Replicon Particle Vaccine for White Spot Syndrome Virus in Marine Shrimp Phase II
Currently there are no truly effective interventions or therapeutic treatments for White spot syndrome virus (WSSV) in farmed shrimp. Current production practices focus on pathogen exclusion by stocking specific pathogen free (SPF) larvae, decontamination and filtration of water to prevent pathogen introduction, and strict biosecurity at hatcheries and grow out pond sites. This is extremely challenging due to the prevalence of WSSV in estuarine waters in shrimp producing areas, resulting in devastating financial losses, even in SPF populations. WSSV was first discovered in 1992 after several outbreaks of a high mortality disease occurred in shrimp farms in Taiwan. Within a decade it has spread throughout the world and is now endemic in most shrimp producing areas. WSSV has a wide host range of over 50 separate species including all penaeids and crayfish. In the United States, a 2007 APHIS study showed that 66% of tested samples were positive and it has been declared endemic by the state veterinarian and OIE in the Louisiana freshwater crayfish population. The combined economic impact of WSSV in farmed shrimp is tremendous. It is estimated that Asia alone has lost over $6 billion since 1992, and the Americas about $1-2 billion since WSSV introduction in 1999 with countries such as Ecuador showing the greatest economic impact. In addition to the tremendous economic effect on shrimp production, there is a rising concern for an introduction of WSSV into native crustacean species. Avenues exist for the introduction of WSSV into naive species such as reprocessing of frozen emergency harvested product or animal movement. In addition, the United States possesses over 350 of the estimated 500 species worldwide of crayfish species. In North America, 65 out of the estimated 400 resident species are endangered and half of these are listed as needing protection. The outcome of the proposed project would be the first effective commercially available vaccines that protect against disease caused by WSSV in shrimp. Harrisvaccines intends to market vaccine to be used in two different shrimp production settings. First, an injectable vaccine for adult breeding females will be targeted to SPF production companies and larger integrated intensive shrimp producers abroad who possess their own hatcheries for the purpose of restocking their ponds. The second would be an orally administered vaccine for post larvae (PL) shrimp that would aid in protection of the shrimp prior to entry into the ponds. This accomplishes disease prevention in the hatcheries as well as the ponds. The goal is to prevent disease that can cause increases in the variable costs of raising shrimp. In addition to the observable clinical signs of disease, WSSV is directly responsible for a reduction of feed conversion rates which result in increased feed costs and a reduction in harvest weight combined with 70-100% mortality. The costs associated with restocking ponds lost to disease add to this devastation. A vaccine against WSSV is undoubtedly a valuable insurance for the investment of shrimp rearing.
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