Fig. 28

Diagram of feline heartworm disease and HARD. Heartworm-associated respiratory disease (HARD) is induced at the first arrival of immature adult worms as early as 70 to 90 days after infection. The inflammation develops even if the cat “self-cures” and all immature adults die, and no adult heartworms develop. The lung lesions continue for up to 8 months after infection and perhaps longer. The antibody (Ab) response is present if cats are started on selamectin 28 days after the infection even if immature adults do not reach the heart. The antibody response continues after the arrival of immature adults; in cats which develop only the immature adults with HARD, the antibody response is present in 50% of the cats 8 months after the infection. Cats that develop the adult heartworms continue to live for up to 4 years, often with no symptoms, and the cats develop a decreased responsiveness of their pulmonary intravascular macrophages (PIM). When adult heartworms eventually die, acute symptoms may develop