HEARTWORM TREATMENT: A.S.A.P.!

Our records show your dog has heartworm disease, and needs to start its heartworm chemotherapy. How did this happen, and what are the details of how to cure your pet? Please read on, to learn what you need to know about your dog's heartworm disease, and why we urge all dogs with heartworm disease to be treated as soon as possible.

Heartworm Lifecycle

Heartworms have what is called an obligate indirect life cycle. This means they require two separate hosts in order to complete their life cycle.

Adult heartworms live in dogs, occasionally in cats, rarely in humans, and can infect numerous species of wildlife and marine mammals. These adult worms are about 6 to 14 inches long. They live in the right side of the heart and the large blood vessels. Their rough cuticle or "skin" causes severe irritation to the delicate tissues lining the right ventricle, the pulmonary arteries, and the caudal vena cava. This irritation leads to permanent, irreversible damage to the heart and lungs, as well as the characteristic symptoms of heartworm disease: exercise intolerance, weight loss, and congestive heart failure. That's the main reason we want all heartworm-positive dogs to be treated for their heartworms as soon as possible.

Heartworms are live bearers, rather than egg layers (similar to guppies). Adult male and female worms produce thousands of microscopic baby worms, or microfilaria. These baby heartworms are visible in a fresh drop of blood under the microscope; they look like tiny transparent snakes. The next step in the life cycle involves a mosquito. The mosquito comes along and bites the infected dog, accidentally sucking up baby heartworms. Over the next 3 weeks, the baby heartworm develops into the next stage of the life cycle while inside the mosquito. Next, the mosquito bites another dog, infecting the new dog with the baby heartworms it is carrying. It takes 4-6 months for the baby heartworms to go through 5 more stages of development while migrating through the tissues to the host's heart. Once there, the baby heartworms mature into adults, start producing baby heartworms, and the life cycle is complete. Because a heartworm-positive dog helps perpetuate the life cycle, we want all heartworm-positive dogs treated, so that they can't contribute to infecting other dogs.

Heartworms in Texas

Heartworms flourish in any environment where mosquitoes do well. As you are well aware, Texas has a very warm climate.. Mosquitoes have plentiful areas to breed, and fly any day it's warmer than 45 degrees Fahrenheit. Consequently, mosquitoes are flying year round. Therefore, all dogs, cats, marine mammals and numerous species of captive exotics and wild carnivores should be protected with heartworm preventative 12 months a year. 

Hurricane Katrina, in 2005, has had a lingering effect on the health of dogs, cats and all heartworm-susceptible animals all over the United States and Canada.  Thousands of dogs were rescued from the floodwaters of New Orleans, and air-lifted to animal shelters all over North America.  Unfortunately, a high percentage of these dogs were heartworm-positive.  As a consequence, mosquito populations that were previously uncontaminated with heartworm larvae have been contaminated, and dogs living in those heretofore heartworm-free areas now must be maintained on heartworm prevention.  Calgary and  Las Vegas are two notable examples.  The Abilene area and all of the Big Country here in central west Texas saw a significant jump in heartworm cases since 2005, due to the Katrina dogs brought to our area.

Heartworm Treatment

Although heartworms can be fatal and treatment for the disease involves risk, the condition is nearly always curable. Treatment requires careful medical care and complete rest at home afterwards.

The first thing we will do is evaluate your dog's condition, performing a physical examination, laboratory tests and chest x-rays to evaluate the condition of the heart and lungs. We might find other health problems that need attention first, or if the heartworm infestation is very severe, we might want to modify our treatment plan.

Adult heartworms are 6 to 14 inches long and live mostly inside the heart. Baby heartworms are microscopic and live within blood vessels throughout the body. Each stage must be treated separately.  First, we put your dog on a systemic antibiotic for 30 days that will help weaken the heartworms by killing a critical bacteria that lives in the heartworm intestine.  In addition, we'll put your dog on anti-inflammatants to help minimize the damage caused by the heartworms.  Next, we'll start your dog on a monthly heartworm preventative, under very careful supervision, to prevent any further heartworms from developing, as well as to slowly remove the baby heartworms from your dog's bloodstream so that he isn't contagious to other dogs.  

Once your dog has been on the monthly heartworm preventative for at least 4 months, we know that there aren't any immature heartworms "in the pipeline" between the mosquito's infective bite and arriving in your dog's heart.  Now, it's time to eliminate the adult worms by giving 2 sets of chemotherapy injections, spaced a month apart..

After each set of chemotherapy injections, your dog's heartworms will be dead or dying. That's good, but the heart is still full of worms. The worms gradually break into smaller and smaller pieces until the fragments are tiny enough for the body to eliminate them. The critical period is when worm fragments are small enough to disperse into the body but still large enough to plug small arteries in the lungs. Vigorous activity makes the heart pump faster, pushing bits of dead heartworm out into small blood vessels where they can cause trouble, so it's critically important that your dog be kept very quiet.

Home Care

Your dog needs rest (indoors or on a leash) for four weeks. Dogs that are kept outdoors must become an indoor dog until the recovery period is through. If you see any sign of illness such as poor appetite, coughing, depression or vomiting, there may be a problem. Check your dog's temperature using an ordinary human rectaldigital thermometer. Lubricate the thermometer with Vaseline or KY Jelly, insert halfway and read when it beeps. The morning temperature should be below 102.4. Dogs with a morning temperature higher than this should be examined. Early treatment will control most complications.

After the initial chemotherapy, you'll need to bring your dog back in for brief recheck visits once a week. Not only will one of our staff doctors thoroughly examine your dog, we'll also interview YOU about what you've observed during the week.

After four weeks, the adult heartworms are gone but there may still be thousands of baby heartworms in the bloodstream. First, we'll do a quick minor blood test to check if there are/are not baby heartworms in your dog's blood.  If there are, we will schedule your dog to spend a day with us about four weeks after the second chemotherapy treatment. First we give a drug to reduce possible reactions. Then, about half an hour later, we give the oral medication to remove the baby heartworms from the blood. Two weeks later, we'll draw a small blood sample to verify all the baby heartworms are gone--at that time, it's safe to allow moderate exercise. Because the heart and lungs are not yet completely back to normal, it is a good idea to avoid heavy exercise like hunting or ball chasing for an additional eight weeks.

Follow-up Testing

Sometimes a few heartworms survive treatment. To detect these worms, we do a final test six months later. If any heartworms are still alive, the injections must be repeated

Summary

· antibiotics, antiinflammatants, heartworm prevention for 4 months

· hospital treatment for adult worms (about 3 days)

· Rest at home for 4 weeks

· Second hospital treatment for adult worms (about 3 days)

· Rest at home for another 4 weeks

· Hospital treatment for baby heartworms (if needed)

· Rest at home another 2 weeks

· Test to make sure all baby heartworms are gone

· Monthly Interceptor or Sentinel, permanently

· After 6 months, test for surviving adult worms

Although other drugs have been used in the past, practically all veterinarians use an arsenic-containing drug called Immiticide - safer than what we used in the past but more expensive. It is given by injection deep into the muscles of the lower back. With proper pre-treatment evaluation through physical exam, blood work, and chest films, the use of newer and safer drugs, diligent control of pain and attentive nursing care, we can treat dogs for heartworm much more safely and a lot more comfortably.