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parasitic disease Dog Transmissible to humans

Canine heartworm disease

Heartworm disease is caused by long, threadlike worms transmitted by mosquito bites. Two forms exist: the cardiopulmonary form, due to Dirofilaria immitis, where the adult worms settle in the arteries of the lungs and the right heart, and a...

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Definition Signs Causes Transmission Diagnosis Treatment Prevention Complications When to see a vet Zoonosis Prognosis FAQ Sources Affected species

What is it?

Heartworm disease is caused by long, threadlike worms transmitted by mosquito bites.

Two forms exist: the cardiopulmonary form, due to Dirofilaria immitis, where the adult worms settle in the arteries of the lungs and the right heart, and a subcutaneous form, due to Dirofilaria repens, where the worms lodge under the skin.

The disease sets in slowly: several months separate the infective bite from the first signs, so that the dog appears in great shape for a long time.

Key point

Serious and progressive disease: prevention during mosquito season is infinitely better than treatment.

Commonly observed signs

These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.

Related signs — each one links to its page:

Cough Fatigue Difficulty breathing Rapid breathing Weight loss Reduction Edema Dark urine Shortness of breath on exertion

Cardiopulmonary form, in usual order of appearance:

Persistent dry cough, initially on exertion.

Abnormal fatigue, refusal to play, shortness of breath after a modest walk.

Rapid, labored breathing at rest in advanced stages.

Weight loss, depression, decreased appetite.

Swelling of the stomach due to accumulation of fluid, edema of the limbs when the right heart becomes exhausted.

Discomfort, even loss of consciousness during exercise.

In a sudden and serious form, very dark urine and shock.

Subcutaneous form: mobile nodules under the skin, itching or skin lesions, with a general condition lasting for a long time.

When to consult without delay

This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.

Causes and risk factors

Filarial worms transmitted by mosquitoes: Dirofilaria immitis for the heart and lung form, Dirofilaria repens for the subcutaneous form.

The adult worms live for several years and release microscopic larvae into the blood that mosquitoes take during a blood meal.

The severity depends on the number of worms, the time elapsed and the dog's physical activity.

Living in a region where mosquitoes are abundant: coastal areas, oases, around bodies of water, rice fields, irrigated gardens.

Dogs living outside, especially at night, when mosquitoes are active.

Absence of pest prevention during the risky season.

Travel or importation from an area where the disease is present.

Stagnant water near the home: basins, buckets, blocked gutters, tires.

Transmission

Exclusively through the bite of a carrying mosquito: there is no direct contagion between dogs, nor from dog to human.

The mosquito infests a carrier dog, then inoculates larvae into another dog during a subsequent bite.

Transmission requires temperatures high enough for the larva to develop in the mosquito: it is therefore seasonal, with an extended risk period in warm regions.

The dog, and to a lesser extent other carnivores, constitute the reservoir of the parasite.

Diagnosis and care

Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.

The diagnosis is based on a blood test: test for detection of adult worm antigens and search for microscopic larvae in the blood.

There is a delay between the infective bite and the positivity of the tests: too early detection can be falsely reassuring, the veterinarian chooses the right moment.

Chest x-rays, an ultrasound of the heart and a complete blood test reveal damage to the pulmonary arteries and the right heart.

The subcutaneous form is diagnosed by examination of nodules and blood analysis.

Before any treatment, screening is essential: treating an already carrier dog with a simple preventative exposes you to accidents.

Treatment

The treatment is exclusively veterinary and takes place in stages over several weeks to several months: there is no solution to give yourself.

It combines medications to eliminate adult worms, others for blood larvae, and often additional antibiotic treatment targeting bacteria hosted by the worm.

Strict rest throughout the duration of treatment is the most important measure: the worms that die fragment and can block pulmonary vessels, and exercise increases this risk.

Anti-inflammatories often accompany the worm destruction phase.

In the most serious forms, with worms in the heart, surgical removal by vascular route can be attempted in a specialized structure.

Follow-up and staged blood tests confirm complete elimination.

Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.

Prevention

Drug prevention, prescribed by the veterinarian, is the only reliable protection: it regularly eliminates inoculated larvae before they become adult worms.

It is given throughout the high-risk season, or even all year round in hot regions, depending on the veterinarian's opinion.

A blood test is carried out before starting, then repeated periodically.

Limit bites: external antiparasitics repelling mosquitoes prescribed for dogs, bring the animal in at dusk, mosquito nets.

Remove stagnant water around the house: this is the measure that most reduces the mosquito population.

Possible complications

Right heart failure, with accumulation of fluid in the abdomen.

Hypertension of the pulmonary arteries and irreversible damage to the lungs.

Sudden obstruction of large vessels by a pack of worms, acute form accompanied by very dark urine and life-threatening.

Renal or hepatic damage in old infestations.

Accidents during treatment if rest is not respected.

When to see a veterinarian

Your dog has been coughing for several days for no obvious reason.

He gets tired quickly, refuses walks or gets out of breath abnormally.

His stomach swells or his limbs become edematous.

He felt unwell or fell during exercise.

His urine is very dark and his general condition is deteriorating: it is an emergency.

You adopt or bring back a dog from a mosquito-prone area without knowing if it has been screened.

Transmission to humans

Humans can be bitten by the same mosquitoes and, very rarely, be infested. It is never a direct transmission from the dog: without mosquitoes, no risk.

In humans, the parasite does not complete its cycle. It most often forms a small nodule under the skin or an isolated pulmonary nodule, discovered incidentally, without a circulating adult worm.

Protection is the same as for the rest of the family: fight against mosquitoes and eliminate stagnant water.

Protecting and detecting dogs also helps reduce the parasite reservoir in the neighborhood.

Prognosis

Good when the disease is detected early, before the pulmonary arteries are damaged: the dog can recover completely.

Reserved in advanced forms with heart failure, where pulmonary lesions persist even after elimination of the worms.

Dark in the peracute form due to vascular obstruction, which is an emergency.

The subcutaneous form has a much better prognosis.

Prevention remains largely preferable to treatment, which is longer, riskier and more expensive.

Frequently asked questions

My dog hardly goes out, is he safe?

Not completely: mosquitoes enter homes, especially at dusk and at night. In an area where the disease circulates, prevention is discussed even for an indoor dog.

Can we start prevention without doing a test?

No, this is not prudent in a dog that may have been exposed. Giving a preventative to a dog who is already a carrier can cause a serious reaction. Blood screening always precedes implementation.

Why should my dog rest during treatment?

Because the destroyed worms fragment and circulate in the vessels of the lungs. The effort accelerates circulation and greatly increases the risk of obstruction. Rest is not a comfort tip, it is a safety measure.

Does this disease really exist in North Africa?

Yes, it is present in the Mediterranean region, with a risk linked to the abundance of mosquitoes, humid and irrigated areas. The local veterinarian is best placed to assess the risk in your area.