Chapter 24: Microbial Disease of the Respiratory System

upper respiratory system

nose, pharynx, middle ear, & eustachian tubes

• saliva & tears protect mucosal surfaces

lower respiratory system

larynx, trachea, bronchial tubes, & alveoli

• ciliary escalator moves particles toward the throat vis ciliary action

• alveolar macrophages destroy microorganisms in lungs

• respiratory mucus protect mucosal surfaces

the common cold

over 200 different viruses

• rhinoviruses (30-50%)

• coronaviruses (10-15%)

• enterovirus D68 (EV-D68)

rhinoviruses

thrive in temperatures lower than body temperature

common cold symptoms

sneezing, nasal secretion, congestion

• can lead to laryngitis & otitis media

• not accompanied by fever

common cold relief

cough suppressants & antihistamines; antibiotics are of no use

flu symptoms

fever (usually high), headache, extreme tiredness, dry cough, sore throat, runny/stuffy nose, muscle aches, stomach symptoms

flu viruses spread

mainly from person to person through coughing or sneezing; may become infected by touching something else with flu viruses on it & then touching nose or mouth

• can infect others starting day 1 but not have symptoms til up to 5 days after

influenza virus

• usually between 3,000-50,000 death in US annually

• avian, swine, & mammalian strains

  • swine serve as “mixing vessels” for new strains

influenza genome

contains 8 RNA segments & outer lipid bilaterally

structure of influenza viruses

neuraminidase spike, hemagglutinin spike, capsid layer, envelope, 2 of the 8 RNA segments in genome

hemagglutinin (HA) spikes

recognize & attach to host cells

neuraminidase (NA) spikes

help the virus separate from the infected cell

antigenic drift

gradual, ongoing process of small mutations in the virus’s genes, leading to minor changes in the surface proteins

• minor antigenic changes in HA & NA (mutation); allow the virus to elude some host immunity

antigenic shift

more dramatic, abrupt change involving mixing of genetic material from different influenza viruses → results in entirely new surface proteins

• changes great enough to evade host immunity; leads to pandemics; involves the reassortment of the 8 RNA segments

types of influenza viruses

A, B, & C

influenza viruses are distinguished

on the basis of their internal nucleoprotein & matrix proteins which are specific for each viral type

flu A viruses

naturally able to infect a range of animal species, including: humans, swine, birds, seals, & horses

flu B viruses

only infect humans

flu C virus infects

humans & swine

influenza A human infections

have been caused by 3 subtypes of hemagglutinin (H1, H2, H3) & 2 neuraminidase subtypes (N1 & N2)

influenza vaccine

multivalent (protects against multiple strains) for most important strains

• composition of vaccine determined annually by the identification of circulating viruses

  • labor intensive to produce

  • does not provide long-term immunity

flu treatment

zanamivir (Relenza) & oseltamivir (Tamiflu)

• inhibits neuraminidase