The reduction of parasitic diseases is one of the marvels of modern medicine. In the developed world, these infections in people are rare thanks to sanitation and continuously-improving treatments, but worldwide they are still an enormous problem, with an estimated one million annual deaths in people attributable to parasitic diseases. Although most of those deaths are from a single protozoal parasite (malaria), other typically non-fatal parasitic disease are extremely common in the developing world. For example, about one billion people are infected with roundworms, mostly in tropical and subtropical regions. In domestic animals, especially our pets, we can see some of the same patterns. It is unlikely that a Yorkshire terrier who poops on AstroTurf on the 50th floor of a high-rise building will get a roundworm infection.

We have also been very fortunate in the past few decades to have developed very safe and effective drugs such as fenbendazole, ivermectin, and pyrantel pamoate, all of which are used in both people and animals for a variety of parasitic infections. Some of these drugs can be used prophylactically, such the use of ivermectin to prevent tens of thousands of cases of a devastating disease called river blindness. In dogs and cats, we routinely “de-worm” with these drugs to prevent the spread of parasitic disease, often without knowing if a specific animal is infected or not. One of the best examples of this in veterinary medicine is the use of ivermectin-like drugs to prevent heartworm disease. These drugs have been around for decades, are safe, and very effective in preventing this serious infection.

But people being people, and alternative veterinary medicine being what it is, can’t leave a solved problem un-meddled with. There is of course a movement against the use of parasite-preventing drugs based on fear and misconceptions (see my post about flea products). And heartworm disease, arguably the most serious (my definition of serious = incidence x severity) parasitic disease of dogs in the United States, has unfortunately not been spared the bumbling interventions of alternative practitioners.

Dr. Peter Dobias is a veterinarian who has written an alternative heartworm prevention guide (and also here). The pitch is that you’re exposing your dog to dangerous chemicals if you give heartworm preventatives, and that you can completely avoid doing so if you really understand heartworm disease. It is extremely deceptive and factually inaccurate, but the falsely-compelling narrative will probably convince some dog owners. If this were just a silly alternative therapy that wouldn’t cause any problems, it might not require a response. The problem is that this protocol is going to put some dogs at serious risk if it is followed.

Background info: A heartworming story

Heartworm disease in dogs is potentially life-threatening parasitic infection. The extremely condensed life history of this parasite is that it is spread by mosquitoes, mainly infects dogs, has a relatively long incubation period of about six months, and is a seasonal problem in many parts of the world. There is a treatment for heartworm infections, but it does carry some risk of serious complications, so the main strategy used to deal with heartworm is to prevent it altogether. Fortunately, at certain points in their development the larvae can be killed by ivermectin-like drugs known as the macrocyclic lactones (hereafter referred to as MLs) before they ever reach the lungs to cause damage.

The catch is that there’s no good way to know when your dog has just been infected with these vulnerable stages. So instead of only treating after an infection, we prevent infections altogether by giving all dogs in heartworm-endemic areas a ML once a month during heartworm season (since the “vulnerability” window is about 45 days). If any larvae are transmitted to the dog, they get wiped out by the ML without anyone ever knowing.

This is a classic preventative strategy: cover an entire population with an effective tool that stops the spread of an infectious disease since you don’t know exactly who is going to be exposed (think vaccines to prevent viral and bacterial diseases, condoms to prevent STIs, making teenagers listen Nickelback to prevent devolvement into Canadian post-grunge pop rock fandom, etc.). It’s not perfect because you are treating lots of animals that won’t necessarily get infected and lots of dogs never get MLs for heartworm prevention, but overall infection rate is reduced. This is an acceptable strategy, especially when the preventative tool is not or is minimally harmful (e.g. all the above examples except Nickelback).

The claim

So we have this somewhat crude yet effective strategy for preventing heartworm infection. And pharmaceutical companies are involved (they produce the drugs after all). You give me these two conditions and enough time, and I swear there will be spontaneous generation of an alternative medicine pseudoscience pharma-conspiracy. It’s like having Ben Affleck and Jennifer Lopez hang out in the early 2000s, something terrible is going to come out of it.

Not to disappoint, Dr. Peter Dobias and have promised to expose a corrupt industry (a) and cooked up an alternative guide on how to prevent heartworm without medication (b). They claim MLs are dangerous (c), and he has created a safer, smarter way to go about things (d). Except that: (a) they don’t, (b) they didn’t, (c) they aren’t, (d) and he really hasn’t.

This is his alternative protocol: use a new PCR test to detect the early stages of the infection and only treat dogs that actually need it. It sounds brilliant because it bypasses all of the crudeness of the current strategy where we treat every dog without knowing which ones actually need it. But (not to give too much away), it’s based on inaccurate or baseless information and is a self-contradictory pile of lukewarm mush. However, in the principle of charitability, I will present his argument.

He states that heartworm preventatives are largely unnecessary and dangerous. His reasoning is that heartworm has about a five-month incubation (or prepatent) period between when the infection is transmitted and when clinical disease starts, and during this entire period you have an opportunity to easily kill the worms before they become adults, thus arresting the infection. His method of determining when you need to treat your dog is based on a different heartworm test than the usual heartworm antigen test run in most veterinary clinics. According to Dr. Dobias:

Advances in heartworm diagnostics now offer DNA testing on the basis of PCR (polymerase chain reaction) technology. This test done by Healthgene allows you screen for any presence of heartworm and is very reliable with practically no false negatives.

He suggests that instead of giving your dog a preventative, you test it every four months. If the dog stays negative, congratulations! You’ve just avoided paying for all those preventative drugs!* If the test is positive, however, he says don’t worry, your dog has the worm larvae but you can easily treat it. Wanna know what he recommends treating your dog with? A heartworm preventative drug. Yes, these were dangerous chemicals before but now they’re okay. There is not a hint of irony in his guide about this, he says at this point it’s safe but be sure to check with a holistic veterinarian first. He congratulates himself on his clever protocol by concluding:

It is possible to completely eliminate heartworm drug use if DNA testing is done on a regular basis.

If you’re wondering how the words “completely eliminate heartworm drug” and “heartworm preventative can be safely administered” can be just a single page apart in this guide, and what this mind-numbingly erroneous reasoning means for the entire protocol, you’re on the right track.

The problems add up

There’s a reason (besides the Illuminati and Lizard people running the government) that Dr. Dobias hasn’t shaken up the entire veterinary industry and devastatingly exposed pharmacorporate corruption. He dun messed up. He made a few boo boos. Actually, he got completely mixed up and wrote a fatally flawed protocol with a fundamental misunderstanding of the disease he is supposedly an expert on, and he’s potentially put pet dogs’ lives at risk.

A number of screaming red flags should be obvious already, but wait, there’s more. In the guide he states that the DNA test can detect “microfilariae” (presumably he means the third and fourth stage larvae since microfilariae infect mosquitoes, not dogs, but more on that in a second) in the dog before they have a chance to mature into the harmful adults, and therefore as soon as you get a positive DNA test you still have an opportunity to prevent a full-blown infection. He thinks he’s got the worms by their little cuticular gubernaculae**!

That the presence of microfilariae will lead to a positive DNA test is true, as the research validating the DNA test show. The problem is that microfilariae are not the vulnerable, infectious stage of the heartworm parasite that indicate there’s still time to prevent adult worms. They are in fact an absolute indicator of adult worms in the body, since microfilariae are the brand-new babies of heartworms made by… adult worms. If your dog has microfilariae in its blood, it’s got adult heartworms.

Okay, let’s give him the benefit of the doubt and assume that he knows microfilariae mean an established infection. Let’s assume that he meant the DNA test will be positive before that established infection, when the actual larvae are deposited by the mosquito. Because if that were true, then intermittent testing and treating positives would still be a good idea. Let’s be generous.

Say that you have a 3.99-month-old heartworm infection (i.e. your last test was negative but immediately afterwards your dog got infected and now you’re positive). You decide to give a ML because this is Dr. Dobias’ holistic protocol. Can you expect that treatment to be effective? No, dogs that get a ML 3.5 months after exposure to heartworm infection are still very much at risk for developing infection, because the efficacy of the drugs decreases as the larvae mature. In other words, your limited window of opportunity to prevent heartworms with a ML is less than 3 months, and probably less than 2 months. It’s been well established that waiting 4 months results in larvae maturing to adults.

Ok let’s give this protocol any chance to be effective and say you’ve got a more recent infection or that you’re testing once a month and the larvae are vulnerable to a ML. If you know that you have these vulnerable larvae, then you can give a ML and you should clear the infection. So, you do the DNA test on a blood sample from your dog. Will this sample be positive? Nobody knows, but heartworm larvae don’t enter the bloodstream for 45-65 days, so it’s completely plausible the test will be negative. The larvae are in the body but is their DNA reaching the bloodstream to be detectable? It’s not impossible since you could imagine some larval cells being shed, or some white blood cell granule blasting off a piece of the worm, and having that debris make its way into the bloodstream. But no one has published any data on this all-important question. If you miss any of these larvae, you are going to let them establish the infection. In other words, you need this test to be 100% sensitive (meaning no false negatives). Do you trust Dr. Dobias on this? It’s dubious enough to put any dog on this protocol in a heartworm-endemic area at serious risk of developing a heartworm infection

Conclusion: Alternative heartworm testing is literally risky business

I think we’ve stretched our generosity to the max, like a dachshund trying to get scraps off the dinner table. We have some dangerous misinformation presented as classic pseudoscience, and careful reading of the alternative heartworm protocol shows just how poorly-thought-out it is. There is, however, very often a “kernel of truth” in pseudoscientific claims. It seems to be just enough of a science-y scent to throw off the average person. And this case is no different. Dr. Dobias does correctly state that not every dog needs a heartworm preventative every single month, because heartworm is neither endemic nor year-round in every region. He is also correct that pharmaceutical companies and testing laboratories are motivated by profit to encourage prophylactic use of the drugs and tests in areas where it might not be appropriate.***

These points conceded, he gets most everything else wrong, and writes a dangerous protocol while ignoring the gigantic neon “hypocrisy” sign above his head as he pushes unnecessary tests. I didn’t want to go any further down the rabbit hole, but unfortunately, I clicked on his link for holistic heartworm treatment and it only gets worse. He’s recommending black walnut hulls to treat (or prevent, it’s not clear) heartworm, and says that as long as you don’t feed processed foods, don’t vaccinate, and give the right supplements (I’ll give you one guess where you can buy them), your dog shouldn’t get heartworm. This is bad, bad, bad veterinary medicine, nose to tail and needs to be expunged from the internet before it causes some real harm.

One last thing. Thanks for reading this far down and sticking with me on this far-too-long rant about a topic that should be almost immediately dismissible. Before I finish though, I cannot, CANNOT write a post about worms without shamelessly plugging my vet school’s epic rap noir track, “Worm Burden“. Since it covers some heartworm biology, I think it’s allowed. That is NOT the reason I wrote this entire post though. It’s not.

*Which runs around $10 per month (you just paid for the test, and for your vet to collect and ship the blood sample, which if it’s more than $40…well you see where I’m going with that one).

**My possibly incorrect understanding of what heartworm reproductive organs are called.

***These last two points are VERY controversial in the veterinary field. There are several factors that are important to consider here, none of which will fit into this post.

Posted by Greg Bishop

Greg Bishop is a veterinarian in Southern California who works mainly with dogs and cats. As a fan of the SBM blog, he sees the enormous amount of bad science and information in the field of veterinary medicine as an opportunity, not a problem! But also a problem.