Christine McFadden: Stay on track to prevent heartworm in your pets

Moonshadow gently waved his tail from side to side, tongue pink as he greeted us.

The older black lab moved with a stately grace across the exam room, a gentle cough escaping from his throat. “There, did you hear that? Why is he coughing like that?” his owner queried anxiously. I stared down at him, mind running through possibilities. Moonshadow was old, so I had to put cancer on the list. Not a happy place to start.

I said nothing as I began a full exam, checking out his teeth, moving over areas where lymph nodes lurked, probing his tummy, riffling through his fur. Moonshadow cooperated with everything, seeming to enjoy it all as one big petting fest. I pulled out my stethoscope and listened carefully to his chest, timing his heart rate and listening to his lungs expand and contract with each breath.

A lot of times you don’t hear much listening to healthy lungs, maybe a quiet whoosh. Today I was hearing crackles and rales, sort of like Rice Krispies cereal when you first pour the milk on. Not a good thing to hear. I stood up from the floor where I’d been kneeling at Moonshadow’s side. He sideswiped me with a lick of appreciation, then coughed gently with the extra effort.

His owner, in her late 20s, shifted from foot to foot anxiously. “We’ve been through so much together. He’s traveled across the country with me.” Her voice trailed off, tears threatening. Her dog walked over to her and pushed his head up under her hand.

I asked to run a blood panel and take a set of chest X-rays. The X-rays would show me any masses in his chest that could be cancerous or might point to an odd disease like the fungal infection Valley fever. I could evaluate his heart size and shape and find markers for other lung diseases. The blood work would check for signs of infection, diabetes, thyroid disorders and see if his liver and kidneys were functioning OK.

Not much point in making a diagnosis of one problem and later finding out that my patient’s renal function was toast. Obtaining a complete picture up front was in the best interests of my patient so I could help him – or know that I couldn’t, should that be the case.

One of the blood tests was for heartworm, Dirofilaria immitis, a long spaghettilike worm that lives in the bloodstream, bobbing around through little capillaries and veins as larvae until they eventually grow up and take up residence in the lungs and heart. There can be a fistful of worms clogging the heart, nothing microscopic about it. Unfortunately, the patient is usually dead when you get to see it that graphically.

Heartworm goes through one of its life stages in the mosquito. It is when the mosquito bites your dog, sucking out a bit of blood (the mosquito’s meal) that it injects the microscopic larval form of Dirofilaria into your pet’s bloodstream. If you give your dog the heartworm preventative each month, it kills all first-stage larvae encountered and the story ends there.

If your dog isn’t protected by a heartworm preventative, or you forget to give it for a couple weeks (even if you restart it and get back on track), then there is a window of opportunity for the first-stage larvae to grow on to the second stage and into the adult worms living in the chest.

The whole process from mosquito bite to worms clogging the lungs and heart can take up to two years. The symptoms your pet shows may range from something mild like restless sleeping, to wheezing, to full-out coughing and heart failure.

Today’s tests are very sophisticated, requiring only a few drops of blood to detect antigens, the body’s response to invasion by a foreign invader, in this case the heartworm. If your dog does test positive for heartworm, a second test is done to look for actual microfilaria larvae circulating in the blood, which helps stage the disease’s progression and predict the prognosis for your pets chances of beating this disease.

Is there a treatment for dogs that have heartworm? Yes, an injectable form of arsenic.

Can some dogs die from the treatment or get very sick from it? Yes.

Does the treatment work 100 percent of the time? No.

Once a dog has had heartworm and been successfully treated do its lungs go back to normal? It depends. Sometimes.

Can cats get heartworm? Yes, statistically 5 percent to 10 percent – as often as the dogs in a given area of California.

In February there were two cases of heartworm diagnosed in local dogs – a little Yorkie in Merced and a medium-size dog that lives in Atwater. Both are house pets and neither has ever traveled outside of town.

For years we have known that pets that travel to the foothills, such as Mariposa, Sonora or the Delta area of Stockton are at very high risk. Most of the United States is infiltrated, so all traveling dogs and cats should be on monthly preventative.

Heartworm is here in Merced County. Most dogs can be protected for less than $100 a year. Talk to your veterinarian about the best choices for your pet and family.

And Moonshadow? He tolerated the arsenic treatments. His lungs were permanently damaged and he needed medicine for the rest of his life to keep the post-heartworm immune reaction under control. He was a dog that appreciated everything done for him and gave another two years of love to all he met in his journey through life.

This story was originally published March 27, 2015 at 11:00 AM with the headline "Christine McFadden: Stay on track to prevent heartworm in your pets."