Togaviridae, Flaviviridae and

ArteriviridaePETER 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

ObjectiveStudents 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)

EpidemiologyCarrier 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.