Dog Heartworm Prevention & Treatment｜Vet's Guide to Protecting Your Pet

Dog heartworm is a deadly parasitic disease transmitted by mosquitoes. In Hong Kong's humid and hot environment, mosquito problems are severe, and dogs face an extremely high risk of infection. Heartworms parasitise a dog's heart and pulmonary arteries, and without early detection and treatment, can lead to heart failure or even death. The good news is that heartworm prevention is very simple and effective—just one monthly preventive medication or one annual heartworm injection can provide 100% protection for your pet.

What Is Dog Heartworm?

Dog heartworm is a parasite called Dirofilaria immitis. Adult worms look like thin white noodles, measuring 15–30 cm in length, and reside in the dog's right ventricle and pulmonary arteries. An infected dog may harbour dozens or even hundreds of heartworms.

Heartworm Life Cycle

1. A mosquito bites an infected dog and ingests heartworm larvae (microfilariae)
2. Larvae develop inside the mosquito for 10–14 days into infective larvae
3. When the mosquito bites a healthy dog, it transmits the larvae under the skin
4. Larvae migrate within the dog's body and reach the heart after about 6 months to develop into adults
5. Adult worms can live 5–7 years and continuously reproduce

Dog Heartworm Symptoms

Dog heartworm symptoms are not obvious in the early stages of infection—this is the most dangerous aspect. When obvious symptoms appear, the infection is usually already at a moderate to advanced stage:

Infection Stages and Symptoms

Common Symptoms

• Persistent Dry Cough: More noticeable after exercise or excitement
• Exercise Intolerance: Easily winded, reluctant to be active
• Decreased Appetite, Weight Loss
• Abdominal Swelling: Fluid accumulation (ascites)
• Rapid/Difficult Breathing
• Lethargy
• Fainting: Collapsing after exercise in severe cases

Heartworm Prevention Methods

Heartworm prevention is much simpler, cheaper, and safer than treatment. Hong Kong has mosquitoes year-round, so continuous prevention throughout the year is recommended:

1. Monthly Oral Preventive Medication

The most commonly used heartworm prevention method:

• Once monthly, given with food
• Common brands: Heartgard, Interceptor, NexGard Spectra
• Some products also prevent intestinal parasites
• Highly palatable—dogs eat them like treats

2. Monthly Topical Spot-On

• Applied to the skin on the back of the neck for absorption
• Common brands: Revolution, Advocate
• Also prevents external parasites like fleas and ticks

3. Annual Injection (Heartworm Injection)

Heartworm injection (ProHeart 12) is a long-acting prevention option:

• Only one injection per year
• Administered by a veterinarian at the clinic
• No need to worry about forgetting monthly medication
• Ideal for owners who often forget monthly treatments

Prevention Method Comparison

Heartworm Testing

Before starting heartworm prevention, testing must be performed to confirm the dog is not already infected:

Why Is Testing Required First?

• If a dog is already infected with heartworm, taking preventive medication may cause severe reactions
• Mass die-off of microfilariae can lead to anaphylactic shock
• Prevention can only be safely started after a negative test result

Testing Methods

• Rapid Antigen Test: Results in 10 minutes at the clinic; detects adult worm antigens
• Blood Smear: Microscopic examination for microfilariae
• Annual testing is recommended to ensure prevention is effective

Dog Heartworm Treatment

If dog heartworm is unfortunately diagnosed, treatment is complex, expensive, and carries risks:

Treatment Steps

1. Stabilisation Phase: First address complications (heart disease, pneumonia)
2. Killing Adult Worms: Injection of Melarsomine (arsenic-based drug) to kill adult worms
3. Strict Rest: Must be crate-rested for 4–6 weeks during treatment; exercise must be avoided
4. Killing Larvae: Preventive medication used to kill microfilariae
5. Follow-up Testing: Confirm successful treatment

Treatment Risks

• Dead worms may block pulmonary arteries, causing pulmonary embolism
• Dogs with severe infections have higher mortality rates during treatment
• Treatment costs can reach tens of thousands of dollars
• Requires prolonged activity restriction

Prevention is far simpler and safer than treatment—spending a few dozen dollars monthly on preventive medication can avoid treatment costs of tens of thousands of dollars and the risk to your pet's life!

Heartworm FAQs

Petcore Veterinary Clinic Heartworm Prevention Services

Petcore Veterinary Clinic provides comprehensive dog heartworm prevention and treatment services:

• Rapid Heartworm Testing: Results in 10 minutes
• Monthly Preventive Medication Prescriptions: Oral medication and spot-on options
• Heartworm Injection: Once-yearly long-acting prevention
• Cardiac Ultrasound: Assessing extent of heart damage
• Infection Treatment: Complete treatment protocols
• Prevention Plan Consultation: Customised plans tailored to your pet

Contact Us

• Yuen Long Clinic: G/F, 30A Fuk Tak Street, Yuen Long, N.T. | Phone: 2394-7300
• Sai Kung Clinic: Shop 2, 66 Yi Chun Street, Sai Kung, N.T. | Phone: 2394-4228
• WhatsApp: 9889-5518
• Website: www.petcore-vet.com

Heartworm prevention is an essential responsibility for every pet owner. One monthly preventive medication or one annual heartworm injection can provide 100% protection for your pet against this deadly parasite. Contact Petcore Veterinary Clinic today to create the most suitable prevention plan for your dog!