VIRAL INFECTIONS OF THE RESPIRATORY TRACT DR. JEYAKUMAR NELSON UNIT OF MICROBIOLOGY MBBS ( BATCH-17)

LEARNING OBJECTIVES discuss the defense mechanism of the respiratory tract. enumerate the viruses that can cause respiratory tract infections. explain the common types of viral respiratory tract infections. highlight the common manifestations of viral respiratory tract infections. describe the principles of the laboratory diagnosis of viral infections of respiratory tract. The objectives of this lecture are to

enumerate the viruses that can cause respiratory tract infections. associate and match the various types of viral respiratory tract infections with the common aetiological agents. construct a flowchart of the steps involved in the laboratory diagnosis of the causative agents of viral respiratory tract infections. At the end of the lecture, student should be able to: Learning Outcomes

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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Key to Respiratory virus RESPIRATORY VIRUS FAMILY (PIECE OR CAP) Viral naming (Ex. Adenovirus – Adenoid tissue) Mostly RNA virus (Expect Adeno, Herpes –DNA virus) Enveloped virus (Except Adeno,Picorna virus –Non enveloped ) Segmented RNA genome (ortho) Negative sense RNA virus (Ortho,Para) Pleomorphic (Ortho,Para, Corona) Common Respiratory virus ( RSV-A,B Influenza-A,B,C Adeno A,B,C,D,E,F,G (1-51) Parainfluenza-1-4 Herpes virus 3,4,5 ) Intelligence without ambition is a bird without wings.

Common respiratory tract viral pathogens

RHINITIS Invade nasopharynx. Induce a flow of virus rich fluid from the nasopharynx when sneezing reflex is triggered large number of viral particles are discharged in the air. Transmission is by aerosol & virus contaminated hands. Viruses possess surface molecules that bind firmly to host cells or cilia or microvilli protruding from the cells. Not washed away in secretions & able to initiate infection in healthy host. Example-Rhino virus, Corona virus.

PHARYNGITIS - Commonly called sore throat. (70% Sore throat caused by virus) -Throat becomes sore either because the overlying mucosa is infected or because of inflammatory & immune responses in the lymphoid tissue. -Common viral agents Rhino viruses, Corona virus, Adenovirus.

Viral infections of the upper respiratory tract may spread downwards to involve larynx & trachea. Pharynx & trachea have non-expandable rings of cartilage in the wall,& are easily obstructed in children because of narrowness. Swelling around vocal card may lead to barking cough (croup) Common viruses are Influenza virus Para influenza virus (75%). LARYNGITIS & TRACHEITIS

BRONCHIOLITIS Restricted to children less than 2 years of age. Bronchioles of children have fine bores if their lining cells are swollen by inflammation, the passage of air is severely restricted. Infection results in necrosis of epithelial cells & spread to lung fields leading to pneumonia. Commonest is Respiratory syncytial virus.

PNEUMONIA Infection of lungs. Air sac filled with exudates, inflammatory cells, fibrin. Virus invade the lung from the blood stream as well as directly from respiratory tract. Common viruses- Influenza, Parainfluenza, Respiratory syncytial virus.

PARAMYXOVIRDAE - CLASSIFICATION

ORTHOMYXOVIRIDAE

 antigenic shifts by a major genetic recombination- “Mixing vessels” (between the RNA of animal viral strains and human strains) where do “new” HA and NA come from? ~ 16 types HA ~9 types NA (144 possible combination) –71 combination circulate in birds

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).

ADENOVIRIDAE 51

SARS VIRUS

HERPESVIRIDAE EPSTEIN-BARR VIRUS(HHV-4)

REFERENCES

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