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"The ability to prevent or, in some cases, cure disease by turning on the immune system is really an incredible opportunity," according to Scott Nordstrom, DVM, Merck Animal Health director of new product development.
Along with some insightful vaccine history, Nordstrom shared specifics about the role of mucosal immunology in young calves, during the American Hereford Association’s educational forums at the organization’s Annual Membership Meeting and Conference in Kansas City, Mo, Oct. 22, 2021.
Calf and mucosal immunology
"Almost from the moment of conception, a calf has an innate immune system. It recognizes foreign pathogens, though it may not yet be able to produce antibodies," Nordstrom explained. "Around the second trimester, the calf is starting to develop a specific acquired immune system, meaning it will see a foreign pathogen, it will create antibodies, it will create cell-mediated immunity and it will be able to expel the pathogen."
Once born, Nordstrom said the single most important thing for the immune system of the calf is to make sure it receives colostrum. But, colostrum poses a challenge to vaccination.
"When we give a traditional subcutaneous vaccine, calves typically do not respond well because those circulating antibodies they’ve gotten from the colostrum will bind the antigen and prevent it from providing the full and robust immune response," Nordstrom explained. "The other problem is that antibodies wane at different levels."
For instance, he said protective bovine respiratory syncytial virus (BRSV) antibodies last a short time, while protective antibodies for infectious bovine rhinotracheitis (IBR) and bovine viral diarrhea (BVD) can last six or seven months.
Those are reasons Merck Animal Health continues to research mucosal immunology and develop mucosal vaccines. In simple terms, equate "mucosal" with the skin’s surface, as well as the surfaces of the respiratory and gastrointestinal tracts. The mucosal system contains cells that react uniquely to pathogens.
"If I give a vaccine intranasally, I produce IgA [Immunoglobulin A], which is an antibody that coats the mucosal surfaces. If I give the same vaccine subcutaneously, the only thing I get is IgG [Immunoglobulin G], which circulates," Nordstrom explained. "If you use an intranasal vaccine, it stimulates the IgA, which binds the pathogen at the surface. It also creates memory and IgG, so if the pathogen does breech the surface it gets bound up by the circulating IgG."
According to Nordstrom, the advantages of intranasal vaccines are that they are needle-free, they appear to be less objectionable to young calves, they create a comparable immune response, and they provide better response in the face of maternal antibodies than most subcutaneous antigens, with the exception of BVD.
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