Novel Vaccines Against Johne's Disease: Phase II Trials

Johne & #39;s disease (JD) or paratuberculosis in animals (infection with M. avium ss. paratuberculosis, M. ap) is a contagious, chronic, and potentially fatal disease affecting the small intestine of ruminants. All ruminants are susceptible, but the largest economic impact is felt in dairy farming, where infected cattle suffer from chronic diarrhea, weight loss, low milk yield and low (but persistent) mortality. Estimated annual losses to U.S. dairy farms range up to $500M. Evidence indicates a link between JD in dairy herds and Crohn & #39;s disease in humans. Currently, no feasible antibiotic regimen or efficient control strategy exists to combat JD. It spreads through fecal shedding of M. ap by infected cattle. The current (killed) vaccine does not prevent shedding from vaccinated and infected animals;failing to control JD transmission within a herd. Because of these deficiencies, some farmers no longer use the vaccines, instead using a reactive test and cull strategy: diagnose JD infection and isolate affected cattle. However, the lack of reliable diagnostic tools to detect early stage JD means that farmers rely M. ap antibody development and shedding, which can occur two to four years after initial infection. In addition, whole organism vaccines can cause false positive antibody diagnostic tests. Thus, a diagnostic that can differentiate vaccinated from infected animals is important for any vaccine/monitoring strategy. An efficient vaccine and a reliable diagnostic assay together represent cornerstones of an effective control strategy for JD. These are the ultimate aims of this Phase II project. During the Phase I project (USDA-SBIR), we tested the performance of 2 live attenuated vaccine (LAV) candidates using a mouse paratuberculosis model. We deactivated key genes involved in M. ap & #39;s virulence and persistence in our candidates. Our analysis showed initial replication and host colonization, followed by a significant decline to levels undetectable by culturing. However, the candidates generated robust cellular, humoral, and protective immune responses in a challenge. Compared to controls, vaccinated animals showed significantly lower M. ap tissue levels after challenge. Additionally, during Phase I, we also developed a proprietary LAMP-based assay that can differentiate infected and vaccinated animals. In Phase II of this project, we will evaluate the performance and safety of our candidates in ruminant (goat and calf) paratuberculosis models. Our specific goals for this project are to optimize the vaccine candidates for use in farm animals, evaluate their protective efficacy in ruminants (goats and young calves), and then characterize the candidates immune responses and environmental impact. LAV candidates will be compared to na & iuml;ve controls and commercially-vaccinated animals. We will also evaluate our diagnostic assay to differentiate infected and vaccinated/infected animals. If this project is successful, we will have identified a very promising LAV vaccine candidate that will elicit a strong and consistent immune response while allowing for little tissue colonization and shedding. We will also have an efficient assay that can differentiate vaccinated animals from infected animals. This research will provide a basis for licensing, and commercialization of these necessary products. Once commercialized, these products will provide two vital components for the world-wide goal of controlling JD and limiting its economic impact. With more than 100 million head of cattle worldwide, the commercialization potential for these two products is enormous. In addition, this research lays a foundation for vaccination of other ruminants (sheep, goats, and camels) that are harmed by M. paratuberculosis.