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It's logical, therefore, that draft breeds are the desired horses for use as plasma donors. Using the above-mentioned measurements, a 2,000-pound cold-blooded horse probably has around 65 liters of blood at all times, 35 liters of which is plasma. In a process called plasmaphoresis, the horse's blood is drawn and the plasma filtered. Dr. Baker maintains three draft mares that are quarantined and used purely as plasma donors. Every two weeks, eight liters of plasma are extracted from each horse with the majority cellular component being returned to her bloodstream. The drawn plasma is then bagged, labeled and frozen. Also, every two weeks each of the mares is vaccinated for 15 different diseases. The repeated immunizations build antibodies in the horse's blood, creating a strong defense against viral, bacterial and toxic sicknesses. The process of building antibodies involves a chain reaction on the cellular level. When a virus, bacteria or toxin, referred to as the antigen, enters the body, the cells work fast to produce Y-shaped proteins called immunoglobulins (Ig). Antigens attach themselves at the arms of the Y and the base tells the protein exactly how to destroy the invader. It's a very complicated process called a humoral immune response. Once the antigens are attached to the Y, antibodies are immediately produced. These are categorized into five divisions with IgM being the first line of immunological defense. After several days, the IgG antibodies appear, followed in unison by three more versions. There is a different antibody recipe for each and every virus, bacteria and toxin. It's simply a matter of the cells educating themselves to produce the appropriate antibodies. Horses respond uniquely to antigens with some building more antibodies and a higher immunity to disease than others. The more antibodies an animal has to protect itself from a certain antigen, the higher its "titer level" for that particular sickness. "When you first immunize an animal, it doesn't have a titer," said Dr. James Bowman, who with wife, Barbara, owns and operates Lake Immunogenics, a USDA-licensed commercial plasma producer in Ontario, New York. "Then you immunize it again and the titer rises and the third time, it really skyrockets up. So you get this curve that heads toward the sky." Real life application It used to be that Alpha Equine, owned by Dr. Baker and his wife, Kay, purchased all of its plasma from Lake Immunogenics. But these days Dr. Baker uses three personally owned Percheron mares to supply his practice with around 250 liters per year. Many sick horses and all foals born at the clinic or at Alpha Equine's breeding facility, are immediately given plasma. This fluid carries precious antibodies for at least 15 different diseases plus a host of necessary blood ingredients. As soon as the plasma enters the recipient horse's bloodstream, immunity is up and working and lasts three to four weeks. That's long enough for a sick horse to fight a disease, an unvaccinated animal to be immunized and build his own antibodies or a foal to gain strength and temporary immunity through its mother's colostrum. In the fall of 2001, Ft. Dodge received conditional licensing for a West Nile Virus vaccine. Not long thereafter, Dr. Baker added the preventative to his donor protocol. "For some reason, I don't know why, we had the foresight to vaccinate our plasma mares early," he said. "By the time we had the first case, those mares had had seven vaccinations." Taking care to make sure the mares were building adequate immunity, Dr. Baker sent blood samples from each horse to the National Disease Laboratory for West Nile Virus antibody analysis. "We got a call from them and they just couldn't believe these titers were this high in these mares," Dr. Baker recalled. "There had been no titers tested this high, even in the original experiment horses. When that came back, we pretty well knew we were into something that was probably going to work." Although using plasma was not out of the ordinary at the clinic, there was a certain cost factor associated with treating West Nile horses with blood products. Costing around $150 to $200 per liter and with around three used over a three-day period, the plasma was not an inexpensive alternative. But then again, taking the wait-and-see-route was not an option with Dr. Baker. Horses were treated with every available option or were not allowed to suffer. "Our stance was, don't try to treat them cheaply, because you're not going to win," he said. "Historically we know that 30 percent of the horses die, no matter what you do," said Dr. Maureen Long, assistant professor at the University of Florida. Recognized for her pioneering West Nile Virus research, Dr. Long is currently conducting studies on the efficacy of using plasma to treat the virulent disease. "Given the chances for a 30 percent mortality, I want to give that horse any chance that I can. I would do all the things that I am comfortable doing, which would include plasma." When horses finally reached the Alpha Equine Hospital, they were typically exhibiting symptoms of neurological distress, including incoordination, shaking and inability to stand. Some were so progressed into the disease that they could not walk, were down in trailer and had to be moved to the treatment area on a cart. Immediately the medications and plasma were administered and the horse relocated to a heavily bedded stall. Since many of the horses did not seem to go off feed, ample hay and water was provided while an IV was given to maintain hydration. Amazingly enough, those convalesced horses seemed to respond within 24 hours and after two days' time, most appeared to have left all West Nile Virus symptoms behind. Not one horse had to be propped up or pulled to its feet with a sling. Within 48 hours of receiving the plasma, the horses were able to get up on their own, keep mobile and maintain balance. After two weeks, every horse Alpha Equine treated, with the exception of the pregnant mare, was completely back to normal. Similar success was echoed at Lake Immunogenics. Beginning in December 2001, Dr. Bowman started vaccinating his plasma donors and sent samples from each horse to Dr. Long every three weeks. As the titers rose, Dr. Bowman categorized his donors according to their ability to produce high antibody levels. At the time, the vet was unsure if he was on to an effective course with using plasma for the treatment of the West Nile Virus. Though it worked to prevent and cure many diseases, plasma still was not locked up and solid when it came to Rhodococcus equi, a serious illness that afflicts a significant number of foals. "It's very hard to predict, particularly on a new disease, whether or not antibodies are going to work or not," Dr. Bowman said. Lake Immunogenics provided its IgG plasma to five universities and though the blood product was not USDA approved for the treatment of West Nile Virus, it proved a viable corrective for that particular disease. Word of the cure rate eventually reached the vets in Texas, and the orders started coming in. Although there was no scientific way to track the success of Lake Immunogenics' plasma in treatment of West Nile Virus on outside horses, the feedback Dr. Bowman received was certainly positive. "The reports that I got back, once they started using plasma they had no more death loss," Bowman said. "They began to tell us about these horses that they'd seen two weeks earlier and they'd be dying, and were unable to walk. By the next day, the horses were normal." According to Dr. Long, commercial plasma was a modality typically not used until the horse was far progressed and standard treatments exhausted. She noted that many West Nile positive horses got sick and about two weeks after the initial symptoms, appeared to be improving but then suddenly regressed significantly with even more shaking and incoordination. "There were a lot of vets that basically gave horses plasma at that point and they thought there was, what they thought, a remarkable turnaround within hours of getting the plasma," Dr. Long said. Those results shocked the researcher. "It didn't scientifically make sense to me." But she did find literature citing similar results for the use of plasma to treat humans suffering from severe complications due to West Nile Virus. Dr. Long noted two cases that were documented in Israel, where comatose patients responded to plasma. Hoping to prove a similar connection with equine plasma, she and Dr. Bowman set up a double blind study where West Nile positive horses were given plasma, half with disease-specific antibodies and the other half without. The final results are due out soon. Continued. Go back to Part 1.
Reprinted with permission of Quarter Horse News
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