Porcine Epidemic Diarrhoea virus (PEDv) has taken the US pig industry by surprise in the last ten months. While researchers have been developing new vaccines, the United States also needs to consider its eradication strategies.
By Dr D.L. ‘Hank’ Harris, founder & CEO of Harrisvaccines; and Joel Harris, head of marketing & sales, Harrisvaccines
In less than a year, an amazing set of developments has occurred in the swine industry that has raised an array of concerns for commodity groups, consumers, and state and federal governments in North America. Porcine Epidemic Diarrhoea virus (PEDv) has caused an awareness of the strengths among diagnosticians, scientists, and veterinarians and their ability to coordinate; while at the same time identifying key weaknesses and threats due to the ever-shrinking world and associated global agricultural product movement complex.
Within hours of the initial PEDv outbreak of severe diarrhoea in suckling piglets on an Indiana farm in April 2013, diagnostic laboratory personnel especially at Iowa State University, South Dakota State University, Purdue, and University of Minnesota were working long hours to diagnose the condition and then develop the necessary tests to assist producers in making difficult management decisions. Simultaneously, vaccine companies, researchers, and entrepreneurs began to gather resources in order to develop products that might either help prevent or treat the condition. These same tests would soon be used to develop and evaluate products to help producers combat the disease. Interestingly, one of the first weaknesses identified was the country’s inability to survey, isolate, and prevent the spread of the virus. Perhaps more importantly, a very poor attempt was made to determine the route of entry of the virus into the US.
In the time before PEDv entered North America, the US Department of Agriculture (USDA) considered it a transboundary disease and not a Foreign Animal Disease (FAD); thus mobilisation of a major USDA effort to control and eradicate the virus did not occur. Other diseases such as Foot and Mouth Disease (FMD) and Classical Swine Fever (CSF) are categorised as FADs and as a result, regulations currently in place would have set off a much different response by the USDA. The occurrence of a transboundary disease has no apparent impact on pork exports (based on the experience of the previous year) while a FAD would likely cause major disruption in meat exports.
Based on government preparedness planning documents and personal communications, it has been assumed that the occurrence of a FAD in the US could be readily eradicated by the use of stamping out campaigns combined with vaccines, if necessary. If there is a lesson that has come out of the PEDv transboundary occurrence, it is that even an occurrence of an FAD would likely result in a similar overnight spread of the virus to multiple states, Canada, and Mexico in a matter of days. The spread of PEDv demonstrates this. Movement of livestock could not be stopped in time or maintained in order to allow for eradication of an FAD virus. Furthermore, vaccine stockpiles are inadequate or non-existent to be deployed in a timely manner for the array of FADs that could occur.
At this time, over 4,000 farms (and counting) have tested positive for the disease in 27 states. Several dozen cases also have been confirmed in Canada. More recently, new strains of PEDv and a new related disease, Swine Coronavirus Delta virus, have been isolated in the US. The impact of these new strains and pathogens remains to be seen.
PEDv, like Transmissible Gastroenteritis (TGE), is a coronavirus similar to Severe Acute Respiratory Syndrome (SARS). It causes severe diarrhoea and vomiting among older pigs and mortality up to 100% in piglets that are two to four days of age. In 2004, the human vaccine company AlphaVax that licensed the RNA particle technology to Harrisvaccines for veterinary use, showed they had been able to protect non-human primates against the disease by expressing the ‘Spike’ gene of SARS virus in the vaccine platform. This experience with the SARS vaccine helped the company’s researchers with the development of a PEDv vaccine. Also, peer-reviewed literature and unpublished data showed that technologies similar to – but not as robust as – the RNA particle technology platform might have promised. By using this vaccine platform, the company is able to insert the Spike gene within the RNA particle so that an animal specifically expresses high levels of virus-neutralising (VN) antibodies after the animal is vaccinated.
When PEDv was identified in the US, the company located the Spike gene sequence online from the Chinese strain of PEDv and electronically inserted it into our production platform process. For the vaccine to be a success, the researchers strived for the following characteristics:
* Protect naïve animals;
* Differentiate Infected from Vaccinated Animals (DIVA);
* Efficacious in positive herds as a booster;
* No reversion to virulence or virus enhancement;
* Multivalent (if need be).
This Chinese strain was later found to be 99.6% related to the strain occurring in the US and by synthesising the Spike gene from a Chinese strain of the virus to make the vaccine, it is likely that it would be a useful tool in Asia.
By that time, the vaccine was inducing VN antibody levels in experimental pigs, allowing us to release a vaccine for veterinary prescription (iPED) just six months after the first confirmed case of PEDv in the US. Five months after that, the product was refined and a second-generation vaccine (iPED+) was released. After the confirmation of PEDv in Canada at the end of January 2014, the Canadian government approved this second-generation vaccine to be used in animals on an emergency basis. These users of the vaccine will work with the Canadian Food Inspection Agency’s Canadian Swine Health Intelligence Network (CSHIN) to monitor clinical signs and production data on a weekly basis and test the effectiveness of the vaccine as the outbreak continues to spread throughout North America.
PEDv has entered and will remain in North American for the foreseeable future unless eradication efforts are made. Yet that would mean the continued use of novel vaccines and to discontinue developments of modified live vaccines and the practice of feedback to bring herd immunity to a system under an outbreak scenario. As for the future of the swine industry, the lessons learned are difficult but have enlightened producers, regulators, and pork consumers of the dangers of FADs. Foot and Mouth Disease, Classical Swine Fever, African Swine Fever, and East Coast Fever are lurking in the corners of an ever-shrinking world. All of the aforementioned diseases easily could come into the US similar to PEDv, or more directly as in the case with agri-bioterrorism.
Source: Pig Progress magazine 30.3 (2014)
First PED vaccine
Harrisvaccines was the first company to develop a vaccine for the treatment and/or prevention of Porcine Epidemic Diarrhoea virus in the United States. The vaccine was developed within 60 days of the outbreak and made available by prescription via veterinarians in August 2013. This rapid response to the introduction of transboundary virus was possible due to the company’s non-traditional vaccine platform. The vaccine is for sows only at this point. Studies to the results of the vaccine are currently being conducted.