Overall prevalence of EHV-1/4 infection
Out of 253 serum samples analyzed, 42 serum samples were found positive for presence of antibodies against EHV-1/4, which gave 16.60% overall prevalence among the horses of south Gujarat, India.
Risk factor analysis of EHV-1/4 infection
Various risk factors
viz. spatial distribution of infected horses, age, sex and breed were statistically analyzed to view any significant importance of these factors in prevalence of disease. The results are shown in below (Table 1).
Spatial distribution of disease
The district-wise sero-prevalence of equine herpes virus infection in Navsari, Surat and other districts of south Gujarat was 15.60% (22/141), 17.48% (18/103) and 22.22% (02/09), respectively (Fig 1). No significant effect of geographical area on sero-positivity was observed.
Sex wise distribution of disease
Prevalence of equine herpes virus infection in males and female was 16.15% (26/161) and 17.39% (16/92), respectively. Similar to the geographical area wise prevalence, effect of sex on sero-prevalence of equine herpes virus infection was non-significant.
Age wise distribution of disease
During present study, sero-prevalence of equine herpes virus infections was 17.07% (7/41) and 16.51% (35/212) in horses aged <2 years and >2 years, respectively. The effect of age on sero-prevalence was also found non-significant.
Breed wise distribution of disease
Sero-prevalence of equine herpes virus infection in Sindhi breed, Kathiawari breed, Marwadi breed and Non-descript breeds was 18.02% (20/111), 16.67% (2/12), 20.69% (6/29) and 13.86% (14/101), respectively. The effect of breeds on sero-prevalence of equine herpes virus infection was also non-significant.
Haematological analysis of sero-positive and sero-negative horses
The mean values of all haematological parameter under study were within the normal range. Similarly, the difference between various haematological parameters of sero-positive and sero-negative horses was non-significant except mid cell percentage which was noted significantly higher (p<0.05) in sero-positive horses. The values of various haematological parameters are given in (Table 2).
In this study, sero-prevalence of EHV-1/4 infection was measured in horses using indirect ELISA. The samples were taken largely from unregistered animals in small private ownerships. These types of equids are traditionally used as transport and pack animals in the rural areas or as status symbol and hobby in urban areas. The study revealed overall sero-prevalence of EHV-1/4 infection as 16.60% in region under study. Several epidemiological investigations have been performed for the prevalence of EHV-1 and EHV-4 infections. Previously, 1.64% - 38.12% sero-prevalence of EHV-1 was recorded in different states of India
(Anonymous, 2019). The sero-prevalence rate of EHV-1 and EHV-4 infection was reported within 8% to 85.2% across various countries of world
(Ata et al., 2020; Ataseven et al., 2009; Avci et al., 2019; Mohamed et al., 2017; Singh, 1999;
Yildrim et al., 2015). The difference in sero-prevalence may be attributed to many factors including the difference in the epidemiology of EHV-1/4 among different horse populations, the difference in the testing methods, and the antibody titre could be under the detection limit especially in latently infected animals
(Dunowska et al., 2015). The present findings indicated the presence of natural infection with the virus and/or latent cases reactivation as vaccination against EHVs in the study region is not in practice.
As per findings of present study, effect of risk factors
viz. geographical location, age, sex and breed on occurrence of disease were non-significant. Sex may not considered as an influential factor on occurrence of disease
(Hafshejani et al., 2015). On contrary to findings of present study, in certain studies higher sero-prevalence of EHV-1 was found in females than in males
(Ata et al., 2020; Senthil and Parameswaran, 2014). This might be due to unequal gender wise sample collection. Moreover, in urban areas people kept mostly male horses as status symbol and hobby purpose. Similarly, on contrary to present study, some studies found age as an important factor that can influence the occurrence of disease
(Ata et al., 2020; Hafshejani et al., 2015). Standardbred and thoroughbred horses have higher susceptibility than local Arabian and Turkoman breeds
(Hafshejani et al., 2015). Certain horse breeds have slight higher susceptibility to equine herpes virus infection than others, but variation in immune status and rate of infection should be taken into consideration before establishing the facts
(Lunn et al., 2009). Presently, in region under study, most of reared horses are lineage of Arabian horses and non-descript horses are mostly cross over off-springs in between this breeds. This might be the reason behind equal distribution of disease among different breeds under study.
Haematological as well as serum biochemical examinations are neither specific nor diagnostically significant, as major detectable variations in both examinations are not present in EHV-1 and 4 infected horses
(Constable et al., 2017). In agreement to this, mean values of all haematological parameters under study were within the normal range. The mean values of mid cells in sero-positive horses were found significantly higher than the values of sero-negative horses. Similarly, two studies found increased monocyte count in EHV-1 infected working horses
(Mason et al., 1989; Fararh et al., 2016). Correct timing of sample collection during specific phase of disease is immensely important, even though it only indicates non specific viral infection
(Slater, 2014).
