Permissivity of various cell cultures to lumpy skin disease virus

Lumpy skin disease (LSD) is a transmissible and highly contagious transboundary emergent bovine viral disease that has become especially important for the Russian Federation since 2015 when it entered the Republic of Dagestan from Azerbaijan. In 2016, the infection was found in the Krasnodar Territory and later on in six more regions of the Russian Federation. The infection causes up to 50 % drops in milk productivity, body weight loss, abortions or stillbirths, skin damage, and reproductive disorders in affected livestock up to including a complete loss of bovine fertility and animal deaths due to secondary infections. LSD is caused by a DNA virus of family Poxviridae, genus Capripoxvirus. The virus isolation, identification and vaccine or diagnostic preparation construction largely depends on the adequate culture system used. This research was aimed at characterization of the cultural properties of an LSD virus isolate detected in internal organ (lung, spleen and lymph nodes) or affected subcutaneous tissue samples from Volgograd region of Russia. In order to isolate the virus, a goatling testicle primary culture (GT), a calf kidney (MDBK) and a rabbit kidney (RK-13/2-03) continuous cell lines were used. In passage 3, the virus titer obtained in cells MDBK and RK-13/2-03 was 4.67 to 5.00 lg TCID50/cm3. Using PCR analysis, a LSD virus genome was detected in the virus-containing culture medium. The obtained LSD virus strain was deposited to the State Collection of Microorganisms of the Federal Research Center for Virology and Microbiology, # 3161. Also, the permissivity of some other cell lines including elk embryo skin (KEL/07), African green monkey kidney (CV-1) and VERO cells, a hybrid line of porcine embryo kidney cells (SPEV TK-) × porcine spleen splenocytes (A4C2/9k), and sheep kidney (ShK), rabbit kidney (RK-13/2-03) and calf kidney (Taurus-1) cells to this LSD virus strain were determined. We found that some continuous cell lines of both homologous (MDBK, Taurus-1, KEL/07, ShK) and heterologous (RK-13/2-03, VERO, CV-1, A4C2/9k, SPEV) origin were sensitive to the LSD virus. This work has revealed for the first time ever that LSD virus can proliferate in cells of wildlife species like elk. Also, permissivity of some heterologous continuous cells, RK-13/2-03 and A4C2/9k, to LSD virus was revealed for the first time. The virus culture period until 95 to 100 % CPE depended on the cell substrate selected and the multiplicity of infection. Thus, for MDBK or VERO cells it was 48 hours, and for Taurus-1, SkK, RK-13/2-03 or CV-1 the maximal destructive alterations in the cell monolayers were observed within 48 to 96 hours post infection. With an optimal multiplicity of infection of 0.001-0.00001 TCID50 per cell and 2-5 % cattle serum in the maintenance medium the LSDV titers were 6.0 to 6.8 lg TCID50/cm3 in the ShK and VERO cells, and 5.8 to 6.6 lg TCID50/cm3 for RK-13/2-03.