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EQUINE VETERINARY EDUCATION / AE / SEPTEMBER 2018
Stallion for Breeding Test for neutralising antibodies to EAV at least 60 days prior to breeding
Seropositive Stallions (Titer ≥1:4)
Test two separate semen samples by virus isolation
Virus isolation positive
Virus isolation negative
Test breed to two seronegative mares twice each on two consecutive days (four covers)
28 days post breeding of test mares – check for neutralising antibodies to EAV
Seronegative mares Classified as “seropositive nonshedding stallion” •
Stallion is qualified for breeding (annual vaccination required)
Seroconversion of one or two mares
•
Stallion should have been seronegative before vaccination (valid vaccination certificate should be available)
•
If seropositive, owner should provide the previous vaccination certificate
Seronegative Stallions (Titer <1:4)
Vaccinate* •
• • •
A serum sample should be collected at the time of vaccination
Record vaccination
Isolate for 28 days after vaccination
Do not use for natural or artificial breeding within 28 days after first vaccination
Annual booster vaccination after initial vaccination
Carrier stallion
• • •
Carrier stallion must be housed, handled, and bred in a facility separated from uninfected stallions The carrier stallion should be approved by the State Veterinarian for breeding
The carrier stallion should be bred only to mares that are seropositive either by natural exposure or by vaccination (neutralising antibody titer ≥1:64)
Fig 3: Guidelines and recommendations for the diagnosis and prevention of EVA in stallions. RT-PCR, reverse transcription–polymerase chain reaction. 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.
available at the time of the first vaccination (Fig 3). To date, there is no evidence that a stallion vaccinated with the MLV vaccine will develop the carrier state with this attenuated viral strain (Timoney et al. 1988; Summers-Lawyer et al. 2011). However, vaccination of persistently infected stallions does not induce clearance of the carrier state.
Vaccination of mares to be bred to carrier stallions Carrier stallions should only be bred to seropositive mares resulting from either natural infection or vaccination against EVA (McCollum et al. 1988). Determination of neutralising antibody titres in serum of mares should be performed at least 30 days before being bred to a persistently infected stallion or artificially inseminated with infective semen; antibody titres ≥1:64 are considered protective (Fukunaga et al. 1982, 1996). Mares in compliance can be bred to carrier stallions or artificially inseminated with infective semen without prior vaccination (McCollum et al. 1988). Otherwise, mares need to be vaccinated at least 3 weeks prior to breeding, and isolated for not less than 21 days for the reasons described above (Fig 4). After being either bred to a carrier stallion, artificially inseminated with infective semen or
© 2016 EVJ Ltd
embryo transferred from a donor mare bred to a carrier stallion or its semen, mares should be isolated from other seronegative horses for a minimum of 21 days. Vaccinated mares should be revaccinated on an annual basis, 21 days prior to the breeding season if planning to be naturally or artificially bred to carrier stallions, but it is not required to keep them isolated after breeding them for a second time. Vaccinated mares naturally bred to a carrier stallion or inseminated with infective semen can become re-infected as evidenced by the transient detection of viraemia in buffy coat cells and viral shedding through nasal secretions, but do not develop clinical signs of EVA (McCollum 1986; McCollum et al. 1988).
Future directions for EAV vaccines Notwithstanding the efforts to develop second generation vaccines that could be safer and elicit effective immune responses in order to prevent re-infection (Castillo-Olivares et al. 2001, 2003b; Balasuriya et al. 2002a; Giese et al. 2002; Zhang et al. 2012; van Kasteren et al. 2015), no candidate vaccine has reached the market so far. Moreover, it is not possible to differentiate vaccinated from infected animals
* Modified live virus vaccine (ARVAC®)
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