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Friday, December 30, 2011

A Reevaluation of Opinions

Part of being a life long learner is to actively seek out new knowledge AND to critically evaluated the beliefs and opinions you currently hold and test them against the new information that you learn.  Vet school is a perfect environment for this.  Most of my animal knowledge is related to husbandry and performance, not medicine - however medicine is intimately linked with husbandry practices and training and I do my best to integrate medicine into my existing knowledge framework. 

There are 3 subjects in particular that I have either reconsidered or developed a more rounded views on, since adding medicine to the mix. 

Vaccinations - In general, I’ve become more strident about vaccinations and timing of vaccinations for younger animals, and more relaxed about vaccinating older animals.  In my last post I touched on why the timing of vaccinations given to young animals is important, however I didn’t get to the older animal part - specifically Arthus reactions and vaccines.  The term “Arthus reaction” is a term used for a *type III sensitivity and is characterized by pain and swelling at the site of injection.  It can happen with a wide variety of drugs, however, during class it was presented (and is the classical example) as occurring when a vaccine is given to a hyperimmunized animal.   The typical patient that this occurs in is the older horse - probably more common in horses than shorter lived species like dogs because horses receive more vaccines over their lifetime than dogs by virtue of time. 

Imagine a horse in it’s late 20’s, who has routinely been vaccinated twice a year, every year for the recommended vaccines.  This wouldn’t be atypical.  I think most horse owners are very conscientious about following protocols by route - consider the worming schedules and how many people insist on worming every 8 weeks, even though their risk is low and the indications are that it isn’t needed?  If this older horse had a performance career, it’s likely they were vaccinated 4x a year - thus by the time it’s in it’s 20’s, likely it’s immune system is highly sensitized to the vaccine.  Do older horses still need vaccines?  Sure - if it doesn’t have the antibodies, the vaccine will do exactly what it's suppose to do.  However, if I’ve owned this geriatric horse for most of it’s life, never missed a vaccine, and the horse is retired on my property - I’m more likely to skip the vaccine, or at least discuss the issue with my vet before routinely popping the needle into the neck. 

The protocols for dogs may be changing as well - vet clinics are reducing the number of “core vaccines” recommended for older dogs with a known vaccine history.

The bottom line?  I wouldn’t be afraid to talk to your vet about the possibility of reducing the number of annual vaccines for your older pet.  Based on the number of mainstream vets and the recommendations at the Davis teaching hospital, you won’t come off as a wackadoo and you may save your pet/horse some discomfort. 

Growth plate significance - For those of you that missed it, go back and read my post on growth plates and the consequences of damaging them.  If you own a large breed dog or a horse, you should care - a LOT.  I may have been a bit ambivalent before on the subject - but no more!

Old injuries - I’ve purchased every singe horse I’ve owned without a vet exam.  After learning about various types of diseases, injuries, and compensation injuries, I’m not sure I would consider a new horse without a pre-purchase exams with radiographs as indicated to check out old injuries.  I’ve had the attitude that an old injury healed (depending on the nature of the injury) isn’t that big of a concern.  Now, without checking out the injury thoroughly, and checking for compensation injuries in the rest of the body, I wouldn’t even consider the horse as a prospect.  The body compensates for injury in wonderful ways - however not all those compensation mechanisms are conducive to a lasting performance career.  The feed bill for a forced-early-retirement-pasture-ornament dwarfs what I would spend up front to check out a horse throughly before purchase. 

Flexion tests - ….are one tool in the tool box.  Don’t take the results of a positive flexion test too seriously - especially if there’s no other indications of a problem.  You can make a sound horse look lame, a positive flexed horse may never go lame, and a negative flexed horse may be lame.  For an interesting look at flexion, read chapter 8 “Manipulation” by Mike W. Ross in Diagnosis and Management of Lameness in the Horse.

CBC panels  - If I think there is one change vets should be making, it’s encouraging owners to do routine CBC panels.  These blood panels tell vets SO MUCH about what is going on with the animal, and it doesn’t cost that much.  Tess will be getting a CBC before getting spayed, where as before I probably would have tried to find a clinic that would do the spay without it. 

In my (humble as always) opinion, vets should stop bemoaning the loss of income from vaccines being given less often or being given by clients, and instead educate clients on other diagnostics that valuable to keeping animals sound and healthy - such as CBC panels.  I would love to see vets be more open to clients giving their own vaccines who want to (except for those with a public health zoonosis risk such as rabies) and perhaps even offer to demonstrate correct technique.   Also, encouraging vaccination protocols that align with current research  (such as every 3 year boosters etc.).  As an educated consumer, I know I can effectively give my own vaccines and I know that it isn’t absolutely critical for some vaccines to be given annually.  Thus, I feel a bit ripped off when vets insists that only they can properly give vaccines, and use vaccines as the excuse for the yearly wellness exam.  Instead - give me a reason to bring my animal in yearly by offering something that only you can do (like a CBC) and supports the animal’s health. 

Of course, there could be a whole point to this issue that I’m not seeing - but at this point and based on my experiences at small animal clinics, this is where opinion on the whole subject is.  I’ll update you if it changes.  :)

*type III Sensitivity - Localized reaction, soluble antigen forms immune complexes - kicks off an inflammation cascade - which includes swelling and pain. 

Wednesday, December 28, 2011

The immune system

I’m working up to a reader request of the how’s, why’s, and when’s of the bone, tendon, and muscle conditioning.  That series is going to be rather involved, so before diving into “why bone is cool and what that means to you as the endurance rider”, I wanted to share an equally cool, but much less involved concept. 

The Youngen’s
I’ve just been informed by my boyfriend that the above is not a word, and therefore I can “fake” the spelling.  I think I disagree, but as looking up a dialect spelling in “Where the Red Fern Grows” may be overkill for a Wednesday morning topic about immunity, I’ll let it go for now. 

I’m not sure what you’all (pretty sure that Matt would think that isn’t a word either, but you and I know better) thought was the basis of vaccinating puppies and young animals multiple times, and their vulnerability to infection, but I thought it went something like this:

-puppies (and other young animals) are always susceptible to infection until they get their full set of vaccines because they have immature immune systems that can’t respond to vaccination, so the immune system needs to be stimulated over and over.  The time period is important because the immune system responds the most efficiently during the period early in puppy development. 

Sort of a “young animals are inherently broken and therefore you throw stuff at them a couple of times randomly and hope for the best” hypothesis. 

Because all my readers are brilliant, I’m sure you immediately see the fallacies of this hypothesis.

Turns out that the real mechanisms is a tad more sophisticated than that.  Imagine that. 

In my difference I’ve NEVER had an anatomy or physiology class that addressed immunity, and thought that the spleen was a vestigial organ with no apparent function. 

Yeah.  I may have learned a thing or two in my immunity block. 

Here’s the real story:

There’s all sorts of variations on the theme, but we can safely assume for the discussion here that newborn animals (mammals, such as dogs) have a bunch of antibodies floating around in their system from their mom.  These antibodies protect them from disease.  These acquired antibodies start to wear off eventually and the little pup has to manufacture it’s own.  This is where vaccination comes in - to stimulate the immune system to manufacture protection against certain diseases. 

Why don’t we vaccinate at birth?  Because, those acquired antibodies from the mom prevent the vaccine from working - vaccinations are only effective when the mom-antibodies start to go away.  This why some vaccines are given to the mom at specific times during gestation - the mom will give protection to the youngster through her antibodies.  However, you can’t “make up” for not giving the mom the right vaccines by giving them to the youngster at birth, because the vaccine won’t work!   In summary, you start vaccinating when the the acquired antibodies are going away, and the pup is starting to produce it’s own, which in dogs is about 6 weeks of age. 

The time between the mom antibodies going away, and the pup’s antibodies being produced is an especially vulnerable time for the puppy getting sick, because it’s literally building it’s immune system while the immune system that used to protect it is going away.  This is why it’s important to protect your puppy from unknown dogs and public places - it has a unique vulnerability at this time (which unfortunately also coincides with the socialization period). 

Vaccines try to bridge that dip in the immune system.  We start vaccinating BEFORE the mom antibodies totally go away - which means those early vaccines aren’t very effective.  It’s a desperate effort to give the pup some protection against a disease that could kill them so they aren’t totally unprotected.  Then, we re-vaccinate several times over the next couple of months, each vaccine being more and more effective as the concentration of mom-antibodies are less and less and the pup’s own immune system can respond to the vaccine more and more. 

This same concept explains why dogs with an unknown vaccination history don’t go through the same protocol as puppies.  They have a fully functional immune system, and while we may give a vaccine several times to make sure that the immune system is properly stimulated, we aren’t working with an immune system that is actively rejecting the vaccine. 

Large breed dogs develop slower - which can explain why it’s often recommended to give large breed puppies an extra series or two of their puppy boosters - That “gap” between the loss of the mom’s antibodies, and the development of their own may be bigger, requiring additional vaccines to both “bridge” that gap and to make sure that final vaccine isn’t given too early, before it’s really effective. 

Of course, the information is simplified, as I’m totally ignoring the facts about how 2 or 3 stimulations of the adaptive immune system (which is the immune system primarily stimulated by vaccines) is far more effective than just one exposure etc, but this is the basic concept of “why” behind the “how” young animals are vaccinated.

Here’s some graphical representations of all this from “Veterinary Immunology: An introduction” by Tizard

FIGURE 17-9     The presence of maternal antibody in a newborn animal effectively delays the onset of immunoglobulin synthesis through a negative feedback process.
(Tizard, Ian R.. Veterinary Immunology: An Introduction, 8th Edition. W.B. Saunders Company, 032008. p. 215).

FIGURE 18-8     Effect of the presence of maternal antibodies to canine parvovirus in 653 puppies on their response to a modified live parvovirus vaccine. The prevaccination antibody titer profoundly inhibits the response of the puppies to the vaccine. (From Carmichael LE: Compend Contin Educ Prac Vet 5:1043-1054, 1983.)
(Tizard, Ian R.. Veterinary Immunology: An Introduction, 8th Edition. W.B. Saunders Company, 032008. p. 235).

Knowing this mechanism of how young animals respond to vaccines and how critical the timing of the vaccines is has substantially changed how I view vaccination of the younger animal.  Knowledge truly is power. 

Unfortunately it’s now 10:30 and I have to actually get my day started so we’ll leave my revelations of vaccinating the older animal for another day!  (and yes, my opinion of vaccinating the older animal, changed just as much as my views on vaccinating the younger one.)