Respiratory Infections 1 Flashcards
strict pathogens
- Exogenous transmission cause primary infections
- Overcome local host defense
- Adheres to healthy mucosa
Opportunistic pathogens
- Endogenous transmission cause secondary infection
- Needs alteration of host defenses
- Binds to damaged epithelium, foreign bodies
Increased risk for severity of primary infections
- Pre-existing lung conditions or intubation
- Smoking
- Immunocompromised
- Age extremities
- Environmental risks
Innate host response to primary infections
- Interferon alpha and beta: control viral infection initially by inhibiting translation
Nonspecific Febrile Disease
- Generalized flu like symptoms (malaise, fever, aches, anorexia) are a result of type I interferons and T cell proliferation
Adaptive Host Response to viral infection
- CD8 Cytotoxic Lymphocytes which detect viral peptides through MHC Class I are able to kill virus-infected cells by release of granzymes and perforins with assistance from CD4+ T Helper cells
Baltimore classification recap
Common cold is mostly caused by which viruses
- Adenovirus: naked, dsDNA; common throughout; stays on surface 2hrs-7days
- Coronavirus: enveloped, ss+ RNA; common in winter; stays on surface for 3 hrs
- Rhinovirus: naked, ss + RNA; common in summer; stays on surface 7days-3months
Rhinovirus: Biology
- Family: Picornaviridae
- Small, non-enveloped, ss(+)RNA, icosahedral viruses • Over 100 antigenically distinct serotypes
- Labile at acidic pH
4 Viral Capsid Protein: VP1, VP2, VP3, VP4
How is rhinovirus transmitted
Transmission is via aerosol, direct contact and indirect contact
• Sneezing/Coughing
• Nose-to-hand, hand-to-hand
• Fomites
Rhinovirus Pathogenesis
- VAP (VP7 capsid) binds to host receptor ICAM-1 on respiratory epithelium
- Viral replication triggers Interferons, histamine and bradykinin. Replication is preferential to nose at ~33C
- host immune response: Infection is transient, self- resolving
• Interferon-α
• Natural Killer cells
• Cytotoxic Lymphocytes
Clinical presentation of Rhinitis/Rhino-pharyngitis aka “Common Cold”
- Watery eyes
- Nasal congestion
- Runny nose
- Sneezing
- Scratchy/sore throat
- Dry Cough
- Fever (low to none)
Coronavirus: Biology
- Family - Coronaviridae
- Single molecule of linear, ss(+)RNA
- Largest positive strand RNA viruses
- Latin word ‘corona’ means ‘crown’ or ‘halo‘
- Enveloped, Helical nucleocapsid
Human coronaviruses are of the genera
Alpha coronavirus
Beta coronavirus
2nd most common cause of common cold
Common corona
Adenovirus: Biology
• Family: Adenoviridae
• Linear, ds DNA
• Non-enveloped, icosahedral
• Medium-sized (90-100 nm)
• Naked capsid has fiber with penton base (Viral Attachment Protein)
• 100+ serotypes known; at least 55+ types infect humans
Immunity is transient!
Prevention of adenovirus
- Live oral vaccine against Type 4 & 7 for military
* Vector for gene therapy and COVID-19 vaccines (Johnson & Johnson, AztraZeneca-Oxford)
What diseases does adenovirus cause
- pharyngo -conjunctival fever
- mild URTI- 3rd most common
- interstitial pneumonia/ARDS
Adenovirus: Pathogenesis
Fiber protein attaches to CAR (Coxsackie-Adenovirus Receptor)
• Exhibits hemagglutination activity (ability to clump RBCs in vitro)
Internalization of virus is by receptor mediated endocytosis
• Penton base has cytolytic toxic activity
• Inhibition of cellular mRNA synthesis
• Cell rounding, enlargement, intra-nuclear inclusions
Clinical Presentation: Pharyngo-conjunctivitis “Pink Eye”
- Low-grade fever
- Swollen cervical lymph nodes
- Sore throat
- Itchy red eyes, often with clear discharge
Prognosis for viral URTI
No Vaccines for Rhino and Common Coronavirus
▪ Usually mild and self-limiting illness
▪ Complete recovery is usually within 7 days for adolescents & adults; within 10-14 days for children
▪ Severe Complications not common (<10% Secondary Bacterial); very rarely causes fatal disease
Prevention of URTI
▪ Live vaccine for Adeno (military)
▪ Hand-washing, hand sanitizer
▪ Emphasize other environmental measures to control infections:
▪ Avoiding finger-to-eye, finger-to-nose contact
▪ Coughing and sneezing into the crook of the elbow
▪ Mask wearing
▪ Social Distancing
