Caleb had been doing really well for a Bouvier about to turn 10, when his health took a mysterious dive last summer. We would learn that he was infected with an intestinal parasite called Giardia. But until he was correctly diagnosed and effectively treated, he suffered and his condition deteriorated.

A problematic Giardia infection is often overlooked or mistaken for other illnesses. Until only two or three years ago it was believed to be uncommon in dogs, says Dr. Andrew Peregrine, Associate Professor of Clinical Parasitology at the Ontario Veterinary College, University of Guelph.

However, recent studies have found that between 6 percent and 7 percent of dogs are infected with Giardia at any given time. And 8 out of 10 of these show no clinical signs of disease! Young dogs (up to one year old) may contract Giardia as much as six times more often than adults.

These findings suggest Giardia is a more significant issue for dogs than previously realized. It appears that dog people and practitioners have some catching up to do!

Elusive Giardia Symptoms

Caleb’s tale illustrates how humans can go astray when viewing Giardia through an outdated lens.

In early summer, Caleb had diarrhea for a day or two, but then it cleared up. He vomited once, and again a few weeks later. The diarrhea came and went again, but even his better-formed stools smelled bad. Our local clinic did a “float” test of a stool sample, telling my friend Janice and I that this could detect both worms and Giardia. When they found neither, we figured parasites weren’t Caleb’s problem.

The elusive pattern continued for weeks, then months. At times, Caleb went off his food. He’d wake up at night panting and clearly distressed, and sometimes couldn’t fall back to sleep for hours. His gut gurgled loudly and he released stinky gas – unusual, for him. I suspected intestinal cramps.

Then, almost overnight, his normally sweet breath became so foul that we had to open a car window for relief when he rode with us. It sometimes smelled like feces. Our vets insisted that Caleb probably had an oral problem, but like other dogs on a raw food diet, Caleb has healthy teeth and gums. Oddly, his chronically itchy skin and achy joints also seemed much worse, which logic said was unrelated to digestive issues; yet all this happened in tandem.

Caleb’s chiropractic vet noticed he had muscle-wasting. His weight had plummeted from 90 to 81 pounds; he was thin-skinned and ribby, although he ate well enough. She asked if he’d been checked for Giardia; we reported his negative results. Alarmed now that he might have cancer, she wanted to biopsy an irritated wart on his knee.

I just didn’t feel he had cancer. Afraid that surgery would add to his stress, we decided to hold off on it while continuing to search for other explanations.

Caleb’s homeopathic vet matched a remedy to his issues, and put him on probiotics and enzymes to help his digestion. When he did not improve, she tried to warn us that we should expect a 10-year-old dog to start having problems. “This isn’t aging,” I insisted. “Caleb is sick.”

Finally, Toronto holistic veterinarian Paul McCutcheon astutely asked what kind of Giardia test we’d had done. “Oh, no,” he said, by long-distance phone. “I don’t test in-clinic for Giardia anymore; it’s not reliable. Have an antigen test done right away. You’ll have to have it sent to a lab, but it’s the only way you’re really going to know whether he has it or not.”

So we did – and it came back positive. Giardia did not explain why Caleb’s itchy skin and achy joints seemed so much worse; we’d try to figure that out later. But thankfully, the parasite is treatable, and he’s now back to his old self.

About Dog Breath

Although vets don’t consider it a feature of the disease, the rise and fall of Caleb’s outrageously bad breath coincided with the course of his infection. Also, while his chronically itchy skin and arthritis appeared much worse when his digestive system went off the rails, they, too, eased off afterward. I offer the following suggestions.

First, it’s no wonder vets don’t look to breath quality as an indicator of health (except for possible oral problems). So many dogs have chronic halitosis that lots of people believe they naturally have bad breath! However, owners who’ve switched to raw or natural foods frequently report their dogs having pleasant, inoffensive breath like Caleb’s. We should not overlook our dogs’ breath as an important meter of wellness, particularly of the digestive system.

Second, like many dogs with autoimmune issues, Caleb has been on nutriceuticals such as glucosamine, MSM, marine oils, vitamins, and medicinal herbs for years. If he goes off them for long, his itchy skin and achy joints bother him more. Since Giardia interferes with the absorption of nutrients, it may also interfere with absorption of nutritional supplements. If so, this could further confuse the diagnostic picture when dogs in similar situations have Giardia infections.

What is Giardia?

Giardia is a microscopic, single-celled parasite that infects the guts of fish, birds, or mammals. It’s a major cause of diarrhea, and thereby a major cause of death of children under five in tropical and developing countries when there is poor hygiene and lack of water filtration. The Centers for Disease Control describes it as one of the most common causes of waterborne disease in the United States.

Giardia has two basic life-stages. As a “trophozoite,” it attaches itself to the lining of its host’s intestines with its sucker. There, it feeds, reproduces, and dies while actively colonizing its new dwelling-place.

Like any parasite, Giardia must seek new worlds to exploit. In its trophozoite form it can’t survive long outside a host’s digestive tract, so it transforms itself into individual “cysts” enclosed in resilient protective casings. In this form, the cysts exit an infected animal in the host’s excrement, chancing to end up somewhere they can remain viable until another host comes along.

The primary way to acquire Giardia is through oral contact with Giardia cysts. It happens mostly by drinking infected water, but, as you’ll see, it’s possible through other means, too. According to Dr. Peregrine, the ingestion of as few as 10 cysts can start an infection in dogs (and people). And the cycle continues.

To remain viable, Giardia cysts need a damp or wet environment in the right temperature range. They do best in woodland pools, ponds, streams, and lakes, but will also survive on a bedding of moist, organic matter such as a shaded forest floor. Dryness quickly destroys cysts, so they’re less a problem in deserts than elsewhere. They do well in humid warm climates. A rapid temperature drop to below freezing will kill most cysts as long as they’re actually caught in the ice, or in the part of the droppings or soil that becomes frozen.

But if they are protected, some cysts may survive for awhile even in extreme cold. For example, they might endure in fluid water beneath a layer of ice, or on soil insulated from frigid air by a good snow-cover. However, even in water cysts don’t live indefinitely; probably only for months, but not years, says Dr. Peregrine.

He adds, “Cysts that pass into water don’t multiply. They only multiply in the guts of animals.” In other words, in water, their numbers build up only through fecal matter that infected animals deposit in or near it.

This happens several ways. Infected land animals, including canids but not excluding infected humans, poop nearby and rains or melting snows wash the cysts into lakes or streams. Or water animals, such as beavers, excrete cyst-ridden feces right into the water. (Disease from Giardia is sometimes called “Beaver Fever,” but Dr. Peregrine thinks beavers may be unfairly blamed for the parasite’s success.) Giardia may also contaminate streams or lakes via untreated human sewage.

How Dogs Get Giardia

Dogs acquire Giardia primarily by drinking water that contains cysts. But chowing down infected feces will also do the trick!

However, not all types of Giardia affect dogs. Researchers now believe that it comes in different genotypes, and that most animals have at least one that’s limited to their own species. For example, one genotype is known to only infect dogs; another, only humans; yet a third is “shared” by both dogs and humans.

“Until recently,” says Dr. Peregrine, “we assumed that Giardia in dogs will always infect people, but it’s quite clear now that’s not the case. Some types of Giardia from dogs will infect people.” And sometimes, the opposite happens. He tells of a student who came home from Greece with a confirmed Giardia infection. A week later, the student’s dog became infected, too. “The dog almost certainly got Giardia as a result of drinking out of a toilet bowl,” he concludes. “So infection will go both ways! But not all human infections will infect dogs, and not all dog infections will infect people.”

How might we catch it from our dogs? If an infected dog’s anal area has traces of moisture, it could harbor cysts. As they dry up, the cysts lose viability. But in the meantime, if you brush against them and, yes, if they end up in your mouth, you may become infected. Being smooched by a dog dripping infected water from her muzzle might also expose you. However, there’s probably no point in getting too paranoid, as none of us can avoid Giardia completely.

The number of cysts a dog (or person) takes in affects his likelihood of getting infected; the more he ingests, the greater the odds are that it will happen. Environmental conditions influence this. For example, active streams or lakes can distribute cysts widely, whereas they may collect at the edges of quieter waters. Hot, dry spells can shrink smaller pools and ponds, concentrating existing cysts even closer together.

Dogster published a list of 7 things to know about giardia, which might be helpful. Check it out here.

Giardia Might Look Like Something Else

Too often, vets and owners haven’t even thought to suspect Giardia as the cause of a dog’s diarrhea. Why not?

Dr. Peregrine suggests that vets have only just realized how common it is, thanks to the new data. “I think we didn’t understand it before. Seven percent of dogs (testing positive) is a very high figure!”

Furthermore, since the disease has no distinctive clinical signs of its own, it can mimic “just about anything that produces diarrhea!” Dr. Peregrine laughs. “Except diarrhea with blood. It’s extremely unusual to see blood with Giardia.”

And veterinarians tend to test first for what they believe is most common. Morag McMurray, DVM, of Kingston, Ontario, gives examples.

“If a dog comes in with skin and digestive problems, you’d look for a generalized inflammatory reaction first. Or, if he had hypothyroid and diarrhea, you’d thoroughly examine the thyroid first. If he had diarrhea but no vomiting, you’d wonder about a foreign body,” Dr. McMurray says.

These reasons may explain why vets have overlooked Giardia as a potential cause of disease. But it’s time for a change in perspective.

When should you suspect that Giardia may have infected your dog?

Signs of Giardia Infection

Over half of the approximately 80 percent of infected dogs without clinical signs may eventually clear it on their own. But the other 20 percent can become pretty unhappy campers. Giardia usually, but not always, affects dogs up to one year old, or unwell dogs with challenged immune systems, more harshly than it affects healthy dogs.

When a dog has signs, diarrhea may be the first and only one you’ll see. He may also throw up. But the diarrhea may be intermittent and vomiting occasional, making it hard to know whether your dog is ill or simply ate something untoward. Stool, whether loose or formed, may stink and contain mucous. If the parasite interferes with nutrient absorption, you may see weight loss, weakness, and muscle-wasting.

Abdominal pain can be another feature of the disease. Two humans I know who have had it insist, “It’s terrible! You have spasmodic intestinal cramps, like colic!” One reported a metallic taste in his mouth.

Giardia infections are not normally life-threatening. But the dangers of dehydration (from excessive diarrhea) or malabsorption are real. Ideally, we should look for the parasite well before things get to this point.

Different Giardia Tests

Giardia can be tough to identify in tests, and routine fecal examinations don’t normally detect the parasite. But several tests, with varying levels of accuracy, can. Repeat a test up to three times to be sure of negative results, or switch to one that’s more dependable. Many vets do in-clinic tests by default (they’re less expensive); if you want a specific test done by a lab, request it.

• The “ELISA” test. Considered the most reliable and becoming more popular. Looks for antigens. Goes to a lab. Most likely to get correct results the first time. Note that the ELISA test for Giardia will not detect other parasites or problems that your dog may have.

• The “float” test. Done in-clinic. Designed to look for worms. May also find cysts, but much more reliable when performed by technicians who are specifically trained to find Giardia this way.

• The “fecal smear.” Performed in-clinic on fresh feces; looks primarily for trophozoites before they die off. A less effective way to find cysts. Dr. McMurray calls it more of a rough guide/initial screening test.

• The “fluorescent antibody test” (FAb). Done at a lab. Generally more reliable than the fecal smear, but either can give false positives or negatives.

Testing for Giardia should not replace routine stool checks.

Giardia Treatment for Dogs

To treat, or not to treat? Just because your dog tests positive does not mean you should automatically treat him. If he has no clinical signs of disease, he may recover by himself. Using drugs if they’re not truly necessary may encourage Giardia to develop resistance, hampering our ability to help a severely infected dog down the line. (Possibly also for this reason, many doctors today do not treat Giardia-infected humans who have no symptoms.)

But sometimes it makes more sense to treat. Dogs like Caleb, overwhelmed by too many cysts, or whose weak immune systems can’t throw off the infection, need help. Also, if a dog lives with a human or another pet who has a compromised immune system (from cancer or AIDS, for example,) Giardia could hit that individual hard. To protect the immune-suppressed family member, Dr. Peregrine advises treating even Giardia-positive dogs who show no signs.

Owners may choose to treat their dogs for Giardia with conventional pharmaceutical drugs that kill the parasite in the gut, or by attempting to bring about intestinal balance through natural means. Whichever method you use, first carefully shampoo the hair around the dog’s rear end to remove any cysts that may be present.

The conventional pharmaceutical drugs used to kill Giardia are:

• Fenbendazole (Panacur, SafeGuard). Originally used for dogs as a de-wormer, it eliminates Giardia, too. Dr. Peregrine asserts that it’s generally more effective against Giardia than the old stand-by, metronidazole. It appears to have fewer side effects, too; consisting, if anything, of vomiting. “It’s probably one of the safest drugs we use in veterinary medicine,” he says. Individual dogs may be allergic to it.

The use of fenbendazole for Giardia is pretty new on the scene; two out of four practicing vets I consulted did not yet know of its use for that purpose. It’s given once a day for three days; if the dog still tests positive a month later, your vet will probably repeat treatment for a longer duration.

• Metronidazole (Flagyl). The drug of choice for years, it’s also the mainstay for treating Giardia in humans. It has a good success rate. However, it also has a rather daunting list of possible side effects: neurologic disorders, lethargy, weakness, effects on blood cells, damage to the liver, blood in urine, anorexia, vomiting, and diarrhea. It’s not considered safe for pregnant females. Still, many vets rely on it because it has worked well for them and they’ve had few, if any, problems with it.

Clinical experience suggests Giardia is becoming resistant to metronidazole, according to Dr. Peregrine. But he advocates keeping both drugs in use, because if everyone switched to fenbendazole, “sooner or later, we’re going to get resistance to that, too! We want to be sure, in 50 years’ time, we’ve still got one or two drugs that work.” For this reason, he advises against using either drug preventively for high-risk dogs.

• Natural methods. Grapefruit seed extract, oregano oil, and colloidal silver, among others, reputedly kill microbes, among them bacteria, viruses, and parasites. You can find these and other preparations in health food stores; follow instructions for treating parasites.

Although these methods may help with many things, it appears that holistically oriented folk haven’t yet reached consensus on their effectiveness against Giardia. In my survey of eight natural pet care books – some classic, others hot off the press – six didn’t mention Giardia at all; the seventh did, but only in passing. Only Mary Wulff-Tilford and Greg Tilford, in their book All You Ever Wanted to Know About Herbs for Pets, deal with it. After noting that herbal preparations for Giardia are “moderately successful at best,” they suggest combining low-alcohol tinctures of the following:

2 parts Oregon grape
2 parts licorice
2 parts cleavers
1 part garlic

They instruct giving this to the dog at least one hour before a meal. Dose at about ¼ teaspoon (1 milliliter) per 20 pounds of body weight, twice daily for up to 10 days; if the dog does not improve significantly by then, consult a holistic veterinarian.

Given the Tilfords’ cautions, perhaps we simply haven’t yet found the most effective nonconventional remedies for Giardia. If you do want to try one, remember it may take awhile to work – a consideration if your dog is already in poor condition or in pain.

Unfortunately, regardless of treatment, Giardia may persist. Dogs often reinfect themselves during therapy. Take precautions to reduce exposure. Also, your dog’s Giardia may be nonresponsive to the drug used. A change of drug might help. She may have an underlying issue suppressing her immune responses. Observe her closely and consult with your vet. Finally, neither dogs nor people develop immunity against Giardia. They, and we, can always have it again.

Giardia does not do permanent damage, but once it’s gone, a dog may need a little time to heal her intestinal lining. Probiotics can help with digestion in the meantime. Feed clean, non-irritating foods. If she had malabsorption, add nutritional supplements to help her regain what she lost.

Caleb did not respond to maximum doses of grapefruit seed extract and oregano oil, given for five days. But after two treatments with fenbendazole, he finally tested clear and regained his ideal weight. His digestion recovered over a few weeks, and his breath cleared along with it. Plus, his aggravated, itchy skin and achy joints calmed again to their “normal” level of irritation. Maybe the Giardia had interfered with his absorption of the supplements we give him to ease those problems.

A Word About Giardia Vaccines

Wyeth makes a vaccine called GiardiaVax,® which, the company claims, can prevent dogs from developing disease (diarrhea) caused by Giardia; it does not prevent infection. Dr. Peregrine conducted a study to look at whether the vaccine might also clear infections in dogs who have been nonresponsive to traditional treatment, but did not find that it had any effect on this. Further, he states that some people believe, on the basis of clinical experience, that the vaccine provides no significant benefit either preventively or therapeutically.

It should also be noted that the vaccine contains thimerosol, a preservative that contains mercury. Many holistic practitioners believe that preservatives that contain mercury can cause abnormalities of the nervous system, such as problems with coordination, vision, and learning

Giardia Prevention

You probably won’t be able to avoid Giardia completely, but you can certainly reduce your dog’s chances of contracting it.

• Support her immune system so that she can handle Giardia better. This requires a proper diet, regular exercise, enough natural light, and a minimum of problem stress. But even if she does contract the parasite, she still may not have an immune issue; a sufficiently high number of cysts could infect even the healthiest dog.

• Keep your dog’s living quarters and hindquarters clean and dry. Gentle shampoo followed by clean water will look after the dog personally; soaps lift cysts away from the body so you can rinse them off.

Concerning floors, here’s the most effective solution: flush them frequently with lots of plain water and let dry thoroughly before the dog comes back in. Concrete runs, especially, benefit from this. Many disinfectants don’t affect Giardia, and heavily soiled areas shield cysts from chemicals, anyway. Keeping clean is better. Steam-cleaning can also help as Giardia can’t survive temperatures over 60°C/152°F. Wash your hands well after clean-up.

• When you go out with your dog, avoid quiet waters where cysts may gather and to visit streams or bigger lakes, instead. Walk in woods after vernal pools have dried up in summer. Discourage him from eating feces. In your yard, see what you can do about standing water, but don’t worry about things like raised bird baths; if they’re too high for mammals to poop in, they likely won’t collect Giardia that could infect your dog.

What if, like us, you’re surrounded by swamp, or your dog loves the water and you don’t want to deny her that pleasure? Have your high-risk dog tested for Giardia annually. And if she develops diarrhea, think of Giardia first instead of last, and prompt your vet to look into it.

• Water treatment. Town water systems should deal with Giardia, but not all do. If yours doesn’t, you’re on a private well, or you take your dog camping, boil water for at least one minute to destroy cysts. Properly maintained ultraviolet light systems for private wells kill them. Filters with an absolute pore size of one micron, or that are rated “for cyst removal,” will snag them. Remember: you can’t detect Giardia just by looking or sniffing at water. Cysts may dwell there even if it appears pristine and delicious!

Finally, don’t get discouraged if you’re trying to do everything responsibly but your dog still gets Giardia. There’s no such thing as zero risk with the parasite; just do what you can, be realistic, and get out there and have fun with your dog.

GIARDIA IN DOGS: OVERVIEW

1. Consider Giardia first rather than last as a possible cause of your dog’s diarrhea.

2. Request that your veterinarian send a sample away for an antigen test, or, if they’re doing a “float,” ask for a technician who’s been specifically trained to find Giardia that way.

3. Don’t let your dog drink from the toilet! They can become infected by an infected person this way. Remember, an infected person (or dog) may not exhibit symptoms.

4. Ask your vet to make Giardia part of your dog’s annual parasite test.

Susan Weinstein is a freelance writer with a strong interest in animals and holistic healthcare. Presently, she is working on a book about pets and stress with Paul McCutcheon, DVM. Weinstein and Caleb live in Grafton, Ontario.

by Mary Straus

Editor’s note: In last month’s article “Heartworm: Don’t Take It Lightly,” Mary Straus discussed the life cycle of the heartworm, and how it infects dogs. She also discussed heartworm prevention strategies. This month, she explains treatment for dogs who are already infected with heartworm.

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Whether or not you choose to use conventional heartworm preventatives, there is always the possibility that you may one day find yourself with a heartworm-positive dog, and be faced with the decision of how to treat her. Unfortunately, there is no one right answer when it comes to heartworm treatment. Decisions must be tailored to the individual dog, taking into account both the extent of the heartworm infestation, and the dog’s overall age, activity level, and health.

There are a number of reasons why someone may have a dog who is heartworm-positive. One of the most common is adopting a dog from a rescue organization. Especially in the South where heartworm is ubiquitous, most dogs that are not given heartworm preventative regularly will test positive for heartworm.

There is also a small chance that your dog could become infected with heartworms if you choose to extend the time between doses of the heartworm preventative you give your dog beyond what is recommended on the label, if you give less than the recommended dose, or if your dog should vomit up the pill without your knowledge. Your dog has a much higher risk of becoming infected with heartworms if you choose not to use preventatives or if you use alternative methods that have not been shown to be effective.

It is important to understand that heartworm infections are not detectable until about six months after a dog has been bitten by a heartworm-infected mosquito. (This is why it’s not possible to have a heartworm test performed monthly and give the preventative only if an infection is found.) Blood tests will not detect heartworms in a dog until the larvae have matured into adult worms, which takes about six months following initial infection. Symptoms, such as coughing, lethargy, and difficulty breathing, will not show up until the infection is advanced.

Judy Wilds, of Corpus Christi, Texas, adopted her dog, Taffy, in September 2004. Taffy tested negative for heartworms when adopted, and was started on a regular heartworm preventative schedule. Six months later, a routine heartworm test showed that Taffy was heartworm-positive. “Thankfully, a holistic vet had suggested that I have her rechecked six months after her first test, as it was possible (though unlikely) that she could have heartworms,” says Judy. In this case, Taffy was obviously infected when she was adopted, but had not had the infection long enough for it to be detectable.

It’s a good idea to run a heartworm test on an adopted dog with an unknown medical history immediately upon adoption and then again about six months later. The same would apply if there was a lapse in heartworm preventative dosing for more than two months during the heartworm “season.”

Staging the infection
A heartworm antigen test is the most commonly used procedure for detecting heartworm infection. These tests are extremely specific and have almost no false positives, but it is still a good idea to confirm any positive test results with a second test. There are a number of different heartworm antigen tests, so it is best to confirm using a different test than the one that gave the initial positive result.

If the dog has not been given heartworm preventative recently, then a test for circulating microfilariae can also be done, which will confirm the presence of adult, breeding heartworms in the body. However, a negative microfilariae test cannot be used to rule out heartworm infection for a number of reasons.

All heartworm preventatives kill the microfilariae that are in the dog’s blood, so any dog who has been given heartworm preventatives recently may be negative for microfilariae but could still have an infection. There are also cases of single-sex heartworm infection where no microfilariae are produced. A population of all male or all female worms cannot produce microfilariae. And, finally, in any dog with a very low heartworm burden – say, just a couple of worms – the microfilariae may not be detected (this can also cause a false negative on the antigen test).

Once heartworm infection has been confirmed, additional tests should be done to try to determine how extensive the infestation is. Radiographs can reveal inflammation and damage to the arteries and the heart, and blood tests will show whether the liver and kidneys have been affected.

Heartworm infection is divided into four or five stages (depending on the model used), based on the severity of the infestation and the age and health of the dog.

Stage 1 (mild) consists of young, healthy dogs with no symptoms and minimal changes evident on X-rays.

Moderate (stage 2) infection will show heartworm disease that is evident on X-rays, but symptoms are minimal, mostly coughing. Stage 3 is a severe infection, with weight loss, coughing, difficulty breathing, more damage visible on X-rays, along with liver and/or kidney damage.

Stages 4 and 5 are considered critical, with the dog often collapsing in shock. These dogs will not survive ordinary heartworm treatment, and must have the worms surgically removed if they are to have any hope of survival.

Heartworm treatments
There are three conventional methods of treating heartworm: a “fast kill” method using Immiticide (melarsomine); a “slow kill” method employing Heartgard (iver-mectin); and a surgical method in which the worms are surgically removed from the arteries. In addition, there are so-called holistic treatments such as Paratox homeopathic or herbal preparations.

In each case, and indeed even if no treatment is done, there is a risk of the dog dying from a pulmonary embolism caused by worm die-off. In addition, there is risk while the worms are present of damage to the heart, the arteries, and the rest of the body, due to inflammation and immune reaction.

When deciding which method to use, you need to take into account the age of your dog, his level of activity, and the severity of the infestation.

Immiticide (fast kill)
Standard treatment with Immiticide consists of giving two injections 24 hours apart, then keeping the dog strictly confined for the next four to six weeks. The injections must be given in a painful location – the muscle close to the dog’s spine in the lumbar (lower back) area. The worms start to die immediately. As their bodies begin to decompose, pieces are “shed” into the dog’s bloodstream and filtered out through the dog’s lungs. This can cause the dog to cough and gag, or lead to a fatal pulmonary embolism.

The dog must be kept confined and his physical exertion kept to an absolute minimum, in order to prevent pieces of the dead worms from being forced by a rapid heart rate and/or increased blood pressure into clogging the tiny blood vessels in his lungs, causing embolisms. This generally means that the dog must be kept crated or penned and allowed out to potty only on a leash. Aspirin may be prescribed to lower the risk of blood clots, though this is controversial. Remember that it’s dangerous to combine aspirin with any other nonsteroidal anti-inflammatory drug (NSAID) or with prednisone, and to give it only with food.

A safer approach, sometimes called a “split-dose,” “staged-kill,” or “three-dose” protocol, consists of giving one injection, waiting one month or more, then giving two more injections 24 hours apart. This has the benefit of reducing the worm burden by about 30 to 50 percent with the initial treatment, before the balance are killed by the second set of injections.

This protocol is more expensive, requiring three injections of the drug instead of two. Also, the dog must be kept strictly confined for a longer period of time. Nevertheless, this split-dose protocol over two months is recommended for dogs with heavy worm burdens or other health problems (Stage 3), and is also considered safer for dogs with a lower worm burden.

Judy Wilds treated Taffy (described above) using the fast kill method with Immiticide. Although it is recommended to keep treated dogs in a crate to limit their exertion, Taffy was unused to being confined, and her vet was concerned that crating her could be dangerous, as excess stress and barking could cause lung problems. Wilds used a small outdoor pen for Taffy, instead.

“Taffy handled the heartworm treatment quite well. One evening, however, she gave me quite a scare when she began gagging. Later, I realized that this was related to her heartworm treatment,” Wilds says.

Some coughing or gagging is considered normal in dogs being treated for heartworm infection. However, it is important to understand that, whatever method of heartworm treatment is used, any respiratory difficulty in dogs receiving therapy should be considered a life-threatening emergency.

If the coughing or gagging is very heavy, seems uncontrollable, or causes the dog distress, get her to a vet right away. Vomiting or any bloody discharge combined with lethargy, fever, and/or pale gums should also be considered an emergency, and the dog should be taken to the veterinary or emergency clinic immediately. Corticosteroids, fluids, and oxygen may be needed at this time to help the dog survive.

Immiticide (melarsomine) has a much lower risk of complications than its historical predecessor, another arsenic compound called Caparsolate (thiacetarsemide sodium). Unlike Caparsolate, Immiticide does not damage the liver and kidneys, and kills a higher percentage of worms, so that fewer treatments are needed.

However, the Immiticide injections will cause muscular pain and soreness for a few days. It’s critical that the injections be done in an exacting fashion in order to minimize this effect. This includes changing needles after filling the syringe before injecting, choosing the site with care, putting pressure on the site after injection, and alternating sites for future injections.

Corticosteroids (e.g., dexamethasone) can be given at the same time as the Immiticide injection to lessen the reaction. Combination painkiller and sedative drugs, such as xylazine, may also be used to reduce the pain of the injection. Pain medications, such as NSAIDs, are often prescribed for a few days.

Christie Keith, a Scottish Deerhound breeder from Northern California, had two dogs who were heartworm-positive. “Raven had some obvious clinical changes, and was showing some symptoms (coughing). Due to her hyperreactive immune system, I was concerned that the presence of the worms in her pulmonary arteries, with their known ability to stimulate autoimmune reactions, would further worsen her existing allergies. So I opted to do the conventional Immiticide heartworm treatment, with the thought that it would be best to get the worms out of her more quickly.”

Christie intended to treat Raven with the split-dose schedule, but a couple of weeks after the first dose, Raven, despite having been completely confined and kept from activity more strenuous than going out into a tiny potty yard on a leash, developed a series of pulmonary emboli (clots), and nearly died. “We rushed her to the ER and when we got there, my mom, who was with her in the back of the van, thought she had died. She was blue,” recalls Keith. Emergency treatment saved Raven’s life. Tests conducted after the first treatment revealed no trace of heartworms, so Raven didn’t have to undergo another round of treatment.

Heartgard (slow kill)
The “slow kill” method, which is a newer approach, consists of giving the dog Heartgard on a monthly basis. This heartworm preventative medication has some effect against the adult worms and should gradually eliminate them over a period of one to two years; without treatment, the worms can live up to five years. The earlier the treatment is started after infection, the more quickly it will work to eliminate the adult worms. Note that only Heartgard (ivermectin) should be used, as Revolution (selamectin) affects far fewer adult worms, and Interceptor (milbemycin oxime) almost none at all.

Although this method is gentler than the use of Immiticide, the danger from the dying worms is still present, and for a much longer period. A recent Italian study showed that pet dogs (as opposed to the caged laboratory dogs this method had been tested on before) did get pulmonary emboli and some of the dogs died of it. The more active the dog, the higher the risk.

In addition, damage is being done to the arteries leading to the heart, and possibly to other areas of the body due to inflammation and immune response as long as the adult worms are present in the body. Most vets recommend using the fast kill method to treat heartworms, unless the dog’s health will not permit it or the owners cannot afford it. In those cases, or in the case of a very mild infection, the slow kill method may be used instead.

Janice Adams adopted Pepper, a Border Collie/Chow-mix, in June 2000. A blood smear in the vet’s office at the time of adoption was positive for microfilariae. “Pepper didn’t seem to have any symptoms of heartworm disease, no coughing or shortness of breath, so, at the recommendation of my regular vet, I elected to start her on Heartgard monthly,” says Adams.

“Pepper is a very calm dog, and didn’t have any activity restrictions. I kept her on Heartgard monthly for about 18 months, then switched her to a low dose of Interceptor on a 45-day schedule. We live in Florida, so I give heartworm preventatives year-round. All subsequent heartworm tests have been negative. She didn’t seem to have any problems related to the heartworm disease or treatment.”

Christie Keith’s second heartworm-positive dog, Bran, had no radiographic changes and no allergies, so Keith opted not to do the Immiticide treatment on him. “I put Bran on Heartgard monthly. At the time, there was less research on the ‘slow kill’ method with Heartgard than there is today, but there was enough that I felt confident it would be effective. And it was; within a few months or a year, he tested heartworm-negative.”

Other heartworm treatments
Surgical methods of heartworm removal require specialized training and instrumentation, and are generally reserved for high-risk patients who would not otherwise be expected to survive. The surgery is followed by one of the standard treatments a few weeks later to kill any remaining worms.

So-called alternative methods to kill heartworms, such as Paratox, are no safer than conventional drugs, since they rely on the exact same action – they kill the larvae/worms in the bloodstream. It is the death of the worms that causes the greatest danger to dogs during treatment.

In addition, no studies have been done to show that alternative treatments are effective. If these treatments do have any effect, they would be comparable to the slow kill method, with the same drawback of continued damage to the body while the worms remain present.

Finally, some of the herbs used to treat heartworm are considered dangerous and may be toxic in the amounts used to try to kill the worms.

Additional information
Once the adult worms have been killed, there may still be circulating microfilariae in the bloodstream. Although these microfilariae will not develop into adult worms (they mature further only inside a mosquito), they can be a source of transmission of heartworm disease to other dogs, so it is best to treat the dog with heartworm preventative four to six weeks after heartworm treatment in order to kill them.

Normal monthly preventative doses of Interceptor (0.5 mg/kg) or high doses of Heartgard (50 mcg/kg, approximately eight times the preventative dose) will eliminate most microfilariae immediately. Normal monthly doses of Heartgard or Revolution will also work for this task, but more slowly, over a period of several months.

Because heartworm treatments can cause an allergic reaction due to the death of the worms and the microfilariae, veterinarians will usually give dogs Benadryl and/or cortico-steroids prior to each treatment. Monthly Heartgard (ivermectin), at preventative doses, should not be strong enough to cause this kind of reaction, although it’s a good idea to stay home the day you give it to your dog.

If Interceptor (milbemycin oxime) at normal doses, or Heartgard at high doses, is used to kill microfilariae following heartworm treatment, anaphylactic shock can occur, especially in dogs with high microfilariae counts. This treatment is best done at the veterinarian’s office under close observation for any adverse reaction.

The damage done
Although heartworm treatment can be dangerous, so are the heartworms themselves. Adult heartworms are large, growing up to 12 inches in length and living as long as five years. They can plug up the pulmonary arteries, and when the infestation becomes severe, they will start to back up into the heart and eventually fill it. They can cause blood clots, and force the heart to work abnormally hard to pump blood through the clogged arteries. In addition, heartworms cause an extreme inflammatory response in the arteries that can affect other parts of the body, especially the kidneys and liver.

Treatment for heartworm infection is one area where conventional veterinary medicine offers valuable options. Whether you elect to do the fast-kill method using Immiticide, or the slow-kill method using monthly Heartgard, either is preferable to leaving the dog untreated, or using unproven, alternative methods that may have no effect or even be harmful.

This is also a situation where steroids and antibiotics can be lifesavers, when used judiciously during treatment.

The decision of how to treat a heartworm-infected dog is not an easy one, and is best made after consulting with your veterinarian regarding the safest method to use for your dog.

Also With This Article
Click here to view “Heartworm Treatment Options”
Click here to view “Heartworm: Don’t Take it Lightly”

-Mary Straus does research on canine health and nutrition topics as an avocation. She is the owner of the DogAware.com Web site. She lives in the San Francisco Bay Area with her dog Piglet.