Carbón beats heartworm: treatment and recovery journal

Starting a new thread to document Carbon's heart worm treatment in the hopes that it may help someone else down the line. Also an effort to keep his other thread more about his/our travel adventures than all the medical stuff!

First, some background. Carbon is a rescue Labrador from Spain. He's anywhere from 1,5 to 2 years old and weighs 29 kgs. Info from the shelter in Spain is sketchy, but we know that he was left in a killing station to be euthanised as a young puppy. Instead of that fate, he was kept in a cage outdoors, likely with several other dogs. He would have had no vaccines or any parasite preventatives.

Around 8-12 months old he was rescued by a local private shelter. At this point he was tested for most diseases and given the normal round of injections. At the time he test positive for Leishmaniasis and negative for everything else, including heart worm.

The type of blood tests run in the shelter are 'snap' tests. From a quick search: "a snap test in the veterinary world is a blood test that is run in the hospital and provides results in 8 minutes. The test is a screening process for six vector-borne diseases: Heartworm, Lyme, Ehrlichia canis, Ehrlichia ewingi, Anaplasma phagocytophilum and Anaplasma platys."

What we guess is that this initial snap test at the shelter resulted in a false negative for heart worm. This is because it takes up to five months post-infection for the snap test to detect the heart worm, due to the worm's lifecycle (more on this in a follow up post). It is also possible that the monthly preventatives he was given subsequently were not effective and he was infected at a later date.

However, there seems to be a good argument for Carbon having been infected from puppyhood with heart worm. When I met him two weeks after arrival at the private shelter, he had a normal amount of energy. He subsequently developed anaemia, which was blamed on his Leish. He also started suffering bouts of lethargy and weakness when I brought him home as a foster six weeks later. But these also corresponded to when he started getting heart worm preventative tablets.

In preparation for traveling with Carbon back through a heart worm-prone zone (vs. in Germany where heart worm doesn't factor in), I had him tested prior to starting him again on a monthly preventative such as Milbemax. That brought us to yesterday, where we got his positive diagnosis.

NEXT: What is heartworm?
Along with Carbon, I also took his cage-mate out of the shelter. That was the lovable Bodeguero named Paul (now Vizzy), who was heart worm positive. Even before he came to my house for good as a foster, he stayed with me after his painful injections for heart worm. When he was adopted with the support of the rescue organization Bodeguero UK, the leader of the rescue asked me to write a short primer on heart worm for other people thinking about adopting a heart worm positive Spanish dog.

Here is what I came up with. Note: I don't have a medical or scientific background, so I've just summarized reliable online resources and cited them at the end of the document. If you see anything that looks incorrect, please let me know!

The ironic thing: if I would have paid better attention to what I'd written here, not only would I have tested Carbon a couple months ago, but I also wouldn't have been so shocked that he tested positive. :rolleyes:
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Heartworm Basics for Potential Adopters
(Originally written for Bodeguero UK)

If you are thinking of adopting a rescue dog from Spain, first of all – congratulations and thank you! There are dogs in need, especially Spanish breeds like our charming Bodeguero, who will make wonderful additions to your family. You may have concerns, however, about potential health issues from diseases that exist in Spain but are not in the UK such as heartworm (also known as filaria or filariasis).

This document is a short primer to help de-mystify heartworm.

Heartworm may seem particularly scary to those in the UK, where it only exists in imported dogs. To most of the rest of the world (the entire USA, for example), it’s just something to regularly prevent against – like protecting your dog from fleas and ticks. A once-a-month tablet plus a yearly test as part of your dog’s regular vet checkup and…voila! No heartworm danger.

However this easy prevention rarely happens for dogs in need in Spain. A relatively high presence of infected mosquitos in many parts of Spain and the fact that many dogs have lived most of their lives out of doors means that if you have decided to adopt a dog from Spain, heartworm is something you should be aware of.

Any dog coming from Spain to the UK via a private shelter or rescue will have been tested for heartworm along with other diseases.

If the dog tests positive for heartworm, he will be given treatment before transport to the UK for fostering or adoption. Depending on how long ago your new dog’s heartworm treatment took place, he may need follow-up care post-adoption in the UK (more info in FAQ below).

If your dog tests negative, it is also a good idea to have him tested by your vet six months after his arrival as a precautionary measure (more info in FAQ below).

In either case (negative or positive/treated) it is very important to inform your UK veterinarian that your dog has come from Spain and could potentially have been exposed to heartworm. Discuss with your vet the best time to administer your dog’s follow-up heartworm test.

Be aware and educated but try not to let heartworm frighten you. It is preventable, treatable and not contagious.


What is heartworm?
Heartworm is caused by a parasitic worm called Dirofilaria immitis and spread through the bite of an infected mosquito. The dog is the host for the majority of the parasite’s lifecycle (mature into adult, mate, produce offspring) while the mosquito essentially acts as a carrier for larvae. From the time a dog is first bitten by an infected mosquito, it takes 6 to 7 months for the larvae to mature into adult heartworms inside the host dog.

Where is heartworm most prevalent?
Heartworm is not just a problem in Spain, but also in many southern European countries such as Portugal, France, Italy, Slovenia, Bulgaria, Romania, Greece and Turkey. This interactive map from Bayer shows incidence worldwide of heartworm and other diseases such as Leishmaniosis. Within Spain, the risk is higher along the southern and Mediterranean coasts as shown in this map.

If my dog tested negative for heartworm in Spain, do I need to worry about it once he is home with me in the UK?
If the dog tests negative, then usually there should be no further concerns. However, because of the life cycle of the parasite, it is unlikely but possible that an infected dog could test false-negative.

A lot depends on how long your dog as been cared for by rescue. Typically private refuges and rescue groups test for standard diseases, including heartworm, when the dog comes under their care. At this time, a dog can test false-negative if he is newly infected. This is because it takes time (a minimum of five months) for the larvae to be mature enough to be detected in blood antigen tests.

For this reason, it is advised to re-test your adopted dog for heartworm six months after arrival from Spain. This is because 5-6 months is the minimum time from infection (mosquito bite) to ability to detect the disease in a blood antigen test.

How is a dog tested for heartworm?
A veterinarian uses blood tests to check a dog for heartworms. An antigen test detects specific heartworm proteins, called antigens, which are released by adult female heartworms into the dog’s bloodstream. In most cases, antigen tests can accurately detect infections with one or more adult female heartworms. The earliest that the heartworm proteins can be detected in a dog’s bloodstream is about 5 months after it is bitten by an infected mosquito.

Another test detects microfilariae in a dog’s bloodstream. Microfilariae in the bloodstream indicate that the dog is infected with adult heartworms (because only adult heartworms can mate and produce microfilariae). The earliest that microfilariae can be detected in a dog’s bloodstream is about 6 months after it is bitten by an infected mosquito (because it takes about that long for the heartworms to develop from infective larvae into adults that mate and produce microfilariae).*

*Information in this section taken verbatim from the USA FDA website

If I travel out of the UK with my dog in future, will he need a heartworm preventative?
Yes! Many people think that if they are just passing through an affected area that their dog is at no risk. Most of southern Europe, including France, has heartworm. Italy is particularly endemic, with some regions such as the Po Valley having an infection rate of 80%. If you are traveling with your pet, please discuss a preventative before your holiday.

Also remember that no heartworm preventative is 100% effective, so it is a good idea to get your dog tested after returning home to the UK as well. This is true for a dog adopted from Spain or native to the UK.

What are the symptoms?
Heartworm affects a dog’s lungs, heart and other organs. Symptoms can be completely invisible, especially in young and otherwise healthy dogs. This is one reason it is very important to test for heartworm, even if no symptoms are present.

Visible symptoms include coughing, difficulty breathing, blood in urine, loss of appetite and loss of energy.

Is heartworm contagious to humans or other animals?
No. It is spread only via infected mosquitos, not from animal to animal or animal to human.

What is the treatment?
Heartworm treatment in dogs is 95% effective. Dogs that experience more risk are those with more advanced infestations and/or pre-existing liver or kidney issues that make the active ingredient in the medication harder to break down.

Treatment is in two stages. The first stage is an injectable drug, Melarsomine dihydrochloride. This kills the adult heartworms in the heart and nearby blood vessels over the next 30 days. Then the second stage is another injectable drug to kill the microfilariae. In some cases there are no microfilariae present – in that case the second drug isn’t needed.

The initial injection is into the muscle of the dog’s back and makes the dog very sore and listless for about 24 hours. Steroids (prednisone) are usually prescribed over the month following the injection and during that same month it is very important to restrict physical activity.

Because parasites will slough off into the bloodstream for 16 weeks or more following treatment, it is necessary to wait at least four months following treatment to retest to make sure the treatment has worked. It is possible that a second round of injections may be needed if a dog still tests positive for heartworm antigens six months following the initial treatment.

If my dog was treated for heartworm in Spain, how do I care for him once he is home with me in the UK?
If it is less than one month since his treatment, he needs to be kept calm. Talk to your vet, but for a young and otherwise healthy dog this doesn’t mean full activity restriction. Rather no running full out or hard play with other pets.

You will need to go to your vet and have a follow up blood antigen test for heartworm 4 to 6 months after your dog’s treatment date in Spain. In rare instances, your dog may need another round of treatment if he tests positive in the follow up tests.

Can heartworm affect my dog’s future health?
Every dog is an individual, but if your dog was otherwise healthy prior to his heartworm treatment, he’ll go on to live a healthy life post-treatment. Once the heartworm parasites are gone, they are gone and there is no risk of reoccurrence from an old infection.

So on to Carbon's specific treatment.

Today we started 20 mg once per day Omeprazol, a stomach protector, and 150 mg twice per day of Doxycycline, an antibiotic.

He'll continue this medication for two weeks, at which time he'll be tested again for heart worm. If he still tests positive, he will continue the meds another two weeks, then be tested again. If he tests positive a third time, he will move on to the injections.

In addition to the stomach protector from the vet, I've ordered Florentero online, which is a probiotic that did wonders for Brogan back in the day. I'll start that asap.
That's a very thorough summary. It's great to see that a couple of things stand out on the positive side: the treatment is 95% effective and (once treated) there's no risk of recurrence from an old infection.

I'm so sorry that you and Carbon are having to go through this, but Carbon couldn't have chosen a better person to be there for him. Let's just all hope that he doesn't need those horrid injections!


Great information, thanks @Emily_Babbelhund.

@Aitch - it sounds like you would be well advised to have Alex re-tested; I wasn't aware of the incubation period. He was treated with spot-on preventatives and Milbemax for the last few months he was in the shelter, so I'm sure he will be fine, but better to have the test so it's not on your mind.


Queen of Turnips
Devon, UK
Thank you for this thread @Emily_Babbelhund , and the title which is very well chosen. It would be fabulous if his first round of meds did the trick, but whatever happens he has the best possible human in his corner to help him on the road to recovery.
Great information, thanks @Emily_Babbelhund.

@Aitch - it sounds like you would be well advised to have Alex re-tested; I wasn't aware of the incubation period. He was treated with spot-on preventatives and Milbemax for the last few months he was in the shelter, so I'm sure he will be fine, but better to have the test so it's not on your mind.
Thank you. I think I will. It would be a bit silly not to really. It will put my mind at rest if nothing else. :)
Very thorough! I know it's a risk here, and it's required to be tested annually before they give the preventative each spring. My friends adopted a great dane mix and she later tested positive for heartworm. They think the treatments made her turn gray prematurely, but no other long term effects. Carbon has youth on his side!
Carbon and I just got back from his heart ultrasound, or echocardiogram. Very easy process: Carbon stood on the exam table, got two little patches of fur shaved and then the vet spent about 10 minutes using the ultrasound to view his heart from both sides of his body.

The vet tech - who happily spoke perfect English - explained that sometimes you can actually see the adult worms 'waving' from the heart on the video. :eek:

Happily in Carbon's case, all the vet saw was normal dog heart. No thickening of the heart walls (another sign of heart worm) and certainly no waving worms.

They explained to me that this doesn't mean that he DOESN'T have heart worm, but it does mean that he has no advanced stage infestation. This bodes well for the success of his treatment and the possibility of no long-lasting damage.

The cost was EUR190, well worth it to get some good news at this early stage! :giggle:


That is really. really good news! :) I know you have had Carbon on preventative heartworm meds already, and with a low infection level, certain vets will just continue with those for a longer treatment programme with it may though depend on which type of anti-parasitic medication you were using.
Very thorough! I know it's a risk here, and it's required to be tested annually before they give the preventative each spring. My friends adopted a great dane mix and she later tested positive for heartworm. They think the treatments made her turn gray prematurely, but no other long term effects. Carbon has youth on his side!
We have heartworm in Australia too but I've never known a vet test for it (unless there was a reason to). Dogs are given heartworm prevention from day one, either by monthly wormer or annual vaccination and that's the end of it.

Do you know why you test prior to the preventative? Is there a risk that the preventative isn't effective?


As I understand it....The test is done because if there are heartworms present and you give the normal heartworm prevention medications the heartworms can die suddenly and cause a toxic shock reaction in the dog. Dealing with already present heartworms requires a different program of medication.

We use the annual heartworm vaccination injection for Obi as it’s an easy, ‘set and forget’ approach. Much easier than monthly tablets.