EQUINE VETERINARY EDUCATION / AE / SEPTEMBER 2018
505
Breeding a Mare to an EAV Shedding Stallion Test for neutralising antibodies to EAV at least 30 days prior to breeding
Seropositive Mares (Titer ≥1:4)*
• •
Can be bred to a shedding stallion (natural breeding) or inseminated with EAV-infective semen (artificial breeding) without being vaccinated
Following breeding mares should be kept in isolation for 24 hrs to avoid possible indirect transmission of the virus
Seronegative Mares (Titer <1:4)
• Vaccinate with the MLV vaccinef • •
Record vaccination
Isolate the mare for 21 days and should not be bred during this period
Vaccinate*
Booster vaccination •
• •
Annual booster vaccination against EAV 21 days prior to breeding
Vaccinate*
No isolation necessary following booster vaccination
Subsequent breeding - no need to isolate the mare after breeding to a carrier stallion
* Neutralising antibody titer of ≥1:64 is regarded as protective against EVA.
f Current MLV vaccine is not recommended for vaccinating pregnant mares (see text). Foals should be healthy and at least 6 weeks of age before its dam is vaccinated.
*Modified live virus vaccine (ARVAC®)
Fig 4: Guidelines and recommendations for the use of EAV carrier stallions for breeding purposes. These EVA control and prevention recommendations are based on USDA and AAEP guidelines used in the US. Other countries could follow these recommendations but need to adhere to the guidlines or code practice provided by their respective government or veterinary/industry organisations.
(DIVA) with the currently available vaccines and serological tests. Thus, the development of a DIVA vaccine would be of significant benefit for the equine industry worldwide, facilitating the serological identification of infected from vaccinated animals, facilitating national and international movement of horses, and aiding surveillance programmes that may lead to eradication of EAV. However, this strategy would require very strict vaccination programmes. Previous studies used alphavirus replicon particles expressing the major viral envelope proteins GP5 and M as a vaccine candidate (Balasuriya et al. 2002a). This recombinant vaccine candidate induced neutralising antibodies against EAV and provided protection against a heterologous challenge (Balasuriya et al. 2002a). While this type of vaccine is advantageous since it enables identification of vaccinated from infected horses, the use of a Venezuelan equine encephalitis virus vector renders it unacceptable due to interference with serosurveillance of Venezuelan equine encephalitis. In spite of this, several vector alternatives are currently available and could be utilised to design a novel, effective and safe vaccine against EVA. The use of canarypoxvirus as a vector has proven to be safe and efficacious. Recombinant vaccines using this approach against West Nile virus and equine influenza are commercially available (Minke et al. 2004; Seino et al. 2007; El Garch et al. 2008; Soboll et al. 2010). Moreover, an infectious cDNA clone
of the MLV strain (pEAVrMLVB) was developed and shown to be safe, capable of inducing an antibody response, and afford protection levels comparable to the MLV vaccine (ARVAC) (Zhang et al. 2012). This infectious clone could be further manipulated by genetic engineering (i.e. introducing deletions or insertions of foreign DNA sequences) to generate a second generation DIVA and/or broadly protective vaccine candidates in the future.
Control and prevention strategies
Current EVA control and prevention strategies are aimed at preventing EAV spread in susceptible equine populations, are based on appropriate quarantine and laboratory testing procedures. The management practices used to mitigate the risk of spread of EAV include the identification of carrier stallions, the quarantine of new arrivals, the segregation of pregnant mares and foals from other horses, implementation of biosecurity measures, and enforcement of vaccination programmes (NAHMS 2000; USDA-APHIS 2004; OIE 2015). Even though there is no established domestic EVA control
programme in the USA, the minimum standards for control, detection, and prevention of EVA, as well as minimum EVA requirements for the interstate and intrastate movement of horses are described in Equine Viral Arteritis: Uniform Methods
© 2016 EVJ Ltd •
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After 21 days, breed to the shedding stallion (natural breeding) or inseminate with EAV-infective semen (artificial breeding)
After being bred for the first time to a shedding stallion - isolate the mare for 21 days
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