Prof. Dalia M. Mohsen Prof. In Microbiology. Viral the level of order and follows as thus, with the...

Medical Virology

Dr. Dalia M. Mohsen Prof. In Microbiology CLS 413

Lecture (3)

Prof. Dalia M. Mohsen Prof. In Microbiology

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


Classification of Viruses

• Most clinically important viruses can be classified into groups according to their structural characters into:

A • RNA Viruses

B • DNA Viruses


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

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


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


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.


Virus Causes Disease


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

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.


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.


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.


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.


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.


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.


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.


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


Virus shift can take place when a person or animal is infected with two different subtypes of influenza. .


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


Thank you


Prof. Dalia M. Mohsen Prof. In Microbiology. Viral the level of order and follows as thus, with the...

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