JMD, MGR, and JM drafted the work or revised it critically for important intellectual content

JMD, MGR, and JM drafted the work or revised it critically for important intellectual content. (23.40C59.26)Mato Grosso112152.38 (32.37C71.66)Esprito Santo102050.00 (29.93C70.07)Rio Grande do Sul51533.33 (15.18C58.29)Gois61540.00 (19.82C64.25)Mato Grosso do Sul1119.09 (1.62C37.74)Year2005548464.29 (53.62C73.70)0.000520067213055.38 (46.81C63.65)20078718247.80 (40.67C55.03)20084011933.61 (25.76C42.50)2009309631.25 (22.85C41.09)2010206530.77 (20.89C42.80)201161931.58 (15.36C53.99)2012195038.00 (25.86C51.85)2013163151.61 (34.84C68.03)2014153345.45 (29.84C62.01)2015 and 2016371450.00 (26.80C73.20)2017102737.04 (21.53C55.77) Open in a separate window 1Pure-breed horses included Appaloosa ( em n /em ?=?44), Arabian ( em n /em ?=?55), Brazilian pony ( em n /em ?=?31), Campolina ( em n /em ?=?59), Mangalarga ( em n /em ?=?138), Paint horse ( em n /em ?=?41), Quarter horse ( em n /em ?=?145), Thoroughbred ( em n /em ?=?43), Other ( em n /em ?=?32, Crioulo, Andaluz, Brazilian sport horse, Breton, Lusitana, American trotter, Minihorse, Friesian, Westfalen, Haflinger) 2As the numbers sampled in Minas Gerais ( em N /em ?=?10) and Rond?nia ( em N /em ?=?2) were too low to meet the assumption that no cells have an expected count of ?5 in Pearsons chi-square test, they were not included in the analysis 3In order to meet the assumption that no cells have an expected count of ?5, samples obtained in 2015 and 2016 were merged for Pearsons chi-square test Data including age, sex (male/female) and breed, and location (state) and year of sampling were collected. There was no consistent data regarding the status of influenza vaccination among horses sampled, and this information was not used to further analysis. Antibody levels against influenza A/equine/Richmond/1/2007 (H3N8), a representative of Florida clade 1, were measured Scopolamine using the single radial hemolysis (SRH) assay performed as described in the OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals [9]. The area of zones of hemolysis (mm2) was calculated from the diameter measured using digital calipers. All SRH areas below the lower limit of detection (4?mm2; [15]) were Scopolamine set to 4 for analysis. Statistical analysis Overall seroprevalence was GATA3 estimated using the Wilson method to determine confidence limits [16]. Pearsons chi-square test was used to find associations between serological results and explanatory variables in SPSS 25.0 (Statistical Package for Social Sciences, Inc., Chicago, IL, USA). For statistical analysis, animals were divided into three age categories ( ?5?years?=?young, 5C14?years?=?adult, and ?15?years?=?old). Due to the occasional use of the same horse in two activities, this parameter was not considered in further statistical analysis. Results Antibodies against influenza A/equine/Richmond/1/2007 (H3N8) were detected in 380 of the 850 horses tested giving an overall seroprevalence of 44.7% (95% CI: 41.4C48.1%). There was no significant difference in seroprevalence between male and female or mixed and pure-breed horses or location of sampling; however, the majority of samples (82%) were obtained from S?o Paulo State (Table ?(Table1).1). There was a significant difference in seroprevalence according to age (𝜒2?=?3.30, em p /em ?=?0.001), with 52.1% of adult and 50.7% of old horses versus 38.6% of young horses seropositive. The age range of animals sampled was from 4?days to 33?years. There was also a significant relationship between year of sampling and seroprevalence (𝜒2?=?41.11, em p /em ? ?0.0005), with the highest seroprevalence in 2005 (64.3%) and Scopolamine lowest seroprevalence (around 31%) in 2009C2011. The mean SRH antibody value was 52.7?mm2 (range 4C238.9?mm2), a low antibody level likely to be insufficient clinical protection as it is below the threshold of 85?mm2. Furthermore, only 4.7% of horses had SRH antibody levels above 150?mm2, associated with protection against infection, and only 19.8% had levels between 85 and 150?mm2. When individual SRH antibody values were plotted for different age groups (Fig.?1), it was apparent that the highest mean SRH values were seen in horses aged 1?month or less (75.63?mm2) but with a clear division with half of the foals having SRH values 109.8C193.9?mm2 and half (6/12) having values of 4C34.8?mm2. Mean Scopolamine SRH values were similar in all other age groups (35.9C58.3?mm2). The highest median SRH values were also seen in horses 1?month old or less (72.3?mm2). However, the median SRH value was lower in 29 horses classified as 6?months old (33.6%) and the median value in horses aged 1C4?years was below the lower limit of detection (4?mm2). In 5C9-year-old horses, the median SRH value was 51.0?mm2, but was again 4?mm2 in horses aged 10?years or older. Open in a separate window Fig. 1 Single radial hemolysis (SRH) values of equine influenza. Dotted lines represent the thresholds for clinical and virologic protection at 150?mm2 and clinical protection only at 85?mm2. Brazil, 2005C2017 Discussion The seroprevalence of equine H3N8 influenza estimated using SRH in this study was 44.7% (95% CI: 41.4C48.1%). This value is in good agreement with the mean (52%) and mode (42%) seroprevalence estimated from HI data in 14 studies in different states and regions from Brazil published between 1985 and 2014 [12]. Prevention and control of EI is based mainly.