IDENTIFICATION AND CHARACTERIZATION OF THE CURRENTLY CIRCULATING RABBIT HEMORRHAGIC DISEASE VIRUS ISOLATES.

Even among vaccinated rabbits, the virus that causes rabbit viral hemorrhagic disease (RHDV) has been increasing in Egypt recently. So, the current study screened the emergent RHDV of vaccinated and unvaccinated domestic rabbits in some Egyptian provinces between 2022 and 2023. 40 pooled Samples were collected from different rabbit flocks with age range of 2 months up to 4 months with high mortality rates, clinical symptoms, and post-mortem lesions related to RHDV. Hemagglutination (HA) test, reverse transcriptase-polymerase chain reaction (RT-PCR) targeting the partial VP60 and sequencing and phylogenetic analysis were conducted for genotyping of RHDV strains. The results revealed that 16 out of 40 cases that were positive for RHDV and were hemagglutinin-positive, with titer ranging from 2³ to 214 Randomly six isolates were selected for genetic sequence and phylogenetic analysis which revealed their clustering with RHDV2 strains which were detected for the first time in Upper Egypt and submitted on GenBank as (OQ925947 Assiut .vac1 to OQ925952Assiut .vac6). The nucleotide sequence identities of the six isolates were 98.8-100 % compared to each other. The recently isolated strains had nucleotide difference 23, 1 % when compared to commonly vaccinal strain (JQ995154Giza 2006). The inoculated rabbits expressed RHDV-typical signs and postmortem findings and Ninety percent (90 %) mortality rate was recorded within3-6 days post-infection. Microscopic examination revealed that presence of acute necrotizing hepatitis, congestion and widespread hemorrhages in all internal organs; liver, lungs, spleen, kidneys and brain. In conclusion, the presence of RHDV- 2 strains was detected for the first time in some Upper Egypt provinces. [ABSTRACT FROM AUTHOR]