REOVIRIDAE ROTAVIRUSES AND ORBIVIRUSES PETER H RUSSELL BVSc

REOVIRIDAE: ROTAVIRUSES AND ORBIVIRUSES PETER H. RUSSELL, BVSc, Ph. D, FRCPath, MRCVS Department of Pathology and Infectious Diseases, The Royal Veterinary College, Royal College Street, London NW 1 OTU. E-mail Web site

LEARNING OBJECTIVES Students should be able to: • Relate the pathogenesis of rotaviruses to the methods used for their control. • Discuss the difficulties of making an accurate rotavirus diagnosis. • Explain the control measures adopted for African horse Sickness Virus.

FAMILY CHARACTERISTICS:

ROTAVIRUSES (RVs) DISEASE & PATHOGENESIS

ROTAVIRUSES (RVs) ANTIGENICITY:

ROTAVIRUSES (RVs) HOST RANGE

ROTAVIRUSES (RVs) EPIZOOTIOLOGY:

ROTAVIRUSES (RVs) DIAGNOSIS Care is needed to interpret positive results as RVs are commonly found in the faeces of clinically normal neonatal animals. Compare the number of RV+ve diseased animals with the number of RV+ve unaffected, age-matched animals on the farm. Diagnosis of outbreaks should not be based on single faecal samples.

ROTAVIRUSES (RVs) CONTROL: The following relates to group A RVs but may also relate to the other groups. By an inter-relationship between passive immunity & virus exposure. It is impossible to prevent infection of the young but disease can be supressed/eliminated by keeping the infection pressure low and ensuring neonatal animals receive adequate levels of passive antibody orally while at risk.

AFRICAN HORSE SICKNESS VIRUS (AN ORBIVIRUS) "orbis" = ring (latin) - ring-shaped capsomeres are seen on the surface of virions by electron microscopy. Recognized in Africa since 1780. It is one of the most feared viral diseases of horses but does not occur in the UK.

AFRICAN HORSE SICKNESS VIRUS (AN ORBIVIRUS) ANTIGENICITY: Nine serotypes.

AFRICAN HORSE SICKNESS VIRUS (AN ORBIVIRUS) HOST RANGE: Horses; mules, donkeys & zebras appear to be more resistant to the disease.

AFRICAN HORSE SICKNESS VIRUS (AN ORBIVIRUS) CONTROL:

OTHER MEMBERS Many REOVIRUSES infect the alimentary and/or respiratory tract of cattle, sheep, dogs and cats without causing disease (REO= Respiratory-Enteric-Orphan).

Summary • Rotaviruses pathogenesis is confined to the gut; passive maternal antibody in the gut lumen is important to control the disease. • Care is required in RV diagnosis as RVs are also found commonly in sub-clinical infections • Control of African Horse Sickness Virus centres around vaccination and removal of infected horses and vectors.