Risk factors for human heartworm infections (dirofilariasis) in the South

Human pulmonary dirofilariasis (HPD) is caused by the transmission of infective third stage larvae of the canine heartworm, Dirofilaria immitis, during blood-feeding by several species of infected mosquitoes. Since humans are incidental hosts and cannot support the parasite's life cycle, infective larvae die after migrating to the pulmonary vascular bed, where an initial subclinical inflammatory reaction is typically followed by a single pulmonary granuloma. The resulting nodular granuloma is described radiographically as a "coin lesion" that resembles a neoplastic lesion, which must be ruled out by invasive lung biopsy. Since HPD cases have been reported mainly from regions with high canine heartworm prevalence, such as the southern United States (US), the objectives of this review were (1) to describe the microbiology of the parasite; (2) to resolve any misconceptions regarding the pathophysiology and outcomes of canine versus human heartworm infections; (3) to describe the prevalence and parasite burden of canine dirofilariasis in the South compared to other areas; (4) to describe the prevalence of HPD in the South; (5) to identify the most important species of mosquito vectors of dirofilariasis based on seroprevalence rates of infection and transmission efficiency; (6) to identify the key risk factors for HPD in the South; and (7) to recommend new strategies for the diagnosis, management, control, and prevention of HPD. Future investigations should focus on targeting specific mosquito species for improved vector control of D. immitis transmission and on developing new immunologic and molecular methods for diagnosing HPD and eliminating the need for invasive diagnostics for differential diagnosis of innocuous, parasitic "coin lesions".