Health
A positive test in a dog who seems perfectly well, a cough after walks, a lump under the skin. Heartworm arrives with mosquitoes and stays hidden for years.
Caution. A dog who collapses, struggles to breathe at rest, coughs up blood, faints on exercise or has a suddenly swollen belly needs a vet the same day. During treatment, report any new cough or fever at once.
Do not look for the answer in a Facebook group, on TikTok or on a forum. Look for someone trained for this: your dog's own veterinarian, the only person who can examine, investigate and treat them.
Use this page to know what to observe, what to note and what to ask at the appointment, not to treat at home. If you still have doubts after a consultation, ask another vet or a specialist (dermatologist, internist) for a second opinion, not a group. And if you do not have a regular vet yet, find one now, while your dog is healthy: how to choose a veterinary clinic.
Your dog runs, eats and greets you at the door like nothing is wrong. At the annual check-up the vet takes a few drops of blood, sets the test on the counter and ten minutes later tells you it is positive for heartworm. Another story we hear just as often: an eight-year-old dog who spends his summers in a garden near a river has started coughing after walks, and stops for a breather on the stretch where he used to drag you along. Or you were stroking him and found a small lump under the skin that slides away under your finger, and someone said "it could be a worm".
All three can be the same disease. Dirofilariasis is caused by two thin worms that mosquitoes carry from dog to dog. Dirofilaria immitis, the one people call heartworm, lives in the arteries of the lungs and, once the disease is advanced, in the heart itself. It can grow to 20 to 30 cm. Dirofilaria repens lives under the skin, where it causes lumps and sometimes itching. It is milder for the dog but can pass to people, again through mosquitoes. Both are found across southern and eastern Europe, Romania included, mostly in low, warm, damp country around rivers, deltas and standing water, and both have been moving north.
What makes it tricky is the timescale. A mosquito bites an infected dog and picks up tiny larvae from the blood. It carries them for around two weeks, and only in warm weather, then passes them on to another dog with its next bite. In the new dog the larvae grow slowly and reach adulthood after about six months. Only then can the usual tests turn positive. The signs come later still, often years later.
Most infected dogs look fine for years, and when signs do show they creep in. A few situations, though, do not wait for next week's appointment:
That last one needs a word of explanation. During treatment, the worms that die break into pieces and the pieces end up in the lungs. Your vet will warn you about this at the start. If you see these signs, ring straight away, not in the morning.
The best tool you have at home is his breathing while he sleeps. Vets use the same measure for heart disease in general. Wait until he is properly asleep, count how many times his chest rises in 30 seconds and double it. Under 30 breaths a minute is usually normal. If it comes out above 30 consistently, tell your vet. Do it on several days in a row and keep the numbers on your phone.
Then watch how he copes with exercise. Does he stop on walks where he never used to? Sit down after the stairs? Look at the ball on the third throw and stay put? You see these things first. Your vet does not see them in the consulting room.
Describe the cough as precisely as you can: when it happens (after exercise, at night, when he gets excited), what it sounds like (dry or moist) and how long it lasts. A one-minute clip on your phone beats any description.
Besides breathing, stamina and the cough, keep track of a few things your vet will ask about anyway:
Dogs adopted from southern Europe or from shelters in high-risk areas get tested regardless, however well they look.
| Dirofilaria immitis | Dirofilaria repens | |
|---|---|---|
| Where it lives | Lung arteries, heart | Under the skin |
| What you see | Nothing for years, then cough, tiring on exercise, weight loss, fainting, swollen belly | Lumps under the skin, sometimes itching, often nothing |
| How serious for the dog | Can be very serious | Usually mild |
| Risk to people | Very rare | Yes, rarely: lumps under the skin or in the eye |
| How it is confirmed | Blood antigen test, larvae test, imaging | Larvae test, PCR, removed lump examined |
A product given monthly or, in some cases, a longer-acting injection. You choose it with your own vet according to where you live, the breed and the weight. The rest is down to you. During the season, bring the dog in at dusk and have him sleep indoors. Fit screens to the windows. Empty anything in the garden that holds standing water: buckets, plant pots, old tyres, anywhere mosquito larvae can grow. Some topical products that keep mosquitoes off help as well; ask your vet which one suits your dog.
If you are taking him somewhere warmer for a summer holiday, such as Greece, Italy or the Black Sea coast, talk about prevention before you pack. The mosquito season there is longer and the risk higher.
One test a year in spring, prevention right through the mosquito season, and most dogs never meet this disease at all. The ones who end up on treatment are nearly always dogs who had neither the test nor the prevention.
What dog owners search for most often on the internet about this problem, with the short answer. The answers are a guide only: the decision belongs to your dog's own vet, after an examination.
For years, usually none. Then, gradually, a cough (especially after exercise), tiring on walks, faster breathing, weight loss and a dull coat. Advanced cases bring fainting, a swollen belly and dark urine. That is why dogs living where mosquitoes are common have a blood test every year.
Not directly. It only spreads through mosquitoes. Dirofilaria repens, the one under the skin, occasionally infects people and causes lumps under the skin or in the eye. Dirofilaria immitis very rarely reaches people. Prevention in the dog and mosquito screens at home lower the risk for the whole family.
Usually in spring, before the mosquitoes start, and always before starting prevention in an adult dog who has already spent a summer in a risk area. The test only turns positive six to seven months after infection. Dogs adopted from high-risk regions or shelters are tested at their first visit.
In most cases, yes. Treatment is long, though, given in stages over several months, and needs strict rest. How it goes depends on how much damage the heart and lungs have already taken. Prevention asks far less of you and is much safer for the dog.
The information on this page is educational and does not replace an examination. For full details and a diagnosis, consult your dog's own veterinarian.
They often come together: the same causes, plans that complement each other.
A murmur picked up at the booster, a faint in the park, a cough that comes at night. Heart disease is common from middle age on, and you track it with one simple number.
A goose-honk cough a week after kennels, a night-time cough in an old dog, bursts of sneezing after a field walk. Three sounds, three directions, one first step: film it.
A hard bead with legs on his neck after the woods, or black specks on the sofa that turn red when wet. Both can be sorted out, and neither with oil or garlic.
A bare ring round the eyes, nails that grow too fast, a dog adopted from southern Europe. Leishmaniasis can be kept under control and, above all, largely prevented.
We work with your dog's behaviour, not its health. For any sign described here, book an appointment with your own vet; the related services page explains how to choose a clinic.