A parasite is dependent on its host and obtains some benefit, such as survival, usually at the host's expense. The effects of parasites can range from annoying to deadly. Left untreated or uncontrolled, parasites such as heartworms can be life threatening. Others, such as fleas, can simply cause discomfort or in severe cases, blood-loss anemia.
Some parasites present a potential health risk to humans as well.
In less severe cases, it just adds to the itching and misery. In more severe cases, it can cause skin problems. It's important to protect your pets for their sake as well as yours. Left unchecked, several parasites can be transmitted from dogs and cats to humans. This process, called zoonosis, can cause a variety of health problems.