VN June 2021

Vetnuus | Junie 2021 32 Regulars I Zoetis Livestock Column The immune response of the bovine to alpha-herpesviruses is quite extensive and involves both the innate as well as the adaptive immune systems. Various vaccines against bovine herpesvirus 1 (BHV-1) are available to equip the adaptive immune system with the capacity of an amnestic response to better fight off a potential field challenge. Knowledge of the immune response, along with being well- acquainted with the pros and cons of the various vaccine options, will better enable the ruminant practitioner to make informed decisions in various scenarios. Immune response to BHV-1 Innate The first immune response to a BHV-1 infection is the innate immune response, which kicks in as soon as viral replication begins. Infected host cells recruit innate immune cells to the site of infection via cytokine signalling. These cells include (amongst other) macrophages, dendritic cells and neutrophils.The innate immune cells then launch their attack by secreting more cytokines, killing and phagocytosing virus infected cells and acting as antigen presenting cells (APCs) to facilitate the adaptive immune response. Humoral The humoral immune response refers to the production of immunoglobulins (antibodies) against BHV-1. These antibodies are formed primarily against various glycoproteins present in all BHV-1 viruses and act mainly in one of two capacities. Firstly, they fulfil a neutralising action, whereby they bind virus and prevent normal functioning and secondly, they contribute to antibody dependant cellular cytotoxicity against viral infected cells. Humoral immunity protects against infection and viraemia (often associated with severe disease) and has the capability of a strong amnestic response through memory B-cells that can proliferate into plasma cells upon reinfection and produce vast amounts of antibodies. Immunoglobulins passed passively to the calf through colostrum, also provide protection against the disease in the neonate and in young calves. It is, however, interesting to note that passive immunity does not protect fully against BHV-1 and calves can develop latent infection despite ingesting colostrum from seropositive cows. Cell-mediated Cell-mediated immunity is stimulated by the intracellular (viral replication) stage of the infection that recruits cells from the innate immune system that act as APC’s. Typically, these cells will engulf infected cells and present processed antigen to the T-lymphocytes. Helper T-lymphocytes facilitate the process to develop cytotoxic T-lymphocytes, which then have the ability to kill host cells infected with virus. As with humoral immunity, cell-mediated immunity also has an amnestic response that reacts quicker and at a higher amplitude upon reinfection. The cell-mediated cytotoxic response seems to be more involved with clearing of virus and recovery after infection, compared to the humoral response that is mainly involved in preventing infection viraemia. Diagnosis of BHV-1 Clinical symptoms of the various syndromes causedby BHV-1 arewell described in part 1 of this article series, with non-specific symptoms such as pyrexia, depression, decreased feed intake and anorexia seen in all the various forms. Pustules and ulcerations of affected mucosal surfaces is also a common finding that correlates with the lytic life cycle of the virus. Post-mortem diagnosis reveals little specific lesions on macro pathology, withmorepronouncedhistopathologic lesions associated with the disease. Various laboratory diagnostic techniques for both antigen and antibody are summarised in table 1. Zoetis Animal HealthPages FOR ANIMALS. FOR HEALTH. FOR YOU. Bovine Herpesvirus 1 Part 2 (of 2): Diagnostics, Immunology and Control Measures Schabort Froneman