Development and evaluation of an experimental inactivated vaccine against lumpy skin disease

Lumpy skin disease (LSD), caused by the LSD virus (LSDV), results in severe economic losses, reduced productivity, and restricted livestock trade. Although live attenuated vaccines are available, they pose risks such as viral shedding, recombination, and reversion to virulence. Inactivated vaccines, being safer alternatives, are particularly suitable for disease-free regions. This study aimed to develop an inactivated oil-adjuvanted vaccine using a local LSDV isolate and evaluate its immunogenicity and protective efficacy in rabbits.

Scab samples were collected from clinically suspected LSD cases, and LSDV was isolated through the chorioallantoic membrane route in embryonated chicken eggs. The virus was adapted to Madin-Darby bovine kidney (MDBK) cells, inactivated with binary ethyleneimine, and formulated with Montanide Immune System Activator 50 V2 adjuvant. Sterility and safety were evaluated in laboratory animals. Twenty-four rabbits were divided into three groups: Group A received the experimental inactivated vaccine intramuscularly, Group B received a commercial live attenuated vaccine subcutaneously, and Group C served as controls. Antibody responses were assessed using enzyme-linked immunosorbent assay (ELISA) and virus neutralization tests. A challenge study with a virulent local LSDV strain was conducted to evaluate protective efficacy.

The inactivated vaccine elicited robust antibody responses, with ELISA sample-to-positive ratios increasing from 4.3% at baseline to 166.6% on day 42, compared with 210.1% in the live vaccine group and 6% in controls. Neutralizing antibody titers ranged from 1:32 to 1:128 (mean 1:80) in the inactivated group, compared with 1:32-1:256 (mean 1:148) in the live vaccine group, both surpassing the protective threshold (≥1:16). Post-challenge, the inactivated vaccine conferred 86% vaccine efficacy, with only mild clinical signs observed in one rabbit, while the control group developed typical LSD symptoms. No adverse reactions were recorded in vaccinated animals.

The experimental inactivated oil-adjuvanted vaccine induced strong protective immunity in rabbits, comparable to the live attenuated vaccine but with an improved safety profile. Its inability to revert to virulence or transmit between animals makes it a promising candidate for large-scale use, especially in regions aiming to maintain disease-free status. Further evaluation in cattle under field conditions is warranted to confirm its long-term protective efficacy and potential for inclusion in control strategies.