Treatment of Heartworms (Dirofilaria) in Humans
Surgical removal of the worm is the primary treatment for human dirofilariasis, with antiparasitic medications playing a supportive role in some cases.
Clinical Presentation and Diagnosis
- Human dirofilariasis is a rare zoonotic disease caused primarily by Dirofilaria immitis (dog heartworm) or Dirofilaria repens, with humans serving as accidental hosts 1
- Most patients are asymptomatic and present with an incidental finding of a pulmonary nodule (D. immitis) or subcutaneous nodule (D. repens) 1, 2
- Some patients may experience pulmonary symptoms during the acute phase due to pulmonary arterial occlusion and inflammation 1
- Diagnosis is typically made through histopathological examination after surgical removal of the lesion, as serologic tests are not widely available commercially 1, 3
- Eosinophilia is uncommon in human dirofilariasis, with most patients showing normal blood counts 4, 3
Treatment Approach
Primary Treatment
- Surgical excision is the definitive treatment for human dirofilariasis, whether pulmonary or subcutaneous 1, 4
- Most cases require complete surgical removal of the nodule containing the parasite for both diagnostic confirmation and curative treatment 1, 3
Adjunctive Medical Therapy
- Following surgical removal, oral diethylcarbamazine (DEC) at 2 mg/kg three times daily for 4 weeks has been used as adjunctive therapy 4
- In some cases, ivermectin (150 μg/kg as a single dose) followed by DEC has been reported as an effective combination therapy 4
Important Cautions
- Before using DEC, it is crucial to exclude co-infection with onchocerciasis, as DEC can cause severe reactions including blindness, hypotension, pruritus, and erythema in patients with onchocerciasis 5
- A test dose of 50 mg DEC can be used to detect onchocerciasis co-infection (will precipitate mild Mazzotti reaction if present) 5
- Similarly, in patients with potential Loa loa co-infection, microfilarial counts should be determined before DEC administration, as high counts (>1000/ml) increase the risk of encephalopathy 5, 6
Special Considerations
- Unlike veterinary heartworm disease, where specific adulticidal therapy with melarsomine is standard, human dirofilariasis is primarily managed surgically 7
- Consultation with specialists in tropical medicine or infectious diseases is strongly recommended before initiating any antiparasitic treatment 5, 6
- Follow-up imaging may be necessary to ensure complete resolution, particularly for pulmonary lesions 1
Clinical Pitfalls to Avoid
- Misdiagnosis as malignancy is common, leading to unnecessary extensive surgical procedures; consider dirofilariasis in the differential diagnosis of solitary pulmonary nodules in patients with travel history to endemic areas 1, 3
- Failure to consider potential co-infections with other filarial parasites before initiating antiparasitic therapy can lead to severe adverse reactions 5
- Relying solely on eosinophil counts for diagnosis is unreliable, as most patients with human dirofilariasis do not present with eosinophilia 4, 3