Understanding Heartworm Disease In Dogs

Dr. Loudon’s Prevention and Treatment Protocols

Heartworm disease is a serious, potentially fatal condition caused by Dirofilaria immitis, a parasitic worm spread through mosquito bites. It primarily affects the heart and lungs, leading to severe health complications if left untreated.

Symptoms of Heartworm Disease

Signs of heartworm infection can vary depending on the severity. Some dogs may show no symptoms early on, making routine testing essential. As the disease progresses, symptoms may include:

  • Persistent cough

  • Fatigue after mild exercise

  • Decreased appetite

  • Weight loss

  • Labored breathing

  • Swollen belly (fluid accumulation)

  • Fainting or collapse (in severe cases)

The 4 Stages of Heartworm Disease

  • Class 1: No symptoms or mild signs (occasional cough).

  • Class 2: More noticeable symptoms, including persistent coughing and fatigue.

  • Class 3: Severe symptoms such as frequent coughing, labored breathing, lethargy, and possible heart failure.

  • Class 4 (Caval Syndrome): Worms physically block blood flow to the heart, which is often fatal without immediate surgery.

High-Risk Regions for Heartworm Disease

Heartworm disease is most prevalent in warm, humid climates where mosquitoes thrive, including:

  • Southeastern U.S. (Florida, Texas, Louisiana, Alabama, Georgia, South Carolina)

  • Midwest river valleys (Mississippi, Missouri, Ohio River Valleys)

  • Coastal regions with high mosquito populations

  • Any area with stagnant water, especially in summer

How Dogs Get Heartworm

Heartworm is only transmitted through mosquito bites. The cycle includes:

  1. A mosquito bites an infected animal and picks up microfilariae (baby heartworms).

  2. Inside the mosquito, these microfilariae mature into larvae.

  3. When the mosquito bites a new dog, it transfers the larvae.

  4. The larvae develop into adult heartworms over 6-7 months.

  5. Adult worms reproduce and release more microfilariae, continuing the cycle.

Heartworm Testing & Diagnosis

Routine heartworm testing is critical, especially in high-risk areas. Dogs should be tested every six months to detect infections early.

Diagnostic Tests for Heartworm

  • Antigen Test: Detects adult female heartworms (but not males or immature worms).

  • Microfilaria Test: Identifies microscopic larvae in the bloodstream.

  • Chest X-rays: Assess heart and lung damage in severe cases.

  • Echocardiogram: Provides detailed imaging of the heart for advanced infections.

If no microfilariae are found, the infection may be in an early stage or consist only of female worms. In such cases, treatment may be less urgent but still requires monitoring.

Treatment Options for Heartworm Disease

Conventional Fast-Kill Treatment (Melarsomine/Immiticide)

This is the standard veterinary protocol but is expensive, painful, and comes with risks.
Step-by-Step Conventional Treatment
  1. Start Monthly Preventive: Eliminates immature worms and prevents new infections.
  2. Administer Doxycycline (30 Days): Targets Wolbachia bacteria to reduce inflammation.
  3. Melarsomine Injections (Day 60, 90, 91): Kills adult worms but carries significant risks.
  4. Steroid Support (Prednisone): Helps manage inflammation.
  5. Follow-Up Testing (Day 120 & 150): Checks for remaining microfilariae.
  6. Final Test (One Year Later): Confirms elimination of all heartworms.
Risks of Melarsomine Treatment
  • Severe pain at the injection site
  • Blood clots from dying worms
  • Risk of respiratory distress
  • Death rates:
    • 5.2% of Class 1 & 2 cases
    • 18.2% of Class 3 cases
Because of these risks, many dog owners explore safer alternatives.

Slow-Kill Method (Recommended Alternative)

This gentler, long-term approach involves gradually eliminating worms with lower risk.
Step-by-Step Slow-Kill Treatment
  1. Start Monthly Preventive: Prevents new infections and weakens adult worms (milbemycin oxime recommended).
  2. Administer Doxycycline 5mg/kg: Targets Wolbachia bacteria. One month of Doxycycline followed by two months off, repeated for a total of four cycles over one year.
  3. Test & Restore the Microbiome (After Doxycycline): Use a gut test (AnimalBiome) and supplement with FMT therapy (Legacy Biome).
  4. Strict Activity Restriction: Prevents complications from dying worms.
  5. Heart & Immune Support — Suggested Dosages

    • Omega-3 Fatty Acids (Fish Oil, EPA + DHA)
      Dose: 100 mg combined EPA + DHA per 10 lbs body weight daily
      (e.g., a 50-lb dog = ~500 mg daily).
      Note: Use high-quality, purified fish oil or algae oil. Look for products tested for heavy metals.

    • Hawthorn (Crataegus spp.)
      Dose: 0.5–1 mg per lb body weight, 2x daily (standardized extract).
      Note: Supports heart muscle strength and circulation. Safe long-term, but best under vet supervision if your dog is on heart meds.

    • Turmeric (Curcumin)
      Dose: 15–20 mg per lb body weight daily, split into 2 doses.
      (e.g., a 50-lb dog = ~750–1,000 mg/day).
      Note: Absorption improves if given with a healthy fat (like fish oil) and a pinch of black pepper.

    ⚠️ Cautions for Guardians:

    • Always start at the low end of the range and increase gradually.

    • Check for interactions if the dog is on prescription meds (especially for the heart, blood pressure, or clotting).

    • Turmeric can stain light fur — mix well into food.

  6. Liver & Kidney Support:

    • Detoxification Support Doses for Dogs

      • Milk Thistle (Silybum marianum, standardized to 70–80% silymarin)
        • 20–50 mg per 10 lbs body weight daily
        (Example: 100–250 mg daily for a 50-lb dog).
        Note: Excellent liver support. Often used in cycles (4–6 weeks on, then break).

      • Dandelion Root (Taraxacum officinale)
        • 100 mg per 10 lbs body weight daily (dried herb or capsule equivalent)
        OR 1–3 drops tincture per 20 lbs, 2x daily.
        Note: Supports liver, gallbladder, and mild diuretic action.

      • Burdock Root (Arctium lappa)
        • 1 tsp dried herb per 20 lbs body weight daily (in food, tea, or capsule equivalent)
        OR 0.5–1 ml tincture per 20 lbs, 2x daily.
        Note: Gentle detoxifier; supports skin and kidneys.

      ⚠️ Cautions for Guardians:

      • Avoid milk thistle if a dog is on certain chemo drugs unless cleared by a vet.

      • Dandelion is not ideal for dogs with gallstones or severe kidney disease.

      • Burdock root can interact with diuretics or hypoglycemics.

    • Fresh, filtered water
  7. Monitor for Side Effects: Watch for coughing, lethargy, breathing issues (contact a vet if symptoms worsen).
  8. Retest Every 6 Months: Most dogs test negative within 12-24 months.
Pros & Cons of Slow-Kill Method
  • Pros: Safer, fewer side effects, natural detox support
  • Cons: Takes longer (1-2 years), still requires monitoring

Preventing Heartworm Disease

Natural Mosquito Repellents

 

Neem Oil (Topical) 4-Legger Neem Shampoo for bathing.  

Dr. Peter Dobias' product: TickHex® Body Spray 

Contains Apple Cider Vinegar, Neem Oil, Cedar Oil, Rosemary Oil, Tea Tree Oil, Lemongrass Oil, Peppermint Oil, Rose Geranium Oil

Apple Cider Vinegar (Small Amounts / Diluted Spray) 4-Legger Restore

Cedar Oil Spray Cedarcide Cedarwood All-Purpose Dog & Cat Bug Spray — for pets, home, etc.  

Diatomaceous Earth (Outdoor / Bedding / Surroundings)

Safer Brand Food Grade Diatomaceous Earth – 4 lb Animal Feed / Pet Safe — food-grade, safe around pets when used properly. 

Lemongrass- Flea|Tick Protect Spray (Lemongrass)

Heart Health Supplements

 

Hawthorn (Supports Circulation) Dose: ~1 drop per lb body weight, 3–4x daily (tincture). Product: Five Leaf Botanicals Hawthorne Tincture – Dr. Judy Morgan

CoQ10 (Strengthens Heart Muscles) Dose: 1.0–1.6 mg per lb body weight daily (split AM/PM) Product: VetriScience Coenzyme Q10 10 mg Capsules

Omega-3 Fatty Acids (Reduces Inflammation) Dose: 100 mg combined EPA + DHA per 10 lbs body weight daily. Product: Woof Creek Omega

L-Carnitine & Taurine (Essential for Heart Function). L-Carnitine Dose: 50–200 mg per kg body weight daily, divided 2–3x

Taurine Dose: 500 mg every 12 hrs (<50 lbs) OR 1000 mg every 12 hrs (>50 lbs). Product: Carnicare DuoMax – Ace Canine (L-Carnitine + Taurine)

 Prevention Strategies

 

Regular heartworm testing (every 6 months): Catching heartworm early ensures treatment is more effective and less damaging to your dog’s body.

Avoid over-vaccination (to reduce immune stress): Following a tailored vaccine schedule or using titers helps protect your dog without unnecessary strain on the immune system. 

Whole-food, high-quality diet (avoid processed kibble): Fresh, nutrient-dense foods strengthen your dog’s immune system and overall resilience against disease.

Maintain a healthy gut microbiome: Probiotics and prebiotic-rich foods support digestion, immunity, and long-term wellness from the inside out.

Milbemycin is my recommended heartworm preventative in states where heartworm is prevalent, and I advise dosing by rounding down to the lower weight range rather than up to ensure the safest protection.

Final Thoughts

Heartworm disease is serious but preventable. While conventional fast-kill treatment is effective, it carries risks. The slow-kill method, when properly managed, offers a safer alternative with fewer side effects. Combining routine testing, natural prevention, and heart support supplements can help protect your dog’s health and minimize risks.