Friday, March 15, 2013

Why a 1 year vaccine?

There are a few vaccines that we deem as "core" vaccines that are highly recommended in cats.  One in particular is a vaccine against the rabies virus.  Fortunately, in most area of the United States (Illinois included), rabies is not a huge problem and only few cases of rabid animals and very rare cases of human exposures are reported.  One of the main reasons for this is the implementation of rabies vaccines in our pet population, who can be carriers and propagators of the disease.  In areas were mandatory rabies vaccination of pets and wild dogs is not required (such as India) rabies is a huge problem with over 20,000 people killed each year.

You may say that my cat is indoor only, so I don't think they need to be vaccinated as they won't be exposed to any other potential carriers of the disease.  This may be true, but in our area the most common carrier of the virus are bats, which on occasion to get in the house and may cause exposure to your pet.  Because of this, the public health concern, and the fact that County laws requires it, we highly recommend that your cat be vaccinated against rabies.

Okay, now that we have decided that we should vaccinate your cat for rabies, what is the best vaccine to use?  There are a few vaccines available that are effective in protecting your cat from rabies.  The one that we recommend is the Merial PureVax vaccine.  This uses a recombinant canarypox-vectored vaccine technology.  Basically what that means is they take little snipets of the rabies virus' DNA and implant them into the DNA of a canarypox virus.  Once this is injected under the skin, your cat's body recognizes the canarypox virus as a foreign virus, so mounts an immune system response to fight off the virus.  In doing so, the body also mounts a response to the snipets of the rabies DNA, which gives your cat protection against rabies.  We rarely see side effects to the virus and are very happy with the results.  The one downside to this vaccine is that it is only labeled for protection for 1 year, so has to be boosted annually (as County laws are strict about following the labeled protection).

Why do we use the 1 year vaccine over available 3 year vaccines?  The main reason that we do this is safety.  In the late 90's and early 2000's, the veterinarian community noticed an uptick in aggressive skin tumors call fibrosarcomas.  When looking at cats with these tumors they noticed that many of them were occurring over the shoulder blades where most vaccines were previously given (lots of loose skin here that made for easy administration).  Pathologists looking at these tumors under the microscope also noticed that they saw some foreign material that could be associated with previous vaccines.  Many vaccines use a slightly different technology for vaccines where a portion of killed virus is added with an adjuvant and injected under the skin.  The adjuvant is a caustic substance (usually not disclosed by the vaccine maker) that is meant to stimulate the immune system to react and subsequently react to the killed virus (which is typically too weak to stimulate the immune system itself).  It was hypothesized that the adjuvant was doing such a good job that it caused chronic inflammation in these areas that eventually would end up transforming into cancerous cells.

Planning for removal of large tumor on the back.
 These tumors are very aggressive and tend to metastasize (spread to other organs like the lungs) readily and without extensive surgery (sometimes removing parts of the scapular bones or chest wall) tend to grow back quickly (as soon as 2-3 months).  Even with extensive surgery these tumors can recur or spread and many cats don't make it longer than 1.5-2 years after they are diagnosed.

A cat after removal of a vaccine associated fibrosarcoma
In response to these tumors, a company switched to the canarypox vaccines and we have seen a declined in these tumors.  Because of a problem with a control group during testing of the vaccine, the vaccine was unfortunately denied a 3 year label, so we are stuck with the 1 year vaccine for the time being.  However, the safety of the vaccine (in my opinion) outweighs the inconvenience that may come with a 1 year vaccine.

Please let me know if you have any questions.

Thursday, March 7, 2013

Food Allergies

Now that we have discussed environmental allergies, we should discuss other possible causes of itchiness in pets, in particular food allergies.

Does my pet have a food allergy?
Diagnosing a food allergy can be difficult with pets.  The only reliable way to judge whether a pet is having a reaction to food is performing a food elimination trial which can be cumbersome and lengthy, but if an owner is committed can be very rewarding.  If your pet has itchiness throughout the year and it tends to be around the feet and ears, then a food allergy should be strongly considered.  The allergies tend to start prior to a year of age, but can start anytime throughout a pets life (even if they have been on the same diet for a long time). 

Well, does my pet have a food allergy?
If you think your pet is allergic because they are itching a lot and go to the veterinarian’s office, they will likely ask you a series of questions to get a handle of what is going on.  There are some common criteria that food allergies fit into:

1.      Young age of onset: Most pets with food allergies start showing symptoms prior to one year of age.  In a dog who develops itchiness after 6 years of age with no history of previous problems, a food allergy should also be suspected.

2.      Time of year: A food allergic pet should be itchy during all times of year, since they are being constantly exposed to the allergen.  Some pets may show worsening symptoms during certain times of year because they have a concurrent airborne allergy.

3.      Response to steroids: Food allergies typically do not respond well to steroids.  In early stages of food allergies, the itchiness may improve.  If your pet once responded well to steroids and now doesn’t, then a food allergy should be suspected.

4.      Areas of itchiness: The typical adage for food allergies is, “ears and rears.”  That being said the distribution can be elsewhere including

5.      Concurrent gastrointestinal signs: Around 20% of food allergic dogs will also have consistent or intermittent gastrointestinal signs (vomiting or diarrhea).

We suspect my pet might have a food allergy, now what?
The “gold standard” for diagnosing a food allergy is an 8-12 week food elimination trial followed by rechallenging your pet with their previous food.  If your pet improves on the food trial and then symptoms reoccur after reintroducing their previous food, then a food hypersensitivity is diagnosed.  The offending agents in the food that cause problems are the proteins.  Common proteins that cause problems include beef, milk, lamb, wheat, corn, chicken egg, soy, chicken in dogs, and adding tuna and salmon to the list in cats. 
Prior to starting a food trial it is a smart idea to compile a list of foods that your pet has been exposed to in the past.  This includes any commercial dog diets, table scraps, treats, supplements, and drugs (particularly heartworm prevention).  We do not want to use a diet that has a protein source that your pet has already been exposed.  We also want to know whether your pet has unsupervised access outside as some pets forage outside and may be exposed to things that you may not know about.  Once we have a good idea about previous exposures we can make suggestions on foods for a food elimination trial.

What is a food elimination trial?
An elimination trial is a period of 8-12 weeks where a “hypoallergenic” diet is fed exclusively to your pet and their itchiness and skin issues are monitored and graded for improvement.  It is important that during this trial ONLY the chosen diet is being fed.  Your pet should not have any treats (table scraps, biscuits, popcorn, etc) during this time and any flavored medications (in particular heartworm preventatives) should be stopped (if during the summer a topical or unflavored heartworm prevention should be used).  

ONLY the “hypoallergenic” diet should be fed during this time.  If your pet has a food allergy and the diet chosen is the proper one for him/her, then you should only see improvement on the diet trial.  If your pet ever gets worse symptoms (AND you are sure that they did not receive any outside food source), then the food trial should be stopped and a different diet should be chosen.  Improvement are not always immediate, so we suggest giving a minimum of 8 weeks to see whether any improvement is noticed.

If your pet improves on the food and is doing significantly better, then we suggest following up with a “challenge” of their previous food.  Prior to starting the new diet, save some of their old food and freeze it for the challenge.  The “challenge” involves reintroducing the old diet.  If your pet has recurrence of the itchiness and skin issues (usually show up between 15 minutes after eating, but some can take as long as 2 weeks), then the food allergy is diagnosed and one of the protein sources from the old diet is the offending allergen.

What food should I use for the elimination trial?
There are a few routes that can be taken for the type of food used during the trial:

1.      Homemade diet: The home cooked diet is a simplified diet of one protein source (1 part) and one carbohydrate source (2 parts).  Although this is not balanced (minerals and vitamins), it is not meant to be fed long term and will not cause major problems if fed for the 8-12 weeks.  Protein sources currently available for home-cooking include kangaroo, camel, ostrich, emu, bison, elk, venison, rabbit, duck, fish, and whole chicken egg.  Carbohydrate sources can include oatmeal, quinoa, rutabaga, sweet potato, and white potatoes.  Ideally, a protein and carbohydrate that your pet has not been exposed to should be used.  This simplified diet eliminates any other food source and is very effective.  Once we have identified that your pet is food allergic (improvement on this diet), then we can seek out a commercial dog diet with similar ingredients that can be used or consult with a veterinary nutritionist to help balance the homemade diet so your pet will not be vitamin or mineral deficient.

2.      Prescription novel protein diet: These diets use a similar idea as the homemade diet as they use protein and carbohydrate sources that are novel.  Common ingredients include duck, kangaroo, venison, potato, green pea, or rice.  Companies offering these diet include Royal Canin, Science Diet, and Purina and these diets have to be obtained through a veterinarian.  The companies are very throughout about preventing cross contamination of foods during production and guarantee that the proteins listed are the only ones in the diet.  The advantages of these diets are the convenience of not having prepare the diet and knowing that there is no cross contamination.  The disadvantage is the price which typically run $33 for an 8# bag, $64 for an 18# bag, and $84 for a 28# bag. 

3.      Prescription hydrolysed diet: These diets are a little different in that instead of using novel proteins they process the proteins so they are very small and should not cause an allergic reaction.  They have similar advantages and disadvantages as the prescription novel protein diets.  Some pets do also have some gastrointestinal issues (mostly diarrhea) with these diets.

4.      Over-the-counter limited ingredient diets: These diets are similar to the prescription novel protein diets in that they use protein and carbohydrate sources not typically seen in commercial diets.  The disadvantage is that there may be some cross contamination during the production process that can leave small amounts of other common proteins (beef, chicken, etc) in the foods.  These proteins can be at high enough levels to continue to cause adverse skin problems.  The advantage is that they are typically cheaper than the prescription brand foods: $15 for 5# bag, $40 for #15 bag, and $58 for a 28# bag.  If choosing this option, I do like the Natural Balance Limited ingredient line.

Just because you start on one diet it doesn't mean that you have to continue on this diet forever.  You can use a prescription novel protein diet or homemade diet for the diet trial and if you see improvement, we can try to find an over-the-counter alternative that may do a similarly good job.  Using the prescription diet or homemade diet first at least makes cross-contamination from other proteins less likely and we can rule out a food allergy much easier.

I am not seeing improvement on the food trial, now what?
Please be patient with the food trial.  It can sometimes take 12 weeks to see a major improvement in skin issues with dogs on a new diet.  Try to make a conscience effort to grade your pets skin issues every 2 weeks.  You should see gradual improvement in itchiness over time if the food trial is working.  If there is ever a worsening of signs (AND you are certain your pet didn't get any other food and it is not the time of year for seasonal airborne allergies) then your pet may not have a food allergy or the diet being used is not appropriate.  Please contact your veterinarian to discuss things further.

Here is a website that discusses common pitfalls of food trials.