Table 3.
Frequency of PCR detection of equid herpesvirus 2 (EHV-2) and EHV-5 in nasal swabs collected from Polish horses (n = 540) stratified by age, stud farm, breed, season at the time of sampling, and disease status
| Category | Horses [n] | EHV-2 | EHV-5 | ||||
|---|---|---|---|---|---|---|---|
| n (%) | RR (95% CI) | p | n (%) | RR (95% CI, p) | p | ||
| Age (years) | |||||||
| < 1 | 173 | 155 (89.6) | 1.3 (1.2–1.4) | < 0.0001* | 52 (30.1) | 0.6 (0.4 to 0.7) | < 0.0001* |
| 1 | 99 | 83 (83.8) | 1.1 (1.0–1.2) | 0.0862 | 87 (87.9) | 2.3 (2.0–2.7) | < 0.0001* |
| 2–3 | 101 | 66 (65.4) | 0.8 (0.7–1.0) | 0.0024* | 57 (56.4) | 1.3 (1.0–1.5) | 0.0462 |
| 4–9 | 83 | 52 (62.7) | 0.8 (0.7–0.9) | 0.001* | 29 (34.9) | 0.7 (0.5–1.0) | 0.0171 |
| 10–15 | 69 | 49 (71.0) | 0.9 (0.8–1.1) | 0.2182 | 23 (33.3) | 0.7 (0.5–1.0) | 0.0196 |
| 16+ | 15 | 12 (80.0) | 1.0 (0.8–1.3) | 1 | 6 (40.0) | 0.9 (0.5–1.6) | 0.6119 |
| Stud farm | |||||||
| I | 64 | 43 (67.2) | 0.9 (0.7–1.0) | 0.0556 | 46 (71.9) | 1.6 (1.4–2.0) | < 0.0001* |
| II | 19 | 17 (89.5) | 1.2 (1.0–1.4) | 0.2693 | 8 (42.1) | 0.9 (0.5–1.5) | 0.8159 |
| III | 18 | 18 (100.0) | 1.3 (1.3–1.4) | 0.018 | 16 (88.9) | 2.0 (1.6–2.4) | 0.0004* |
| IV | 42 | 31 (73.8) | 1.0 (0.8–1.2) | 0.5686 | 26 (61.9) | 1.4 (1.1–1.8) | 0.0532 |
| V | 42 | 39 (92.9) | 1.2 (1.1–1.4) | 0.0115 | 29 (69.1) | 1.5 (1.2–1.9) | 0.0035* |
| VI | 37 | 34 (91.9) | 1.2 (1.1–1.3) | 0.0254 | 13 (35.1) | 0.7 (0.5–1.1) | 0.1718 |
| VII | 47 | 41 (87.2) | 1.1 (1.0–1.3) | 0.1016 | 27 (57.5) | 1.3 (1.0–1.6) | 0.1683 |
| VIII | 48 | 36 (75.0) | 1.0 (0.8–1.2) | 0.7191 | 13 (27.1) | 0.6 (0.3–0.9) | 0.0038 |
| IX | 30 | 27 (90.0) | 1.2 (1.0–1.3) | 0.1151 | 11 (36.7) | 0.8 (0.5–1.2) | 0.264 |
| X | 44 | 24 (54.6) | 0.7 (0.5–0.9) | 0.0005* | 4 (9.1) | 0.2 (0.1–0.5) | < 0.0001* |
| XI | 60 | 54 (90.0) | 1.2 (1.1–1.3) | 0.0134 | 27 (45.0) | 1.0 (0.7–1.3) | 0.7847 |
| XII | 49 | 41 (83.7) | 1.1 (1.0–1.3) | 0.2896 | 27 (55.1) | 1.2 (0.9–1.6) | 0.2934 |
| XIII | 40 | 12 (30.0) | 0.4 (0.2–0.6) | < 0.0001* | 7 (17.5) | 0.4 (0.2–0.7) | 0.0001* |
| Breed | |||||||
| Arabian | 101 | 78 (77.2) | 1.0 (0.9–1.1) | 1 | 70 (69.3) | 1.7 (1.4–2.0) | < 0.0001* |
| Coldblood | 49 | 41 (83.7) | 1.1 (1.0–1.3) | 0.2896 | 27 (55.1) | 1.2 (0.9–1.6) | 0.2934 |
| Hucul | 42 | 31 (73.8) | 1.0 (0.8–1.2) | 0.5686 | 26 (61.9) | 1.4 (1.1–1.8) | 0.0532 |
| Malopolska horse | 42 | 39 (92.9) | 1.2 (1.1–1.4) | 0.0115 | 29 (69.1) | 1.5 (1.2–1.9) | 0.0035* |
| Polish Halfbred | 37 | 34 (91.9) | 1.2 (1.1–1.3) | 0.0254 | 13 (35.1) | 0.7 (0.5–1.2) | 0.1718 |
| Polish Konik | 40 | 12 (30.0) | 0.4 (0.2–0.6) | < 0.0001* | 7 (17.5) | 0.4 (0.2–0.7) | 0.0001* |
| Silesian horse | 44 | 24 (54.6) | 0.7 (0.5–0.9) | 0.0005* | 4 (9.1) | 0.2 (0.1–0.5) | < 0.0001* |
| Thoroughbred | 60 | 54 (90.0) | 1.2 (1.1–1.3) | 0.0134 | 27 (45.0) | 1.0 (0.7–1.3) | 0.7847 |
| Wielkopolska horse | 125 | 104 (83.2) | 1.1 (1.0–1.2) | 0.088 | 51 (40.8) | 0.8 (0.7–1.1) | 0.1254 |
| Season | |||||||
| Spring | 186 | 121 (82.3) | 1.4 (1.2 to 1.6) | < 0.0001* | 185 (44.3) | 0.8 (0.7 to 0.9) | 0.0179 |
| Summer | 104 | 55 (52.9) | 0.6 (0.5 to 0.8) | < 0.0001* | 53 (51.0) | 1.1 (0.9 to 1.4) | 0.3837 |
| Winter | 18 | 18 (100.0) | 1.3 (1.3 to 1.4) | 0.018 | 16 (88.9) | 2.0 (1.6 to 2.4) | 0.0004 |
| Respiratory disease | |||||||
| Yes | 43 | 41 (95.4) | 1.3 (1.2–1.4) | 0.0019* | 26 (60.5) | 1.3 (1.0–1.7) | 0.0796 |
| No | 497 | 376 (75.7) | 228 (45.9) | ||||
| Total | 540 | 417 (77.2) | 254 (47.0) | ||||
Associations between categorical variables included in the analysis and infection with EHV-2 or EHV-5 were tested using contingency tables. Fisher’s exact test was used to analyse 2 × 2 tables, and Pearson’s Chi-square test to analyze tables with more than two variables. To calculate relative risk (RR) for EHV-2/5 infection within each main category, horses from each subcategory were compared with the remaining population enrolled into the study, and the p values were adjusted using Bonferroni correction
*Results were considered statistically significant for the following Bonferroni-adjusted p values: Age (< 0.0083), Stud farm (< 0.0038), Breed (< 0.0055), Season (< 0.017)