The infected dog then becomes the host of these heartworms. Some of the clinical signs of infection are chronic cough, lack of stamina and lack of energy for exercise. Adult heartworms may interfere in the heart's functions and blood can't be pumped properly for the circulation. The right heart will swell, followed by damage to the lungs, liver, kidneys, abdomen, chest and lastly limbs. The period of incubation in the dog host varies.
Some dogs remain infected for a long time before showing any clinical signs of the disease.
All dogs are susceptible to heartworm infection. Dogs with outdoor kennels are very likely to be bitten by mosquitoes and thus are exposed to higher risks of contacting heartworm disease. If there are large masses of heartworms near the liver, this will cause serious illnesses in the liver. The dog will experience loss of appetite, liver disease, blood pigments in the urine, yellowing skin, jaundice and eventually the dog dies. When worms of only 1 sex or immature worms are inside a dog, there are no microfilariae in its blood circulation.