Evaluation of the rat (Holtzman strain) as an experimental infection model for bovine leukosis

The aim of this study was to verify if rats of the Holtzman strain can be infected with the enzootic bovine leukosis virus (VLB) when they receive blood and colostrum inocula from bovines infected by the virus via orally and intraperitoneally. This is to find new species of animals that can be used in bioassays and that provide management facilities compared to the ovine species. For this, 28 rats of the Holtzman strain were used plus 8 crossbred sheep that were used as a control group. The 28 rats were distributed into three experimental groups: i) 8 rats inoculated with blood intraperitoneally, ii) 10 rats inoculated with blood orally, and iii) 10 rats inoculated with colostrum orally. The control group of sheep was inoculated with blood intraperitoneally. The inoculum was prepared from blood and colostrum samples from a cow diagnosed as serologically positive for VLB and with persistent lymphocytosis. The phlogistic layer was separated from the blood sample to prepare the inoculum and the colostrum sample was diluted to obtain the desired concentration and was directly inoculated. All animals were confirmed as VLB seronegative. After inoculation, follow-up was carried out at the third and sixth week using the INgezim BLV Compac 2.0 kit to check if there was seroconversion. No infection was found in any of the groups inoculated orally, 12.5% (1 individual) was positive in the group of rats inoculated intraperitoneally, while 100% of the sheep seroconverted at the third week. There were significant differences between the experimental groups and the control group. It can be concluded that the rat, Holtzman strain, was unsuitable for the experimental infection or bioassay with the bovine leukosis virus (VLB) with the inoculation methods used.