7.1 Viral and orofacial infection Flashcards
1
Q
Describe the general properties of a virus.
A
- 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
2
Q
What are the 2 types of viral infection?
A
- Acute
- Chronic
3
Q
What is meant by the term acute viral infection?
A
- 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
4
Q
What is meant by the term chronic/persistent viral infection?
A
- 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
5
Q
Describe the structure of a virus particle (virion).
A
- 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.
6
Q
What are the ways in which a virus can be classified?
A
- 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
7
Q
What system is used to classify viruses based on genome structure?
A
Baltimore classification (I to VII)
8
Q
What does viral tissue tropism mean?
A
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.
9
Q
What are the 2 ways that a virus can enter a cell?
A
- Receptor-mediated endocytosis
- Membrane fusion
10
Q
What cells can HIV infect?
A
CD4+ cells
- T helper cells
- Macrophages
- Dendritic cells
10
Q
Name 5 methods used for diagnosis/confirmation of viral disease.
A
- Electron microscopy
- Cell culture
- Serology (blood sample)
- Fluorescent microscopy
- Quantitative/real time PCR
11
Q
Describe the use of electron microscopy in viral detection.
A
- Only method that can be used to view the virion
- High resolving power
- Not routinely used for diagnostics in practice
12
Q
Describe the use of serology in viral detection.
A
- 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
13
Q
Describe the use of viral cultures in viral detection.
A
- 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
14
Q
Describe the use of a quantitative/real time PCR in viral detection.
A
- 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
15
Q
What are the routes of viral infection?
A
- 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)
16
Q
What viruses are part of the Herpesviridae family?
A
- 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)
17
Q
Describe the herpesviridae family virus types.
A
- Herpes virus
- Chronic, recurrent nature
- Double stranded linear DNA
- Icosahedral capsid
- Nucleocapsid covered in a protein layer called Tegument
- Lipid envelope with viral glycoproteins
18
Q
Describe the HSV lytic cycle.
A
HSV replication cycle:
- Virus binds to receptors on epithelial cells
- Triggers cells to internalise virus via membrane fusion
- Nucleocapsid delivers DNA genome to nucleus
- Virus released via exocytosis or direct cell-cell transfer- or through cell lysis which causes blistering of the host tissue
19
Q
The 8 human herpesviruses are divided into what 3 categories?
A
- Alpha (1,2,3)
- Beta (5,6)
- Gamma (4,7,8)
20
Q
Describe HSV-1 and -2 infection.
A
- Virus present in saliva and lesions
- Can cause eye infection, oral or genital lesions, skin infection
- Latency in dorsal root ganglion
- Recurrent cold sores or keratoconjunctivitis
21
Q
Describe HSV-1.
A
- 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
22
Q
How is HSV-1 managed?
A
- Limit contact with lips/mouth to reduce risk of spreading to other body site
- Chlorhexidine mouthwash
- Analgesics
- Soft diet and rest
- For severe cases Aciclovir is recommended (200mg 5 times a day)
23
Q
Describe HSV-1 secondary infection.
A
- 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)
24
How are cold sores managed?
Topical antivirals:
- Aciclovir
- Valacyclovir
- Penciclovir
25
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
26
Describe HSV-4.
- Epstein-Barr virus
- Spread through droplets
- 70% of people aged 30 have established latent infection
- Effects B-lymphocytes
- Can cause infectious mononucleosis
- Can lead to Burkitt's lymphoma or nasopharyngeal carcinoma
- Also implicated in aetiology of oral hairy leukoplakia
- EBV is associated with HIV positive patients
27
Describe infectious mononucleosis.
- Glandular fever
- Headache, fever, lymph node enlargement, signs of tonsilitis
- 30% of pts develop leasions on the palate
- Some experience gingival bleeding and ulceration
- White pseudomembrane develops on tonsils
28
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
29
Describe HSV-5.
- Cytomegalovirus (CMV)
- By the age of 80, 90% of population are infected
- Rarely associated with oral disease
- Can present similarly to oral symptoms of infectious mononucleosis (IM)
- Significant if present in immunocompromised patients and pregnant women, can cause deafness and learning disabilities in foetus
30
Describe HSV-6 and HSV-7.
- HSV 6 causes common childhood disease called Roseola Infantum
- Infectious mononucleosis like illness
- Shed in the saliva of most adults
- Establishes latency in lymphoid tissue
31
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
32
Describe human papilloma virus (HPV).
- Small, icosahedral, non-enveloped
- ds DNA virions
- More than 170 serological types of HPV have been described
- Virus infects epithelial cells
- Causes hyperplasia of epithelium (benign proliferation) or carcinoma
33
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
34
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
35
How does HPV cause oropharnygeal carcinoma?
- HPV causes 5% of all cancers
- HPV 16 and 18 implicated in oropharyngeal cancer
- Some HPV types are known to possess oncogenes that cause cancer, including the E6 and E7 proteins
- E6 protein inhibits action of p53, the "guardian of the genome"
- E7 protein inhibits action of retinoblastoma protein (involved in cell cycle control)
36
Describe coxsackie virus.
Group of enterioviruses
- Small
- ssRNA
- Non-enveloped
- Composed of 60 subunits
- Subdivided into group A and B
37
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
38
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
39
Describe paramyxoviruses.
- Negative sense ssRNA viruses
- Enveloped
40
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
41
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
42
Name the common antivirals.
- Main antiviral is aciclovir
- Others include valaciclovir and famciclovir
- All have the same modes of action
Resistance is rare
43
Describe the mode of action of aciclovir.
- Prevents viral replication in host cells, does not eradicate the virus from tissues
- In a virally infected cell it is converted to aciclovir monophosphate and then to aciclovir triphosphate
- During viral DNA replication, aciclovir is added to the growing strand rather than GTP- this halts further elongation of the DNA and stops viral replication
- Drug is only selective to viral infected cells
