Lecture 35: Common Viral Diseases DR. N. JEYAKUMAR UNIT OF MICROBIOLOGY MBBS ( BATCH-17)

Lecture 35: Common Viral Diseases OBJECTIVES: The objectives of this lecture are to introduce emerging viral infections such as SARS, Influenza, Nipah viruses discuss the mode of transmission and pathogenicity of these viruses describe laboratory diagnosis of these viruses discuss the methods of prevention

Learning Outcomes At the end of the lecture, students should be able to: describe the pathogenicity and laboratory diagnosis of SARS, Influenza and Nipah viruses. discuss the prophylactic measures available to prevent an epidemic.

Infections of the Respiratory tract Upper respiratory tract –nose, nasal cavity, sinuses, mouth, throat. Lower respiratory tract –Trachea, bronchi, bronchioles and alveoli in the lungs. Most common microbial entry point for infections

DEFENSE MECHANISMS OF RESPIRATORY TRACT Mucus Acts as a protective barrier, inhibiting the adherence of viruses to the respiratory epithelial cells, preventing its access to the body. Mechanical removal Trapped viral particles in adhesive mucus removed by -ciliary action -coughing -sneezing Presence of normal flora in upper respiratory tract interfering with colonization of pathogen. The ciliary defense of the respiratory tree.

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ORTHOMYXOVIRIDAE

Morphology of influenza virus nm in diameter Spherical in shape Has a viral envelope that contains glycoprotein: -Hemagglutinin (HA) Made up of lecitin mediates cell binding -Neuraminidase (NA) A hydrolytic enzyme that cleaves the sialic acid

 Symptom  Symptom : chills, fever, headache & general muscular aches (associated with the IFN production during infection ) occasionally “stomach flu” Infection  Infection : usually restricted to the upper respiratory system, but some change in virulence allowed the virus to invade the lungs and cause viral pneumonia Recovery Recovery : a few days Influenza (Flu) Influenza (Flu)

Pathogenesis

Pathogenicity of influenza virus 1.Hemagglutinin (HA) serves as receptor by binding to sialic acid, have antigenic site 2. Neuraminidase (NA) Acts as an enzyme, cleaving sialic acid from HA Serves as important antigenic site Necessary for penetration of virus through mucin layer of respiratory epithelium Antigenic drift in NA

3. Nonstructural Protein 1 (NS1) inhibit splicing of pre-mRNA suppress interferon response in virus- infected cells Leads to unimpaired virus Production

4. Nucleoprotein (NP) -bind and protect DNA -has a signal that allows the protein to actively migrate to nucleus -interaction of NP with the viral polymerase protein complex (Switching Transcription mode  Replication mode)

Primary replication Where does the primary replication occur? In humans: Epithelial cells of the upper and lower respiratory tract

Epidemiology of Influenza Epidemiology of Influenza ~ 16 types HA ~9 types NA (144 possible combination) –71 combination circulate in birds pigs –can be infected by avian and human influenza viruses

Influenza Virus- New human strains every year by Mutations

Bird flu is an infection caused by avian (bird) influenza (flu) A viruses. This flu virus can affect domestic and wild bird species including chickens, turkeys, ducks, geese, gulls, shorebirds. Aquatic birds (ducks, shore birds, and gulls) are the natural reservoirs for the avian flu viruses. The waterfowl do not develop disease when infected with avian influenza (asymptomatic).

Specimens Nasal swab Nasopharyngeal swab Nasopharyngeal/throat/ bronchial aspirate Serum