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RNA viruses

RNA viruses. Themes :. Picorna, calici Picorna, Calici Calici Calici Reo. Persistent infections Antigenic variation Immune evasion, Emerging disease Arthropod-transmitted viruses. Picornaviruses and Caliciviruses. Stable in environment. Replication. replicate in cytoplasm

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RNA viruses

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  1. RNA viruses

  2. Themes : Picorna, calici Picorna, Calici Calici Calici Reo Persistent infections Antigenic variation Immune evasion, Emerging disease Arthropod-transmitted viruses

  3. Picornaviruses and Caliciviruses Stable in environment

  4. Replication • replicate in cytoplasm • +ve sense genome (genome RNA is infectious) • encode viral polymerase • mature viral proteins generated through proteolytic cleavage • virions released on cell lysis

  5. PicoRNAviruses ss, positive sense RNA, icosahedral capsid, 25nm, and no envelope Pico= small [Greek] Positive sense ICOsahedral RNA genome 4 coat proteins VP1, VP2, VP3,VP4 simple capsid : 60 capsomere (composed of VP1,2,3)

  6. Picornaviruses • Restricted host range (except FMD) • Resistant in environment • Transmission faecal-oral (fomites, aerosol) • Antigenic variation • Persistent infection (FMD) • Associated with vesicular disease and encephalomyelitis • Diagnosis usually by ELISA (Ag detection) or virus isolation

  7. Picornaviridae 9 genera Important veterinary viruses: Cardiovirus encephalomyocarditis virus ECMV Hepatovirus avian encephalomyelitis Enterovirus swine vesicular disease, porcine enteroviruses Aphthovirus foot and mouth disease Teschovirus porcine teschovirus

  8. FMDV • virus extremely infectious • rapid replication cycle, high virus yield • large volumes in aerosols, virus stable • short incubation period • wide host range • dissemination pre-diagnosis - virus excreted up to 4 days pre-clinical signs + mild clinical picture in some hosts (sheep) • carriers - persists in pharynx • transmitted by animals/contaminated items/ people/environment, windborne

  9. Foot and Mouth Disease Virus Vesicles on foot Ruptured Vesicles on tongue • Aphthovirus genus NOTIFIABLE First animal virus discovered (1898); one of most contagious viruses cloven hoofed animals - cattle, pigs, sheep….. low mortality but high morbidity - fever, oral/feet/teat lesions dairy herds - reduced milk yield beef cattle - reduced growth

  10. FMD excretion

  11. FMD : broad host range Amount of virus shed Clinical picture Sensitivity to infection Carriers ‘amplifier hosts’

  12. A O UK 2001,7 SAT2 Namibia SAT2 SAT3 FMDV serotypes endemic in south america, africa, asia, middle east 7 immunologically distinct FMD types (serotypes) SAT3 SAT1 C Asia-1 • animal with immune response to one serotype is not protected against infection by a different serotype • vaccines must contain serotypes of all strains circulating in that region

  13. Foot and mouth disease : UK 2001 2030 cases Slaughter policy 9500 premises 4 million animals [40 total] £8 billion Serotype O FMD-free areas ? illegal importation of W. Asian meat + inadequate treatment of swill fed to pigs

  14. Control FMD-free countries [post vaccination/eradication campaigns] importation controls - animals, meat, animal products surveillance and reporting procedures [World Reference Lab UK] Ban on swill feeding (instigated due to 2001 outbreak) - outbreak UK 2001 - slaughter policy (infected, contact premises), animal (+ personnel) movement controls, disinfection Endemic countries vaccination (multivalent) first virus eradicated worldwide : smallpox 1977 first animal virus rinderpest (paramyxovirus) [goal 2010] second targeted virus : poliovirus (picornavirus) [ongoing]

  15. Caliciviruses ss, positive sense RNA, icosahedral capsid, 40nm, no env • EM - Star of David - cup-shaped • on capsid surface (calyx=cup) - single capsid protein - 2 or 3 open reading frames • caliciviruses typically associated with respiratory, vesicular, haemorrhagic disease, gastroenteritis • emerging diseases – Rabbit haemorrhagic disease virus (RHDV) • Humans: main cause of non-bacterial gastroenteritis

  16. Veterinary Caliciviruses vesivirus : feline and canine calicivirus vesicular exanthema of swine lagovirus : rabbit haemorrhagic disease virus European brown hare syndrome virus Caliciviruses exist in marine species : Ocean reservoir

  17. Feline Calicivirus respiratory disease - (40% cases), usually associated with feline herpesvirus (cat flue) main clinical feature: chronic stomatitis - nasal/ocular discharge (rhinitis/conjunctivitis, oral lesions, fever, lameness), can be fatal in kittens

  18. Theme : virus persistence FCV (calicivirus) vs FHV (herpesvirus) • major viral causes of upper respiratory tract disease (cat 'flu‘) [note NOT influenza virus (orthomyxovirus)] • upper respiratory tract, mouth ulcers • FCV - chronic, productive infection • FHV - periodic virus shedding (due to reactivation of latent virus)

  19. Rabbit haemorrhagic disease virus • European rabbit : necrotic hepatitis - death in 2 days, acute respiratory/cardiac failure, up to 95% mortality Notifiable • foecal/oral transmission (inhalation, insects) • some rabbits may be carriers • control : inactivated vaccines available (infected rabbits)

  20. Birna- and reoviruses replicate in cytoplasm, virus polymerase stable in environment * potential for reassortment

  21. Bi-rna-viridae dsRNA, non-enveloped, 60nm Two segments RNA genome 60nm aquabirnavirus infectious pancreatic necrosis (IPN) : fish avibirnavirus infectious bursal disease : chickens

  22. Infectious pancreatic necrosis (IPN) • affects young salmon, trout • high mortality - gut haemorrhage, pancreatic necrosis • Shetland 10% production (>1 million fish) £2 million 2001 • IPN (& Infectious salmon anaemia) - major threat to salmon • farming industry

  23. Infectious bursal disease of chicks IBDV (Gumboro disease) • 3-6 week old chicks • Virus kills immature B-lymphocytes in • bursa of Fabricius • Virus kills T-lymphocytes in the thymus • Causes severe combined immunodeficiency • Very virulent (VV) strains 50% mortality • Recovered chicks immunosuppressed : • - increased susceptibility to pathogens • - decreased efficacy of vaccines • Vaccination of breeders, chicks enlarged bursa of fabricius Notifiable

  24. Reoviridae ds RNA, non-enveloped, cubic symmetry, double capsid, 60nm. Respiratory Enteric Orphan VIRUS • Rotavirus • Orbivirus 11 genera : important veterinary genera - outer capsid (ico) inner capsid (ico) capsid - layered core

  25. Rotavirus latin: 'wheel' • a major cause of diarrhoea (scours) in very young calves, • - foecal/oral transmission (waterborne) • - vaccines available for dam - boost colostral Ab

  26. Rotavirus infection infection of enterocytes at TIPS of villi in small intestine

  27. Orbiviruses latin : 'ring' Bluetongue African horse sickness Theme : Arthropod transmitted arboviruses - replicate in insect vectors

  28. Bluetongue • Africa, Middle East, Asia, Americas • 24 serotypes – antigenically diverse (vaccination implications) • Disease in sheep (+deer) • Cattle important reservoirs (subclinical) • Transmitted by midge vectors : late summer fever, changes to the mucous linings of the mouth, nose (cyanosis of tongue), coronary band: reproductive disorder, vascular disease Notifiable disease

  29. Culicoides spp. 'no-see-ums' • female midges feed every 4 d (2 month lifespan) • once infected pass virus in saliva

  30. African Horse Sickness • endemic in Africa (outbreaks in Spain, Portugal 1980s) • >75% mortality (horses) • with VEE, most important, lethal viral disease of horses • cardiac/respiratory disease - death within 1 week • horse sickness fever - mild [zebra, donkeys (maintenance hosts)] • fever + swelling forebody, coughing • transmitted by midge (culicoides) vectors • control : vector control, quarantine, vaccination Notifiable disease

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