Determination of lumpy skin disease virus in bovine meat and offal products following experimental infection

Abstract

Lumpy skin disease (LSD) has recently expanded its range northwards to include the Balkans, Turkey and Russia. Because there was no solid evidence conclusively verifying the transmission mechanism in the field and LSDV viraemic animals with overt and asymptomatic presentation of disease and their products may represent a risk as an indirect transmission pathway. In this work, we used PCR positivity and infectivity in clinical and subclinical infection to evaluate the safety of meat and offal products from cows infected with the virulent LSDV strain Russia/Dagestan/2015. At day 21 post infection, seven of the 12 animals developed the generalized disease, and four animals became subclinically infected without apparent clinical signs. Upon examination and necropsy, the animals with the generalized disease had skin lesions; noticeably enlarged lymph nodes; and lesions in the lungs, trachea and testicles; whereas subclinically ill animals exhibited only enlarged lymph nodes and fever. For both disease presentations, testing of skeletal meat by PCR and virus isolation showed that the skeletal meat did not contain live virus or viral genome, whereas in cattle with generalized disease, meat with gross pathology physically connected under the site of a skin lesion was positive for the live virus. In subclinical infection, only enlarged lymph nodes carried the infectious virus, while the other internal organs tested in both types of disease manifestation were negative except for the testicles. Overall, our findings demonstrate that clinically and subclinically infected animals are reservoirs of live LSDV in lymph nodes and testicles, whereas deep skeletal meat in both types of infection do not carry live virus and the risk of transmission through this product seems very low. The detection of LSDV in testicular tissues in subclinically ill animals is concerning because of the potential to spread infection through contaminated semen. This aspect requires reconsideration of surveillance programmes to identify these Trojan horses of LSDV infection.

Keywords: lumpy skin disease; meat; subclinical infection.