Heartworm is spread by mosquitos. An infected mosquito bites the dog, injects the dog with larvae which travel through the muscles and tissues, this takes a few months.

Eventually they enter the blood stream and migrate to the heart and lungs. Here they grow into adult worms and can be up to 30 centimeters long. These worms eventually produce offspring called “microfilaria” which is what the mosquito sucks up and starts the cycle again. The worms inside the heart and lungs cause very serious damage to the dog.