Download Immune System and Vaccines

Cow Tales Vaccines and immunology basics Have you ever considered why your local veterinarian recommended a specific vaccine at a specific time? Have you ever wondered why some vaccines come in boxes and others don’t? I wanted to spend a little time covering the immune system, vaccines, and the major respiratory pathogens or bugs that cause pneumonia. This installment will cover the immune system and vaccine basics. The immune system is as complicated as the hormonal blitzkrieg waging war in teenage boy and involves the entire body. On the surface are the non-­‐specific defenses of physical barriers and self-­‐
cleaning mechanisms. The skin represents a tough and very important barrier to foreign invaders. A rancher only needs to remember their last encounter doctoring a calf with a broken leg. Fractures that puncture the skin carry a grave prognosis for long-­‐term survival. Self-­‐cleaning mechanisms expel foreign material from the body. These mechanisms include coughing, sneezing, and the mucus lining airways that traps foreign material acting like a sticky rodent trap allowing it to be removed. I have seen a five pound snot ball stick and hang from the ceiling of processing barn for months. These are the draft mules of the immune system that trudge along all day, every day. Dig a little deeper and we arrive at innate immunity. These defenses are collectively known as inflammation. When tissue is damaged or the presence of a foreign chemical or pathogen is recognized by the body there is an increased blood flow to the area causing redness. Cells accumulate to attack and clean away the pieces and parts of the foreign presence. Enzymes are released that bore holes into the invaders. The area becomes swollen and slightly painful. Though not specific to any intruder, the innate immune response acts as a great second line of defense. Active immunity is the last line of the immune system. This team of sentinels is very specific and highly regulated within the body. Active immunity is a pillar of defense standing on two legs; humoral and cell mediated immunity. The term humoral reminds me of ancient Greek medicine when community healers would perform blood letting procedures to “remove excess humors” and “restore the body to balance”. The term survived but now refers to antibody production in response to foreign invaders of the body. Antibodies are small proteins that play a very important role. Specialized white blood cells receive signals to produce antibodies to recognize specific molecules or parts of molecules on the surface of specific pathogens. The specificity is comparable to a lock and key. When the antibody contacts and adheres to the pathogen a whole cascade of events ensues leading to recognition and destruction of the foreign invader. Cell mediated immunity involves other specialized white blood cells. Some pathogens live within a host cell. This is a perfect place to avoid being detected by antibodies circulating in the body. However, the host cell can recognize its unwelcome guest and produce signal molecules which it secretes onto its surface. These signal molecules wave around like a white flag of surrender. When the white blood cell recognizes the signal molecule it destroys both the host cell and its parasite within. Viruses, some bacteria, and some protozoa invade cells. Most bacteria and protozoa survive outside host cells. Therefore antibodies are extremely important for bacterial pathogens. They also have an important role deflecting viruses and other cell invaders before they can parasitize their host cell. Cell mediated immunity, on the other hand, is more important for viral diseases. Vaccines are used to sensitize the active humoral and cell mediated immunity to specific pathogens. Priming the immune system enhances the speed of the response and gears the body to fight infection minimizing the deleterious effects. One hundred years ago children with diarrhea might not survive. Today, few children die from rotavirus, one diarrhea causing agent, in part due to effective vaccines. The same applies to our beef cattle. Producers have a wide variety of vaccines available from many pharmaceutical companies to help prevent disease. Vaccines fall into one of two categories; killed and modified live. Killed vaccines are pathogens that have been inactivated and injected to cause an immune response. Killed vaccines generally lead to a humoral (antibody) response. An adjuvant is added to enhance the effect and can help create a more balanced immune response. Killed vaccines come in bottles and don’t need to be mixed with a diluent to be reconstituted. Modified live vaccines are live pathogens that replicate in the target host cell but are modified to not cause disease. Most modified live vaccines target intracellular pathogens that hide from the antibodies circulating in the body. Consequently, most are viral vaccines. Modified live vaccines come in a box and need to be reconstituted. Sometimes the diluent will contain killed vaccine to reduce the number of injections required. Vaccines should be treated with great care. They should always be swirled and not shaken to mix. Some vaccines can release potentially dangerous endotoxin when shook. Producers need to refrigerate stored vaccine and protect from light. Modified live vaccines need to be used quickly because they lose their desired effect when warmed or exposed to too much sunlight. Additionally, these vaccines can become inactivated when squeezed through a dirty syringe or one that contains disinfectant residue. Ideally one syringe is identified and labeled for modified live vaccines. You can vaccinate a watermelon but you can’t immunize one. This is the analogy we use in our practice to help instill how complicated vaccines and immune system are. Producers should work with their veterinarian to establish a vaccine protocol tailored to their production system. Timing of vaccinations, both biological and environmental stressors, trace mineral nutrition, and pathogen pressure should be discussed.