Name: Heartworm Disease
Cause: Dirofilaria immitis, a parasitic roundworm
At Risk: All 50 states, warmer portions of Canada, South America, southern Europe, Southeast Asia, Middle East, Australia, and Japan. (1) Though more prevalent in the summer months, mosquitos and the parasite can survive "warmer" winters.
Victims: Dogs, cats, and other mammals. (Human infection is rare, as the parasite cannot complete it's life cycle. It usually presents as a small, round lesion that resembles a tumor.)
Transmitted: Via the bite of an infected mosquito. The mosquito bites an infected animal, then transmits the parasitic worm to the healthy pet when feeding/biting.
Disease Course: After maturing near the site of the mosquito bite, the parasite migrates to the muscles of the chest and abdomen around 45-60 days. Between 75-120 days, after further maturation, the immature heartworms enter the bloodstream, and end up in the pulmonary artery. For 3-4 months the worms gradually increase in size, eventually mating and releasing their offspring, microfilariae. The microfilariae then circulate in the bloodstream waiting for the next stage in their life cycle in the gut of a bloodsucking mosquito. (1)
Symptoms: Varies depending on length of infection, activity levels, and the animal's immune response. There are four stages of the disease. The higher the class, the worse the disease (similar to cancer ratings in humans)
Class I: Asymptomatic, or mild symptoms. (Occasional coughing)
Class II: Mild - moderate symptoms. (Occasional cough and tiredness after moderate activity)
Class III: General loss of body condition, a persistent cough, and tiredness after mild activity. Trouble breathing and signs of heart failure are common.
Class IV: Caval syndrome; bloodflow back to heart blocked by worms. Caval syndrome is most often terminal. (2)
Diagnosis: Bloodwork to test for a specific antigen (protien) released by the female heartworm. (This is one of the reasons your veterinarian may draw blood at your pet's annual examination) In Class II & III heartworm disease, heart and lung changes can be seen upon x-ray.
Treatment: Heartworm disease is VERY expensive to treat. For Caval syndrome, surgery to remove blockage of heartworms is the only option. In less advanced stages, multiple injections of a drug known as immiticide into the deep muscles of the back are used to kill off the heartworms. Strict cage rest and veterinary monitoring is required, as are regular check ups for pets being treated for the disease.
Prevention: Prevention is the best treatment. There are multiple monthly medications (Heartguard, Iverhart, Trifexis, Sentinel) as well as an injectable version (Proheart) that is administered every six months. All must be presecribed by a veterinarian, but some companies even have a product guarantee and will reimburse the cost of treatment if your pet was on the medication year round and it was administered appropriately.