ORTHOMYXOVIRIDAE- INFLUENZA VIRUSES PETER H. RUSSELL, BVSc, PhD, FRCPath, MRCVS Department of Pathology and Infectious Diseases, The Royal Veterinary College, Royal College Street, London NW1 OTU. E-mail Web site Objectives Students should be able to: • realise that most isolates of influenza viruses are species-specific • define antigenic shift and drift and comment on the mechanisms of each. • explain how vaccines are made and why they become out of date. • describe in outline the pathogenesis and control of equine influenza. Introduction Influenza viruses cause epidemics of respiratory disease in most species (but not dogs or cows). New antigenic variants can infect recovered or vaccinated hosts. This is why these fragile viruses have not been eliminated by vaccination. Antigens 1. Type specific. 2. Subtype specific antigens on H and N. 3. Antigenic drift - variation of H within a subtype within a host species 4. Antigenic shift - change of subtype of H within a host species. 1.Type specific antigenic. 2.Subtype specific antigens on H and N detected by HI and NI tests. 3.Antigenic drift - evolution of a variant within a subtype, meaning imperfect protection by old vaccines 4.Antigenic shift. Complete change of H molecule meaning no protection by old vaccines. Shift occurs by a) gene reassortment, b) change of species specificity Vaccines Virus is grown to high titre in millions of hens eggs then inactivated with 1/4000 betapropiolactone. BPL was once used to polymerise bakelite e.g for brown radio facias. It is now used to polymerise nucleic acid during vaccine production. The vaccine is purifed by differential centrifugation and mixed with an adjuvant for injection. EQUINE INFLUENZA Introduction Clinical equine influenza (stable cough) used to be a problem in cities. Equine 1 (H7N7) has been absent from the UK since 1977. In 1998 an American-like isolate of equine 2 (H3 N8) caused an outbreak in UK/EU. Both are controlled by a vaccination scheme administered by the jockey club. EQUINE INFLUENZA Immunity and epidemiology: As with most viruses the period of virus excretion from nasal secretions is during the first 10 days following infection before spec-immunity kicks in. Vaccinated animals can excrete virus without disease and have carried the virus between countries eg to South Africa from USA. As with other resp viruses spread is by personnel and instruments (which most vets do not realise) as well as by aerosol eg at race meetings. No zoonotic risk. EQUINE INFLUENZA Control: Isolate coughing horses to minimise spread and use disposable syringes when treating them. EQUINE INFLUENZA References Duration of protective efficacy of equine influenza immunostimulating complex/ tetanus vaccines. Mumford et al., Vet Rec (1994) 134 158- 162 Equine influenza in the UK in 1998. Newton et al., Vet Rec (Oct 16th 1999) 145, 449-52. SWINE INFLUENZA H1N1 variant 1992. This is the primary pathogen of current concern, others cause little disease. Bronchiolitis with interstitial pneumonia giving consolidation of lungs and 'meaty' appearance. Jerky respiration (USA, the thumps). SWINE INFLUENZA Diagnosis Clinical pneumonia is suggestive. Paired serum samples to show seroconversion by HI. AVIAN INFLUENZA BOVINE INFLUENZA INFECTIOUS SALMON ANAEMIA (and haemorrhagic kidney syndrome) Summary Antigenic shift and drift of H is crucial to immunity. Virulence and tissue tropism are controlled by the cleavage site of H0. Vaccines are grown in eggs. Equine influenza is diagnosed by ELISA but isolates are characterised by the growth of virus collected in transport medium. Coughing is prevented by vaccination. A more virulent isolate of porcine influenza is now circulating in the UK, no vaccine is licensed in the UK.