Heartworm Disease in Pets

Heartworm Disease in Pets

PSA-DVM Paola Moreno Estanol

The disease's global prevalence is noted, particularly in temperate, tropical, and subtropical zones. Clinical presentations range from asymptomatic to severe conditions, including pulmonary artery, lung, and cardiac diseases, with complications like glomerulonephritis, anemia, and thrombocytopenia in chronic cases. Transmission is through mosquitoes, with larvae maturing into adult heartworms. Annual antigen testing is crucial for diagnosis, followed by adulticide treatment and post-treatment testing. Year-round prophylaxis with monthly preventives is recommended due to the disease's severity and prevalence. The document aims to provide comprehensive information on diagnosis, treatment, and prevention, focusing on dogs and domestic cats as primary hosts.

Overview:

Etiology: Caused by the parasite Dirofilaria immitis.

Primary Hosts: Primarily affects canids, but also found in cats, ferrets, sea lions, and other mammals.

Geographical Distribution: Widespread in temperate, tropical, and subtropical zones, notably in the Southeastern U.S. and Mississippi River Valley.

Prevalence: Over 1 million cases estimated in the U.S., with varying risk factors.

Transmission: Vector-borne, spread through mosquito bites.

Clinical Presentation: Varies from no symptoms to severe lung, heart, and arterial disease. Chronic infections can cause glomerulonephritis, anemia, and thrombocytopenia.

Severe Cases: May lead to critical conditions like caval syndrome and disseminated intravascular coagulation.

Diagnosis: Annual antigen testing for adult heartworm proteins, followed by confirmatory testing.

Treatment: Involves stabilization of the animal and adulticide therapy. Post-treatment testing confirms heartworm elimination.

Prevention: Year-round prophylaxis is advised, using monthly preventatives targeting immature stages of the parasite.

​

Life cycle of Dirofilaria immitis:

Vector Transmission: 

Over 70 mosquito species can transmit D. immitis, but less than fifteen are key vectors.

Microfilariae Production:

Mature female heartworms release microfilariae into the host's circulation.

Development in Mosquito:

   - L1 stage begins after a mosquito ingests microfilariae.

   - L1 progresses to L2 and then to L3 within 8 to 17 days, depending on temperature.

L3 Stage:

   - Infective stage; transmitted to a new host, typically a canine, by the mosquito.

   - Molts to L4 in the host's tissues within 1 to 12 days post-infection.

L4 to Immature Adult Development:

   - Takes place over 50 to 68 days post-infection.

   - Immature adults (1 to 2 cm long) migrate to the vascular system, heart, and lungs.

Maturation of Adult Heartworms:

   - Males grow to 15-18 cm, females to 25-30 cm.

   - Final maturation and mating occur in the heart and lungs.

   - Complete cycle from infection to mature heartworms spans approximately 184 to 210 days.

Canine Host Microfilaremia:

   - Canines may become microfilaremic as early as 6 months, typically by 7 to 9 months post-infection.

   - Microfilariae numbers peak in evenings and summer months.

Longevity of Heartworms:

   - Adult heartworms can live 5 to 7 years in dogs.

   - Microfilariae may survive up to 30 months.

Onset of Heartworm Disease:

   - Disease begins with the transition to Stage 5, leading to vascular and lung disease marked by eosinophilia.

   - Early disease stages often precede current diagnostic capabilities.

Pathophysiology of Canine Heartworm Disease:

​

Primary Location and Damage: 

Adult heartworms primarily inhabit the pulmonary arterial system, not the heart, causing significant damage to pulmonary arteries and lungs.

Severity Factors:

Lesion severity and clinical impact are influenced by worm burden, duration of infection, and host-parasite interactions, including toxic substances, immune responses, and physical trauma.

Vascular and Lung Impact: 

Heartworms can cause vascular obstruction, endothelial damage, and proliferative lesions, leading to conditions like pulmonary thromboembolism (PTE), eosinophilic pneumonitis, and pulmonary consolidation.

Cardiac Implications: 

Increased pulmonary vascular resistance can result in right heart pressure overload, leading to eccentric hypertrophy and potentially right heart failure. Secondary issues may include tricuspid insufficiency and arrhythmias.

Pulmonary Infarction and Edema: 

These are rare due to the lung’s collateral circulation. Increased vascular permeability may cause perivascular edema, usually not indicative of left heart failure.

Role of Exercise:

Physical activity can exacerbate pulmonary vascular disease, thromboembolic heartworm disease (HWD), and pulmonary hypertension (PHT), with more severe lesions observed in active, outdoor dogs.

Post-Adulticidal PTE: 

The risk of pulmonary thromboembolism can increase following adulticide treatment, especially if combined with exercise.

Parenchymal Lung Lesions: 

These may result from eosinophilic pneumonitis in occult HWD or from pulmonary eosinophilic granulomatosis.

Systemic Effects: 

Can include proteinuria, potential renal failure, and aberrant migration of heartworms leading to neuromuscular, ocular, and systemic arterial thrombosis.

Role of Wolbachia pipientis: 

This symbiotic bacterium within heartworms is crucial for their development and its proteins can exacerbate inflammatory reactions during worm death.

Clinical signs of chronic Canine Heartworm Disease (HWD):

Symptom Variation: 

Depends on the severity and duration of the infection, primarily affecting the pulmonary arteries, lungs, and heart.

Asymptomatic Cases: 

Most dogs with heartworm infection (HWI) show no symptoms.

Common Clinical Signs:

• Weight loss

• Reduced exercise tolerance

• Lethargy

• Poor physical condition

• Cough

• Breathing difficulties

• Fainting

• Abdominal swelling

Physical Examination Findings:

• Detectable weight loss

• Heart sound abnormalities

• Heart murmurs

• Cardiac gallop rhythm

Right Heart Failure Indicators:

• Jugular vein distension

• Enlargement of liver and spleen

• Accumulation of fluid in the abdomen

Cardiac Arrhythmias:

Uncommon in chronic HWD.

Lung-Related Symptoms:

• Persistent cough

• Pulmonary crackles

• Rare granulomatosis symptoms: muffled lung sounds, difficulty breathing, cyanosis

Massive Pulmonary Thromboembolism (PTE) Symptoms:

• Severe breathing difficulty

• Fever

• Coughing up blood

Overview of Diagnosis of heartworm disease (HWD) in dogs:

​

Microfilarial Detection:

Commonly used to identify heartworm infection (HWI) through detecting microfilariae (Mf) in blood. Modified Knott test and millipore filtration are sensitive methods but cannot conclusively rule out HWI due to potential false negatives and amicrofilaremic infections.

Immunodiagnostic Antigen Tests:

These tests detect antigens from adult female heartworms, though they may miss new or low-burden infections. Some can estimate worm burdens based on antigen levels. ELISA is commonly used to monitor adulticide therapy effectiveness, with antigen levels typically falling to undetectable within 8 to 12 weeks post-treatment.

Radiography:

Thoracic radiographs help assess the severity of HWD and pulmonary changes but are not effective as a primary screening tool. They can show heart and pulmonary artery enlargement and lung changes due to heartworm damage.

Electrocardiography (ECG):

Useful for detecting arrhythmias but less sensitive for heart enlargement. ECG changes suggesting right ventricular enlargement are considered accurate for HWD diagnosis.

Echocardiography:

Sensitive in detecting heart changes caused by HWD, including altered dimensions and abnormal heart chamber movements.

Clinical Pathology:

Laboratory tests can support HWD diagnosis. Findings often include anemia, eosinophilia, and liver enzyme level changes.

Biomarkers:

Studies are exploring biomarkers like C-reactive protein and cardiac troponin for HWI staging and therapy monitoring, but their clinical application requires more research.

Early Detection: 

Ideal to diagnose HWD before onset of clinical signs, with annual testing recommended for dogs in endemic areas, especially without preventive treatment.

Limitations of Microfilarial Counts:

Mf count in blood does not correlate with infection severity; false negatives can occur, especially with low Mf counts or small blood samples.

Importance of Combined Testing:

In antigen-positive dogs, a microfilarial test is recommended for complete assessment. Combining antigen and microfilarial tests is useful, especially in dogs not on preventive treatments.

Potential Underestimation of Infections:

There might be an underestimation in infections with positive microfilarial and negative antigen tests, possibly due to antibody-antigen complexing.

Immunodiagnostic antigen tests used in diagnosing heartworm infections (HWI) in dogs:

​

Amicrofilaremic Infections: 

   - Occur in about 10-20% of dogs not on macrocyclic lactone (ML) preventives.

   - Common in early-stage, single-sex infections, immune-mediated destruction of microfilariae (Mf), or drug-induced conditions.

   - Dogs on ML preventives typically display amicrofilaremia.

Antigen Tests Utilization:

   - Highly sensitive and specific, primarily used for screening and suspected HWI cases.

   - Mainly detect antigens from adult female heartworms.

Sensitivity and Specificity of Antigen Tests:

   - Varies with female worm burden: 64% sensitivity for one worm, increasing to 85-89% for two to four worms.

   - High specificity at 97%.

ELISA Antigen Tests:

   - Can semi-quantitatively predict worm burdens based on antigen levels.

   - Antigen levels typically decrease to undetectable levels within 8-12 weeks after successful treatment.

AHS Recommendations:

   - Prefers "no antigen detected" term over "negative" to highlight limitations in detecting certain HWI types.

Impact of ML Therapy:

   - ML therapies can clear Mf within 6-8 months.

   - Microfilarial tests are not suitable for dogs on ML preventives, but still hold supplemental value.

Heat Treatment of Serum:

   - Improves detection of D. immitis antigen.

   - Involves heating serum to about 104°F (40°C) for 10 minutes to denature proteins that bind to heartworm antigens, increasing test sensitivity.

   - Used particularly in cases where standard tests return negative results despite clinical signs or presence of microfilariae.

Study Findings:

   - Heat treatment increased test sensitivity from 86.9% to 94.6%.

   - Slightly reduced specificity from 97.8% to 96.1%.

Clinical Implications:

   - Highlights the complexity of heartworm infections and the need for improved diagnostic techniques.

   - Recommends caution in interpreting post-heat treatment positives.

   - Suggests further research for better detection of immature infections.

Study on Test Kits for Low Worm Burdens:

    - Compared different test kits for sensitivity and specificity.

    - Found microwell format and ELISA technology-based tests to be more sensitive.

    - Sensitivity varied with the number of adult female worms, being less effective in their absence.

Importance for Veterinary Practice:

    - Vets should consider the type of test kit and technology used, especially for low worm burden cases.

Thoracic radiography in diagnosing heartworm disease (HWD) in dogs:

Detection and Severity Assessment:

While radiography isn't effective for initial heartworm infection (HWI) screening, it's excellent for detecting HWD, assessing its severity, evaluating changes in lung tissue, and identifying other possible diagnoses.

Common Radiographic Abnormalities:

In heartworm-infected dogs, common radiographic signs include:

   - Right ventricular enlargement (60% of cases).

   - Increased prominence of the main pulmonary artery (70%).

   - Increased size and density of the pulmonary arteries (50%).

   - Pulmonary artery tortuosity and "pruning" (50%).

   - If heart failure is present, enlargement of the caudal vena cava, liver, spleen, pleural effusion, and ascites may be seen.

Radiographic Projections: 

   - Ventrodorsal projection is preferred for evaluating the heart's silhouette and is less stressful for the patient.

   - Dorsoventral projection is better for assessing the caudal lobar pulmonary vessels.

   - Lateral projection is best for evaluating the cranial pulmonary artery.

Pulmonary Parenchyma Evaluation:

Radiography can effectively assess lung tissue. In pneumonitis, a mixed interstitial to alveolar density is often observed, typically most severe in the caudal lung lobes. Eosinophilic nodular pulmonary granulomatosis shows interstitial nodules, bronchial lymphadenopathy, and sometimes pleural effusion. Pulmonary thromboembolism (PTE) is indicated by coalescing interstitial and alveolar infiltrates, especially in the caudal lobes, suggesting increased pulmonary vascular permeability and inflammation. Consolidation may occur with massive embolization or pulmonary infarction.

Electrocardiography and Echocardiography in diagnosing heartworm disease (HWD) in dogs:

Electrocardiography (ECG):

Arrhythmia Detection:

ECG is useful for detecting arrhythmias but is generally less sensitive for identifying cardiac chamber enlargement in HWD compared to radiography and echocardiography.

Limitations:

If radiography doesn’t indicate HWD, ECG is unlikely to be helpful except for arrhythmias, which are rare in HWD (2-4% of cases) except in cases with Caval Syndrome (CS) and heart failure.

Supportive Evidence:

ECG can support HWD diagnosis if it shows a pattern of right ventricular enlargement. Studies found ECG abnormalities in 38-62% of dogs with moderate to severe echocardiographic changes due to HWD.

Sensitive Parameters:

Specific ECG parameters, such as lead II S waves deeper than 0.8 mV, mean electrical axis greater than 103 degrees, and multiple parameters indicating right heart enlargement, are more sensitive for HWD detection. The presence of P-pulmonale (tall P waves) is rare in HWD.

​

​

Echocardiography:

Sensitivity:

Echocardiography is more sensitive in detecting changes in diastolic dimension, septal, and right ventricular function.

Abnormal Septal Motion:

Abnormal septal motion has been observed in some cases of HWD.

Dimension Ratio:

The ratio of left-to-right ventricular internal dimensions, normally 3 to 4, is reduced to an average of 0.7 in HWD cases.

Worm Detection:

Echocardiography can sometimes demonstrate heartworms in the pulmonary artery, and less frequently in the right ventricle, except in cases with CS or high worm burdens.

Clinical pathology in diagnosing and managing heartworm disease (HWD) in dogs:

Hematologic and Serum Chemical Abnormalities:

These are often used to provide supportive evidence for HWD and evaluate concurrent diseases. Common findings include:

   - Low-grade, non-regenerative anemia in 10% of mild to moderate cases, up to 60% in severe cases.

   - Neutrophilia in 20-80% of cases.

   - Eosinophilia in up to 85% and basophilia in about 60% of cases.

   - Thrombocytopenia after arsenical therapy.

   - Elevated liver enzyme activities and occasional hyperbilirubinemia in severe cases.

   - Azotemia in 5% of cases, potentially due to dehydration or heart failure.

   - Albuminuria in 10-30% of cases, leading to hypoproteinemia in severe glomerular disease.

Tracheobronchial Cytology:

Useful particularly in dogs with cough, pneumonitis, occult HWD, and minimal radiographic evidence of HWD. Microscopic examination may reveal eosinophilic infiltrate and occasionally microfilariae.

Abdominal Fluid Analysis:

In cases of congestive heart failure (CHF), typically shows a modified transudate. Dogs with HWD and right heart failure have elevated central venous pressure (CVP), but ascites can develop at lower CVPs if hypoalbuminemia is present.

Biomarkers:

Recent studies have explored biomarkers for HWI/HWD. Elevated C-reactive protein (CRP) levels correlate with pulmonary artery damage and pulmonary thromboembolism (PTE). D-dimer, cardiac troponin I, and myoglobin levels are abnormally high in HWD, indicating PTE and myocardial damage. The clinical application of these biomarkers for diagnosis and evaluation of HWI/HWD requires further study.

Preventing heartworm disease (HWD) in pets:

Prevention Challenges:

The main obstacles in preventing HWD include owner ignorance or misunderstanding about heartworm infection (HWI), non-compliance, and inadequate veterinary instruction. Studies show that less than a third of dogs in care receive adequate heartworm prophylaxis.

Macrocyclic Lactone (ML) Antibiotics:

Introduced in 1987, MLs like ivermectin, milbemycin oxime, selamectin, and moxidectin are derived from Streptomyces soil microorganisms. They are effective heartworm preventives, administered orally, topically, or by injection, with a large window of efficacy. They also have microfilaricidal properties and some have adulticidal activity if used long-term. However, there is growing concern about heartworm resistance to MLs.

Ivermectin:

An avermectin derivative, effective against various parasites and marketed for heartworm prevention. It offers a "reach-back" effect, providing some protection even with lapses in administration. Ivermectin has microfilaricidal and potential adulticidal properties, but care must be taken in breeds with the ABCB1 gene mutation due to toxicity risks.

Milbemycin Oxime:

Effective against larval stages of heartworm and certain intestinal worms. It has a two-month "reach-back" effect but can cause adverse reactions in microfilaremic dogs.

Moxidectin:

Initially marketed as an oral heartworm preventive, it is also available in topical and injectable forms. It is microfilaricidal and safe for breeds with the ABCB1 mutation but not recommended for very young animals.

Selamectin:

A semisynthetic ML offering broad-spectrum protection with topical use. It has a reach-back effect and is effective against heartworms, fleas, and other parasites.

Eprinomectin:

Originally for cattle, now available for cats. It has good bioavailability and efficacy against heartworms and other parasites.

Prevention Strategies:

Prophylaxis should start at 6-8 weeks of age in endemic areas. Yearlong prevention is advocated by some, though controversial due to seasonal transmission of heartworms. For dogs older than 6 months, testing before starting MLs is recommended. In case of lapses in preventive administration, testing for HWI 7-8 months after the last possible exposure is advised.

Repellent Insecticides:

Permethrin-based repellents are effective against mosquitoes, thus reducing the risk of heartworm transmission. They provide an additional layer of protection, especially against ML-resistant heartworm strains.

Medications for preventing Dirofilaria (heartworms):

Ivermectin:

• Dosage: 6 to 12 mcg/kg/month.

• Best time to give: Monthly, starting as early as 6 weeks of age.

• Note: Has a "reach-back" effect for up to 2 months; also microfilaricidal.

Milbemycin Oxime:

• Dosage: 0.5 to 1 mg/kg.

• Best time to give: Monthly, starting as early as 2 months of age.

Note: Effective against developing larval stages; has a "reach-back" effect of 2 months; also a broad-spectrum parasiticide.

Moxidectin:

• Dosage: Varies depending on formulation (oral, topical, or injectable).

• Best time to give: Monthly for oral and topical forms; every 6 or 12 months for injectable form.

Note: Safe in Collies and other breeds with the ABCB1 mutation; not recommended for dogs under 6 months or cats.

Selamectin:

• Dosage: 6 to 12 mg/kg topically.

• Best time to give: Monthly, starting as early as 6 weeks of age for puppies.

Note: Broad-spectrum protection; has at least a 2-month "reach-back" effect.

Eprinomectin:

• Dosage: Not specified for dogs; for cats, it's part of a combination product.

• Best time to give: Topically, as indicated for cats.

Note: Used primarily in cattle and cats; not commonly used for dogs.

For all these medications, it's important to:

• Start prophylaxis no later than 6 to 8 weeks of age in endemic areas.

• Test dogs older than 6 months before starting treatment.

• Maintain consistent administration without interruption for optimal protection.

• Understand the "reach-back" capability but not rely on it for routine prevention.

Adulticidal therapy for heartworm disease (HWD):

Melarsomine:

Replacing thiacetarsamide (Caparsolate), melarsomine (Immiticide) is an organo-arsenical used for treating HWD. It's safer and more effective than its predecessor. It has a high efficacy rate (90% with two doses, 99% with repeated therapy), but a 90% worm kill does not guarantee all dogs will be clear of infection. Adverse reactions, including thromboembolic events, can occur, so exercise restriction post-treatment is crucial. The split-dose protocol (one injection followed by two more a month later) is safer, especially in severe cases, but involves more expense and arsenic administration.

Split-Dose Protocol:

This method involves an initial half dose to kill 50% of the worms, reducing the chance of embolic complications. The subsequent two-dose regimen follows after a month. This approach is recommended for all cases unless financial or health issues (like severe renal or hepatic disease) arise. It has shown better outcomes, including higher seroconversion to negative antigen status, reduced lung and cardiac damage, and better resolution of proteinuria.

Doxycycline and Ivermectin Pre-treatment:

Administering doxycycline and monthly ivermectin for a month prior to melarsomine reduces lung lesion severity and provides other benefits.

Macrocyclic Lactones (MLs) as Adulticides:

MLs like ivermectin, selamectin, and moxidectin have some adulticidal properties but are not recommended as the primary treatment for adult heartworms due to lower efficacy compared to melarsomine.

Exercise Restriction:

Essential post-adulticide treatment, it may require tranquilization or crating at home. Failure to restrict exercise can lead to severe thromboembolic complications.

Treatment Process:

Includes initial diagnosis, a minimum database (blood tests, radiography), starting ML preventive, and waiting up to 2-3 months before administering melarsomine. During this time, larvae mature to adulthood, becoming susceptible to adulticidal therapy.

Adverse Reactions Management:

In microfilaremic dogs, corticosteroids and antihistamines may be used to reduce the risk of adverse reactions to the first dose of MLs.

Surgical and ancillary therapies for heartworm disease (HWD) in dogs:

Surgical Therapy:

Method:

A method using flexible alligator forceps for mechanical worm removal was described, showing 90% effectiveness in a study of 36 dogs.

Safety and Efficacy:

This technique is considered safe in skilled hands and has shown better outcomes than melarsomine, with fewer pulmonary thromboembolism (PTE) and Caval Syndrome (CS) cases.

Limitations:

It requires general anesthesia, skilled operators, fluoroscopy, and may not completely eradicate heartworms. Post-surgical administration of melarsomine may still be necessary.

​

​

Corticosteroids:

Use in HWD:

Prednisone, a commonly used steroid, can reduce pulmonary arteritis but may worsen proliferative vascular lesions. It’s used for pulmonary complications, to treat or prevent reactions to microfilaricides, and possibly to minimize tissue reaction to melarsomine.

Dosage and Administration:

Prednisone is administered early for 3-5 days and continued or tapered as needed. However, caution is advised due to potential adverse effects.

​

​

Aspirin:

Role in HWD:

Aspirin has been studied for its antithrombotic properties in HWD, with mixed results. While it can reduce vascular damage and improve pulmonary conditions, recent studies have shown controversial outcomes.

Usage:

If used, it’s started 1-3 weeks before and continued 4-6 weeks after adulticide administration, with monitoring of packed cell volume and serum total protein.

​

​

Heparin Therapy:

Application:

Studied in severe HWD cases, particularly with heart failure, heparin showed reduced thromboembolic complications compared to aspirin. It’s administered before and after adulticidal therapy.

​

​

Doxycycline

Significance:

Doxycycline targets Wolbachia, an endosymbiont in heartworms, and is beneficial in managing HWI. It has been shown to reduce heartworm burden, PTE after melarsomine therapy, and helps in the slow-kill approach with ivermectin.

Treatment Regimen:

Various regimens combining doxycycline with ivermectin have been effective in experimental infections.

​

​

Microfilaricidal therapy for heartworm disease (HWD) in dogs:

1. Traditional Timing:

• Microfilaricidal therapy is usually started 3 to 6 weeks after adulticide administration.

2. Macrocyclic Lactones (MLs):

• MLs like ivermectin and milbemycin oxime are safe and effective alternatives to older drugs for microfilarial clearance. Ivermectin at 50 mcg/kg (eight times the preventive dose) and milbemycin oxime at 0.5 mg/kg (preventive dose) are used off-label for rapid microfilarial clearance.

3. Adverse Reactions:

• These can occur, particularly in dogs with high microfilarial loads. Reactions include shock, depression, hypothermia, and vomiting. Treatment with fluids and corticosteroids (dexamethasone) is effective in managing these reactions. Diphenhydramine and dexamethasone can also be administered preventatively.

4. Slower Microfilarial Kill Rate:

• Achieved with preventive dosages of ivermectin, selamectin, and topical imidacloprid-moxidectin. This approach is safer, with little chance of adverse reactions.

5. FDA-CVM Approval:

• Imidacloprid-moxidectin has an FDA-CVM label claim as a microfilaricide.

6. Combination Therapy with Doxycycline:

• Administering doxycycline along with an ML (like ivermectin) eliminates microfilariae promptly and safely.

7. Alternative Approach by the Author:

• Beginning administration of an ML and doxycycline at diagnosis, prior to adulticidal therapy. This method is simpler, safer, and provides immediate protection against further heartworm infection.

8. Precautions and Administration Advice:

• Owners should be informed about the potential for adverse reactions, especially with large microfilarial burdens. The first dose of milbemycin oxime, if used, should be administered in a hospital setting, potentially with pre-treatment using dexamethasone and diphenhydramine.

Complications and specific syndromes related to heartworm disease (HWD) in dogs:

1. Asymptomatic Heartworm Infection: 

• Most dogs with HWD are asymptomatic but may develop symptoms after adulticidal therapy due to pulmonary thromboembolism (PTE).

• Treatment involves melarsomine in a split-dose regimen and a macrocyclic lactone (ML) preventive.

• Risk of PTE can be estimated by semi-quantitation of worm burden and severity of radiographic lesions.

• Corticosteroids or heparin may be used to manage high-risk cases.

2. Glomerulonephritis: 

• Common in chronic HWD, it poses a therapeutic dilemma when presenting with proteinuria and azotemia.

• Treatment approach includes hospitalization and intravenous fluids prior to administering the first dose of melarsomine.

• 
  

3. Eosinophilic Pneumonitis: 

• Affects 14% of dogs with HWD, often early in the disease course.

• Signs include cough, dyspnea, weight loss, and exercise intolerance.

• Prednisone effectively reduces clinical signs and radiographic findings.

4. Eosinophilic Granulomatosis: 

• A more serious but rare condition.

• Treatment with higher doses of prednisone can induce remission, but recurrence is common.

5. Pulmonary Embolism: 

• Can occur spontaneously or post-adulticidal therapy, often presenting suddenly after failure to restrict exercise.

• Management includes strict confinement, oxygen therapy, and possibly corticosteroids, with other therapies like cough suppressants and vasodilators being speculative.

6. Congestive Heart Failure: 

• Results from increased right ventricular afterload due to chronic pulmonary arterial disease and thromboemboli.

• Treatment focuses on reducing signs of congestion, reducing pulmonary hypertension, improving cardiac output, and blunting the neurohumoral response.

• Medications used include diuretics, ACE inhibitors, vasodilators, and pimobendan.

7. Melarsomine Administration in Heart Failure: 

• If heart failure is present prior to adulticidal therapy, melarsomine is avoided if the heart failure is refractory; otherwise, it may be offered once clinical response to heart failure management is positive.

8. Slow Kill Approach: 

• Employed if melarsomine cannot be used due to heart failure, using ivermectin and doxycycline.

9. Exercise Restriction: 

• Strongly advised indefinitely to mitigate the risk of complications.

Complications, specific syndromes, and the prognosis associated with heartworm disease (HWD) in dogs:

1. Caval Syndrome (CS): 

• A severe variant of HWD, mostly affecting male dogs with heavy worm burdens. 

• Characterized by worms in the right atrium and vena cavae, leading to inflow obstruction, tricuspid insufficiency, and pulmonary hypertension (PHT).

• Clinical signs include hemolytic anemia, hepatorenal dysfunction, and acute onset of symptoms like anorexia and weakness.

• Treatment involves fluid therapy and surgical removal of heartworms from the right atrium and vena cavae.

• Prognosis is poor unless worms are successfully removed, with a high risk of mortality.

2. Glomerulonephritis: 

• Common in chronic HWD, presenting a treatment dilemma in dogs with proteinuria and azotemia.

• Approached with hospitalization, intravenous fluids, and cautious administration of adulticidal therapy.

3. Eosinophilic Pneumonitis: 

• Early complication in HWD, treated effectively with prednisone.

4. Eosinophilic Granulomatosis: 

• A more serious, rare condition, treated with higher doses of prednisone and possibly immunosuppressive drugs.

​

5. Pulmonary Embolism: 

• Occurs spontaneously or after adulticidal therapy.

• Managed with confinement, oxygen therapy, corticosteroids, and other supportive measures.

​

6. Congestive Heart Failure: 

• Results from increased right ventricular afterload due to chronic pulmonary arterial disease and thromboemboli.

• Managed with diuretics, vasodilators, and inotropic support.

7. Prognosis: 

• Generally good for asymptomatic HWI, guarded for severe cases.

• Post-adulticidal therapy, resolution of underlying manifestations of HWD begins.

• Poor in cases with severe complications like DIC, CS, massive pulmonary embolism, or heart failure.

• Glomerular lesions and heart failure signs can resolve with successful treatment.

8. Aberrant Migration: 

• Occurs when heartworms migrate to unusual sites like the brain, spinal cord, or eyes.

• Treatment varies depending on the affected site, ranging from surgical removal to symptomatic treatment.