Development of Monitoring System for Equine Respiratory Disease and a Equine Kidney Cell Line for Equine Herpes Virus Replication

Abstract

Respiratory diseases among horses cause economic losses in foals and productivity decreases in horses being raised and in adult horses. In South Korea, fundamental studies of horses' respiratory diseases and those related to disease occurrence are insufficient. Therefore, the aim if the current study was to use diverse hematological indicators, obtained through hematological tests and measurment of blood antibody level in horses suffering form respiratory diseases, to monitor disease occurrence and prognosis evaluation. Viral respiratory infections are common in horses, notably equine herpesvirus infection and equine influenza, which primarily initiate secondary bacterial respiratory infections such as strangles caused by Streptococcus equi equi. A decline in the production of stallions has been associated with these respiratory diseases leading to adverse financial implications. Ⅰ.Investigations of infection states by horses' bacterial respiratory diseases, susceptible drugs, and resisted drugs according to pathogens showed differences between farms. Among the β-lactam-based antibiotics, cephalosporin-based antibiotics showed some efficacy against Streptococcus spp. To review age-based changes in erythrocytometer hemograms in hematological tests of riding horses, red blood cell (RBC) tended to gradually decrease with increasing age this tendency was statistically significant. In addition, leukocytometer hemograms analyzed by age showed that total white blood cell counts tended to decrease with increasing age.. Ⅱ.A low level of equine herpesvirus type 1 (EHV-1) (11.36%) antibodies was detected from stallions, however a high level of EHV-4 (95.84%) antibodies was detected from horses without vaccination against this infection suggesting that EHV-4 is ubiquitous in this horse population. In case of equine influenza, ranch stallions showed low positive rate (12.06%) whereas stallions from Subtropical Livestock Research Institute displayed higher positive rate (81.32%). Antibody responses against equine influenza and strangles revealed positive rates of 26.32% and 55.12%, respectively. Ⅲ. Immortalized primary equine epithelial cell lines for mass-producible EHV have been established by primary culturing of the equine fetal kidney. In order to set up the conditions, we separated two different cell lines, JNUEK-1 and JNUEK-2, from immortalized primary equine epithelial cells by single-cell cloning. The virus titer of EHV-1 TCID50/ml was calculated by inoculation of serially diluted virus into a 96-well plate of Madin–Darby bovine kidney (MDBK) cells. The optimal multiplicity of infection (MOI) was approximately 0.1 for both JNUEK-1 and JNUEK-2 to obtain the highest titers: 2×109 TCID50/ml and 4×108 TCID50/ml, respectively. The maximum titers of EHV-4 came from JNUEK-1, at 7×109 TCID50/ml. As a result, JNUEK-1 was more successful at EHV-1 and EHV-4 production than MDBK.