Raccoon-pox (RCN) cross-reacting antibodies in prairie dogs Do they interfere with RCN-vectored plague vaccination?
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Black-footed ferret (Mustulus nigripedes) families and prairie dog (Cynomys) colonies can be decimated by 90% due to plague (Yersinia pestis infection). The prairie dog has a key role in the lifestyle of the black-footed ferret and various other endangered species. Besides that, one of the four prairie dog species of the United States is endangered itself, the Utah prairie dog. To protect the prairie dogs from great losses due to Yersinia pestis infection, the USGS – National Wildlife Health Center is developing a vaccine against Yersinia pestis in cooperation with other institutes. This vaccine is a raccoon poxvirus-vectored plague vaccine, which is administered orally. Raccoon pox (RCN) is an orthopoxvirus (large, DNA virus) and one of the three orthopoxviruses (OPX) endemic in North America. Skunkpox, volepox and RCN cause mostly asymptomatic infection in rodents and are known to give cross-immunity. The prevalence and host distribution of these viruses is not known. Prior exposure of the prairie dog to OPX could therefore interfere with the immune response to a RCN vectored vaccine. In this research an indirect ELISA against prairie dog RCN antibodies was developed. Pre-vaccination and post-vaccination samples (from previous NWHC research) of 200 prairie dogs (3 different species) were screened by this ELISA. The aim was to answer the research questions: Are prairie dogs previously exposed to orthopoxviruses and does this interfere with the oral raccoon poxvirus plague vaccine? This research has shown that the RCN-vectored plague vaccine gives better survival chances. These higher survival chances seem due to the response to the vaccine and not to individual pre-vaccination or post-vaccination statuses. However, the answer to the main question whether prairie dogs were previously exposed to orthopoxviruses and whether this interferes with the oral raccoon poxvirus-vectored plague vaccine remains uncertain. Further research can be done on various scales to answer these questions. First the post-booster vaccination samples could be screened. From the animals that are suspected of previous exposure, PCR for OPX virus can be performed on tissue samples. An animal trial can be done, by infecting prairie dogs with an OPX followed by vaccination. On a scientific level it would be interesting to look into the immune system of the prairie dog. The immune response needed to survive a plague infection in different species is known to be humoral and cellular.