Pet Columns, Office of Public Engagement, College of Veterinary Medicine at the University of Illinois at Urbana-Champaign

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Prevent Heartworm Infection


Pet Column for the week of May 24, 1999


Office of Public Engagement
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907
By Sarah Probst
Information Specialist

Yesterday evening was lovely. After a couple hours of yard work I lay in the hammock in
the backyard with a book, some ice water, and Maxie, my indisputably adorable Lab-mix.
Hmmmmm. Nice. Until-BZZZZ ... zzt ... Slap! Slap! Yikes, the mosquitoes are back! And
for pet owners like myself, it's time to make sure our best friends don't get a serious and
possibly deadly parasitic infection: heartworms.

Heartworms (Dirofilaria immitis) are long, slender parasites that can reach up to 12
inches in length. A larval stage of this spaghetti-like worm is transmitted by our airborne foe,
the mosquito. "Immature forms of the worm circulate in the blood of infected animals and
are picked up by the mosquitoes that bite them," says Dr. Allan Paul, small animal
Extension veterinarian at the University of Illinois College of Veterinary Medicine in Urbana.
"Mosquitoes then pass the infection to other animals they bite. Dogs and cats of all ages and
all breeds are susceptible to heartworms.

"The worms live in the right side of the heart and adjoining vessels and are capable of
causing substantial damage to the heart and lungs before the animal shows any signs of
disease," explains Dr. Paul. Signs of heartworm include coughing, difficulty breathing,
lethargy, and weight loss. The disease is easier to detect in dogs than in cats.

With dogs, the disease slowly compromises the circulation and impairs the amount of blood
pumped from the heart. Your dog could have over 100 worms in its heart and could live
with this burden and spread infections to more mosquitoes and other dogs and cats for as
long as the dog can live with the burden ... sometimes up to 7 years.

In cats, detection is more difficult. Cats usually have only two or three worms and live only
two years after infection. The infection could mimic other diseases or cause no signs at all.
Cats may appear healthy, then suddenly die from heartworm infection.

Treatment of the disease is a long, difficult, risky process, and is almost always unsuccessful
in cats, so prevention is key to keeping your mosquito-bitten pet healthy and alive. A plus
to prevention is that most preventive medications also protect your pet from other parasitic
infections, such as hookworm, whipworm, and roundworm (but not, unfortunately,
tapeworm). Prevention is also easily administered in a monthly tablet formulation. I give
Maxie her preventative the first of every month. My rent payment is my reminder.

Before your veterinarian dispenses preventive medicine, your pet's blood must be tested to
see if it is infected already. It could be dangerous to administer preventive medicine to
infected pets. When tests show the pet is not yet infected, preventive medication is given to
kill a stage of the heartworm in the blood, before it infests the heart.

Consult your veterinarian for a heartworm prevention medication schedule for your pet.
Then you can enjoy the lovely spring and summer weather knowing your pet is safe from
this life-threatening infection.