During the month of April, we celebrate National Heartworm Awareness Month and work to educate pet owners on the prevention of heartworm disease! Heartworm disease is not to be taken lightly as it can lead to irreversible lung disease and death if untreated. Today’s blog will address commonly asked questions about the disease.
How is it Contracted?
Heartworm disease affects many mammalian species, including dogs, cats, several wild carnivores and— in rare instances—humans. When a mosquito takes a blood meal from an infected animal, it ingests microfilaria (immature worms), which develop and mature into “infective stage” larvae over a period of 10 to 14 days while still inside the mosquito. When the infected mosquito bites another dog, cat, or susceptible wild animal, infected larvae are deposited onto the surface of the animal’s skin and enter the new host through the mosquito’s bite. Once inside a new host, it takes approximately 6 months for the larvae to mature into adult heartworms. Once mature, heartworms can live for 5 to 7 years in dogs and up to 2 or 3 years in cats. They can grow up to one foot long and several hundred can be found in an infected dog. A mixed population of mature worms will reproduce, creating microfilariae that can pass infection to mosquitoes and the cycle repeats.
Who Should be Concerned?
All pet owners should be concerned. Heartworm disease was once more prevalent in the south due to higher and more consistent temperatures. However, the geographic distribution of heartworm disease is changing. Warmer winters have become common even in northern locales and the mosquito season often lasts longer. The incidence of disease has also been influenced by natural disasters, such as Hurricane Katrina and Maria. In an outpouring of support for dogs and cats affected by natural disasters, many animals have been relocated to homes all over the country. If these animals are heartworm positive they can act as a reservoir for the disease in an area previously unaffected. Indoor cats, unfortunately are also at risk for contracting heartworm disease. Infected mosquitos may enter the house and can bite cats who reside there. Sadly there is NO treatment for cats that contract heartworm disease!
What Are the Symptoms of Heartworm Disease?
In the early stages, many pets show little to no signs of disease. As the worm burden increases, you may notice a mild persistent cough, reluctance to exercise, fatigue after moderate activity, decreased appetite, and weight loss. When left untreated, pets develop heart failure and the appearance of a swollen belly due to excess fluid in the abdomen. Dogs with large numbers of heartworms may develop caval syndrome, a sudden blockage of blood flow within the heart leading to a life-threatening form of cardiovascular collapse. Caval syndrome, is marked by sudden onset of labored breathing, pale gums, and dark bloody or coffee-colored urine. Without prompt surgical removal of the heartworms blocking blood flow to the heart, dogs are unlikely to survive.
In cats, as they are an atypical host, most worms do not reach adulthood. While this means disease often goes undiagnosed, it’s important to understand even immature worms cause real damage in the form of a condition known as heartworm associated respiratory disease (HARD). Symptoms may include coughing, asthma-like attacks, periodic vomiting, lack of appetite, or weight loss. Occasionally an affected cat may have difficulty walking, experience fainting or seizures, or suffer from fluid accumulation in the abdomen. Unfortunately, the first sign in some cases is sudden collapse of the cat, or sudden death.
How Can It Be Diagnosed?
It is important to remember that heartworm disease is progressive and early detection is vital. Most pet owners are familiar with the heartworm SNAP test, a simple, rapid, blood test, run in-the hospital at your pet’s yearly exam. The SNAP test detects the presence of specific proteins (antigens) found in female heartworms. A microfilariae test scans a blood smear for the presence of circulating immature larvae. If your pet tests positive, further tests may be ordered.
Heartworm infection in cats is harder to detect than in dogs, as cats are much less likely than dogs to have adult heartworms. The preferred method for screening cats includes the use of both an antigen and an antibody test (an antibody test detects exposure to heartworm larvae). Your veterinarian may also use x-rays or ultrasound to look for heartworm infection.
What Happens if Your Pet Tests Positive?
After positive tests have been confirmed by retesting, treatment is initiated. Treatment begins with exercise restriction and a course of antibiotics followed by two injections, 24 hrs apart, of melarsomine. A tapering course of steroids, more rest and a final injection of melarsomine a month later rounds out the treatment. Melarsomine is an arsenic derivative and the only FDA approved treatment for heartworm disease (in dogs only). The treatment is painful, expensive and lengthy.
Unfortunately, no treatment is available for cats. If your cat tests positive for heartworm disease, only monitoring, supportive care and treatment of symptoms is available. A heartworm infection in a cat may dramatically shorten their life expectancy. Prevention is much preferred over treatment in the case of heartworm disease for both dogs and cats.
How Do You Prevent Heartworm Disease?
Prevention is simple and easy: the administration of a heartworm preventative. Fortunately, there are several options available to help ensure the compliance of use necessary to prevent infection.
For Dogs options include Proheart 6; an injection administered in our hospital every 6 months as a scheduled appointment, Heartgard Plus; a monthly oral chew, or a monthly topical called Revolution.
For Cats options include oral Heartgard or topical Revolution.
Cost of prevention generally ranges between $7-$13 dollars per month, a small price to pay to keep your pet happy and healthy! To learn more visit the American Heartworm Society.
Written By: Tara Corridori, LVT
Information Obtained from https://www.heartwormsociety.org/pet-owner-resources/heartworm-basics