Feline Heartworm Disease Study Guide

Overview and Clinical Importance

Feline heartworm disease (FHD) is a potentially life-threatening condition caused by the filarial nematode Dirofilaria immitis. Unlike dogs, cats are aberrant hosts for heartworms, meaning they are not the natural definitive host. This results in significant differences in pathophysiology, clinical presentation, diagnosis, and management compared to canine heartworm disease.

The prevalence of feline heartworm disease is approximately 5-20% of the canine rate in endemic areas. However, this likely underestimates the true prevalence due to diagnostic challenges and the transient nature of feline infections. Importantly, up to one-third of infected cats are indoor-only, highlighting that indoor status does not eliminate risk.

Etiology and Life Cycle

Causative Agent

Dirofilaria immitis is a filarial nematode transmitted by mosquitoes. Adult female heartworms can reach up to 30 cm (12 inches) in length. All life stages of the heartworm harbor Wolbachia pipientis, a bacterial endosymbiont that contributes significantly to the inflammatory pathology of the disease.