Respiratory disease caution

Consider this another friendly vet-student annoucement.

Respiratory disease isn't something I've had to worry a lot about in my endurance riding. My worries have been confined to prevention only - it's one of the reasons I don't allow nose to nose contact between my horse and other horses at events, and I consider Farley's individual risk for respiratory disease when I'm choosing her vaccines.

But actually having to deal with the effects of respiratory disease hasn't been a big topic on the blog, mostly because I haven't to deal with it directly. 

However, as I finish up my large animal respiratory block I saw a post on facebook from a friend about a potentially coughing horse prior to an event and it reminded me of a very important concept I should share with you on the blog.

Here's the *main point summary*.

If you are lucky enough that your horse gets a viral respiratory disease that has very mild symptoms and goes away quickly.....DO NOT RETURN THE HORSE TO WORK FOR THREE WEEKS. 

If your horse had a mild cough and temperature a week ago, IT IS NOT OK TO BRING THAT HORSE TO AN ENDURANCE RIDE. 

Now, you might be thinking that this has something to do with the shedding of organisms and getting other horses sick and this is some altruistic concept.

And you would be wrong.

It has to do with the mechanism of viral respiratory disease and how it sets the stage for a nasty little bacteria to come along and make a mild viral infection into a very nasty bacterial pneumonia. 

And considering that a bacterial pleural pneumonia comes with a price tag of $10K, we should all be REALLY motivated to prevent this from happening to our horses.

Here's the deal.

There's a TON of commensal bacteria that hang out in a normal horse's oropharanyx that if were allowed to travel further on down the respiratory tract, would cause pneumonia. Think about the lining of the respiratory tract as a field of grass. The motile little grass blades protect your tract against this bacterial invasion by not allowing the bacteria to travel down into the lungs, or penetrate the lining.

 

See how pretty and peaceful the little field of grass looks?  All is well......

And then something happens - usually a perfect storm of stress-inducing, immune-suppressing factors (training really hard, travel, heat, dust irritation......) and it allows a little virus to penetrate the respiratory system. 

Besides give the horse a little fever, a little cough, and maybe a little nasal discharge...what else does it do?

It mows down the little field of grass in the respiratory tract.



VROOM!!!!!!!!

Bummer. 

The moat of the castle just got filled with concrete and the alligators got rehomed.

How long does it take the grass to grow back? 

THREE WEEKS.

When does the horse look and feel better after the viral infection?

Much sooner than that.

But here's the problem.

If you stress the horse's body and its respiratory tract and its immune function (training and exercising ABSOLUTELY counts as stress) , those commensal bacteria of the oropharanyx (and perhaps bacteria in the environment that aren't normally found in the horse's respiratory tract) are going to move in and cause BIG problems.

Here's an excerpt from Merck on the predisposing factors for developing pleural pneumonia, which nicely summarized what was presented in my respiratory block:
Viral respiratory infection, long-distance transportation, general anesthesia, and strenuous exercise are common predisposing factors that impair pulmonary defense mechanisms allowing secondary bacterial invasion. Head restraint results in significant bacterial contamination and multiplication within the lower respiratory tract within 12–24 hr and may be the single most important predisposing factor for development of pneumonia associated with long-distance transport. Race and sport horses are particularly at risk.

So let me recap this for you
1. your horse had a mild viral respiratory infection which cleared up without incident a week or two ago and your horse looks fine.
2. You put it in a trailer for 4 hours and drove to an endurance ride
3. You may tied your horse to the trailer +/- being able to lower it's head to the ground for 12+hours.
4. You asked the horse to travel 25-100 miles at an athletic event
5. You may have tied your horse to the trailer for another 12 hours
6. You put the horse back into the trailer for a couple of hours.

Do you see why this is a really really bad idea?

If you get a bacterial pleural pneumonia, you are going to have WAY bigger problems than that little viral infection your horse got over.

And there's no guarantees that everything will be fine with some time off and antibiotics. While the survival rate has greatly increased over the last 20 years (90% survival rate), return to athletic performance is not guaranteed (about 60%). By the way, delaying treatment for more than 48 hours causes these numbers to go way down. 

If I was writing a guide to "avoiding stupid mistakes" in our endurance horses, asking a horse to return too soon after a mild viral respiratory infection would definitely make the list, along with administrating NSAIDs right after finishing an endurance ride. If your horse has a cough, take a temperature, and considering viral infection. And then consider the implications and consequences of taking your horse to an endurance ride in that three week period.