibits the gag reflex.

• Mucociliary action may be impaired by viruses or smoking.

• Phagocytosis by alveolar macrophages may be impaired by smoking, alcohol or oedema in the case of cardiac failure.

• General host immunity may be suppressed: E.g. By steroids or chemotherapy.

Necrotising Inflammation:

This occurs when micro-organisms secrete particularly severe endotoxins causing cell death before the inflammatory response has a chance to arise. This is the case with clostridium perfringens → gas gangrene. Similarly, the parasite Entamoeba histolytica causes colonic ulcers and liver abscesses characterised by estensive tissue destruction with liquefactive necrosis in the absence of inflammatory infiltrate.

NB: An abcess is a focal, localised collection of purulent inflammatory tissue buried in a tissue, organ or confined space.

• Inner zone: Necrotic white cells and tissue debris

• Middle zone: Intact neurtrophils

• Outer Zone: Vascular congestion, fibroblasts, collagen.

Cytopathic-Cytoproliferative Inflammation:

This reaction is characteristic of virus-mediated damage to host cells in the absence of a suppurative inflammation. Viruses replicate within the cells and form aggregates known as inclusion bodies (eg CMV). They may cause the cells to fuse and form polykaryons (eg measles, herpes virus). Focal epithelial damage may cause blistering. Viruses may induce the cells to proliferate and form warts (eg papillomavirus) or papules (eg poxviruses). Viruses can also induce dysplagia and cancer.

Mononuclear and Granulomatous Inflammation:

Granulomatous inflammation is characterised by the presence of a granuloma: A focal area of granulomatous inflammation with an aggregate of epithelioid (epithelial like) cells (modified activated macrophages). It is surrounded by lymphocytes and plasma cells, and may also show “giant cells” which are fusions of the epithelioid cells. Giant cells may be Langerhan’s type (TB) or Foreign body type (in response to inert bodies such as a grain of talc).

Parasites also evoke a mononuclear response in the form of eosinophils. Eosinophils contain granules of MBP (Major Basic Proteins) which they release in response to large parasites such as helmiths. This is mediated by the IgE antibody.

Chronic Inflammation and Scarring:

The final common pathway of many infections is chronic inflammation, which either leads to complete healing or to extensive scarring. Scarring can cause serious consequences for the host. E.g. Scar tissue in the lungs inhibits gas exchange.

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