There are two good reasons. Much of this damage may be irreversible even if the pet is treated for the adult worms and microfilariae. The damage done to those vital organs will reduce the dog s exercise tolerance and shorten its life expectancy, thus limiting its value as a family companion. The cost of prevention is much cheaper than the cost of treatment. The cost of medical care associated with treating a dog for heartworm infection can reach 750 to 1,000 dollars.
Dogs are the domestic pet most involved in general.
In areas of high prevalence in dogs, i.e. the foothill plant climate zones of California, outdoor cats are at increased risk of infection. Infections in horses have been reported but appear to be rare even in areas where dogs are highly infected. Cows, goats, sheep and pigs are even less susceptible than horses.