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What Options Do We Have If Merial's PUREVAX® FERRET DISTEMPER Canary Pox Vectored Vaccine Remains Unavailable ?

1/22/15 My Merial rep says their new univalent CDV canarypox vectored vaccine labeled for dogs should be out next month. She still doesn't know what it will be called.

PUREVAX® FERRET is produced in the Merial Athens, Georgia plant. In late October of 2014, I spoke to some of the scientists currently and formerly involved in the vaccines’ production. They all assured me that Merial recognizes the crucial need for the vaccine in zoological medicine. That can be a touchy subject to discuss because it is illegal for a pharmaceutical producer to encourage the off-label uses of their products.  But they know and they have received a lot of mail from distressed veterinarians.

Merial also assured me that lack of profitability would not factor into their attempts to resurrect Purevax ferret.  We discussed the fact that the pet ferret population, that provided the majority of sales was drifting away to other vaccination options and that Purevax Ferret would likely generate even less revenues for them initially.

If and when it returns to the market, it will be primarily as a humanitarian gesture and an example of corporate responsibility on the part of Merial. Many of us had worried that the consolidation of the animal vaccine industry into a few international conglomerates might lessen the public service philosophy established so long ago by George W. Merck.

PUREVAX® FERRET is produced in a primary chick fibroblast cell system. We all know that it is hard to attain respectable post-vaccination titers in mustela. To obtain a high enough pox virus mass to achieve high titers required growing canary poxvirus near the limits of their tissue culture system. Producing poxvirus, expressing CDV antigens at lower concentrations protective for dogs is considerably easier. That is why RECOMBITEK C3 never went off the market.

Merial could not sell a somewhat lower antigen titer vaccine, perhaps one that required a third initial immunizing dose,  because to do so, they would have had to repeat all the complex submissions demanded by the USDA Center For Veterinary Biologics in Ames, Iowa.  They couldn’t use the zoological need as justification because that was an off-label use. So here is what they did: They asked CVB to agree that if a combination product, such as RECOMBITEK C3 was already USDA-approved as safe and effective in dogs, each ingredient could be assumed to be safe and effective in dogs. They obtained the OK on that from CVB a few months ago. Merial is planning to market the canarypox-vectored canine distemper portion separately under a new name. It will, of course, be labeled for use in dogs. The targeted release date is before 2015.

What's Been Going On In The Interim ?

During this period of unavailability, many US veterinarians began using Merck's Nobivac® Puppy DP in domestic ferrets. I know of it having been used, apparently successfully, in skunks and otters as well. I know that some have used NEOVAC® D monovalent MLV CDV vaccine in ferrets and mink. That is prepared from the Rockborn strain of distemper virus, thought by some, to be “hotter” than the modified Onderstepoort avianized MLV strain in Nobivac. A few veterinarians are giving ferrets Zoetis’ VANGUARD® Distemper measles vaccine. Successfully, in all these cases, means no observed immediate side effects. No one really knows if the animals are adequately protected. I do not know of anyone who has checked post-vaccination titers on naive animals. No one is even certain what a protective titer is. Most ferrets receiving these vaccines were bred in facilities using Distemink® (the old Fervac-D, packaged in bulk – the Lederle CDV strain).So the safety of those vaccines in vaccine-naive animals is less certain.

Big ferret producers rely on Distemink®. It is bulk-packaged in 250 and 500 ml bottles for the mink industry. Distemink® has also been used in raccoon dogs silver and blue fox, as well as mink in Finland without problems.  I was told by a veterinarian formerly with Tri-State Bird Rescue that she had obtained acceptable CDV titers in raccoons after a 3-shot series using Distemink® and used it in fox and coyotes as well.

The veterinary school in Onderstepoort, South Africa prepares and uses a killed canine distemper vaccine in non-domestic animals (Design Biologix). They have done so for a number of years. However, I do not know of any studies that confirm that it provides protective titers.

A second killed ISCOM adjuvanted CDV vaccine was used in German and Dutch zoos in otters and during the several phocine distemper outbreaks in European harbor and grey seals. It was confirmed to produce good HI distemper titers and fair VN titers in seals and river otters. It was intermittently provided to European Zoos under "experimental" license by the European division of Intervet, now a portion of Merck Animal Health. However, when it was used to protect endangered African wild dogs at the Mkomazi Game Reserve, Tanzania, it failed to prevent a serious distemper epidemic. Although it produces good HI titers, VN titers did not match. So they went over to using Merial's PUREVAX® FERRET until they could no longer obtain it. (ref1 , ref2) A Dutch veterinarian told me that Merial's PUREVAX line was never available in Europe due to their strict rules against GMO products. However, they decided that attempting to change that policy would be easier than attempting to produce the ISCOM product. They were in the process of doing so when PUREVAX became unavailable.

What Can I Do To Help ?

Write a letter or an email of thanks to Merial for their efforts.

If you are involved in mixed practice, utilize Merial's monovalent CDV in your client's dogs whenever you can. If not, encourage your colleagues to do so. The trend among informed clients is toward boutique monovalent vaccines based on need.

Make efficacy, dose schedules and titer results in non-domestics widely available through open channels - pharmaceutical companies can't do that for you and not all of us are in a position to discuss our experiences over tea and scones.

Should Other Options Be Necessary

There are a number of smaller firms looking for small niches in the vaccine market. Several of them utilize recombinant baculovirus technology (BEVS) to express a wide variety of antigen proteins in a manner that is effectively recognized by the immune system. One believed that producing a product that expressed key distemper capsid proteins would not be that difficult. Those with the resources and an inclination might contact S. Berger at Medgene Labs .