EQUINE VETERINARY EDUCATION / AE / SEPTEMBER 2018
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Horizontal Transmission
-Semen collection (contaminated artificial vagina & phantom)
-Personnel -Teaser -Fomites
-Masturbation
Stallions Colts
No carrier state in mares, geldings and prepubertal colts
Natural Reservoir of EAV Carrier Stallion
Venereal Transmission
-Natural breeding -Artificial breeding
Raw semen Chilled semen Frozen semen
EVA Outbreak Horizontal Transmission
-Aerosolisation of respiratory secretion
-Direct contact with virus in placental fluids, secretions & fetal tissues
Mare Pregnant and non-pregnant mares, geldings, <6 month-old foals Fig 1: Transmission and outcome of equine viral arteritis (EAV) infection in equine populations. Clinical signs and the disease
The range and severity of clinical signs displayed by EAV acutely infected horses depend on a variety of factors, including the genetics, age, physical condition of the horses, challenge dose, route of infection, viral strain, and environmental conditions (Vaala et al. 1992; McCollum and Timoney 1998; Moore et al. 2002). Although there is only one known serotype of EAV (McCollum 1969a), there is
significant variation in virulence phenotype between EAV field strains, and based on the clinical severity of the disease during natural outbreaks, EAV field strains could be segregated into viruses that cause moderate to severe disease (e.g. EAV KY84, EAV AZ87, EAV IL93 and EAV PA96), moderate disease (EAV PA76, and EAV KY77) mild disease (e.g. EAV SWZ64, EAV AUT68, EAV IL94 and EAV CA97), and asymptomatic infection (e.g. EAV KY63, and EAV CA95) (Balasuriya et al. 1995, 1997; MacLachlan et al. 1996; McCollum and Timoney 1998; Moore et al. 2002, 2003a,b; Zhang et al. 2008, 2010a, 2012; Pronost et al. 2010; Vairo et al. 2012, 2014). The highly virulent horse-adapted Bucyrus strain of EAV (VBS, which causes high mortality in healthy mature horses) and the associated pathology is not representative of that caused by field strains of the virus
isolated to date; it is best regarded as a laboratory derived experimental virus variant. While the vast majority of EAV infections are inapparent
(or subclinical), some acutely infected animals may develop a wide range of clinical signs. After an incubation period of 2–14 days (6–8 days after venereal exposure), EAV infected horses can develop a wide combination of clinical signs, including respiratory disease and reproductive consequences (Fig 2).
Acute infection Acutely infected animals may develop an influenza–like syndrome, with fever, depression, anorexia, dependent oedema (scrotum, mammary gland, ventral trunk, and limbs), stiffness of gait, conjunctivitis and rhinitis with nasal and ocular discharge, periorbital and/or supraorbital oedema, respiratory distress, skin rash (localised to the sides of the neck, face, or widespread), and leukopenia (Doll et al. 1957b; McCollum et al. 1971, 1995; McCollum and Timoney 1984; Timoney 1984; Timoney and McCollum 1993; Glaser et al. 1996, 1997; Balasuriya et al. 1999b, 2002a) (Fig 2). Pyrexia (of up to 41°C) may persist for 2–9 days (McCollum et al. 1988; MacLachlan et al. 1996; Balasuriya et al. 2007; Go et al. 2012b; Zhang et al. 2012; Campos et al. 2014). Other less frequently
© 2016 EVJ Ltd
-Fomites -Personnel
Establishment of persistent infection
Abortion Weak foals
Congenital infections
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