viruses in periodontics
TRANSCRIPT
VIRUSES IN PERIODONTAL INFECTIONS
CONTENTS• Introduction• Virus classification • Viral components and structure• Replication of viruses • Host response to viral infections• Human immunodeficiency virus• Structure • Pathogenesis • Periodontal conditions• Herpes Viruses in periodontal disease• Structure • Herpesviral–bacterial model of periodontitis• Evidence for the viral etiology• Challenges for the viral hypothesis • Summary • References
INTRODUCTION • Virus -
is an infective agent that typically consists of a nucleic acid
molecule in a protein coat, is too small to be seen by light microscopy,
and is able to multiply only within the living cells of a host.
• Smallest living unit
• Viruses – first described – filterable agents
• “Living chemicals” – crystallised like chemicals- Stanley 1935
extraction of “infectious nucleic acid” - Geirer & Schramm 1956
• Organisms at the edge of life
• The etiopathogenesis of periodontal disease is a complex process• Bacterial etiology alone has not been able to substantiate…
• Recently, various HHVs have emerged as putative pathogens in destructive periodontal disease
Slots et al. 2006• HHV-bacterial pathogen model
Slots et al 2007
1. Rapid periodontal tissue breakdown with minimal plaque 2. Phase of disease activity & quiescence 3. Site specificity in periodontal disease 4. Progression to advanced periodontal destruction in a
fraction of given population
EVOLUTION OF VIRUSES
BACTERIA VIRUSIntercellular organisms Intracellular organisn
Size Larger (1000nm) Smaller (20 - 400nm)
Living attributes
Living organismOpinions differ on whether viruses
are a form of life or organic structures that interact with living
organisms.
Structures
DNA and RNA floating freely in cytoplasm. Has cell wall
and cell membrane.
DNA or RNA enclosed inside a coat of protein.
Ribosomes Present Absent
Reproduction Fission- a form of asexual reproduction
Invades a host cell and takes over the cell causing it to make copies of the viral DNA/RNA. Destroys the
host cell releasing new viruses.
Treatment AntibioticsVaccines prevent the spread and
antiviral medications help to slow reproduction but can not stop it
completely.
VIRAL NOMENCLATURE
• Picornavirus - pico + rna
• Papovavirus - papilloma , polyoma , vacuolating viruses
• Retrovirus - reverse – virus directed synthesis of DNA from
RNA template
• Poxviruses - symptoms caused by one of its members , smallpox
BALTIMORE CLASSIFICATION (1971)
Enveloped
Herpesvirusespoxvirus
Nonenveloped
AdenovirusPapillomavirus
Nonenveloped
parvovirus
Enveloped
Retrovirus HIV
Enveloped
Hepandavirus
Enveloped
Togavirus
Nonenveloped
Picornavirus
Nonenveloped
Reovirus Enveloped
Orthomyxovirus, paramyxovirus
VIRAL COMPONENTS AND STRUCTURE
• Virion –is a complete virus particle consisting of RNA or DNA surrounded by a protein shell, constituting the infective form of virus
i. Genome - either DNA or RNA but not bothii. Capsid iii. Envelope iv. Peplomers v. Enzymes
CAPSID
• Shell made of protein building blocks or promoters
• Self assemble into larger capsomere – then into virion capsid
• Simplest structures - symmetrical
i. Helical – form rods
ii. Icosahedral – approximation of a sphere
ENVELOPE
• Similar to cellular membranes
• Consists of lipids , proteins and glycoproteins
• Glycoproteins – extend from surface , act as virus attachment
proteins (VAP) , are major antigens for protective immunity
VIRUS REPLICATION
VIRUS REPLICATION
HOST RESPONSE
I] ANTIBODY MEDIATED ANTIVIRAL IMMUNITY
a) Viral Antibodies :
• IgG – block adsorption and penetration into host cells
• Enhance ingestion by PMN’s and macrophages
• Agglutinate the virus – reduce viral load
• Ag – Ab complex - increase size to trigger phagocytosis
b) Antibodies with activation of complement system• Generation of C3 –viral Ab complex allows binding of C3
receptor – phagocytosis
• Ab and Complement – lysis of virus with envelope – damage lipid membrane
- Lysis of infected cells• Complement alone – activate alternate pathway – lysis or
increased phagocytosis of coated material
c) Ig bound to virus infected cell interacts with Fc receptor bearing lymphocytes (K cells) – cell lysis
II] CELL MEDIATED ANTIVIRAL IMMUNITY
III] NON SPECIFIC FACTORS1. Fever2. Interferon Production3. Natural Killer Cell Activity
ACUTE INFECTIONS
• Events that contribute to cytopathic changes & cell death1) Inhibition of host cell DNA , RNA and protein synthesis2) Virion proteins3) Activation of lysosomal enzymes4) Inhibition of Na K pump
PERSISTENT INFECTIONS
INTERFERON
• Innate mechanism
• Group of peptides – bind to receptors of neighbouring cells -
resistant to infection - limiting focus of infection
• Regulate cell differentiation and immune reactivity
• IFN α – T lymphocytes
• IFN β – virus stimulated fibroblasts
• IFN γ- most potent , Ag activated T cells
IFN
Degrade viral RNA
Cytotoxic T cell
activity
Expression of
adhesion proteins
Production of
cytotoxic factorsMitogenes
is of B cells
APC function
Effects on macropha
ge
NK cell activity
1. synthesis of lysosomal enzymes
2. Expression of receptors for Fc
portion of Ig
3. Decreased migration of
macrophages – expression of MIF
4. Production of IL 1 , TNF alpha
– augment lymphocyte activation
5.Contribute to T cell response -
enhance APC function of
activated macrophagess
HUMAN IMMUNODEFICIENCY VIRUS
• Retrovirus
• HIV 1
• HIV 2
• 1981 – first indication of AIDS in NY and LA
• 1983 – Luc Montagnier et al isolated retovirus and called it
LAV – lymphadenopathy associated virus
• 1984 – Robert Gallo – HTLV III – Human T cell lymphotropic
virus III
• 1986 – International committee of Virus Nomenclature - HIV
STRUCTURE
VIRAL GENES AND ANTIGENS
PATHOGENESIS
• Receptor for the virus is CD4• Primary CD4+ - T lymphocytes (helper/inducer)
5-10% of B lymphocytes 10-20% of monocytes and macrophages• Specific binding to CD4 receptor - envelope glycoprotein gp120.• Cell fusion - transmembrane gp41.• CXCR4 for T cell tropic HIV ,
CCR5 for macrophages –coreceptors
VIRUS ATTACHMENT AND PENETRATION
PATHOGENIC MECHANISM This damage is caused to CD4+ T cells. T4 cells and T4:T8 ratio is reversed.suppress function of infected cells without causing structural damage.T4 cells do not release IL2, IFN, and other lymphokines
•Helper T cell activity is essential for optimal B cell function•Hypergammaglobulinemia is more a hindrance than help because of ‘USELESS Ig’ to irrelevant Ags and also autoantibodies.
• Affected due to lack of secretion of activating factors by T4 lymphocytes.•So chemotaxis, antigen presentation and intracellular killing is diminshed.•Activity of NK cells and cytotoxic T cells is affected
MONOCYTE –MACROPHAGE FUNCTION
HUMORAL MECHANISM
LINEAR GINGIVAL ERYTHEMA
• A persistent , linear , easily bleeding, erythematous gingivitis
• Possible etiology – candida dubliniensis
• Prevalence in HIV patients – 0-49%
NECROTISING ULCERATIVE GINGIVITIS
PERIODONTITIS , STOMATITIS• NUG – destruction of 1 or more interdental papilla ,
confined to marginal gingiva
• NUP- involves PDL and alveolar bone. Bone is exposed
– necrosis – sequestration
• NUS – extends past MGJ into mucosa and osseous
tissues
• Higher prevalence in HIV patients
• NUP – marker of immune deterioration with 95%
predictive value
• Prevalence of Chronic periodontitis –
5-69%
HIV latently infecteted cells
Activation of membrane receptors by pathogens and cytokines
Turns on down stream signaling pathways
Activation of transcription factors like NF-kB
Activation of proinflammatory genes
Production of proinflammatory cytokine
HIV LTR transactivation
Co infection
PROPOSED MODEL OF HIV REACTIVATION DURING CO-INFECTION
HERPES VIRUSES
• Membership in the family herpesviridae is based on four layered structure of virion.
CLASSIFICATION
αHSV1HSV2VZV
βHCMVHHV6HHV7
γEBV HHV8
VIRUS REPLICATION
Capsid Nonstructural proteinsDNA
Attachment andpenetration by fusion
Nucleus DNAgenome
mRNA
DNA
ProteinImmediate earlyProtein synthesis
LATENT
EarlyProtein synthesisand genome replication
ACTIVE
LateProtein synthesis(structural protein)
Exocytosis and release
Assembly and release
Lysis and release
MECHANISMS OF PERIODONTOPATHIC POTENTIAL OF HERPES VIRUSES
1. Direct cytopathic effects
2. Impair cells involved in host defense
3. Promote subgingival attachment and colonization
4. Altered Inflammatory mediator
5. Reducing the cell surface expression of MHC class I
molecules
HERPES SIMPLEX VIRUSES
• HSV1,2 - usually affect skin and mucosa
• HSV1- shed principally in saliva- Orofacial Infections
• HSV2- transmitted sexually- genital infection
• Primary infection - childhood.
• At sites of epithelial infection - viral Ags induce cell
mediated immunity which is the key of recovery and
latency.
Replication in epithelial cells
Viral nucleocapsids ascend local sensory neurons by reterograde
axonal transport
Establish lifelong latency in corresponding spinal or cerebral
ganglion
Reactivation occurs at any time
Virus replication in infected neurons
Virus transproted down the axon to original position
• Primary herpetic gingival disease of viral origin is one of the most common infection(Kuzushima 1991)
• Asymptomatic in childhood.• Clinical features- gingivitis, vesicles that leave ulcerations,
lymphadenopathy and fever.• Healing - 10-14 days.• Recurrence - mucocutaneous junction of lips,palate or gingiva
(recurrent herpetic gingivostomatitis).
VARICELLA ZOSTER VIRUS
• Varicella (chickenpox) - childhood
• Herpes zoster- aged and immunocompromised
• Enters by inhalation - replicates in mucosa of respiratory tract.
• Dissemination - bloodstream and lymphactics.
• Virus multiplies in mononuclear leukocytes and capillary
endothelial cells.
VARICELLA
• Occurs during first 5-10 years of life.• Vesicles and ulcers first appear in mouth on palate, tongue,
gingiva followed by cutaneous rash that spreads centrifugally from head and trunk.
• Oral lesions-painful• Cutaneous lesions-painless but itchy and lead to secondary
infection and permanent scars
HERPES ZOSTER
• Herpes zoster- from reactivation of virus that remain latent in sensory ganglia.
• Lesions similar to varicella but remain confined to single dermatome and are unilateral.
• Intraorally lesions found if 2nd and 3rd branch of trigeminal nerve is involved, which may lead to alveolar bone necrosis.
EPSTEIN BARR VIRUS
• Transmitted by oral secretions or blood.• Virus replicates in epithelial cells or B cells of oropharynx.• All seropositive patients-actively shed virus in saliva.• Resting memory B cells –main site of persistence of EBV.• EBV infection - in children is subclinical,
in adults-infectious mononucleosis.• Symtoms of infectious mononucleosis- fever,
lymphadenopathy, pharyngitis, oral ulcers, palatal petechiae, less commonly gingival ulcerations
Oral hairy leukoplakia• Main lesion of EBV .• Non malignant hyperpalstic lesion of epithelial cells which shows
noncytolytic EBV replication.• OHL-appears as white corrugated lesion on ventral –lateral aspect of
tongue and may be unilateral/bilateral.
HUMAN CYTOMEGALOVIRUS
• Most common cause of congenital and perinatal infections.
• Infants infected through placenta, during delivery or breast
feeding.
• Infects epithelial cells, endothelial cells, smooth muscle cells,
mesenchymal, hepatocytes, granulocytes, macrophages.
• Found in saliva, urine, semen, breast milk.
• In HIV infected patient-oral ulcers as well as gingival
hyperplasia is noted.
HERPESVIRAL–BACTERIAL MODEL OF PERIODONTITIS
Healthy gingiva
Bacterial biolfilm
Gingivitis
Herpes viruses activation
Periodontopathic properties
1. Inflammation2. Collagen degradation
3. Bone resorption
Sufficient time span
Destructive periodontal disease
•Macrophages with latent HSV & HCMV•B cells with latent EBV•T cells with latent HSV & CMV
1. Immunosuppression from infection or cytotoxic therapy2. Inflammation3. Psychosocial or nutritional stress4. Hormonal changes/pregnancy5. Physical or chemical tissue injury6. Tobacco usage7. Aging8. Others
Cytokines or Enzymes
1. IL-1β2. TNF-α3. PGE24. MMPs
Immunosuppression & upgrowth of pathogenic
bacteria
1.P .gingivalis 2. T. forsythia3.A. actinomycetemcomitans 4. D. pneumosintes
Cytotoxicity/Tissue necrosis with severe
immunosuppression
1. HIV-infection2. Nutritionally stressed children/adolescents
HERPESVIRUS : AN ETIOLOGIC FACTOR FOR PERIODONTAL DISEASE?
1. Virus detection in gingival tissue• Cultured epithelial cells and fibroblasts – healthy gingiva – susceptible
to HSV infection – may act as reservoir of latent virusZakay 1982
• Indirect immunofluroscence assay – HSV 1 Ag detected in PD diseased patient’s gingival biopsiesEhrlich et al 1983
• HSV Ag – healthy gingiva Amit et al 1992
• HSV DNA in intact gingival cells – virus present in latent state• In periodontitis patient by using nested PCR –i. Monocytes and macrophages - HCMV , HSVii. T cells – HCMV , HSViii. B cells - EBV
2) Higher frequency of virus detection in the gingival tissue of periodontitis sites than in healthy sites
•In 20 patients with periodontitis HCMV DNA – 13 biopsies, EBV DNA – 10 biopsies HSV DNA-7 biopsies Healthy gingiva – HSV in1/3
Contreras et al , 1999
• Herpes viral DNA in gingival tissues could be detected in periodontally healthy or diseased subjects by nested PCR.
3. Higher frequency of herpes virus detection in GCF from periodontaly diseased sites than from gingivitis/healthy sites
• Parra and Slots (1996)– 78% of advanced periodontitis patients were positive for at least
1/5– HCMV (60%) >EBV (30%)> HSV (20%) HPV (17%) and HIV
(7%).– Only 31% of the gingivitis patients were virus positive
• 89% of the patients yielded at least 1/5 (HCMV) deep pockets, whereas only 56% yielded viral DNA from shallow periodontal sites
4. Higher frequency of virus detection in subgingival plaque from periodontaly diseased than from healthy sites
• Saygun et al 2002...
• Frequency of detection lower compared to previous studies
VIRUS CHRONIC PERIODONTITIS
HEALTHY
HCMV DNA 44 %
14.3%
EBV DNA 17 % 14.3%
HSV DNA 6.7% -
5. Detection of activated herpes virus in the GCF of periodontal lesions
Contreras & Slots 1998 –• Reverse transcriptase-PCR to examine mRNA transcription of
subgingival HCMV.• HCMV major capsid proteins - in deep periodontal pockets but
not in any shallow pocket• Active HCMV replication could occur in periodontal sites
Croen et al 1991• Several risk factors for periodontal disease – have potential to
reactivate Herpesvirus
6. Interaction of herpesviruses with periodontal pathogens
• The subgingival detection of EBV, HCMV could be associated with an increased presence of periodontal pathogens(A.a ,P g)
Contreras et al 1991• LJP – Aa associated with active HCMV infection • HCMV , EBV , HSV along with Pg , D pneumosintes – active
periodontitis• And immunosuppressive properties of herpesvirus –
overgrowth of subgingival periodontal bacteria
• Their can be a bidirectional interaction between herpesviruses and bacteria
• Bacterial enzymes or other inflammation-inducing factors have the potential to activate periodontal herpesviruses
• In addition ,P. gingivalis suppress the interferon-gamma antiviral host response
• Herpesvirus infection predisposes periodontal tissue to the bacterial superinfection
CHALLENGES FOR THE VIRAL HYPOTHESIS
1. Investigators
• Most clinical association studies have been carried out by the same group of investigators
• Samples were analysed in the same laboratory
• Confirmation by other independent researchers is lacking
2. Method
• The nested PCR works with two primer pairs and two different
amplification tests, one after the other
• Display higher specificity& sensitivity
• It is very susceptible to contamination, and can produce false
positive results
3. Sample population
• A higher frequency of co-infection and occurrence of EBV and
HHV-6 has been noted in HIV-positive
Contreras et al, 2001• HIV status was not investigated
• The doubt remains whether the subjects included were true
representative
4. Inferences of causality• One difficulty directly relates to the sampling procedure in
diseased sites• Samples from diseased sites are more likely to contain viruses
present in blood.
• Active HCMV replication has been demonstrated in periodontal sites
• The reactivation - periodontal disease activity, -just the opposite may be the case:
-periodontal disease activity caused by bacterial infection - trigger virus reactivation.
SUMMARY
• Contemporary Oral Microbiology and Immunology- Slots,
Taubman.
• Textbook of Microbiology 7th Edition Ananthnarayan and Paniker
• Pushpa S P, Soumya B G .Herpesviruses in Human Periodontal
disease.Reality or Myth…? J. Int Oral Health 2010,2(2)59-64• Jorgen slots Herpes viruses in periodontal Disease Perio 2000, Vol.
38, 2005, 33–62• I Cappuyns, P Gugerli, A Mombelli . Viruses in periodontal disease
– a review Oral Diseases 2005, 11, 219–229• Jorgen slots. Human viruses in periodontitis Perio 2000, Vol. 53,
2010, 89–110• Uppoor and Nayak HIV and Periodontal Disease: Redemption or Resurrection, J AIDS Clinic Res 2012,