The Novartis Animal Vaccines company has been issued a conditional license for a new equine West Nile Antiserum. Serum neutralizing antibody IgG class is the predominant class of antibody found in the serum. Independent studies at Cornell University confirmed a high titer in the Novartis product, which was also found to protect laboratory animals from West Nile infection.
The effectiveness of this product in actually treating horses with West Nile infection remains to be seen, but expectations are high. Antiserums, antivenoms, antitoxins (e.g tetanus or botulism) and hyperimmune plasma preparations have long been used as a way to provide sick animals or people with high levels of preformed antibodies without having to wait for their own immune systems to come up to speed.
Because universal donors are used, there’s less risk of immediate allergic/anaphylactic reactions or delayed reactions, such as autoimmune liver disease. However, that possibility exists any time a horse receives a blood product from another horse. Another drawback is cost, which is $300 to $400 per treatment. That said, if it works, it’s worth the price.
Interestingly, the Alpha Equine Hospital in Weatherford, Texas, reported high West Nile virus survival rates in horses treated with plasma transfusions from their donor herd. Although those donors weren’t specifically treated to increase their West Nile antibody titers, they were kept outdoors and were also being heavily immunized against other diseases. They may have been naturally exposed.
It is also possible that the highly stimulated immune system of the donor horses was providing the West Nile victims with nonspecific immune-enhancing factors, such as interferon or immune cell activators. For example, studies have shown that foals infected with Rhodococcus equi responded equally well to plasma transfusions in general or to serum/plasma from donors that had been specifically stimulated with Rhodococcus equi.