Equine Health Update EHU Vol 20 Issue 02 - Page 48

EQUINE | African Horse Sickness Myocardial Dysfunction in Horses with AHS – should we be reconsidering our treatment strategy? Hewetson, M.a 1 , Shaik, Tb 2 1. Deptartment of Clinical Science and Services, The Royal Veterinary College, North Mymms, Herts, AL9 7TA, United Kingdom 2. Department of Companion Animal Clinical Studies, Faculty of Veterinary Science, University of Pretoria, Private Bag X04, Onderstepoort, 0110, South Africa Background African horse sickness virus (AHSV) is a lethal non- contagious insect-borne arbovirus affecting all equids. AHSV is a double stranded RNA virus that belongs to the genus Orbivirus within the Reoviridae family. Nine immunologically different serotypes have been identified 1 , and the virus shares properties with other Orbiviruses e.g. bluetongue and equine encephalosis virus 2 . AHSV is transmitted by Culicoides midges, with C. imicola and C. bolitinos playing an important role in Africa 3 . Of all equids, horses are most susceptible to the disease with a mortality rate of between 70-95 per cent 2 . The disease is enzootic throughout sub-Saharan Africa 4 ; however, it has been reported in North Africa and has occasionally extended as far North as Spain 2 . African horse sickness is an OIE notifiable disease, and is currently considered to pose a significant risk to horse populations in Europe 5 . Epizootics outside the African continent are thought to be related to movement of 48 infected animals; however, climate change and the propagation of infected vectors via wind over long distances cannot be ruled out 6-8 . Clinical signs of the disease typically appear 5 to 7 days after infection, and include pyrexia, inappetence, tachycardia, tachypnoea, haemorrhages and oedema of varying intensity and location 2 . Four forms of AHS have been described 4 : acute (pulmonary) form, subacute (cardiac) form, mixed (pulmonary and cardiac) form and a febrile form. Horses with the pulmonary form present with per acute pulmonary oedema, hydrothorax and respiratory distress; whereas horses with the cardiac form present with subcutaneous and intramuscular oedema, hydropericardium and myocardial haemorrhage 9,10 . The mixed form produces changes characteristic of both the pulmonary and the cardiac form and is considered to be the most common form of AHS 2 . The febrile form of AHS is a mild form of the disease seen in horses with immunity to one or more serotypes of AHSV, and is characterised by a pyrexia with no • Equine Health Update •