7.1 Viral and orofacial infection Flashcards
Describe the general properties of a virus.
- Extremely small (diameter of 20-300nm)
- Cannot be visualised with light microscopy
- Require electron microscopy
- Considered as obligate intracellular parastites which require host cells in order to replicate
- Cannot replicate independently
What are the 2 types of viral infection?
- Acute
- Chronic
What is meant by the term acute viral infection?
- Rapid onset of disease and sudden resolution or death (2-3 weeks)
- Short incubation period
- Ferbile disease (causes fever)
- Many infections are subclinical
- E.g. influenza
What is meant by the term chronic/persistent viral infection?
- Symptoms occur over a prolonged period of time
- Slow onset and persistent
- Some viruses establish latency e.g. HSV-1: primary infection and later episodes of reactivation
- Includes oncogenic infections (cause tumours or malignancy) e.g. EBV and Burkitt’s lymphoma, HPV and cervical and oropharyngeal cancer
Describe the structure of a virus particle (virion).
- Nucleic acid (RNA or DNA)
- Capsid (protein coat which aids entry into the host cell and protects the viral genome)
- Nucleocapsid (protecting nucleic acid)
Optional: envelope, a lipoprotein membrane projeting viral glycoproteins imporant for binding and entry to host cells.
What are the ways in which a virus can be classified?
- Type of nucleic acid: DNA or RNA
- Structure of nucleic acid: single or double strand (ss or ds), linear or circular
- Polarity of viral genomes
- Symmetry of nucleocapsid: helical, icosahedral or complex)
- Presence or absence of lipid envelope
What system is used to classify viruses based on genome structure?
Baltimore classification (I to VII)
What does viral tissue tropism mean?
The ability of a virus to infect different cellular types and cause disease.
The viral envelope has viral glycoproteins embedded in the lipid envelope which determine the viral tissue tropism.
What are the 2 ways that a virus can enter a cell?
- Receptor-mediated endocytosis
- Membrane fusion
What cells can HIV infect?
CD4+ cells
- T helper cells
- Macrophages
- Dendritic cells
Name 5 methods used for diagnosis/confirmation of viral disease.
- Electron microscopy
- Cell culture
- Serology (blood sample)
- Fluorescent microscopy
- Quantitative/real time PCR
Describe the use of electron microscopy in viral detection.
- Only method that can be used to view the virion
- High resolving power
- Not routinely used for diagnostics in practice
Describe the use of serology in viral detection.
- Blood sample
- Tested for pathogen specific antigen or antibody
- Commonly used in practice
- Used to monitor disease progression of certain viruses e.g. Hep B
Describe the use of viral cultures in viral detection.
- Growing a culture, if virus is present it will infect cells
- Can then check the virus type by using fluorescent microscopy
- If no virus infects the cells, the culture is negative
Describe the use of a quantitative/real time PCR in viral detection.
- Swab sample, place in fluid which breaks down particles and leaves purified DNA and RNA
- PCR reaction carried out, primers used for specific viral genes, will only bind if the viral genes are present
- E.g. COVID PCR test
What are the routes of viral infection?
- Oral route
- Conjunctiva (HSV)
- Wound (Rabies)
- Skin (Hep B inoculation injury)
- Respiratory (rhinovirus, adenovirus)
- Urinogenital tract
All routes of infection and shedding (except for wound)
What viruses are part of the Herpesviridae family?
- HSV types 1 and 2
- Varicella-Zoster virus (VZV) (HSV type 3)
- EBV (HSV type 4)
- Cytomegalovirus (CMV) (HSV type 5)
- Kaposi’s sarcoma herpes virus (HSV type 8)
Describe HSV-1.
- Most common viral infection of the oral cavity
- Spreads easily through saliva and is shed through symptomatic and asymptomatic periods
- Up to 70% of the population shed the virus once a month asymptomatically
- Infects epithelial cells of the oral mucosa
- Causes primary herpetic gingivostomatitis
- Self-resolves in 10 days
- Some people have severe symptoms: gingival swelling, pyrexia, lymphaenopathy
Describe HSV-1 secondary infection.
- Following resolution of the primary symptoms the virus establishes latency in the trigeminal nerve and local nerve tissue of the oral cavity
- Up to 40% of HSV-1 positive people experience recurrent episodes of seconary infection
- Triggers include UV light, stress, cold and flu, trauma, menstruation
- Causes herpes labialis (coldsores)
- Virus transported back down the nerve axon and reinfects epithelial cells
- Can cause intra-oral ulceration (most commonly affecting the hard palate)
Describe HSV-3.
- Called VZV: varicella zoster virus
- Causes varicella in children (chickenpox)
- Spread through droplets
- Virus becomes latent in ganglia along the sensory nerves
- Reactivation causes shingles in adults
- In adults, the trigeminal nerve is affected in 15% of patients, causes intraoral vesicular eruptions (lesions, usually on hard palate)
- Virus only spreads down 1 nerve branch so symptoms are unilateral
- Antiviral treatment required
- Complication: postherpetic neuralgia
Describe oral hairy leukoplakia.
- White lesions on lateral border of tongue
- EBV particles found in upper keratinocyte layers
- Biopsy required to rule out malignancy or pre-malignancy
Describe HHV-8.
- HHV-8: Kaposi’s sarcoma herpesvirus
- Kaposi’s sarcoma is a neoplasm of endothelial cells
- Seen in immunocompromised patients
- Dark plaques or nodules as a consequence of vascular proliferations
- Biopsy
- Most commonly affects the palate, gingivae and tongue
Describe infective warts.
- Usually develop as a consequence of transmission of infection involving HPV-2 or HPV-4 from warts on the hands
- Intraoral verruca vulgaris
- Some oral warts may be caused by HPV-6, -11 or -16 (due to orogenital contact)
- HIV infection has been associated with a predisposition for developing multiple oral warts
What disease is show in this image?
Heck’s disease
- Cause by HPV-13 and -32
- Discrete or clusters of smooth pink papules on the tongue, buccal or labial mucosa, or gingivae
- Benign and asymptomatic
- No treatment indicated but may be biopsied for cosmetic reasons
Describe hand, foot and mouth disease.
- A group A coxsackie virus
- Transmitted via the faecal-oral route or by nasopharnygeal secretions
- Highly infectious
- Lesions on hands, feet and mucosa of the pharynx, soft palate, buccal mucosa and tongue
- Resolves within 7-10 days
- Can use mouthwash and analgesics to manage symptoms
- Important to differentiate from primary herpes or VSV infection: mild symptoms, distribution of lesions, association with an outbreak
Describe herpangina.
- A group A coxsackie virus
- Transmitted via respiratory droplets
- Predominantly seen in children
- Sore throat, dysphagia, small yellow/grey lesions on the soft palate and tonsils
- Resolves within 7-10 days
- Can use antiseptic mouthwash, adequate fluid intake recommended
Describe measles.
- A paramyxovirus
- Highly infectious
- Rash accompanied by transient small discrete macules on buccal mucosa called Koplik spots
- In malnourished individuals it is implicated in the gross destruction of the orofacial tissues called Noma
Describe mumps.
- A paramyxovirus
- Painful inflammation and swelling of major salivary glands
- Important to differentiate from infection of salivary glands, diagnosed by absence of pus material
