Togaviridae, Flaviviridae and Arteriviridae peter h. Russell, bvsc, PhD, frcpath, mrcvs



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Togaviridae, Flaviviridae and Arteriviridae

  • 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


Objective Students should be able to:

      • describe in detail how louping ill of sheep is transmitted from shrews and grouse to end hosts (eg ruminants, dogs and man) by Ixodes ricinus
      • define the salient features associated with equine viral arteritis and porcine respiratory and reproductive syndrome (PRRS).
      • explain why antigenic variation and persistence make control difficult


Family TOGAVIRIDAE

  • These are medium sized (70nm), icosahedral, enveloped, single-stranded positive-sense RNA viruses with 2-3 glycoproteins as spikes.



Genus ALPHAVIRUS

    • EQUINE ENCEPHALOMYELITIS VIRUS


Genus ALPHAVIRUS

    • EQUINE ENCEPHALOMYELITIS VIRUS (cont.)


Family FLAVIVIRIDAE

  • These are like the togaviruses but smaller.



Genus FLAVIVIRUS, LOUPING ILL

  • Cattle, sheep, deer, dogs and man are all end hosts.

  • Ixodes ricinus is the vector.

  • Shrews and grouse are reservoir hosts.



Genus FLAVIVIRUS, LOUPING ILL

  • Diagnosis

  • Clinical. Virus isolation, serology and histopath to confirm.



Genus FLAVIVIRUS, LOUPING ILL

  • Control



Genus FLAVIVIRUS

          • WEST NILE VIRUS


Family ARTERIVIRIDAE

  • These enveloped RNA viruses have the morphology of togaviridae and the nested mRNAs of the coronaviridae.



PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME (Lelystad virus, Blue ear)

  • The virus was first detected at the Central Veterinary Institute in Lelystad (Holland) in 1990.

  • The European isolates will only grow in cultures of alveolar macrophages, which as with FIPV and feline macrophages, delayed their discovery.

  • Considerable antigenic heterogeneity in Europe. Additional isolates occur in the USA.

  • Isolates of low virulence have now evolved.



PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME (Lelystad virus, Blue ear)

  • Epidemiology:

  • PRRS is highly contagious and disseminated by fomites, wind and AI.



EQUINE VIRAL ARTERITIS

  • (Equine abortion virus) (EVA or EAV)



EQUINE VIRAL ARTERITIS

  • (Equine abortion virus) (EVA or EAV)

  • (cont.)



EQUINE VIRAL ARTERITIS

  • (Equine abortion virus) (EVA or EAV)

  • Epidemiology

  • Carrier animals are important sources of venereal as well as oro/nasal transfer.

  • The virus survives well outside the host on fomites (greek for wood).



EQUINE VIRAL ARTERITIS

  • (Equine abortion virus) (EVA or EAV)

  • (cont.)



Summary

      • Mosquitoes transmit the viral equine encephalitides; and these can be fatal for man – so that all horses and personnel should be vaccinated in areas where the virus is endemic in reservoir hosts.
      • Louping Ill is a problem giving rise to CNS disorders in sheep (and grouse) reared in areas where ticks exist. It can be reduced both by vaccination and by tick control. It is a zoonosis.
      • PPRS is now endemic in the UK pig population and the majority of current strains appear to be avirulent. It can cause respiratory disease, and reproductive failure in sows.
      • EVA has entered the UK but remains rare. The persistently infected stallion sheds virus intermittently in semen and can be a source of outbreaks of abortion.




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