prof. dalia m. mohsen prof. in microbiology. viral the level of order and follows as thus, with the...
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Medical Virology
Dr. Dalia M. Mohsen Prof. In Microbiology CLS 413
Lecture (3)
Prof. Dalia M. Mohsen Prof. In Microbiology
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Classification of Viruses
• Viral the level of order and follows as thus, with the taxon suffixes classification starts at given in italics:
Order
• Virales• e.g.
Herpesvirales
Family
• Viridae• e.g.
Herpesviridae
Genus
• Virus• e.g. Herpes
simplex virus
Prof. Dalia M. Mohsen Prof. In Microbiology
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Classification of Viruses
• Most clinically important viruses can be classified into groups according to their structural characters into:
A • RNA Viruses
B • DNA Viruses
Prof. Dalia M. Mohsen Prof. In Microbiology
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RNA VirusesRNA Non-Enveloped viruses RNA Enveloped viruses
Picorna viruses - Enteroviruses (Polio virus &Coxackievirus) - Hepato virus - Rhinoviruses
Orthomyxoviruses (Influenza virus)
Reoviruses Paramyxoviruses (Measles, Mumps, Parainfluenza)
Caiciviruses Rhabdoviruses (Rabies virus)
Astro viruses Retroviruses (HIV )
Togaviruses (Encephalitis viruses)
Flaviviruses (Yellow fever ,Dengue, HCV)
Bunyaviruses
Filoviruses
Arenaviruses
Corona viruses
Delta virusProf. Dalia M. Mohsen Prof. In Microbiology
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DNA VirusesDNA Non-Enveloped viruses DNA Enveloped viruses
Herpes viruses - HSV 1&2 - Varicella - CMV
Adenoviruses
Hepadna virus (HBV) Papiloma virus
Pox viruses (Smallpox, Cowpox) Parvoviruses
Polyomaviruses
Prof. Dalia M. Mohsen Prof. In Microbiology
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How Virus Causes Disease
• Viruses cause disease after they:
• break through the natural protective barriers of the body.
• evade immune control.
• kill cells of an important tissue.
•Viral and host factors govern the severity of the disease they include:
• The strain of virus
• The inoculums size
• The general health of the infected person
Prof. Dalia M. Mohsen Prof. In Microbiology
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Basic step of virus disease
• Entry into the body.
• Initiation of infection at a primary site.
• Activation of innate protections.
• An incubation period, when the virus is amplified and may spread to a secondary signs.
• Immune responses that limit and contribute to the disease.
• The symptoms of the disease are caused by tissue damage and systemic effects caused by the virus and the immune system.
• The body repairs the damage.
• Virus production in a tissue that release the virus to other people.
Prof. Dalia M. Mohsen Prof. In Microbiology
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Virus Causes Disease
Prof. Dalia M. Mohsen Prof. In Microbiology
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Virus Causes Disease
Group Example
(1)Picornaviruses Polioviruses
(2)Orthomyxoviruses Influenza viruses
(3) Arthropod born viruses Dengue Virus
(4) Paramyxoviruses measles
(5)Retroviridae AIDS
(6)Hepatitis virus (HAV, HBV, HCV)Prof. Dalia M. Mohsen Prof. In Microbiology
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Polioviruses Polioviruses
They cause poliomyelitis which in its full blow picture affects
the CNS and causes paralysis.
Man is the only natural host.
PROPERTIES OF THE VIRUS:
1. It is an icosahedral
2. Non- enveloped virus
3. The genome is a positive sense single stranded RNA.
Prof. Dalia M. Mohsen Prof. In Microbiology
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Pathogenesis of Polioviruses
Infection occurs by the ingestion of food or drink contaminated by stools of cases or carriers.
Incubation period is 7-14 days.
The organism multiplies in the oropharynx (tonsils) then patches in the intestine and excreted in stools.
Infection may stop at this stage i.e. in apparent infection.
Infection may continue and the virus passes to the deep cervical and deep mesenteric lymph nodes then it invades the blood stream. Viremia is associated with mild symptoms of fever, headache, nausea, and vomiting. The disease may be stopped at this stage i.e. abortive infection.
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PARALYTIC POLIOMYELITIS: Occurs only in 0.1-1% of cases. The
virus affects the anterior horn cells of the spinal cord leading to paralysis.
In severe cases, it may affect the posterior horn cells, the vestibular nuclei and motor cortex. Death may occur due to respiratory paralysis.
No permanent carrier state occurs, but virus excretion in stools can occur for several months.
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Diagnosis of Polioviruses:
1. Isolation of the virus from (stools, throat swab, blood, CS) in cell culture. Cytopathic effect appear in positive cases.
2. Detection of antibody by ELISA test.
3. Specific viral RNA can be identified by hybridization or PCR.
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Influenza viruses
Three types of influenza virus are known; A, B and C.
Type A viruses infect humans and several types of animals,
including birds, pigs, and horses.
Type B influenza is normally found only in humans.
Type C is mostly found in humans, but has also been found in
pigs and dogs.
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Structure of Influenza Viruses
Influenza virus is a single stranded segmented RNA virus (gene segments).
The nucleocapside is helical and is surrounded by a lipoprotein envelope
The envelope is covered with two glycoprotein spikes, haemagglutinin(HA) and a neuraminidase(NA).
HA binds to the cell surface receptor (sialic acid) to initiate infection.
Changes in HA and NA determine the antigenicity of the virus and according to which influenza A virus includes 16 HA and 9 NA subtypes that are circulating in birds, human, swine and horses.
Prof. Dalia M. Mohsen Prof. In Microbiology
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Influenza viruses
THE MOST FAMOUS SUBTYPES OF INFLUENZA A VIRUS ARE:
• A(H1N1) Circulating in humans and is causing the 2009 influenza pandemic (Swine flu)
• A(H5N1) circulating in birds causing avian flu and infecting humans who closely handle infected birds. The virus jumped directly from birds to humans.
Prof. Dalia M. Mohsen Prof. In Microbiology
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Influenza virusesANTIGENIC VARIATION:
Is a common phenomenon in influenza viruses due to change in HA and NA. There are two type:
1. Antigenic drifts: These are minor changes due to mutation, resulting in the strains that cause yearly outbreak.
2. Antigenic shifts: These are major changes due to reassortment of gene segments. This occurs when cell is infected simultaneously with two different influenza A viruses( e.g. an avian and a human influenza A virus) mixtures of parental gene segments may be assembled into progeny virions, resulting in a new variant of human influenza A virus
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Virus shift can take place when a person or animal is infected with two different subtypes of influenza. .
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Pathogenesis of influenza virus
Infection occurs by inhalation of airborne droplets.
The neuraminidase of the inhaled virus degrades the protective
mucous layer, allowing the virus to reach the mucous membrane
of the respiratory tract
The incubation period is short 1-4 days.SYMPTOMS:
• fever• Headache• Dry cough • Anorexia
Prof. Dalia M. Mohsen Prof. In Microbiology
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Thank you
Prof. Dalia M. Mohsen Prof. In Microbiology