Sunday, January 31, 2010

Purebred dogs and Disease. Veterinary responsibility?


A couple of  recent posts at Terrierman's Daily Dose makes some good points about the shared responsibility which the veterinary profession holds along with kennel clubs and dog breeders for the health problems that are all too common in many breeds, and are due to breeding (inbreeding) practices which result in horrendous problems directly related to the resulting anatomical and genetic train wrecks that define many purebred pets.
Terrierman's blog and website are worth a look for a perspective on working dogs and  the few breed organizations which actively try to limit and/or discourage the type of inbreeding that is all too common, and perhaps nearly universal in kennel club "show" breeds.

The involvement of the AKC and prominent breeders with the AVMA and some veterinary schools is another area where scientific evidence is falling short in the world of veterinary medicine. Organized veterinary medicine has been strangely silent on the problems associated with the inbreeding of pedigreed dogs. Terrierman seems to have a valid point that financial interests (support of veterinary schools, the AVMA, providing pet insurance, etc) by kennel clubs is suppressing criticism of bad breeding practices by the veterinary profession as a whole.

I think that changing current breeding practices has the potential to improve pet health more than nearly anything other than the development of effective vaccinations did. Many common problems in purebred dogs and cats have dramatically different incidences in different breeds, suggesting strong genetic influences on these diseases. Scientific veterinary medicine can and should encourage kennel clubs to change current breeding practices which result in so many unhealthy dogs being sold to the public. It is also interesting that the AKC pet insurance automatically excludes "any congential/inherited condition" from coverage, while encouraging breeding practices which lead to exactly these problems.

Another interesting aspect of this subject which seems to tie into this topic is the promotion of unproven therapies (Complementary, Alternative and Integrative medicine) by many breeders and in some of the AKC publications. I wonder if the seeming affinity of kennel clubs for CAM is a little extra smoke and mirrors to distract people from the real causes of so many of the problems in purebred pets. These therapies are indeed often promoted in publications such as Veterinary Economics as a good way for veterinarians to increase their income. While I don't agree with Terrierman 100% on his recommendations on vaccination (he goes a bit farther than current evidence would indicate, but not by a whole lot) and a few of his other medical advice, I understand where he is coming from and that his recommendations are a response to many veterinarians who make decisions on vaccine frequency, parasite control, etc. based on what is best for their income, not necessarily what the evidence supports.

I think kennel-club endorsed breeding practices are indeed an area in which the science and evidence based veterinary community could make a difference in the lives of animals and the practice of veterinary medicine.

Thursday, January 28, 2010

Ovaries and Longevity? A new study and a poor report.

I received my copy of Veterinary Practice News today. It is the February issue, which is not yet available online, but one of the front page articles claims that a newly published study links increased longevity to dog's which retained their ovaries for at least 6 years. The actual study is available here. To be fair, Veterinary Practice News is not peer reviewed in any way, and is mostly an excuse to sell advertising. It is sent out for free to practicing veterinarians and is published in a tabloid format with articles of interest to veterinarians. The article in question is titled Study Links Ovaries and Longevity, and claims that their canine model compares well with humans in relation to longevity. The Skept Vet has an excellent summary of the benefits and risks of neutering (click through to download the PDF) which relates to this post, and helps to explain some of the problems I have with the article and the study.

the article itself is a typically hyperbolic report that suggests veterinarians should rethink their spay/neuter practices based on the results of this one study. Unfortunately, the paper draws nearly the same conclusions.
There are a couple of confounding factors which the authors claim to have accounted for, but may not have as well as they could have.

The main problem I have with the study is that it involves only one breed, and has relatively small sample sizes. The breed use for the study was Rottweilers, and the total sample size was 100 dogs of usual longevity and 83 of exceptional longevity. Rottweilers are a breed that has a high incidence of cancer, including osteosarcoma, the incidence of which may be strongly affected by the age at which a dog is spayed or neutered (see The Skept Vet summary linked above). Other cancers in rottweilers may also be affected by reproductive hormones in this way. Indeed, when all the dogs who died of cancer (73% of the usual longevity group and 32% of the exceptional longevity group) were removed from the study, the total sample sizes decreased to 27 and 53 respectively. with these small numbers, the authors still claim that retaining ovaries for six years or longer provided a protective effect.

It would appear that retaining ovaries may protect rottweilers from certain types of cancer that are very common in that breed, but it is not clear to me that simply keeping their ovaries was the only factor which resulted in increased longevity. The exceptional longevity group also averaged 5lbs lighter and a half an inch shorter than  the usual group. This could reflect a protective effect of smaller size, or a difference in breeding which resulted in smaller size and also reduced susceptibility to certain diseases. The authors do not address these potential confounders, and present no data to suggest that the difference in size and weight could have been related to the age of spaying or genetic factors.

Before any claims such as those made in this paper, and especially in the Veterinary Practice News story are taken too seriously, they should be replicated in other breeds and larger populations. At the very least, the most common cancers and other causes of death are much different in rottweilers and humans. That alone should make the authors think the rottweiler model for human longevity may have some problems.

Tuesday, January 19, 2010

The Immortal Life of Henrietta Lacks

For those interested science and a wide variety of issues ranging from the ethics of informed consent and the abuses of patients, especially minority patients which have resulted in some of the mistrust directed toward scientific medicine, this should be an excellent discussion. Rebecca Skloot's (go Colorado State!) new book will be available early in February, and is available now for pre-order. More information at Terra Sig.

Saturday, January 2, 2010

Canine Distemper-a treatment?

      Along with the Rabies outbreak Arizona has experienced this year, wild and domestic animals are also suffering from a Canine Distemper virus outbreak as well. I have seen several puppies with distemper this year, when I only saw three cases in the preceding decade.Canine distemper is very rare in domestic dogs because the vaccine is very effective. Several common types of wild animals-Canids (dogs, foxes, coyotes), Mustelids (skunks and weasels) and Procyonids (raccoons and coatis)-are susceptible to canine distemper and are capable of spreading it. This is a good reason for universal vaccination of dogs, as individual immunity is probably as important as herd immunity when a wild animal reservoir for disease exists. relying on other pet owners having their pets vaccinated ignores the potential of spread from wildlife. Distemper is an RNA virus related to measles, rinderpest, and of particular interest to this discussion, Newcastle virus. All of these viruses are Paramyxoviruses. In the process of treating one of these puppies with distemper, a client asked me about a treatment invented or discovered by a retired veterinarian named Dr. Alson Sears using Newcastle virus vaccine, and primarily promoted online (several websites and a facebook group) by someone named Ed Bond, who apparently has no medical or veterinary background, but who thinks his dog was cured by Dr. Sears' treatment. this treatment is not really "alternative", but it does illustrate how clients and veterinarians can be fooled into thinking something works without taking into account possible confounding factors. At least Dr. Sears and Mr. Bond  seem to be sincere and do not seem to be making much if any money on this treatment.

     Like many viral infections, many factors including varying strains of virus, and multiple host variables affect the severity and course of the disease. Young puppies 3-6 months old are the most susceptible-younger puppies have some protection from maternal antibodies acquired through the placenta, and older dogs are both less susceptible to the virus and more likely to be immune to vaccination or mild infection. Effective vaccinations have been available since the 1960's, and I cannot find any data with specific information about mortality rates. Canine distemper does have a high mortality rate in puppies, probably much greater than 50%, and dogs that survive are likely to have severe neurological complications months or years later. However, depending on factors such as age and immune status, some dog do have mild cases, and some dogs do recover completely. These cases have the potential to convince clients and veterinarians that a variety of ineffective treatments work. It is natural for owners to bond with puppies quickly, and providing supportive care to a very sick puppy is tedious and frustrating, which leads people to look for other potential treatments for the disease.