Download Slide 1 - UAB School of Optometry

Microbiology
10/17/2008
Human Herpesviruses: Dr. Jackie Parker
Transcriber: Kimberly Watkins
56:03
Slide 1: Herpes viruses: Important to understand because of the relevance to ocular and oral diseases.
Slide 2: The main objectives are to give you a broad overview of the herpes viruses, the families, how
the viruses replicate and establish latency. From a test standpoint, it is really important to understand
the clinical manifestations associated with each of these viruses, what antiviral therapies are available,
the mechanism of how the drugs work and how these viruses affect the immunocompromised host.
Slide 3: Herpes are probably the oldest known viruses. The name is derived from the Greek word
“herpein” which means “to creep.” Hippocrates and other Greek scholars used it to describe spreading
cutaneous lesions.
Slide 4: There are 3 subfamilies of the herpes viruses: alpha, beta and gamma. The viral particles are
~290nm in size. This is an electron micrograph of a typical HSV-1. Its genome is a liner dsDNA and can
range from 120 kb (VZV)-230kb (CMV). Both the genome replication and the virus assembly occur in the
nucleus
Slide 5: It is an enveloped virus and the envelope contains the multiple viral glycoproteins that mediate
virus attachment and entry. It is a receptor mediated cellular entry. The tegument area inside the virus is
very important; it brings with it viral proteins that are necessary to initiate early gene expression once it
gets into the nucleus. Other important features include an icosahedral capsid that encloses the viral
DNA and it has dsDNA.
Slide 6: The 3 subfamilies are classified by the reproductive cycle, how fast it occurs, and the target cell
type.
 Alpha: Includes HSV-1, HSV-2 and VZV. They have a variable host range, very short reproductive
cycle and they can establish latent infections, which occur primarily in sensory ganglions. HSV-1
usually establishes latency in the trigeminal ganglion. You can also have it in dorsal root
ganglion.
 Beta: Includes CMV and HHV-6. They have a very restricted host range; very slow infection in
culture (hard to grow) and the latent virus is maintained in secretory glands, lymphoreticular
cells, kidneys, and other tissues.
 Gamma: Includes EBV. These viruses replicate in lymphoblastoid cells (like B cells) and they can
have lytic or latent infection but it is hard to detect infectious progeny.
Slide 7: This is a cartoon to show schematically the genome organization of these different family
members. Herpes simplex viruses are the best studied viruses. These are very large DNA viruses (points
out the size scale (kb) at the bottom).
Slide 8: Here is a summary of the properties of the different subfamilies (alpha-yellow, beta-white and
gamma-green). For alpha, the target cell type is typically in the mucosal epithelium in the oral or genital
Microbiology: Human Herpesviruses
Kimberly Watkins
pg. 2
regions and they all establish latency in neurons. Oral and ocular lesions and encephalitis are typically
associated with HSV-1. Genital, ocular and disseminated infections in newborns are associated with
HSV-2 and chicken pox with VZV. The Simian B virus (herpes B) that can be acquired from infectious
primates can cause lethal encephalitis.
The beta viruses will primarily target monocytes and different lymphocyte populations. There are
numerous diseases associated with CMV especially in the immunocompromised host. HHV-6 typically
appears as a rash (in children).
Gamma viruses (EBV and HHV-8) are associated with tumors.
Slide 9: It is very important to understand that in immunocompromised patients, most clinical illness
with the herpes type viruses with the exception of herpes B virus tend to be self-limiting and mild. The
severe illnesses associated with these viruses commonly occur in the immunocompromised. It can be
due to drugs, cancer will often cause dysregulation in the immune system and also infections (like HIV).
These patients will have more severe and persistent infections. The immune system also changes
throughout life. Newborns are highly susceptible to these viruses. CMV is a major cause of severe
congenital abnormalities and also has a high mortality rate. As people age, their immune system
becomes less effective.
Slide 10: We are going to go through the alpha families.
Slide 11: The best known are the herpes simplex type 1 and 2. They are neurotrophic and only occur in
humans (no animal reservoirs). There are differences between their genomes but their clinical illnesses
are very similar. Cold sores or oral lesions are typically associated with type 1 but can also be caused by
HSV-2. HSV-2 is most typically associated with genital disease but HSV-1 can infect genital mucosa.
Seroprevalence of HSV-1 exceeds 90% (most everyone has been exposed). How it presents and
reactivates depends on the individual. Seroprevalence for HSV-2 is ~18%. Some are asymptomatic while
others get frequent recurrences.
Slide 12: They initially establish a productive infection in epithelial cells and that is how they gain access
to the sensory nerve endings and then transport by retrograde axonal flow to the neuronal cell bodies
and then establish latency. Once they go latent, you do not have much replication in the nerve. When
reactivation occurs, you do get some replication and the virus transports back anterograde to the site of
initial infection or very close to it. It will typically cause a localized lesion. The primary infection will be
the most dramatic (most lesions) while secondary may only have one lesion.
Slide 13: There is nothing in the test that is any of the information in here. It is more to give you an
understanding of how complex the herpes genome is how many different proteins it encodes and why
we still have not figured out a lot of these mechanisms of how the virus goes latent and reactivates.
Important for the replication cycle are these ‘a’ sequences (packaging sequences) for the newly
replicated virus. The genome is divided into 2 segments: unique long and unique short. The inverted
repeats encode for a lot of the transcription regulatory proteins (those needed to initiate viral DNA
transcription). There are also 3 origins of replication.
Microbiology: Human Herpesviruses
Kimberly Watkins
pg. 3
Slide 14: The virus attaches to the target cell by the interaction of a number of glycoproteins. It interacts
with the cell surface proteoglycans and some specific receptors that are members of the nectin family. A
lot of the tropism for all the human herpes viruses is mediated by these different receptors. Once the
virus attaches to the cell surface membrane, it can be either endocytosed in, viral fusion between the
endocytic vesicle and the viral membrane can occur or it can actually fuse directly with the outer plasma
membrane of the cell causing release of the nucleocapsid.
Video: Shows how receptor recognition, entry and insertion of the DNA into the nucleus. You have the
initial interaction between the glycoproteins and the cellular receptors, fusion of the membrane and
release of the nucleocapsid. The tegument proteins are required to initiate early gene expression once
the viral DNA gets deposited into the nucleus.
Slide 15: Once it delivers the viral genome into the nucleus and you get the transcription and replication.
One protein, VP16, is responsible for interacting with a lot of these promoter elements in these early
genes, which are called infective cell proteins. Most of these genes are present in two copies. The
transcription of the viral genome and protein synthesis occur in a tightly regulated fashion. You have the
immediate early genes expressed that allow transcription to take over the cell. The early proteins (beta
genes) include more transcription factors and enzymes including the DNA polymerase that helps
replicate. The late proteins (gamma genes) include the viral structural proteins.
Video: Gives you an idea of how the rolling cell replication occurs. There are 3 origins of replication. You
have the creation of a replication bubble by viral proteins that once expressed can initiate viral DNA
replication. It also allows for the recruitment of other proteins necessary for both the continuous and
discontinuous DNA synthesis. Once that happens, you start to get a bugger bubble and the DNA gets
nicked to form a rolling circle.
Slide 16: It is transcribed by both viral and host proteins. The interplay of these factors determines
whether the proteins are responsible for a lytic, persistent or latent infection are produced. The diagram
shows the relationship between a productive infection or once the infection gets going in the immune
competent individual, the T-cell mediated immunity will kick in and shut down, basically eliminate the
virus infection, but not before you get viral particles that travel up the neuron to establish latency.
Reactivation is basically a virus of this step but the reactivated that occurs will typically be a smaller area
that gets infected.
Slide 17: The neurons harboring the virus express a RNA known as latency associated transcript (LAT).
There is really no role in terms of establishment and maintenance of the latent state, they are just there.
There are no viral proteins associated with latency. We do not know the mechanism by which latency
occurs.
Slide 18: Often times, reactivation has occurred but there is no evidence of clinical lesions and this is
known as shedding. Different stimuli for reactivation include fever, physical stress, UV and it normally
goes to the site of entry but on rare occasion it can go to the eye or CNS.
Microbiology: Human Herpesviruses
Kimberly Watkins
pg. 4
Slide 19: This is a schematic showing the primary site and the path the virus takes during establishment
and reactivation.
Slide 20: The clinical manifestations of herpes simplex infections include: encephalitis (in rare
occasions), conjunctivitis, herpes gladiatorum (seen often in high school wrestlers: transmitted by the
surface of the skin), genital herpes, oral herpes, and herpes whitlow (relevant to someone who has to
stick their finger in someone’s mouth)
Slide 21: Primary orolabial infection is caused primarily by HSV-1.
Slide 22: Typically you have clear lesions that first develop and develop into ulcerations. Usually seen
around the lip area, but can spread to all parts of the mouth and pharynx. There is a spectrum of
severity ranging from a few intraoral ulcers and no systemic features to severe oral ulceration and a lot
of times there is drooling associated with it. Other symptoms include fever, lymph node swelling. At this
stage, especially during primary infection, there is a much higher risk of autoinoculation at other sites
including the eye and fingers. This is much more severe in immunocompromised patients.
Slide 23: She skips this slide because it is repetitive.
Slide 24: Some of the lesions of primary infection. Upper left: cold sores. Upper right: typical cold sore
from reactivated. Lower right: Gingivitis from herpes. Lower left: Exasperation of the disease where you
have multiple lesions over the mouth and tongue (AIDS patient).
Slide 25: Cold sores affect about 20% of the population and as many as 60% of Caucasians show HSV-1
positive serology. The primary infection typically occurs before age 4 but not all of those individuals will
recurrent outbreaks.
Slide 26: There are antiviral drugs available for the treatment of herpes simplex infection. The earlier
you treat the better (faster resolution). You can give high dose systemic therapy in cases where you
have a suspected newborn that has been exposed or to prevent the disseminated disease.
Slide 27: For herpes labialis, a penciclovir cream is often prescribed or in some cases, acyclovir.
Slide 28: This is an example of herpetic whitlow seen in thumb-sucking children. The highest risk in the
adult population is for the dental profession or health care workers who are examining without gloves.
Slide 29: Another disease caused by herpes simplex viruses is Bell’s palsy, which is an acute onset of
facial nerve palsy typically unilateral. There are multiple causes and it seems to be associated with HSV
reactivation. For patients that present with Bell’s palsy, many recommend using valacyclovir with
prednisone but acyclovir has been tested as well.
Slide 30: Encephalitis is rare and in 1250 cases/year you will see a reactivation that leads to HSE (herpes
simplex encephalitis). It will present with personality changes, seizures and fever and the therapy is
acyclovir. Outcome depends on how quickly they catch it. There is a fairly high mortality rate but you
can have a significant portion to recover without long standing effects.
Microbiology: Human Herpesviruses
Kimberly Watkins
pg. 5
Slide 31: Herpes simplex 2 generally causes genital herpes. The primary infection will typically be the
most severe but they can be asymptomatic. There is a variable frequency of recurrences. The key to the
natural history of this virus is it does have a lot of asymptomatic viral shedding.
Slide 32: Antiviral therapy includes acyclovir, valacyclovir, and famciclovir. All are effective against
genital herpes and can help patients with frequent recurrences by reducing severity and amount of
infections.
Slide 33: HSV-1 is usually associated with ocular infections and it is the leading cause of blindness in the
US. It is typically limited to one eye and there are a number of manifestations. Long term suppressive
therapy with an oral antiviral drug can reduce the rate of recurrence of HSV mediated keratitis and
ocular complications.
Slide 34: This picture shows a herpetic lesion.
Slide 35: All anti HSV drugs currently licensed are dependent on being activated by viral enzymes.
Slide 36: They are all nucleoside analogs and activated by a viral enzyme known as thymidine kinase.
The drug is only activated in cells infected with herpes and as a consequence you do not have a problem
with side effects. The best known nucleoside analog to treat HSV is known as acyclovir
(acycloguanosine) but there are other approved drugs including famciclovir and valacyclovir. Drug
resistant mutants do arise with all of these therapies but the resistant strains tend to be less virulent
than the wild types. Mutation in the TK gene makes the virus less fit. Drugs act only against replicating
virus and are ineffective against latent virus.
Slide 37: This shows the mechanism where the herpes thymidine kinase (TK) acts. The drug acyclovir
gets the initial phosphate added by the herpes TK to make it a mono phosphate acyclic GMP. Then
cellular kinases add the remainder of the phosphates which then gets incorporated in the
dioxynucleoside triphosphate pool which is used to replicate the virus. This is a chain terminator; this is
not something that can allow replication to continue.
Slide 38: Here you can see it getting incorporated. There are no 3’ hydroxyl groups for targets of the
phosphate group for another addition of a nucleotide.
Slide 39: For HSV, acyclovir is typically used and it relies on the thymidine kinase. For CMV, the
gancyclovir relies on the viral protein kinase but the mechanisms of how they get activated and what
they inhibit are similar.
Slide 40: All primary infection with VZV (varicella-zoster virus) will cause chickenpox. When you get a
reactivation of this virus, it is known as herpes zoster or shingles. It spreads primarily through the
respiratory route. Local replication occurs in the respiratory tract and can lead to formation of skin
lesions over the entire body. Latency is established in the dorsal root or cranial nerve ganglia (runs down
along your spine, so you get lesions along the trunk). It is antibody immunity that limits viremic spread
of VZV. Cell mediated immunity is also important for limiting progression and resolving disease.
Microbiology: Human Herpesviruses
Kimberly Watkins
pg. 6
Slide 41: These are just some images of VZV. Left: young child with typical chickenpox lesions. Middle:
newborn (more severe because of immature immune system). Right: typical case of shingles.
Slide 42: For chickenpox in children, normally supportive care is sufficient. There is a vaccine approved.
To prevent disseminated infection in immunosuppressed patients, you typically use acyclovir,
famciclovir, and valacyclovir. You can also use the immunoglobulin but it is not really effective if you
already have active disease.
Slide 43/44: Epstein-Barr virus is a gamma herpes virus. It encodes more than 70 proteins. It was first
discovered as the causative agent for African Burkitt’s lymphoma and later identified as the causative
agent for infectious mononucleosis (kissing disease) when serum from infected individual was found to
contain antibody to AfBl. This is normally an asymptomatic infection that occurs in early childhood. As
far as pathogenesis, it is transmitted by salvia. You can get infectious virions that are intermittently shed
from the oral-pharyngeal epithelial cells but it can be transmitted by transfusion or organ transplant.
The tissue tropism is normally B cell lymphocytes that you get infections and you can also get some
productive lytic infections as well. The primary site of latency is in the peripheral blood lymphocytes
**There is a change in the slides but she basically condensed all the information (she said it is basically
the same).
Slide 45: When you get B cell transformation, this is when the virus is taken up by the CD21+ B
lymphocytes following viral replication and that is how it gets shed into the saliva. The B cells are
protected from undergoing apoptosis, so you get a cell transformed and often a tumor formation will
occur depending on the other types of interaction between the infected cells and the immune system.
Slide 46: Burkitt’s lymphoma is a tumor of the jaw and face found in children and is really the result of
this infection that leads to elevated transcription of the oncogene c-myc. A biopsy shows large
multinucleated cells, which you can see here (slide 47: right picture).
Slide 47: This is a Burkitt’s lymphoma tumor in this child.
Slide 48: It is also known to cause tumors in the epithelium and upper respiratory tract and seems to be
a genetic predisposition involved or environmental co-factor. You normally see this in south China,
Alaska, Tunisia, and east Africa (very restricted).
Slide 49: Another disease caused by EBV is called oral hairy leukoplakia and you can see where it got its
name because it forms white lesions on the border of the tongue (left picture) that are non-painful. They
can spread to the mouth floor, tonsil or into the pharynx. This is a manifestation of an EBV infection in
an immunosuppressed individual; not seen often in healthy individuals.
Slide 50: Infectious mononucleosis is probably the best known EBV infection. It characterized by
generally malaise, tonsillitis, enlarged spleen, fever that can last for a while and a rash may also develop.
It takes between 1-4 weeks to resolve. You can get complications. There are about 45/100,000 cases in
the US per year.
**I think she had a new slide**
Microbiology: Human Herpesviruses
Kimberly Watkins
pg. 7
Slide 51: Diagnosis for infectious mononucleosis is typically a blood smear in which you look for these
atypical lymphocytes. There are also serological tests available. However, EBV is one human herpes virus
family member that does NOT encode a thymidine kinase so it is not susceptible to these drugs that are
effective against other family members. That is an important point to remember. A vaccine is under
development.
Slide 52: Cytomegalovirus has the largest genome of the herpes viruses and also only replicates in
human cells. A productive infection can be seen in macrophages and fibroblasts whereas latent
infections can set up in several types including T lymphocytes and stromal cells. This is one of the beta
herpes virus family members. It is found in a significant portion of the population. It spread can be
mediated by any kind of secretion and you can also have mother to fetal spread during pregnancy (very
dangerous for the developing fetus).
Slide 53: It is the most common viral cause of congenital disease. Up to 1/40 newborns are infected by
the virus. It is important for the pregnant mother to not be around small children who are suspected of
having a CMV infection. During primary infection of the mother, the virus can spread to the fetus via
placenta. It can result in hearing loss or retardation if a spontaneous abortion has not occurred.
Neonates can also receive the virus via blood transfusion, in which the virus titer is much higher.
Slide 54: In the immunocompromised host, CMV can cause pneumonia which can be fatal if not treated.
Nearly 20% of patients with terminal AIDS get a very hemorrhagic necrotizing retinitis. In about 10% of
AIDS patients, they can develop a colitis or esophagitis (shown in the two pictures).
Slide 55: For diagnosis, most infections are symptomatic and are undetected. A hallmark of the infection
is the cytomegalic cell “owl’s eye” (how it got its name). You can detect viral antigens using either
fluorescent antibodies or other methods.
Slide 56: Ganciclovir, valganciclovir, cidofovir, and foscarnet have all been approved by the FDA for the
treatment of diseases associated with CMV infection in the immunosuppressed patient. That is really the
only population that you will see these disease manifestations. Progression of retinitis may be delayed in
the sort term by giving intravenous ganciclovir or foscarnet. Both work but foscarnet is not well
tolerated. Acyclovir is NOT effective for CMV infections. That is important to remember. A vaccine is
currently under development as well.
Slide 57: Human herpes viruses 6 and 7 (HHV-6 and HHV-7) are very similar. HHV-6 was described first
and is known to cause roseola and there are two variants. It is found worldwide and is in the salvia of
~90% or more of adults. Almost all children are infected by the age of two and the infection is life-long.
It replicates in both the T and B cells. The disease associated with it in children is known as roseola
infantum and some of the symptoms include fever and upper respiratory tract infection. You get a spike
in fever for a couple of days and three days later the child is fine but they have a rash. This is typical
presentation. HHV-7 is distinguished from HHV-6 in that it binds to the CD4 antigen and replicates in the
CD4+ cells.
Slide 58: These two pictures represent exactly what it looks like.
Microbiology: Human Herpesviruses
Kimberly Watkins
pg. 8
Slide 59: HHV-8 is the virus associated with the development of Kaposi’s sarcoma or KSHV. It was
initially isolated and characterized from biopsy specimens of Kaposi’ sarcomas in AIDS patients. Like EBV,
this is another gamma herpes virus and the B cells are the primary targets but it will infect other cell
types. It is found in about 10% of immunocompetent in peripheral blood lymphocytes. It also encodes
several proteins with homology to human proteins that promote growth and prevent apoptosis of the
infected cell, which is how it leads to some of these tumors. This is a classic opportunistic infection that
is associated with AIDS.
Slide 60: As far as clinically, over 50% of AIDS patients with skin Kaposi sarcoma (KS) will also have oral
KS while 10-20% of AIS patients will only have oral KS and not any of the skin associated. Oral KS is
typically found on the hard and soft palates but is can also develop on the gingiva, anterior palate and
the tongue. It is characterized by generally one or more flat areas that have a reddish-brown or deep
purple discoloration. You can get a hyperplastic or nodular variety that will be seen in the gingiva or on
the tongue and they will frequently bleed. As the disease progress, you will see a change to reddishbrown or even violet color.
Slide 61: This is shows some of the manifestations of these purple lesions in the oral area (left) and in
the skin (right).
Slide 62: Treatment of these lesions is typically systemic chemotherapeutic agents. You can also use
radiation therapy for large lesions and smaller lesions can be treated with surgical or laser excision.
Slide 63: The herpesvirus simiae or B virus is important to those who work with research animals. This
virus is indigenous to Old World monkeys like macaques. It is transmitted to humans either via salvia or
monkey bites and 75% of these cases result in death. Both acyclovir and ganciclovir are recommended
for therapy but there is no good data on efficacy.
Slide 64: Important to understand the clinical diseases associated with the viruses, antiviral therapy, the
mechanism of how it works and the diseases associated with the immunocompromised patient.
Herpes is forever