TABLE 1.
Selected demographic characteristics of study populations.
| Citation no. | Study | Breed | Total number of horses | Sex | Age | Pre‐study EHV‐1 status | Treatments | Comments |
|---|---|---|---|---|---|---|---|---|
| 8 | Allen (2008) |
Thoroughbred (n = 25) Mixed breed (n = 11) |
36 | F | 4 to 28 y | Unvaccinated during year before study | >20 y of age: n = 12 inoculated with EHV‐1 (T953), n = 12 inoculated with EHV‐1 (T262). <15 y of age inoculated with EHV‐1 (T953), n = 12. | Experimental trial. |
| 30 | Allen and Breathnach (2006) | Mixed breed derived from single Standardbred sire | 20 | F (n = NR), M (n = NR) | 7 to 8 mo | Seronegative 1 wk before study | Ten EHV‐1 isolates were used for foal inoculations—five isolates were considered neuropathogenic (n = 10) five were abortigenic (n = 10). | Experimental trial. Data pooled for each viral class. |
| 15 | Brosnahan et al. (2010) | Multiple breeds | 14 | CM (n = 8); F (n = 6) | 2 to 18 y | Negative antibody titer (SN ≤ 1:24) | Horses treated with either sigB3/siOri2 siRNA (n = 10) or siLuc control group (n = 4). | |
| 42 | Burki et al. (1990) |
Haflinger (n = 6) Shetland Pony (n = 3) Thoroughbred (n = 1) |
10 | PF (n = 10) | 3‐12 y | Negative serological titers in sentinel horses during year before experiment | Horses vaccinated with either a live or inactivated vaccine. Challenged 3 wk after last vaccination. | Only data for PF are included in this review. |
| 16 | Edington et al. (1986) | Welsh Mtn Ponies | 8 | F | 6 to >18 y | NR | Mares inoculated with AB4 yearlings with EHV‐1 strain 2252. | Two experiments were performed. |
| Welsh Mtn Ponies | 5 |
F (n = 3) M (n = 2) |
Yearlings | |||||
| 38 | Estell et al. (2015) |
Quarter Horse (n = 5) Standardbred (n = 1) Warmblood (n = 1) |
7 |
F (n = 4) MC (n = 1) M (n = 2) |
3 to 15 y | Previous exposure (via known outbreak or exposure to new additions at boarding facility) | 5/7 horses were treated (eg, flunixin meglumine, steroids, valacyclovir) before referral. | Retrospective case series. |
| 3 | Gardiner et al. (2012) | Ponies (NOS) | 11 |
F (n = 4) PF (n = 7) |
3 y | SN titer < 1:32 | Ponies were inoculated with either OH03 or Ab4. | Two experiments were performed. Mares inoculated at approximately 270‐290 d of gestation. |
| 9 |
F (n = 2) PF (n = 7) |
|||||||
| 43 | Gleeson and Coggins (1980) |
Welsh Mtn Ponies (n = 17) Standardbred (n = 4) |
21 | PF | NR | Unvaccinated during year before study, isolated herd for several years with no known epizootic EHV1 infection | Horses were inoculated with either Army 183 or KyB. | The two studies were conducted over two seasons. |
| 31 | Goehring et al. (2010a) | Mixed‐breed pony | 24 |
F (n = 12) M (n = 12) |
11‐13 mo | Negative SN titers | Ponies were vaccinated 3 times and challenge infected on Day 121 of the experiment | |
| 34 | Goehring et al. (2010b) | Standardbred | 4 | F | 14 to 20 y | Negative SN titer (between 1:128 and 1:256), negative glycoprotein G Ab (ELISA), negative CF titer (≤1:10) | Data from two unexposed controls not included. | |
| 17 | Goehring et al. (2013) | Horses (Western stock) | 8 | Mixed | Yearling | SN titer ≤ 1:32 | Yearlings were inoculated with Ab4 and aged horses were inoculated with OH03. | Two separate experiments were performed with yearlings. Aged horses were part of an antiviral drug study. |
| Ponies (NOS) | 10 | |||||||
| Horses (NOS) | 10 | NR | >18 y | Negative Ab (EHV‐1 specific glycoprotein G) ELISA (<0.5 absorbance) | ||||
| 32 | Goodman et al. (2006) | Mixed‐breed (NOS) | 15 | F | 3‐10 y | Negative EHV1 neutralization titers (SN < 1:24) | Horses (n = 5/group) were allocated to control, inactivated, and modified‐live virus vaccine treatment groups. Challenge occurred 59 d after the initial vaccination. | |
| 35 | Gryspeerdt et al. (2010) | Shetland Pony | 12 | M | 6 mo to 2 y | Negative SN titer (<2), negative IPMA (<10) | Two viral strains used (03P37, 97P70). | Two horses euthanized for tissue virology studies at 1 dpi before onset of fever |
| 18 | Heldens et al. (2001) | Welsh Mtn Ponies | 9 | PF | 3 y | Positive CF and VN antibodies to EHV1 or EHV 4 | Vaccine trial using an inactivated vaccine at 5, 7‐9 mo of gestation and challenged 4 wk after last vaccination. | Data from foals not included in the review. |
| 19 | Holz et al. (2017) | Horses (NOS) | 25 | Mixed | Yearling | SN titer < 4 (EHV1) SN titer < 40 (EHV4) | Multiple viral strains used (Ab4, Ab4 N752, b4 gD4) | Multiple viral strains used (Ab4, Ab4 N752, b4 gD4) |
| 20 | Hussey et al. (2013) | Ponies (NOS) | 10 | NR | NR | SN titer < 1:32 | Three experimental conditions using different virus strains. | |
| 24 | NR | 9‐18 mo | ||||||
| 44 | Kydd et al. (2003) | Ponies (NOS) | 14 | PF | 3 to 20 y | Negative CF antibody titer (1 exception—elevated CF titer present) | Some mares were vaccinated with an inactivated vaccine. Mares previously infected with EHV‐1 were challenged 4 wk after last vaccination. | Third group (multiply infected horses) not included in the review. |
| 33 | Maxwell et al. (2017) | Light horse breeds (NOS) | 12 | F | >20 y | Seronegative for anti‐EHV‐1 antibodies (ELISA) | Therapeutic trial with horses given placebo or prophylactic valacyclovir for 1 or 2 wk. | Data from horses given valacyclovir after detection of fever not included. |
| 22 | Mumford et al. (1991) | Ponies (NOS) | 19 | PF | NR | Unknown | Vaccinated with immune stimulating complexes. Challenge occurred 3 wk after last vaccination. | Two experimental groups: control and mares |
| 21 | Mumford et al. (1994) | Ponies (NOS) | 62 |
PF (n = 61) F (n = 1) |
NR | Isolated and monitored (clinically and serologically) 6 mo before challenge infection. Pre‐challenge VN antibody titers provided for some cohorts (range 10<0.6 to 102.2) | Multiple viruses and doses used. | Data for different doses were pooled. |
| 45 | Patel et al. (2003) | Welsh Mtn Ponies | 18 | PF | NR | No or low virus neutralizing antibody to EHV‐1 or EHV‐4. | Some mares (n = 6/group) were vaccinated at 3.4‐4.1 mo of gestation or between 5.4 and 5.8 mo of gestation. Challenged between 8.4 and 8.9 mo pregnant. | |
| 24 | Perkins et al. (2013) | Horses (NOS) | 13 |
CM (n = 6) F (n = 7) |
3‐20 y | Negative antibody titer (SN ≤ 64). Unknown vaccination history | Trials with small interfering RNAs (siRNAs) or an irrelevant siRNA administered before and after infection. | |
| 23 | Perkins et al. (2019) | Icelandic | 15 | CM (n = 10), F (n = 5) | 2.5 y | EHV‐1 naïve herd. | Horses were initially uninfected (control) or exposed to EHV‐1 (Ab4 or Ab4ΔORF1/71) and then challenged 6 mo later. | Data from second challenge extracted. |
| 41 | Pusterla et al. (2008) |
Thoroughbred (n = 41) NR (n = 27) |
68 | NR | Adult (NOS) | Involved in a reported EHV‐1 outbreak (natural exposure). | Three cohorts of horses: febrile (n = 12), neurologic (n = 15), and subclinical (n = 41). | |
| 40 | Pusterla et al. (2012) | Quarter horse (n = 32), draft breeds (n = 30), standardbred (n = 15), others (n = 5) | 82 |
F (n = 34) CM (n = 48) |
3 to 30 y | Natural exposure at packing station. Unvaccinated during year before outbreak. | Data from mules not included. | |
| 39 | Pusterla et al. (2021) | Warmblood (n = 24), others (n = 7) | 31 |
F (n = 17) CM (n = 14) |
1 to 27 y | Natural infection at performance farm discovered during routine dental care and vaccination | Horses treated with valacyclovir (n = 31), flunixin meglumine (n = 26) and/or heparin (n = 26). | |
| 26 | Schnabel et al. (2018) | Icelandic | 16 |
F (n = 8) CM (n = 8) |
2 to 4 y | Previously infected with EHV‐1 (NY03) at 7 mo. Protective immunity had “waned to values typically observed in EHV‐1 susceptible horses” | Used two viruses (Ab4 or Ab4ΔORF2). | Data from uninfected control group are not included |
| 25 | Schnabel et al. (2019) | Icelandic | 24 |
F (12) M (12) |
3‐5 y | EHV‐1 naïve herd. | Horses were initially uninfected (control) or exposed to EHV‐1 (Ab4 or Ab4ΔORF1/71) and then challenged 9 mo later. | Data from second challenge extracted. |
| 36 | Soboll et al. (2010) | Ponies (NOS) | 26 | NR | 2‐7 y | Previously exposed to EHV‐1 > 12 mo ago | Ponies were challenge infected 8 wk after the last vaccination. | Ponies expressing different MHC I haplotypes were used as well as a recombinant modified vaccine and unvaccinated controls. Clinical scores were derived by allocating 1 point for cough, ocular discharge, nasal discharge, depression, and pyrexia (>38.6°C) and calculating the sum. |
| 37 | Sutton et al. (2020) | Welsh Mtn Ponies | 4 | M | 10 mo | Seronegative for EHV‐1 and EHV‐4, SN and CF assay, no history of EHV infection | Experimental trial—no comparator group or dose‐response data (virulence study). | |
| 10 | Van de Walle et al. (2009) | NR | 9 | NR | NR | SN antibody titer < 24 | Two Ab4 strains used (parental rNY03_N752 of mutant rNY03_D752). | Viremia a score of 0: no virus isolated, score = 1:1‐10 plaques using 5 × 106 PBMCs, score = 4: plaques seen using 5 × 103 PBMCs. |
| 27 | Wilson et al. (2019) | NR | 8 | Mixed (NOS) | Yearling | Unvaccinated, EHV‐1 titers ≤ 1:2, EHV‐4 titers ≤ 1:20 | Data from controls (uninfected) not included. Total of 11 horses used, staggered start with some controls were exposed to EHV‐1 (n = 8). | |
| 28 | Wimer et al. (2018) | Icelandic ponies | 15 |
F (n = 5) CM (n = 10) |
2.5 y | Naïve herd | Groups included uninfected (control) or exposed to EHV‐1 (Ab4 or Ab4ΔORF1/71). | Data from uninfected controls (n = 5) are not included in the review. |
| 29 | Zarski et al. (2021) | Mixed breeds (NOS) | 7 |
M (n = 5) F (n = 2) |
2 y | SN antibody titer ≤ 1:8 for EHV‐1 | Horses received (IN) either a human adenovirus vector expressing the EHV‐1 IR2 protein or a null adenovirus vector 2 d before EHV‐1 challenge. | Data were pooled for these groups. |
Abbreviations: CF, complement fixing; CM, castrated male (gelding); F, female; IN, intranasal; IPMA, immunoperoxidase monolayer assay; M, male; mo, month; Mtn, mountain; NOS, not otherwise specified; NR, not reported; PF, pregnant female; SN, serum neutralization; VN, virus neutralizing; y, year.