Dra consist viruses presentation

DNA-CONSIST VIRUSES

Classification of DNA viruses that infect humanFamily Virion

structureGenom structure Characteristics

Hepadnaviridae lipid-contain. envelope

1 molecule, mainly ds DNA but with a single strand gap

Hepatitis B virus

Parvoviridae Non-enveloped

1 molecule, ss DNA

outbreaks of gastroenteritis following eating of shellfish

PapillomaviridaePolyomaviridae

Non-enveloped

1 molecule, circular ds DNA

human papilomaviruses (genital and oral carcinomas)

Adenoviridae Non-enveloped

1 molecule, ds DNA

Human: infections of respira-tory and the intestinal tracts, of the eyes; Animals: tumors

Herpesviridae enveloped with surface projections

1 molecule,ds DNA herpes simplex virus, cytomegalovirus

Poxviridae enveloped; large, brick-shaped

ds DNA, covalently closed ends

smallpox virus, vaccinia virus

DNA VIRUS REPLICATION STRATEGIES

Viral genomes contain information which: ensures replication of viral genomes ensures packaging of genomes into virions alters the structure and/or function of the host cell to a greater or lesser degree VIRAL STRATEGYViral strategy refers to the manner in which each virus carries out the above

functions. Since a virus is an intracellular parasite, it has to operate within limits imposed by the host cell, or circumvent these limitations.

 GeneralThe virus needs to make mRNAs that can be translated into protein by the host

cell translation machinery. The virus needs to replicate its genome. Host enzymes for mRNA synthesis and DNA replication are nuclear (except for

those in mitochondrion) and so, if a virus is to avail itself of these enzymes, it needs to enter the nucleus.

Nuclear DNA viruses Parvoviridae Papillomaviridae Polyomaviridae Adenoviridae Herpesviridae

Cytoplasmic DNA viruses Poxviridae This means that they must provide their own mRNA and DNA

synthetic machinery.

PAPILLOMAVIRUS FAMILYThe Papillomavirus family was formerly grouped with the Polyomavirus family into the Papovavirus family (PApilloma, POlyoma, simian VAcuolating virus 40) because members of both families have a similar structure. However, it is now clear that the two families have a very different replication strategy and so each group has now been given its own family status

PROPERTIES OF POLYOMAVIRUSES AND

PAPILLOMAVIRUSES

They are small: 40 - 60nm

They are icosahedral: major capsid protein is VP1, with lesser amounts of VP2, VP3

They are non-enveloped

They have circular, double-stranded DNA is associated

with cell histones (nucleosomes)Papilloma virus

POLYOMAVIRUSESThese include SV40, BK, JC and polyoma viruses. All have a similar strategy for DNA replication.  They are small (~40nm diameter), icosahedral, non-enveloped viruses that replicate in the nucleus. Depending on the host cell, they can either transform the cell or replicate the virus and lyze the cell. 

SV40 virus, a polyoma virus

ADENOVIRUSESgot their name from the adenoidal tissues (tonsils) in which they were first identified (in 1953 W.Rowe and collaborators).

MORPHOLOGY

Size – 70-90 nmShape - icosahedral. Their morphogenesis occurs in the cell nucleus, where they also aggregate to form large crystalsTheir genome is a linear, ds DNA Type of symmetry - cubicNaked. Capsid consist of 252 capsomers

ANTIGENIC STRUCTURE OF ADENOVIRUSES

4 soluble antigens are known Hexon – A antigen –common for all serotypes, is the main structural protein of virion (51%)

Penton – B antigen – causes early toxic effect of adenoviruses to the tissue culture (9 % of all proteins of virion)

Appendix, filament – C antigen – causes agglutination of erythrocytes (5 %)

P antigen – inner protein – releases after destroying of the virion

CLASSIFICATIONFamily Adenorividae genera:1 Mammaliadenovirus embracing adenoviruses of humans and mammals species:49 pathogenic for human; 24 – for monkey; 9 – for cattle; 2-6 - for horses, sheep, dogs, mice 2 Aviadenovirus including adenoviruses of birds. species: 9 pathogenic for cheek; 3 – for goose 3 –for turkey-cock About 130 species (serotypes) of adenoviruses are known

ASSEMBLY

Assembly of adenovirus particles occurs in the nucleus. DNA enters the particles after immature capsids are formed. The

capsids then undergo a maturation process, after which the cells lyse and virions leak out.

More structural proteins are made than are needed and excess structural proteins accumulate in the nucleus where they form inclusion bodies.

Adenoviruses code for their own DNA polymerase and DNA packaging proteins.

However, although adenoviruses code for their own DNA polymerase, they use host factors in addition to viral proteins for DNA replication, and they use host RNA polymerase and RNA modification systems and so nucleic acid synthesis needs to be in the nucleus.

Diagrammatic representation of the uptake and uncoating of adenovirus particles. Adapted from Zinsser Microbiology 20th Ed. 

CLASSIFICATION ACCORDING TO THE ANTIGENIC STRUCTURE (TO THE ABILITY TO AGGLUTINATE THE RED BLOOD CELLS)1 subgroup – adenoviruses, which agglutinate monkey’s

erythrocytes (3,7,11,14,16,20,21,25,28)2 subgroup – adenoviruses which agglutinate white rat’s

erythrocytes completely (8,9,10,13,17,19,22,23,24,27,29,30)

3 subgroup – adenoviruses which agglutinate white rat’s erythrocytes partially

(1,2,4,5,6,12,18,31)

CLASSIFICATION ACCORDING TO THE ONCOGENIC-ABILITY Subgroup A – greatly oncogenic (types 12,18,31)Subgroup B weakly oncogenic (types 3, 43, 7, 8, 11, 14,

16, 21)Subgroup C and D – non oncogenic ( all other types)

CULTIVATION

- grow in tissue cells of human beings, monkeys and other animals.

Most susceptible are subinoculated epithelial cells НеLа, КВ, Нер-2, etc., in which the cytopathogenic effect is relatively manifest. The inoculated tissue culture are incubated at 37º C for 14 days.

- Are non pathogenic for laboratory animals - Do not grow on chick embryo membranes.

CYTOPATHOGENIC EFFECTThe process of cell degeneration consists of two phases. During the first phase changes in the cells are induced by toxin-like factors (initial phase of degeneration), while in the second phase viruses multiply within the nucleus and cytoplasm (final phase of degeneration). Inclusion bodies from within the nucleus. They consist of virions which produce aggregates of crystalline structure. Adenovirus multiplication is accompanied by accumulation of excess lactic acid in the tissue culture.

Normal (not infected) НеLа cells (1);

cytopathic effect of adenoviruses on HeLа cells (2)

PATHOGENESIS AND CLINICAL PICTURE

Adenoviruses cause a variety of diseases, which may occur singly or concurrently. The most important are infections of the upper (sometimes lower) respiratory tracts, the eyes, and the intestinal tract.Adenoviruses can persist for months in the regional lymph nodes or tonsils until they are reactivated.The clinical picture of the disease does not strictly depend upon the type of adenovirus. One and the same variant may produce a wide variety of forms of the disease. The ability of various serovars to produce one the same disease has also been ascertained.

Infections of the respiratory tract take the form of rhinitis or abacterial pharyngitis, depending on the virus type as well as presumably on the disposition of the patient.

The eye infections may occur alone but are often concurrent with pharyngitis, range from follicular conjunctivitis to a form of keratoconjun-ctivitis that may even cause permanent partial loss of eyesight.

The intestinal infections An important aspect of the intestinal infections is that the primary

gastroenteritis forms are caused by the viral strains 40 and 41, which are difficult to culture.

ADENOVIRUS- CLINICAL SYNDROMES (COMPILED) Clinical

syndromeFeatures Serotypes

commonly involved

Serotypes rarely

involved

URI Coryza, pharyngitis, tonsillitis, fever 1, 2, 3, 5, 7 4, 6, 11, 18, 21, 29, 30

Pharyngo-conjunctival fever

Fever, conjunctivits, pharyngitis, headache, rash, lymphadenopathy

3, 4, 7, 14 1, 11, 16, 19, 37

LRI Bronchitis, pneumonia, fever, cough 3, 4, 7, 21 14, 1, 2, 5, 35

Pneumonia Fever, respiratory distress, cough, severe in young children and infants

7 1, 2, 3,4, 14, 21, 7b

Pertussis-like Syndrome

Fever, paroxysmal cough, post-tussive vomiting

5 1, 2, 3, 12, 14, 19, 21, 35

Acute Respiratory Disease

Tracheobronchitis, pneumonia, fever; epidemics in military recruits

4, 7 2, 3, 5, 8, 11, 14, 21

ADENOVIRUS- CLINICAL SYNDROMES (COMPILED)

Epidemic Keratocon-junctivitis

Headache, conjunctivitis followed by keratitis, preauricular lymphnodes

8, 19, 37

2-7, 14, 15, 19, 37

Acute follicular/ Hemorrhagic conjunctivitis

Chemosis, follicles, subconjunctival hemorrhage, preauricular lymph nodes

11  

Acute Hemorrhagic cystitis

Blood in urine (macroscopic hematuria) fever, dysuria  

11, 4, 7, 1, 21

34, 35

Gastro-enteritis Diarrhea especially in children <4 years old Low grade fever

40-42, 31, 25-28,

3, 7, 2, 9, 12, 13, 18

LABORASTORY DIAGNOSISMethods Rapid: Microscopy: electron; immuno-fluorescent; Virological: Isolation of viruses in tissue culture (HeLa, Hep -2, KB);Indication by CPE, IFT, CFT, ELISA, RIA;Identification by NT, HIT with monky’s and white rat’s red blood cells Serological - is mainly used for epidemiologic studies

Other detection methods in current use include polymerase chain reaction and nucleic acid probes.

PreventionHandwashingContact precautions, respiratory precautions in health care settingsAdequate chlorination of swimming poolsSterilization / disinfection of ophthalmologic equipment and use of single dose vials of ophthalmic medicationsVaccine:  live, enteric coated, oral vaccine (types 4, 7, 21) ImmunityThe majority of newborn infants possess passive immunity which they lose at the age of 6 months. Susceptibility prevails at the age from 6 months to 5 years. Children older than 5 years of age possess antibodies and rarely contract adenoviral diseases. A relatively low diseases incidence among adults is due to immunity acquired following an acute or asymptomatic form of the disease. The immunity is type-specific in character.

HERPESVIRIDAE FAMILY

Herpes viruses are a leading cause of human viral disease, second only to influenza and cold viruses.

They are capable of causing overt disease or remaining silent for many years only to be reactivated, for example as shingles.

The name herpes comes from the Latin herpes which, in turn, comes from the Greek word herpein which means to creep. This reflects the creeping or spreading nature of the skin lesions caused by many herpes virus types.

Enveloped icosahedral virus180 - 200nm;

Linear, double-stranded DNA

The space between the envelope and the capsid is the tegument. This contains virally-encoded proteins and enzymes involved in the initiation of replication

Capsid contains 162 doughnut shaped capsomeres.

Antigenic structureThe virus contains two antigens: the V-antigen, may be detect in NTand the S-antigen (soluble) – may be detect in CFT, is allergen

There are at least 25 viruses in the family Herpesviridae (currently divided into three sub-families). Eight or more herpes virus types are known to infect man frequently

Subfamily Genera Species pathogenic for human

Diseases

Alphaherpes virinae

Simplexvirus HSV 1HSV 2

KeratoconjunctivitisHerpes labialis, herpes genitalis neonatal herpes, encephalitis

Varicellovirus Varicella-Zoster virus

Varicella, herpes zoster

ILTV-like virus Infection laryngotracheitis virus

Infection laryngotracheitis

Betaherpes virinae

Cytomegalovirus Cytomegalovirus Cytomegalovirus infectionRoseolovirus Human herpes virus

6A (HHV-6A)Human herpes virus

6B (HHV-6B)Human herpes virus

7-HHV-7

Tropism to T-lymphocytesExanthema subitum

(roseola infantum)Exanthema subitum

HERPESVIRIDAE FAMILY VIRUSES PATHOGENIC FOR HUMAN

Gamma-herpes virinae

Lymphocryptovirus

Epstein-Barr virus (EBV)

Mononucleosis, Burkitt’s lymphoma, Nasophayngeal carcinoma, Lymphoma in immunodeficient persons

Rhadinovirus Kaposi’s sarcoma-associated herpesvirus (HHV-8)Cercopiteci (monkey) herpes virus type B

Kaposi’s sarcomaCause acute respiratory diseases at human

CULTIVATION1) on the chorioallantoic membrane of the chick embryo (12-13 days old) on which it forms inflammatory necrotic foci.2) on embryonal lung and kidney tissues of human orrgin and in cultures of НеLа cells, Detroit-6 cells, etc. 2 type of CPE may be observe (at the same time): (a) – foci of proliferation (which consist of some layers of oval cell); (b) – multinuclear syncytium.3) on laboratory animals. In case of intra cerebrum inoculation – encephalitis evolves; in case of inoculation into the cornea - cerato-conjunctivitis will develop.

HERPES VIRUS REPLICATION

PATHOGENESISThe virus infects epithelial mucosal cells or lymphocytes. - then travels up peripheral nerves to a nucleated neurone where it may stay for years followed by reactivation. A reddened area gives rise to a macula which crusts to form a papula. The fluid in this blister is full of virus. As long as the virus is kept moist it can remain infectious.HSV-1 and HSV-2 first infect cells of the mucoepithelia or enter through wounds. They then frequently set up latent infections in neuronal cells. The site of the initial infection depends on the way in which the patient acquires the virus. Once epithelial cells are infected, there is replication of the virus around the lesion and entry into the innervating neurone. The virus travels along the neurone (by a process called retrograde transport) to the ganglion (ex.trigeminal or sacral ganglia).

The virus can also travel in the opposite direction to arrive at the mucosa that was initially infected. Vesicles containing infectious virus are formed on the muscosa and the virus spreads. The vesicle heals and there is usually no scar as a result.

Herpes simplex 1 and 2 can infect both humans and other animals but only humans show symptoms of disease.

Both types of HSV can also persistently infect macrophages and lymphocytes. The presence of the virus is often indicated by the formation of syncytia and inclusion bodies in the nucleus.

CLINIC FORMS OF HERPES INFECTION- Primary and Recurrent

Primary herpes is the result of infection by direct contact or by the air-droplet route.

herpetic fever or, less frequently, as herpes simplex. (an increase of temperature to 39-40С, severe headache, meningeal

symptoms, vomiting, hyperaemia of the conjunctivas, and inflammation of the lymph nodes. On the following day а vesicular eruption usually appears on the lips, the temperature falls, and the disease takes the course of herpes simplex.

Initial infection with herpes simplex type 1 usually occurs in early childhood. The portal of entry is normally the oral mucosa (“oral type”) and the infection usually manifests as a gingivostomatitis. The initial infection with HSV type 2 normally affects the urogenital area (“genital type”) and can be contracted despite an existing HSV type 1 infection.

Herpes recurrence is frequently encountered with certain diseases (malaria, influenza, acute catarrhal conditions, lobar pneumonia, meningitis, intoxications, psychic disorders), traumas, and cooling.

VARICELLA-ZOSTER VIRUS (ALSO KNOWN AS HERPES ZOSTER VIRUS, HUMAN HERPES VIRUS-3)

Zoster means girdle from the characteristic rash that forms a belt around the thorax in many patients. The structure of Varicella virus is very similar to Herpes Simplex virus although the genome is somewhat smaller

This virus causes two major diseases, chicken-pox (Varicella), usually in childhood, and shingles, later in life. Shingles (Zoster) is a reactivation of an earlier varicella infection.

CHICKENPOX The patient is the source of infection. The causative agent is spread by the air-droplet route.The patient is infectious from the last days of incubation and to the time the crusts fall off.The incubation period lasts from 2 to 3 weeks.Pathogenesis The portals of entry are the nasopharyngeal space and the conjunctiva. From there, the virus undergoes a viremic phase in which it is transported by the blood to the skin, where the typical exanthem is produced. Eruption ceases on the fifth day of the disease.

SYMPTOMS OF CHICKEN POXRash is pleomorphic, monolocular, appears with

temperature anywhere on the body, but usually first on the back, than the face, head, mouth, main body and arms and legs (never on palms and foots).

The lessions appear at different times and within a day or so go through a characteristic evolution from macule to papule to vesicle to crusts (without scars).

HERPES ZOSTER (SHINGLES)- is reactivation of varicella.It can occur at any age, but becomes increasingly common with

advancing age.It begins with pain in the area supplied by a nerve of sensation,

often on the chest or abdomen, but sometimes on the face, or arm or leg. After a few days to two weeks the characterisc rash of varicella appears along the course of the nerve. The rash subsides within a week, but pain may persist for weeks or months.

TreatmentAs with HSV, acyclovir (or other nucleoside analogs) can be useful, particular in preventing dissemination in immunosuppressed patients. Varicella immunoglobulin can also be used. Normally, however, only supportive care is used in children who quickly recover if they mount an adequate cell-mediated response.

VaccineThere is a live attenuated vaccine virus and this is used in the United States. It leads to antibody production and cell-mediated immunity. It can be used post-exposure.

LABORATORY DIAGNOSISRapid methods: specimens – smears from mucous membranes, m-l

from vesicles and other rash-elements, biopsy specimens from the lesions :

- IFT (direct and indirect); - electronic microscopy; - studying slides stained by Romanovsky’s or by Morozov’s

technics (to detect intra nuclear inclusions) 2. Virological method: specimens - smears from mucous membranes,

m-l from vesicles and other rash-elements, cerebro-spinal fluid, blood, scrape from cornea

- obtaining: in tissue culture; on chorion-allantois membrane of chick embryo; on labоratory animals

- detection: - by CPE; characteristic cytopathic effects (plaque) including multinucleated cells

- by HAT - identification: - in NT, CFT, PHAT

Herpes simplex 1: Histological stain. Note the multinucleate cell with dark staining inclusions

3. Allergic test – by on cutaneous test4. Biological method (look at virological – cultivation on lab.animals)5. Serological method: serum in serologic tests: NT, CFT, PHAT, IFT, IHAT.

Herpes simplex virus on and in a peripheral blood lymphocyte  © Dennis Kunkel Microscopy, Inc.  Used with permission

Herpes simplex virus in cellular vacuoles and cytoplasm of peripheral blood lymphocyte  © Dennis Kunkel Microscopy, Inc.  Used with permission

EPSTEIN- BARR VIRUS (GAMMAHERPESVIRINAE)

Epstein-Barr virus is the causative agent of Burkitt's lymphoma in Africa, nasal pharyngeal carcinoma in the orient and infectious mononucleosis in the west. It was first discovered as the causative agent of Burkitt's lymphoma and it was later found that patients with infectious mononucleosis have antibodies that react with Burkitt's lymphoma cells.

The virus only infects a small number of cell types that express the receptor for complement C3d component (CR2 or CD21). These are certain epithelial cells (oro- and naso-pharynx) and B lymphocytes. This explains the cellular tropism of the virus.

BURKITT'S LYMPHOMA This is a tumor of the jaw and face found in children

This lymphoma is endemic in equatorial Africa but only occurs rarely elsewhere. Why this is so is unclear but there is probably a genetic reason possibly involving an association with malaria. Persons who are resistant to malaria appear to be susceptible to progression to the lymphoma.

Burkitt's lymphoma histological stain. Notice the large multinucleated cells

INFECTIOUS MONONUCLEOSISThe primary infection is often asymptomatic but the patient may

shed infectious virus for many years. Some patients develop infectious mononucleosis after 1-2 months of infection. The disease is characterized by malaise, lymphadenopathy, tonsillitis, enlarged spleen and liver and fever. The fever may persist for more than a week. There may also be a rash. The severity of disease often depends on age (with younger patients resolving the disease more quickly) and resolution usually occurs in 1 to 4 weeks.

Complications: meningitis, encephalitis, myelitis. Secondary infections, autoimmune hemolytic anemia, thrombocytopenia, agranulocytosis, aplastic anemia may also occur.

As noted above a chronic syndrome may also occur. The symptoms are similar to those reported for chronic fatigue syndrome (headaches, sore throat and low fever) but EBV is probably not the cause of chronic fatigue syndrome.

DiagnosisIn infectious mononucleosis, blood smears show the atypical lymphocytes (Downey cells). There are also serological tests available. Heterophile antibodies are produced by the proliferating B cells and these include an IgM that interacts with Paul-Bunnell antigen on sheep red blood cells.

Leukemia cells that contain Epstein Barr virus using a FA staining

CYTOMEGALOVIRUSCytomegalovirus has the largest genome of all herpes viruses and appears only to replicate in human cells. Its name derives form the fact that, like other herpes viruses, it can form multinucleated cells (syncytia) with characteristically staining inclusions. Some cells such as macrophages and fibroblasts support a productive infection while a latent infection is set up in several cell types including T lymphocytes and stromal cells of the bone marrow. There is only one serotype.

PATHOGENESISCytomegalovirus causes no symptoms in children and at most mild disease in adults. The virus first infects the upper respiratory tract and then local lymphocytes. Circulating lymphocytes then spread the virus to other lymphocytes and monocytes in spleen and lymph nodes. The virus finally spreads to a variety of epithelial cells including those of salivary glands, kidney tubules, testes, epididymis and cervix. Infection is usually asymptomatic (sub-clinical) but glandular fever is sometimes seen in young adults. The virus can inhibit T cell responses. The virus elicits both humoral antibodies and cell-mediated immunity but the infection is not cleared. Cell-mediated immunity, not humoral antibodies, controls the infection

Congenital diseaseThere are two instances in which cytomegalovirus can cause serious disease. During a primary infection of the mother, the virus can spread via the placenta to the fetus and congenital abnormalities can occur; in fact, this virus is the most common viral cause of congenital disease. Up to one in forty newborns in the United States are infected by the virus. Abnormalities include microcephaly, rash, brain calcification and hepatosplenomegaly. These may result in hearing loss (bilateral or unilateral) and retardation. As might be expected, when reactivation occurs in a pregnant mother (usually reactivation in the cervix), the symptoms are less severe because of the mothers seropositivity. In this case, congenital abnormalities are rare.

Besides infection in utero, infants may be infected perinatally

DiagnosisMost infections are asymptomatic and therefore go undiagnosed. There are fluorescent antibody and ELIZA tests. Multinucleated (cytomegalinic) cells with characteristic inclusions can be seen in biopsies of many tissues.

TreatmentGanciclovir, which inhibits the replication of all human herpes viruses, is usually used, especially to treat retinitis. Foscarnet is also approved in the US. Acyclovir is not effective.

A vaccine is being developed but the best way to avoid the virus is to restrict contact between infected children and pregnant women.

Also since cytomegalovirus is sexually transmitted, condoms can limit spread.

H&E stain of lung section showing nuclear inclusions with the appearance of an "owl's eye". The inclusion is surrounded by a clearhalo that extends to the nuclear membrane. CMV infection can occur without the typical cytomegalic cells.

H&E stain of CMV-infected cells in lung of AIDS patient. Nuclear inclusions can be seen 

Specimen of human embryonic lung reveals the presence of cytomegalovirus using immunofluorescent technique. Mag. 25X. CDC/Dr. Craig Lyerla

POXVIRUSES

POXVIRUSES   There are several reasons why poxviruses are of importance:Certain poxviruses are of historic note,  such as smallpox and vaccinia (cow pox, which was used in the smallpox vaccinePox viruses may be possible agents of bioterrorism Pox viruses are used in new techniques of vaccine development (such as genetically-engineered vaccinia) Some members of this family infect man (molluscum contagium , monkey pox, cow pox). Note: chicken pox is caused by a herpes virus which  is not a member of the poxviridae

Possible scheme for the formation of infectious pox virions. The virus core becomes wrapped in cytoplasmic membrane and may escape when the host cell is lyzed. Some other membrane-bound virions may bud through other membranes, in which case they have two membranes. In either case, the virions are infectious. Adapted from  Baron, S. Ed. Medical Microbiology 4th Edition. 1996.