There has been a great deal of concern regarding a recent “outbreak of Parvovirus infection amongst dogs in Chilliwack, BC. The amount of media coverage received by this has caused a heightened level of desperation for pet owners. This has translated into an unprecedented number of phone inquiries in our office from concerned dog owner fearful that their pets are going to get sick. Let me lend some perspective on this circumstance.
Canine Parvovirus is not a new virus. It was initially identified and described in 1978 as a family of viruses with members affecting dogs, cats and various wild carnivores whom it is presumed were the initial host population (i.e. Coyotes, racoons, mink, weasels). Prior to the development of a good and effective vaccine, there were massive outbreaks of this virus amongst domestic dog populations. With a mortality rate of greater than 80%, many veterinary facilities were overrun with infected dogs. When I first graduated from Veterinary School in 1994 (more than a decade after the introduction of a vaccine to prevent the disease), I was treating 1-2 cases of Parvo per week. Now, after 20 years in practice I see a case of Parvo every 1-2 months. What made the difference over these 2 decades? Availability of an effective vaccine and a high rate of compliance with dog owners having their pets vaccinated. As a result, the majority of the domestic dog population was immune to this deadly virus.
Though there has been an upswing in the number of cases being seen in animal hospitals over the last year or so, this is still nothing like what we were contending with even 10 years ago. Why has there been an upsurge in cases? I have seen nothing in the medical literature to specifically answer this question though I have some ideas. Parvovirus like virtually all viruses adapts and changes due to environmental pressures. The family of Parvoviruses has many members and we have been fortunate that the vaccines developed have conferred reasonable cross-productivity to these other strains of virus. The immunity developed is not necessarily 100% and so some strains still may be capable of causing disease. Emergence of new, more virulent strains have been noted which have a higher degree of morbidity (ability to cause sickness) and mortality (ability to kill the host). In addition to these viral characteristics, there has been a movement in both human and veterinary medicine over the last 10 years to move away from periodic vaccination. This movement has been mostly fueled by fears that vaccination may cause other illness despite then document effective of vaccines against disease. In human medicine the presumed connection between Autism and vaccination has been completely debunked by an excellent, long-term retrospective study. The assumptions about the duration of effective immunity following vaccination in our pets have been nearly completely based upon opinion evidence and not rigorous science. Despite this, many individuals have opted to not have pet vaccinations kept “current” believing the duration of immunity to be longer than what has been stated by science. Recent studies with respect to immunity to Parvoviral strains indicate that the duration of immunity is likely shorter than what is commonly believed. This will likely have left a portion of the domestic dog population unprotected. In addition to these issues, the encroachment of development on areas frequented by wildlife has caused an increase in the comingling of wild carnivores (coyotes, raccoons, etc) with territory occupied by our domestic dogs. These unvaccinated creatures may act as hosts for the spread of this and other viruses to our domestic dog population. Sightings of coyotes passing through subdivisions within Chilliwack are commonplace.
So what happens when a dog who is not vaccinated or their vaccination for Parvovirus is overdue (has not been boosted at one year) and they come into contact with the virus (by directly associating with an infected animal or indirectly coming in contact being exposed to feces of an infected animal)? The virus will gain access through the mouth and will attack and destroy rapidly dividing cells in the body (bowel, bone marrow, immune system). After the 5-14 day incubation period where the animal will not appear ill but will be shedding and spreading the virus, they will become very lethargic and weak, develop a profuse bloody, explosive diarrhea and vomiting, completely lose their appetite and will often succumb and die of dehydration and secondary bacterial infections in as little as 48 hours. Puppies are much more prone to contracting the infection and will die much more readily. Once infected, the only chance of survival comes with aggressive supportive and intravenous fluid therapy in an animal hospital setting where the individual is quarantined. With this therapy, the survival rate is likely greater than 80%. For uninfected dogs, vaccination remains an easy and extremely effective preventative measure. For puppies, vaccination at 8, 12 and 16 weeks of age is sufficient to confer protective immunity. For adult dogs 2 vaccinations 14 days apart will do the trick. Then keeping immunity optimal by having a booster vaccination performed yearly is necessary. Once the majority of the domestic dog population is vaccinated in this way, even unvaccinated dogs will enjoy the benefits of what epidemiology refers to as herd immunity and the number of cases seen will plummet.
Now, one might argue about the terms being bandied about at present. If estimates of dog population in urban areas (according to American Veterinary Medical Association) put the population of dogs in Chilliwack at between 25,000 and 30,000 and there have been some 20 cases of infection seen in recent times, it would seem that the cases do not likely constitute an epidemic. Despite this assertion, there are a reasonably sizable number of dogs that I see in my practice that do not have current vaccination status for one reason or another. These dogs are at undue risk for a perfectly preventable disease. Our goal is wellness. One of the most effective weapons we have against disease and for maintenance of wellness is current vaccination. It is my hope that this cost-effective and efficient means of keeping our pet dogs healthy does not get forgotten. If you do not remember when your dog was last vaccinated, they are likely well overdue. If it has been more than a year since their last vaccination, they are overdue. Take advantage of one of medicine’s greatest tools for wellness today.
Posted by: Dr. Mark Steinebach