April is National Heartworm Awareness month. Heartworms (Dirofilaria immitus) are parasitic worms that live in the right side of the heart and are transmitted by mosquitoes. Dogs are the usual host for this parasite, but as we are learning, our feline friends can also get heartworms.
Heartworm disease is different in cats than it is in dogs because felines are not the ideal host, although dogs and cats become infected the same way. Heartworm infection occurs when mosquitoes bite a dog or cat and deposit the third stage larvae at the injection site. The larvae then migrates from the injection site and changes into forth stage larvae in the surrounding muscle tissue. In about 70 days, the immature adult makes it way to the heart through the circulatory system. Felines normally will become infected with about three to six adult worms, which may be of the same sex. Because the worms are normally shorter in length in cats, a blood test will not necessarily show evidence of the larvae. Even though cats are an atypical host, heartworms can still cause severe disease, especially since the lifespan of the parasite in cats is about two to four years.
Heartworm cycle in the Feline
Enlargement of the right caudal lobar artery Photo courtesy of Dr Clarke Atkins, North Carolina State University Heartworm disease in felines can go undetected and symptoms can be vague and sudden. The signs of heartworm disease in felines may be: weight loss, vomiting, cough, or even sudden death. Unlike dogs, cats do not show signs of cardiac symptoms but rather respiratory symptoms. The primary way heartworm disease is exhibited in cats is Heartworm associated respiratory disease (HARD); the signs resemble an asthma attack with intermittent coughing, wheezing, and difficulty breathing. If a cat is suspected of having heartworms, a veterinarian will conduct an antibody test and thoracic radiography to detect infection. Of the two detection methods, thoracic radiographs may provide the strongest evidence of feline heartworm disease by showing changes in the vessels of the heart and lungs. When HARD is detected, the cat is treated with steroids until the respiratory signs diminish. There is no safe treatment to kill the adult heartworms in cats.
The most effective way to prevent feline infection of heartworms is to protect your cat against heartworms. Prevention is important for indoor as well as outdoor cats; even indoor cats can suffer from mosquito bites that place them at risk for heartworm infection. The preventatives that veterinarians recommend are monthly topical solutions which are placed on the skin between the shoulder blades; these also provide flea prevention. Ask your veterinarian how to protect against heartworm disease in your feline friend today.
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