Pathogenesis of veterinary respiratory viruses PETER H. RUSSELL, BVSc, PhD, FRCPath, MRCVS Department of Pathology and Infectious Diseases, The Royal Veterinary College, Royal College Street, London NW1 OTU. Web siteWeb site

Objectives Students should be able to: 1. explain how some viruses spread within the respiratory tract whereas others leave it to cause disease elsewhere. 2. describe in outline how host responses, vaccines and maternal antibody influence pathogenesis. 3. evaluate how to determine whether a respiratory tract virus is a primary pathogen or whether it exacerbates bacterial disease or does nothing. 4. compare and contrast acute and chronic virus infections of the respiratory tract.

Objective 1. explain why some viruses spread within the respiratory tract whereas others leave it to cause disease elsewhere.

Lesions and location Lesions are erosions and inflammation. Secondary bacterial infection of the erosions causes mucopurulent exudate.

Disease is compounded by stress whether crowding, transport or social. The contact allows more interchange of viruse eg Battersea dogs home. The stress reactivates viruses eg herpesviruses or increases virus excretion eg feline caliciviruses. Think of examples for calves, pets, horses.

Objective 2. describe in outline how host responses, vaccines and maternal antibody influence pathogenesis.

Antigenic variation can explains vaccine failures when a new isolate of the same virus arrives eg when the 1998 USA-like strain of equine influenza II (H3N8)entered the UK. Variation can mean vaccines partially protect eg with feline calicivirus. These cats can be silent carriers of the antigenically- distinct FCV and then can enter a cattery undetected and cause lesions in unvaccinated cats (cf FMDV).

How do dead subcut vaccines protect? Via circulating IgG which leaks into the inflamed resp tract

Objective 3. evaluate how to determine whether a respiratory tract virus is a primary pathogen or whether it exacerbates bacterial disease or does nothing

Objective 4. Compare and contrast acute and chronic virus infections of the respiratory tract.

Objective 4. Compare and contrast acute and chronic virus infections of the respiratory tract (Cont.)

Further reading

Further reading (Cont.)

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Your ideas please! Key words, Koch postulates, germ free animals,

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