Researchers test pig virus protein to produce vaccine

A virus protein will be used to trigger antibody production

LONDON, Ont. — Saskatchewan and Ontario researchers have begun testing potential new vaccines they hope will counter the porcine epidemic diarrhea virus.

In Saskatoon, the associate director of the Vaccine and Infectious Disease Organization said the evaluation will use intentionally infected piglets housed in the Level 3 containment facilities at the International Vaccine Centre (Intervac).

“We’re hoping to have something that works soon,” Volker Gerdts said.

VIDO-Intervac is also co-operating with Rima Menassa, who is developing vaccines at the Southern Crop Protection and Food Research Centre in London.

Like the scientists in Saskatoon, Menassa began her vaccine program in February, soon after the disease was identified in Ontario.

She is working with the spike protein, which forms the hair-like appendages that are part of the virus.

Ideally, the entire protein, which is an extremely complex molecule, could be reproduced and used to induce an immune response, but that’s the more challenging and likely more time consuming, Menassa said.

Production of segments of the protein is a quicker option.

The idea is to vaccinate pregnant sows to produce an immune re-sponse to the virus. The sows can then pass on the protection to their young through their milk.

“The protein alone will not cause the disease, but it should trigger the production of antibodies that will provide protection,” she said.

“Even if the sows have already had the disease, it could help to boost the level of immunity.”

Menassa’s program uses a non-transgenic technique known as transient expression to reproduce the spike protein, or sections of it, in the leaves of a dwarf tobacco species.

So far, she and her team have made two of the protein’s sections.

Protein genes are first put into an agrobacterium solution. The solution is introduced to the leaves of the tobacco plants, where the genes are expressed to produce the proteins.

The plants are then harvested in a week or two and undergo a multi-step purification process to extract the protein.

The vaccine will then be tested at Intervac, hopefully before the end of June, to determine if an immune response was triggered and to check for side effects. Menassa hopes field testing could begin on Ontario farms as early as September.

“It’s a little bit scary because when you do research, it never quite goes according to plan,” she said.

The VIDO-Intervac team is also working with the spike protein. The proteins are made using yeast, bacteria and mammalian cells in-stead of plants.

Like Menassa, Gerdts is cautious.

“The key to this is you have to have the right formulation, the right adjuvant and you have to have a vaccine that acts in the intestine of the animals,” he said.

The PED virus infects and damages intestinal cells, which leads to diarrhea and dehydration. Infected piglets have little chance of survival.

“There is one vaccine already on the market. I have not seen any official efficacy data, but I have heard it’s only moderately efficient.”

Gerdts said a combination of bio-security and vaccination will be needed to address the PED virus.

The PED virus identified in Ontario and other provinces is the same strain that has ravaged the U.S. industry.