Heartworm
Dr. Ray Dillon of Auburn University indicates that the last 30 years have increased the basic understanding of heartworm disease
in cats and emphasized the clinical importance of this disease. Several basic concepts have been confirmed by data collected
in clinical practices, shelter cat populations and experimental studies:
> Cats develop bronchial disease as a consequence of immature adult heartworms that never become fully adult and initiate
heartworm-associated respiratory disease (HARD), which can persist for 12 months after a single short-lived infection.
> Cats that get only immature adults that live for two to three months and cats that develop adult heartworms both develop
HARD associated with the death of immature adults.
> Cats get immature heartworms as early as 75 to 90 days after infection, and immature heartworms die creating lung and arterial
disease that persists for up to 12 months.
> Cats that develop lung disease from immature heartworms that have died may be antibody-positive for only a few months although
the bronchial disease persists.
> Cats with only immature adult heartworms will be antigen-negative, and, echocardiographically, worms cannot be visualized
although bronchial disease is evident radiographically.
> The bronchial disease of heartworms in cats has 1) a bronchial epithelium component, 2) a smooth muscle proliferation remodeling
and 3) alteration of bronchial smooth muscle reactivity.
> Some cats do develop adult heartworms that may live for up to three or four years in the cats.
> After adult heartworms develop, the lung's inflammatory reaction is reduced in cats, and signs may be limited for long periods
although radiographic bronchial patterns continue.
> The lung recovery from heartworm infections is not uniform in parenchymal distribution, leaving severely diseased parenchyma
adjacent to relatively normal lung.
> The death of immature as well as adult heartworms may be associated with acute lung injury and severe type 1 cell injury
of alveolar capillary beds.
> Some cats that develop mature adult heartworms demonstrate minimal clinical signs prior to acute crisis typically associated
with adult worm death.
> Most cats that develop adult mature heartworms survive the infection as the worms die over the next two to four years.
Dr. Hoskins is owner of Docu-Tech Services. He is a diplomate of the American College of Veterinary Internal Medicine with specialities
in small animal pediatrics. He can be reached at (225) 955-3252, fax: (214) 242-2200 or e-mail:
jdhoskins@mindspring.com
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