Dr. Timothy Welch of the National Center for Cool and Cold Water Aquaculture led a major effort of stakeholders, extension personnel and a pharmaceutical company to contain the spread of a rapidly disseminating, brain-tropic, trout pathogen.

Two commercial farms in North Carolina experienced heavy and sustained losses in large fish in 2011, and several attempts to culture microbes from these animals failed.

Using media and culture techniques not commonly used in aquatic animal health diagnostics, Dr. Welch identified the causative organism as Weissella ceti. This bacterium has been identified as an emerging pathogen that caused severe outbreaks in farmed rainbow trout in both China (2007) and Brazil (2008). The isolation of this pathogen in North Carolina represented the first identification of weissellosis disease in the United States; and its spread posed, at the time, a significant threat to the continued operation of the aquaculture industry on the East Coast.

Using media and culture techniques not commonly used in aquatic animal health diagnostics, Dr. Welch identified the causative organism as Weissella ceti.

The quick identification of this pathogen provided a unique opportunity to determine its distribution in North Carolina and quickly implement a control strategy to limit its spread and potentially eradicate the disease before it became an industry-wide problem. With these objectives in mind, Dr. Welch worked diligently to develop and rapidly validate an effective autogenous bacterin vaccine as a means to control the disease.

The vaccine developed consisted of a formalin inactivated W. ceti strain that Dr. Welch demonstrated was highly effective for control of W. ceti-caused disease losses. He also demonstrated that the vaccine could be effectively delivered by injection, using techniques currently used to deliver another vaccine in the North Carolina trout industry. This autogenous vaccine is produced by a custom vaccine manufacturer and must be applied by veterinary prescription.

The vaccine strain and vaccine production protocol were transferred to a custom vaccine manufacturer (AQATAQ Vaccines) for large-scale production. Within a year of pathogen discovery, the farms initially affected by the W. ceti outbreak, as well as surrounding farms, were utilizing the commercial vaccine. To date, half of the trout farms in North Carolina have used millions of doses of the delivered vaccine as a preventative measure. One of the farms affected by the disease also built a small disease challenge laboratory, allowing for collaborative studies to validate the “on-farm” efficacy of the vaccine. Since the initiation of vaccine use in 2012, the pathogen has not been detected in the U.S.