05 April 2015

Cats: Exposure to Rabies

One of the most contentious topics in any cat group is the subject of vaccines and whether are not to vaccinate.  Often someone will remark that they have to vaccinate because of the local law.  Some people are unaware that the requirement for rabies vaccination depends on the locality.  Where I live, rabies vaccinations are required by county law for dogs only.  I have friends who live in areas where rabies vaccinations are also required for cats.  The variation in requirements depends in large part on the incidence of rabies in wildlife in an area.

Please keep in mind that the rabies vaccine is NOT for the health of the dog or cat, but to protect humans from the rabies.  This article, Rabies Postexposure Prophylaxis, by M. Gayne Fearneyhough, BS, DVM (p 557-572 in Vol 31, No 3, Vet. Cl. of NA: Small Animal Practice, May 2001) looks at the treatment of humans after they have been bitten by a potential rabid animal.  As I do not particularly care about human medicine, this is a very brief summary.

One statement of interest in this article is "many parts of the western United States are free of terrestrial rabies", which, if you look at the 2010 CDC map for rabies infections in dogs and cats, my area, southern CA, has no cases (despite heavy testing) whereas a state like Pennsylvania is solid yellow in the east.  This explains why my Eastern friends are so adamant about rabies vaccines and here it's a minor concern.

The chart below is the decision tree recommended for humans:

Perhaps the most interesting section had to do with post-exposure treatment in domestic animals.  I have lived under the assumption that if a cat was bitten, that was a death sentence.  Apparently not.  At least 2 studies, one of 713 animals and another of 632 animals (dogs, cats, cattle, horses, sheep, goats, pigs, and 1 llama) were treated.  The first study had a 99.7% survived and 99.5% in the second.  So, yes, a cat bitten by a rabid animal CAN be successfully treated. The main problem mentioned is that the animal may survive but may not be free of rabies. I would think a second problem is to find a place that would quarantine the cat and provide treatment for several weeks.

04 April 2015

Cats: A Brief Introduction to Recombinant Vaccines

The article, Recombinant Vaccine Technology in Veterinary Medicine, by Kent R. Van Kampen, DVM, PhD (p 535-538 in Vol 31, No 3, Vet. Cl. of NA: Small Animal Practice, May 2001) was interesting and difficult.  It's been over 20 years since I did anything serious with DNA and gene-splicing, so I had to dredge up a lot of information from the corners of my mind to understand this article.  The exciting thing is this form of vaccine seems to hold great promise -- not only to develop new vaccines for different diseases, but also because the vaccine avoids some of the adverse reactions.

The standard vaccine types have problems.  The killed vaccines often provide only short-lived immunity. The modified live vaccines have the real risk of causing the disease.  So, researchers developed recombinant vaccines, or, genetically engineered vaccines, which are focuses on specific antigens (reactive agents).  With these vaccines, there is little chance of a cat developing the disease.

The general method (and this is a huge simplification) is to chop up the DNA of the pathogen, such as rabies.  Part of the DNA or RNA is then inserted into a recipient cell, such as a yeast, bacterium or virus. The vaccine is then derived. This manipulation of genes can create vaccines in three general ways:

Type I -- Subunit Vaccines
For this type, the gene responsible for producing the antigen is snipped from the pathogen and spliced into a host.  The host is then cultured, which allows it to produce the antigen.  The antigen is then purified and becomes the vaccine.

Type II -- Gene-deleted Vaccines
For this type, one or several genes are removed from the DNA of the pathogen to decrease its pathogenicity, or rather, it's tendency to produce the disease.  The pathogen is cultured and used as the vaccine.

Type III -- Vectored Vaccines
This is the most complicated type.  The genes from the pathogen that are associated with protection from the disease are isolated and then inserted into a gene-deleted host.  This host replicates, is purified, and then used as the vaccine.  The host organism enters various cells in the cat and 'infects' the cat with the protective genes.  Canarypox is often used as the vector (host) and was licensed for use in rabies vaccines.

This article is the tip of the iceberg when it comes to recombinant vaccines.  It was written as the concept was just beginning to be widely studied, in 2001.  From my limited reading of newer articles, the recombinant rabies vaccine is considered safe, very effective, and without a risk of sarcoma.  I hope to have time this summer to do more reading on this topic.

01 April 2015

Cats: Vaccines and Veterinarian Liability

I only summarized this article because some times when a cat has a reaction to a vaccine, the owner immediately wants to sue the vet.  This article, The Potential for Liability in the Use and Misuse of Veterinary Vaccines by Duane Flemming, DVM, JD (p 515-523 in Vol 31, No 3, Vet. Cl. of NA: Small Animal Practice, May 2001) clearly explains what a vet legally can and cannot do with regards to liability and vaccines.

Basically, a vet's liability regarding vaccines comes down to 3 questions:
1. Did the vet use the vaccine in accordance with standard veterinary practice?  Do other vets reasonably use it that way?  This does not mean the vet followed the labeling guidelines, but that he followed common practice.

2. Did he obtain informed consent?  Did he tell the owner that there was a risk of adverse reactions?  The owner should have been made aware of what the benefits and risks of the vaccines are and if there are options.

3. Did the vet provide undue warranty?  Did he claim that the vaccine was 100% effective?  Basically, no vaccine is 100% effective for all cats.  For example, the calicivirus vaccine lessens the infection but does not prevent it.