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EQUINE VETERINARY EDUCATION / AE / SEPTEMBER 2018


and Rules from the US Department of Agriculture Animal and Plant Health Inspection Service (USDA-APHIS 2004). In some European countries including the UK, Ireland, Germany, France and Italy, the Codes of Practice and guidelines on artificial insemination are distributed as voluntary recommendations to aid in the control and prevention of several equine diseases, including EVA (HBLB 2016). Furthermore, the OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals, and the Terrestrial Animal Health Code (OIE 2013, 2015) establish the international standards for EVA laboratory testing and movement of horses. The interested reader should refer to these documents along with the American Association for Equine Practitioners guidelines for more detailed information (www.aaep.org). In terms of the identification of EAV infected stallions, the


vaccination history, serological status, and virological assessment of their semen is recommended prior to breeding or to the introduction of these animals into new premises to prevent EVA outbreaks both nationally and internationally. All stallions should be tested for the presence of neutralising antibodies in serum at least 60 days before initiation of the breeding season. If the stallion is determined to be seropositive


(neutralising antibody titre ≥1:4) and has no certified history of vaccination against EVA or confirmation of seronegative status prior to the initial vaccination, virological assessment of their semen is required to determine their infection status and potential carrier state (Fig 3). The OIE prescribed test for detection of EAV in semen samples (VI) should be performed on two semen samples from two independent collections that can be performed on the same day, consecutive days, or after an interval of several days or weeks, and should contain the sperm-rich fraction of the ejaculate. The turnaround time for this test is typically more than a week. Alternatively, the test breeding procedure constitutes another method for the identification of EAV carrier stallions. This method consists in test breeding two seronegative mares twice, each on two consecutive days, for a total of four covers. The mares are kept in quarantine and tested for the presence of neutralising antibodies at 28 days after breeding. If the test is performed properly and strict quarantine is maintained, seroconversion in one or both mares bred to the stallion is evidence of EAV infection and, thus, indicates that the stallion is persistently infected (carrier stallion). Similarly, fresh, chilled, or frozen semen can also be tested by this methodology. Confirmed carrier stallions can still be used for breeding


purposes provided that strict requirements are met (Timoney et al. 1987a,c; Timoney and McCollum 1993; Timoney 2000a, b). However, it should be considered that regulatory policies from other countries might not allow the introduction of carrier stallions or their use for either natural or artificial breeding purposes. Carrier stallions should be kept physically isolated from


other horses and only bred to seropositive mares resulting from either natural infection or vaccination against EVA as indicated previously (McCollum et al. 1988). If semen is to be collected from carrier stallions, this should be performed separately from other stallions in order to prevent contamination of collection equipment and other materials (fomites) that could be a potential source of lateral transmission. In regards to embryo transfer, both donor and recipient mares should be vaccinated against EVA at least


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3 weeks prior to breeding and embryo transfer (Broaddus et al. 2011a). Furthermore, it is highly recommended to vaccinate


horses that frequently travel to competitions or comingle with other horses coming from outside on a regular basis. The OIE Terrestrial Animal Health Code establishes the general provisions and recommendations for the international movement of horses (stallions, mares, foals and geldings) and importation of equine semen, and readers are encouraged to refer to this code for more detailed information. In regards to the movement of horses other than stallions, it is required to maintain a quarantine period of 28 days during which no clinical signs of EVA should be observed and stable or declining antibody titres, or a seronegative status demonstrated between two serum samples collected at least 14 days apart before their introduction onto new premises. In the case of stallions, these should be kept under quarantine as indicated for other horses and their serological status determined. If seropositive, subjected to detection of EAV in semen samples as described previously and recommended in the OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals. In the event of an outbreak, the state veterinarian needs


to be notified immediately, and the facilities placed under strict quarantine. Clinically affected and in-contact horses need to be isolated, and all animal movements suspended (http://www.aaep.org/info/guidelines). Furthermore, at-risk horses should be vaccinated and breeding activities interrupted to prevent further spread. It is important to realise that during an outbreak of EVA, the respiratory mode of transmission facilitates the spread of EAV and attack rates can escalate fairly quickly (Olguin Perglione et al. 2010; Zhang et al. 2010a). If facilities are not placed under quarantine, the infection can easily spread to other premises as well. Thus, immediate quarantine and segregation of affected horses should be pursued before laboratory confirmation in order to limit the risk of wider occurrence of EVA, associated abortions, and persistent infection in stallions. Diagnosis of EVA should always be confirmed by laboratory testing, and farm managers and veterinarians should submit appropriate samples immediately. Stalls and other equipment on affected premises should be decontaminated. Any disinfectant including phenolic, chlorine, iodine, and quaternary ammonium compounds is usually adequate to inactivate EAV. The quarantine will be lifted depending upon current regulatory policies that vary among countries; however, it is frequently discontinued when no additional EVA cases or serologic evidence of infection are observed for 3–4 consecutive weeks after the last confirmed case.


Significance to the equine industry


Equine viral arteritis outbreaks have occurred around the world, and there is sufficient evidence that clearly shows an increase in the global incidence of the disease in the past years (McCollum et al. 1998; Balasuriya et al. 1999a; Hedges et al. 1999; Timoney 2000a,b; Guthrie et al. 2003; Zhang et al. 2007, 2010a; Olguin Perglione et al. 2010; Miszczak et al. 2012). These outbreaks have had significant economic consequences in terms of direct financial losses to the equine industry, as they can be associated with the occurrence of widespread abortions in pregnant mares, fulminant disease in young foals, establishment of the carrier


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