Transcript Document

Chapter 13
Characterizing
and Classifying
Viruses,
Viroids, and
Prions
Characteristics of Viruses
• Virus
– Minuscule, acellular infectious agent having
either DNA or RNA
– Causes many infections of humans, animals,
plants, and bacteria
– Causes most of the diseases that plague the
industrialized world
10/15/11
.
MDufilho
2
Characteristics of Viruses
• Cannot carry out any metabolic pathway
• Neither grow nor respond to the
environment
• Cannot reproduce independently
• Recruit the cell’s metabolic pathways to
increase their numbers
• No cytoplasmic membrane, cytosol,
organelles (with one exception)
• Have extracellular and intracellular state
10/15/11
MDufilho
3
Characteristics of Viruses
• Extracellular State
– Called virion
– Protein coat (capsid) surrounding nucleic acid
– Nucleic acid and capsid also called
nucleocapsid
– Some have phospholipid envelope
– Outermost layer provides protection and
recognition sites for host cells
• Intracellular State
– Capsid removed
– Virus exists as nucleic acid
10/15/11
MDufilho
4
Figure 13.1 Virions-overview
10/15/11
MDufilho
5
Characteristics of Viruses
• Genetic Material of Viruses
– Show more variety in nature of their genomes
than do cells
– Primary way scientists categorize and classify
viruses
– May be DNA or RNA, but never both
– dsDNA, ssDNA, dsRNA, ssRNA
– Linear and segmented or single and circular
– Much smaller than genomes of cells
10/15/11
MDufilho
6
Figure 13.2 The relative sizes of genomes
Partial genome
of E. coli
10/15/11
Viral
genome
MDufilho
7
Characteristics of Viruses
• Hosts of Viruses
– Most viruses infect only particular host’s cells
– Affinity of viral surface proteins for proteins on
host cell
– May be so specific they infect only particular
kind of cell in a particular host
– Generalists – infect many kinds of cells in
many different hosts
10/15/11
MDufilho
8
Figure 13.3 Hosts of viral infections-overview
10/15/11
MDufilho
9
Figure 13.4 Sizes of selected virions
E. coli (bacterium)
(1000 nm  3000 nm)
Red blood cell
(10,000 nm in diameter)
Bacterial
ribosomes
(25 nm)
Poliovirus
(30 nm)
Bacteriophage T4
(50 nm  225 nm)
Bacteriophage MS2
(24 nm)
10/15/11
Smallpox virus
(200 nm  300 nm)
MDufilho
Tobacco mosaic virus
(15 nm  300 nm)
10
Characteristics of Viruses
• Capsid Morphology
– Capsids
– Provide protection for viral nucleic acid
– Means of attachment to host’s cells
– Composed of proteinaceous subunits called
capsomeres
– Capsomere made of single or multiple types of
proteins
– Three basic shapes - helical,polyhedral,complex
10/15/11
MDufilho
11
Figure 13.5 The shapes of virions-overview
10/15/11
MDufilho
12
Figure 13.6 Bacteriophage T4-overview
10/15/11
MDufilho
13
Characteristics of Viruses
• The Viral Envelope
– Acquired from host cell during viral replication or
release
– Envelope is portion of membrane system of host
– Composed of phospholipid bilayer and proteins
– Some proteins are virally coded glycoproteins
(spikes)
– Envelope’s proteins and glycoproteins often
play role in host recognition
10/15/11
MDufilho
14
Figure 13.7 Enveloped virion-overview
10/15/11
MDufilho
15
Table 13.2 Families of Human Viruses
10/15/11
MDufilho
16
Viral Replication
• Lysogeny
– Modified replication cycle
– Infected host cells grow and reproduce normally
for generations before they lyse
– Temperate phages
– Prophages – inactive phages
– Lysogenic conversion results when phages carry
genes that alter phenotype of a bacterium
10/15/11
MDufilho
17
Viral Replication
• Replication of Animal Viruses
– Same basic replication pathway as
bacteriophages
– Differences result from
– Presence of envelope around some viruses
– Eukaryotic nature of animal cells
– Lack of cell wall in animal cells
10/15/11
MDufilho
18
Viral Replication
• Replication of Animal Viruses
– Attachment of animal viruses
– Chemical attraction
– Animal viruses do not have tails or
tail fibers
– Have glycoprotein spikes or other
attachment molecules that mediate
attachment
– Uncoating
– Direct penetration
– Membrane fusion
10/15/11
MDufilho
19
Viral Replication
• Replication of Animal Viruses
– Synthesis of animal viruses
– Requires different strategy depending on its
nucleic acid
– DNA viruses often enter the nucleus
– RNA viruses often replicate in the cytoplasm
– Must consider
– How mRNA is synthesized
– What serves as template for nucleic acid replication
10/15/11
MDufilho
20
Figure 13.13 Synthesis of proteins and genomes in animal RNA viruses-overview
10/15/11
MDufilho
21
Viral Replication
• Replication of Animal Viruses
– Assembly and release of animal viruses
– Most DNA viruses assemble in nucleus
– Most RNA viruses develop solely in cytoplasm
– Number of viruses produced depends on type of
virus and size and initial health of host cell
– Enveloped viruses cause persistent infections
– Naked viruses are released by exocytosis or lysis
10/15/11
MDufilho
22
Figure 13.14 The process of budding in enveloped viruses
Enveloped
virion
Budding of
enveloped virus
Viral
glycoproteins
Cytoplasmic
membrane
of host
Viral capsid
10/15/11
MDufilho
23
Viral Replication
• Replication of Animal Viruses
– Latency of animal viruses
– When animal viruses remain dormant in host cells
– May be prolonged for years with no viral activity
– Some latent viruses do not become incorporated
into host chromosome
– Incorporation of provirus into host DNA is
permanent
10/15/11
MDufilho
24
The Role of Viruses in Cancer
• Animal’s genes dictate that some cells can
no longer divide or are prevented from
unlimited division
• Genes for cell division “turned off” or genes
inhibiting division “turned on”
• Neoplasia
– Uncontrolled cell division in multicellular animal
– Mass of neoplastic cells is tumor
• Benign vs. malignant tumors
– Metastasis
– Cancers
10/15/11
MDufilho
25
Figure 13.16 The oncogene theory of the induction of cancer in humans
Normal state:
DNA
Protooncogene
Represses
Gene for repressor
mRNA
Repressor
Result: No cancer
First “hit”:
Virus inserts promoter
DNA
Oncogene
Represses
Gene for repressor
mRNA
Repressor
Result: Still no cancer
Second “hit”:
Virus inserts into represssor gene
DNA
Oncogene
mRNA
10/15/11
Protein
No repressor
protein because
gene is segmented
MDufilho
Causes cell division Result: Cancer
26
The Role of Viruses in Cancer
• Environmental factors that contribute to
the activation of oncogenes
–
–
–
–
Ultraviolet light
Radiation
Carcinogens
Viruses
10/15/11
© 2012 Pearson Education Inc.
MDufilho
27
The Role of Viruses in Cancer
• Viruses cause 20–25% of human cancers
– Some carry copies of oncogenes as part of their
genomes
– Some promote oncogenes already present in host
– Some interfere with tumor repression
– Specific viruses are known to cause ~15% of
human cancers
– Burkitt’s lymphoma
– Hodgkin’s disease
– Kaposi’s sarcoma
– Cervical cancer
10/15/11
MDufilho
28
Are Viruses Alive?
• Some consider them complex pathogenic
chemicals
• Others consider them the least complex
living entities
– Use sophisticated methods to invade cells
– Have the ability to take control of their host cell
– Are able to replicate themselves
10/15/11
MDufilho
29
Other Parasitic Particles: Viroids and Prions
• Characteristics of Viroids
– Extremely small, circular pieces of RNA that
are infectious and pathogenic in plants
– Similar to RNA viruses, but lack capsid
– May appear linear due to H bonding
10/15/11
MDufilho
30
Figure 13.20 The RNA strand of the small potato spindle tuber viriod (PSTV)
Genome of bacteriophage T7
10/15/11
PSTV
MDufilho
31
Figure 13.21 One effect of viroids on plants
10/15/11
MDufilho
32
Other Parasitic Particles: Viroids and Prions
• Characteristics of Prions
– Proteinaceous infectious agents
– Cellular PrP protein
– Made by all mammals
– Normal structure with -helices called cellular PrP
– Prion PrP
– Disease-causing form with -pleated sheets called
prion PrP
– Prion PrP changes shape of cellular PrP so it
becomes prion PrP
10/15/11
MDufilho
33
Other Parasitic Particles: Viroids and Prions
ANIMATION Prions: Overview
10/15/11
MDufilho
34
Other Parasitic Particles: Viroids and Prions
• Characteristics of Prions
– Normally, nearby proteins and polysaccharides
force PrP into cellular shape
– PrP mutations result in formation of prion Pr
10/15/11
MDufilho
35
Other Parasitic Particles: Viroids and Prions
ANIMATION Prions: Characteristics
10/15/11
MDufilho
36
Other Parasitic Particles: Viroids and Prions
• Characteristics of Prions
– Prion diseases
– Fatal neurological degeneration, fibril deposits in
brain, and loss of brain matter
– Large vacuoles form in brain
– Characteristic spongy appearance
– Spongiform encephalopathies
– Prions only destroyed by incineration or
autoclaving in 1 N NaOH
10/15/11
MDufilho
37
Other Parasitic Particles: Viroids and Prions
ANIMATION Prions: Disease
10/15/11
MDufilho
38
Viral Diseases of the Skin and Wounds
• Herpes Infections
– Signs and symptoms
– Slow spreading skin lesions
– Recurrence of lesions is common
– Pathogen and virulence factors
– Caused by human herpesviruses 1 and 2
– Produce various proteins that act as virulence factors
– Pathogenesis
– Painful lesions caused by inflammation and cell death
– Cause fusion of cells to form syncytia
10/15/11
MDufilho
39
Figure 19.11 Oral herpes lesions
10/15/11
MDufilho
40
Viral STDs
• Genital Herpes
– Signs and symptoms
– Small blisters on or around the genitals or rectum
– Pathogen and virulence factors
– Human herpesvirus 2 causes most cases
– Virus can become latent in nerve cells
– Pathogenesis
– Herpesvirus kills epithelial cells at infection site
– Blisters may form at sites far from initial infection
site
– Babies can become
infected during birth
10/15/11
MDufilho
41
Figure 24.12 Herpes lesions of the eyes and skin-overview
10/15/11
MDufilho
42
Viral Diseases of the Skin and Wounds
• Herpes Infections
– Epidemiology
– Spread between mucous membranes of mouth and
genitals
– Herpes infections in adults are not life threatening
– Diagnosis, treatment, and prevention
– Diagnosis made by presence of characteristic
lesions
– Immunoassay reveals presence of viral antigens
– Chemotherapeutic drugs help control the disease
but do not cure it
10/15/11
MDufilho
43
Viral Diseases of the Skin and Wounds
• Warts
– Benign epithelial growths on the skin or mucous
membranes
– Can form on many body surfaces
–
–
–
–
–
Various papillomaviruses cause warts
Most warts are harmless
Transmitted via direct contact and fomites
Diagnosed by observation
Various techniques to remove warts
– New warts can develop due to latent viruses
10/15/11
MDufilho
44
Figure 19.13 Various kinds of warts--lesions caused by papillomaviruses-overview
10/15/11
MDufilho
45
Figure 24.13 Genital warts
10/15/11
MDufilho
46
Viral STDs
• Genital Warts
– Signs and symptoms
– Warts on the genitalia and surrounding areas
– Large growths called condylomata acuminata
may form
– Pathogen
– Caused by human papillomaviruses (HPV)
– HPV can cause various cancers
10/15/11
MDufilho
47
Viral STDs
• Genital Warts
– Pathogenesis and epidemiology
– HPVs invade skin or mucous membranes
during sex
– Most common STD in the U.S.
– Diagnosis, treatment, and prevention
– Diagnosis made by presence of warts
– Variety of methods available to remove warts
– Vaccine available against HPV strain associated
with cervical cancer
10/15/11
MDufilho
48
Viral Diseases of the Skin and Wounds
• Chickenpox and Shingles
– Signs and symptoms
– Chickenpox characterized by lesions on the back
and trunk that spread across body
– Shingles lesions localized to skin along an infected
nerve
– Pathogen
– Varicella-zoster virus (VZV) causes both diseases
– Pathogenesis
– Infected dermal cells cause rash characteristic of
chickenpox
– Virus becomes latent in nerve ganglia
– Reactivated VZV causes shingles
10/15/11
MDufilho
49
Viral Diseases of the Skin and Wounds
• Chickenpox and Shingles
– Epidemiology
– Chickenpox occurs mostly in children
– Disease is more severe in adults
– Risk of shingles increases with age
– Diagnosis, treatment, and prevention
– Diagnosis based on characteristic lesions
– Treatment based on relief of symptoms
– Vaccine available against chickenpox
10/15/11
MDufilho
50
Viral Diseases of the Skin and Wounds
• Other Viral Rashes
– Erythema infectiosum
– Caused by an erythrovirus of family Parvoviridae
– Respiratory disease that manifests as a rash
– Also referred to as fifth disease
– Roseola
– Caused by human herpesvirus 6 (HHV-6)
– Characterized by a rose-colored rash
– Coxsackievirus infection
– Caused by coxsackie A viruses
– Produces lesions like those from herpes infections
– Also causes hand-foot-and-mouth disease
10/15/11
© 2012 Pearson Education Inc.
MDufilho
51
Figure 19.16 A case of erythema infectiosum (fifth disease)
10/15/11
MDufilho
52
Viral Diseases of the Nervous System
• Viruses more readily cross the bloodbrain barrier
• Occur more frequently than bacterial and
fungal infections
• Include meningitis, polio, rabies, and
encephalitis
10/15/11
MDufilho
53
Viral Diseases of the Nervous System
• Viral Meningitis
– Signs and symptoms
– Similar to those of bacterial meningitis
– Usually milder than those of bacterial or fungal
meningitis
– Pathogens and virulence factors
– 90% of cases caused by viruses in the genus
Enterovirus
– Pathogenesis
– Damage to cells in the meninges triggers
meningitis
10/15/11
MDufilho
54
Viral Diseases of the Nervous System
• Viral Meningitis
– Epidemiology
– More common than bacterial and fungal
meningitis
– Spread via respiratory droplets and feces
– Diagnosis, treatment, and prevention
– Diagnosed by characteristic signs and
symptoms in the absence of bacteria in the CSF
– No specific treatment exists
10/15/11
MDufilho
55
Viral Diseases of the Nervous System
• Arboviral Encephalitis
– Arboviruses are arthropod-borne viruses
– Transmitted via blood-sucking arthropods
(e.g., mosquitoes)
– Mosquito-borne arboviruses can cause arboviral
encephalitis
– As zoonotic diseases, they rarely affect humans
– Arboviruses usually cause mild, coldlike
symptoms
– Can cause if cross the blood-brain barrier
10/15/11
MDufilho
56
Table 20.2 Characteristics of Arboviral Encephalitis Diseases and Viruses in the United States
10/15/11
MDufilho
57
Figure 20.15 Transmission of six encephalitis arboviruses
Humans
can be infected
via mosquito bites.
Small mammals
are hosts for VEE and
California viruses only.
Mosquitoes
are vectors.
Encephalitis arboviruses
can overwinter inside
mosquito eggs.
Wild birds
Horses,
Domestic fowls
and rarely other
domestic mammals
are hosts for equine viruses.
10/15/11
MDufilho
Birds are hosts for
all six encephalitis
arboviruses.
58
Figure 20.16 Human West Nile virus encephalitis in the United States
Reported cases
Number of reported cases
Annual deaths
(299)
(124)
(264)
(84)
(86)
(43)
(30)
(9)
Time (months/years)
10/15/11
MDufilho
59
Viral Diseases of the Nervous System
• Arboviral Encephalitis
– Diagnosis based on signs and symptoms
– Confirmed by presence of arbovirus-specific
antibodies in CSF
– Treatment is supportive
– Prevention involves limiting contact with mosquitoes
– Use netting and insect repellents
– Eliminate stagnant water
– Vaccines for horses available against EEE, WEE,
VEE, and WNV
10/15/11
MDufilho
60
Viral Cardiovascular and Systemic Diseases
• Infectious Mononucleosis
– Signs and symptoms
– Severe sore throat and fever occur initially
– Followed by swollen lymph nodes, fatigue,
appetite loss
– Pathogen and virulence factors
– Epstein-Barr virus (EBV or HHV-4) is the
causative agent
– EBV establishes latent infection in host
– EBV implicated in number of other diseases
10/15/11
MDufilho
61
Figure 21.13 Diseases associated with Epstein-Barr virus
Diseases
of EBV
Oral hairy leukoplakia*
Burkitt’s lymphoma (shown)
Chronic fatigue syndrome*
Nasopharyngeal cancer
Asymptomatic
Infectious
mononucleosis
Lacking
Poor
Normal
Vigorous
State of
cellular
immunity
*EBV implicated, not proven
10/15/11
MDufilho
62
Viral Cardiovascular and Systemic Diseases
• Infectious Mononucleosis
– Pathogenesis and epidemiology
– Transmission occurs via saliva
– EBV infects B lymphocytes
– Majority of adults have antibodies against EBV
– Diagnosis, treatment, and prevention
– Diagnosed by presence of large, lobed B
lymphocytes and neutropenia
– Treatment focuses on relieving symptoms
– Prevention is difficult since EBV occurrence is
widespread
10/15/11
MDufilho
63
Viral Cardiovascular and Systemic Diseases
• Cytomegalovirus Disease
– Signs and symptoms
– Asymptomatic in most cases
– Complications in neonates and immunodeficient
individuals
– Pathogen and virulence factors
– Caused by Cytomegalovirus
– Pathogenesis and epidemiology
– Transmit by direct contact with body fluids or
transplacentally
– One of the most common infections of humans
– Diagnosis, treatment, and prevention
– Fomivirsen is administered for eye infections
– No vaccine is available
10/15/11
MDufilho
64
Figure 21.14 An abnormally enlarged “owl’s eye” cell indicates Cytomegalovirus (CMV) infection
“Owls eye” cell
10/15/11
MDufilho
65
Viral Cardiovascular and Systemic Diseases
• African Viral Hemorrhagic Fever
– Signs and symptoms
– Fever and fatigue
– Minor petechiae progress to severe internal
hemorrhaging
– Pathogens and virulence factors
– Caused by Ebolavirus or Marburgvirus
– Pathogenesis and epidemiology
– Occurs primarily in Africa
– Transmitted via contact with bodily fluids of
infected individual
10/15/11
MDufilho
66
Figure 21.17 Filamentous Ebolavirus
10/15/11
MDufilho
67
Figure 21.18 Sites in which locally acquired cases of Marburg and Ebola viruses have occurred
Marburg
10/15/11
Ebola
MDufilho
68
Viral Cardiovascular and Systemic Diseases
• African Viral Hemorrhagic Fever
– Diagnosis, treatment, and prevention
– Diagnosis based on characteristic symptoms
and presence of virus in the blood
– Treatment involves fluid and electrolyte
replacement
– Vaccines are being studied for their
effectiveness in humans
10/15/11
MDufilho
69
Viral Diseases of the Upper Respiratory System
• Common Cold
– Signs and symptoms
– Sneezing, runny nose, congestion,
– sore throat, malaise, and cough
– Pathogens and virulence factors
– Enteroviruses (rhinoviruses) are the most
common cause
– Numerous other viruses cause colds
– Pathogenesis
– Cold viruses replicate in and then kill infected
cells
10/15/11
MDufilho
70
Viral Diseases of the Upper Respiratory System
• Common Cold
– Epidemiology
– Rhinoviruses are highly infective
– Spread by coughing/sneezing, fomites, or
person-to-person contact
– Diagnosis, treatment, and prevention
– Signs and symptoms are usually diagnostic
– Pleconaril can reduce duration of symptoms
– Hand antisepsis is important preventive measure
10/15/11
MDufilho
71
Viral Diseases of the Lower Respiratory System
• Influenza
– Signs and symptoms
– Sudden fever, pharyngitis, congestion, cough,
myalgia
– Pathogens and virulence factors
– Influenza virus types A and B are the causative
agents
– Mutations in hemagglutinin and neuraminidase
produce new strains
– Occurs via antigenic drift and antigenic shift
10/15/11
MDufilho
72
Figure 22.12 Influenzavirus budding from a cell
Neuraminidase
Hemagglutinin
Envelope
ssRNA
molecule
in helical
capsid
10/15/11
MDufilho
73
Viral Diseases of the Lower Respiratory System
• Influenza
– Mutations in hemagglutinin and neuraminidase
produce new strains
– Occurs via antigenic drift and antigenic shift
– Named by type (A or B), location and date or
original identification
– Example – A/Singapore/1/80 (H1N2)
– If isolated from an animal, that is included
– Hong Kong flu or swine flu
– Asia is major site of antigentic shift
10/15/11
MDufilho
74
Figure 22.13 The development of new strains of flu viruses-overview
10/15/11
MDufilho
75
Figure 22.11 A scene from the flu pandemic of 1918-19
10/15/11
MDufilho
76
Viral Diseases of the Lower Respiratory System
• Influenza
– Pathogenesis
– Symptoms produced by the immune response to
the virus
– Flu patients are susceptible to secondary bacterial
infections
– Virus causes damage to the lung epithelium
– Epidemiology
– Transmitted via inhalation of viruses or by selfinoculation
– Complications occur most often in the elderly,
10/15/11
MDufilho with chronic diseases
children, and individuals
77
Viral Diseases of the Lower Respiratory System
• Influenza
– Diagnosis, treatment, and prevention
– Signs and symptoms during a community-wide
outbreak are often diagnostic
– Treatment involves supportive care to relieve
symptoms
– Oseltamivir and zanamivir can be administered
early in infection
– Prevent by immunization with a multivalent
vaccine
10/15/11
MDufilho
78
Viral Diseases of the Lower Respiratory System
• Severe Acute Respiratory Syndrome (SARS)
– Signs and symptoms
– High fever, shortness of breath, and difficulty
breathing
– Later develop dry cough and pneumonia
– Pathogen and virulence factors
– Caused by a coronavirus called SARS virus
– Pathogenesis and epidemiology
– SARS virus spreads via respiratory droplets
– Diagnosis, treatment, and prevention
– Diagnosis based on signs and symptoms of SARS
10/15/11 – Treatment is supportive
MDufilho
79
Figure 22.14 The face of SARS
10/15/11
MDufilho
80
Viral Diseases of the Lower Respiratory System
• Respiratory Syncytial Virus Infection
– Most common childhood respiratory disease
– Signs and symptoms
– Fever, runny nose, and coughing in babies or
immunocompromised individuals
– Mild coldlike symptoms in older children and adults
– Pathogen
– Respiratory syncytial virus (RSV)
– Pathogenesis
– Virus causes syncytia to form in the lungs
to RSV further damages the lungs
10/15/11 – Immune response MDufilho
81
Figure 22.15 A syncytium forms when RSV triggers infected cells to fuse with uninfected cells
Multinucleated
syncytium
Newly
infected cell
Nucleus
RSV
Infected
host cell
Uninfected
cell
Newly
infected cell
Infected
host cell
RSV
Multinucleated
syncytium
10/15/11
MDufilho
82
Viral Diseases of the Lower Respiratory System
• Respiratory Syncytial Virus Infection
– Epidemiology
– Transmission occurs via close contact with
infected persons
– Diagnosis, treatment, and prevention
– Diagnosis made by immunoassay
– Supportive treatment for young children
– Prevention includes aseptic technique of health
care and day care employees
10/15/11
MDufilho
83
Viral Diseases of the Digestive System
• Viral Gastroenteritis
– Signs and symptoms
– Similar to bacterial gastroenteritis
– Pathogens and pathogenesis
– Caused by caliciviruses, astroviruses, and rotaviruses
– Epidemiology
– More cases occur in winter
– Diagnosis, treatment, and prevention
– Serological test distinguishes among viruses
– Treatment is based on fluid and electrolyte
replacement
exists
10/15/11 – Vaccine for rotavirus
MDufilho
84
Figure 23.13 Some viruses causing gastroenteritis-overview
10/15/11
MDufilho
85
Figure 23.14 Deaths from rotaviral diarrhea are most common in developing countries
 1000 deaths
10/15/11
MDufilho
86
Viral Diseases of the Digestive System
• Viral Hepatitis
– Signs and symptoms
– Jaundice, abdominal pain, fatigue, vomiting,
appetite loss
– Symptoms may occur years after initial infection
– Host immune response causes much of the liver
damage
– Pathogen and pathogenesis
– Hepatitis A virus (HAV)
– Hepatitis B virus (HBV)
– Hepatitis C virus (HCV)
– Hepatitis delta virus (HDV)
– Hepatitis E virus (HEV)
10/15/11
MDufilho
87
Table 23.2 Comparison of Hepatitis Viruses
10/15/11
MDufilho
88
Viral Diseases of the Digestive System
• Viral Hepatitis
– Diagnosis, treatment, and prevention
– Initial diagnosis made by observation of jaundice,
enlarged liver, or fluid in the abdomen
– Serological testing can identify viral antigens
– HBV diagnosed by presence of viral proteins in
body fluids
– Supportive care for symptoms
– Prevent with good hygiene and protected sex or
abstinence
– Vaccines are available against HAV and HBV
10/15/11
MDufilho
89
Figure 23.15 The three types of viral particles produced by hepatitis B viruses-overview
10/15/11
MDufilho
90