Heartworm disease is not to be taken lightly. Pet owners everywhere need to be aware of how serious this condition is and how it can impact their pet’s health.
What is heartworm disease?
Heartworm disease is caused by parasite. Transmitted mostly by mosquitos, the Dirofilaria immitis (heartworm) parasite grows into long worms (sometimes up to a foot! Ew!) that can live in your pet's heart, lungs, and associated blood vessels. Baby worms are called microfilaria and live in the blood stream of infected animals. Mosquitos transmit the disease by drinking the blood of an infected animal and then drinking the blood of a non-infected animal. The microfilaria are transmitted to the new host and begin their journey toward maturation and life in the new host. Fully grown heartworms can live for up to five to seven years in dogs.
Is my pet at risk?
Dogs aren't the only pets susceptible to heartworm disease. Cats and ferrets can get heartworm disease and heartworms have been known to live in a number of other mammals, such as wolves, coyotes, foxes, sea lions and—in rare instances—humans.
Warm, wet states where mosquitos thrive have higher heartworm disease rates, but heartworms have been found in all fifty states. Also, don't assume your pet is safe because you live in an urban area or because your pet stays indoors all the time. Foxes and coyotes can be found in urban areas quite frequently and mosquitos like to hang out inside your warm home during the winter.
The Prevalence of Heartworm
It is estimated that a million dogs have heartworm disease in this country, and heartworms can be found in many parts of the world. Areas that are moist and hot tend to have higher concentrations of affected mosquitos, but heartworm has been diagnosed in all 50 states.
Even desert climates and areas with freezing temps are seeing more cases. This is possibly due to the fact that our society is increasingly mobile and dogs from high-risk areas are moving with their humans.
Also, there has been an influx of dogs transported from areas of higher heartworm density through adoption programs. This is because there are more adoptable dogs in the Southeast and rescue organizations are alleviating these overwhelmed shelters by sending homeless dogs throughout the country to get them off of kill lists.
The Cycle and Spread of Heartworm Disease
Heartworm disease is spread through a fairly complicated life cycle. As stated above, the mosquito plays an integral part.
An infected dog, or one of its wild cousins, will have a female heartworm that is producing microscopic worm offspring called microfilaria. These worms spread throughout the bloodstream. When a mosquito takes a blood meal from an infected animal, it ingests these baby worms.
In 10-14 days, these worms develop into larvae which are now at an "infective stage" that will transfer from the mosquito to the new host's skin. When the infected mosquito bites another animal, the larvae that get deposited on the dog, cat, or wild dog-like creature's skin. These larvae find their way into the animal's bloodstream through the mosquito's bite wound.
Once the larvae have burrowed their way into the body of their new host, it takes about six months for the parasites to mature into adult heartworms. Adult heartworms can live up to seven years in dogs and two to three years on cats.
It's easy to see that with the worms thriving in the warm protection of your pet's body, the heartworm offspring are ready and waiting for mosquitos to facilitate a new cycle. This means more and more pets and wild animals have the opportunity to be infected from just one dog... for years.
Dogs are the ideal host for heartworms. Because of this cozy environment, the adult heartworms can mate and produce offspring that mature into adults. Dogs have been known to harbor hundreds of worms in their heart, lungs, and arteries.
Signs and Symptoms of Infection
Dogs: During the early stages of infection, there will be very few, if any symptoms. As the disease progresses, the heart and lungs are essentially being gradually taken over by the heartworms to the point that normal cardiovascular functions are impossible.
The first sign of a heartworm infestation is often a mild yet regular cough. The dog will begin to tire easily during exercises previously tolerated. The appetite may decrease and weight loss is not uncommon.
Dogs in advanced stages may show signs of heart failure which include a swollen abdomen due to excess fluids. Blockages in the heart and vascular system can happen from the sheer volume of worms. Difficulty in breathing, pale gums and dark-colored urine are a sign that your dog is in critical condition. Without immediate veterinary attention and surgical removal of the heartworm blockage, few dogs will survive.
Cats: The symptoms of ringworm in cats is markedly different than in dogs. This is due to the fact that cats' bodies are not nearly as accommodating to the heartworm as dogs are. Some cats show very few symptoms so as to be undetectable. These mild symptoms may include coughing, asthma-like symptoms, and decreased energy and appetite.
Rarely, some cats will show marked symptoms such as decreased motor skills, fainting spells or even seizures. There may also be a distended abdomen due to fluids. Unfortunately, in some cats, the first sign of infection is sudden death.
Given the fact that heartworm disease causes serious health problems, we pet owners must be proactive in preventing the infection. Additionally, treatment for heartworm disease is up to 15 times more expensive than the heartworm prevention medicines. These meds come in a topical form and a pill form. There are formulations made specifically for dogs and for cats. Both oral and topical preventatives must be administered monthly.
Preventative medicines will not prevent the heartworm larvae from entering your pet's body. Instead, the medicine works by killing the heartworm larvae in the bloodstream before they have a chance to mature into adults that will take residence in the heart. A clean bloodstream means a biting mosquito will not be ingesting the microworms that will start the heartworm lifecycle in other animals.
There is an added bonus to treating pets with heartworm preventatives. Heartworm medicines often treat other parasites which may include roundworms, tapeworms, whipworms, and hookworms. Some even treat or prevent fleas, ticks, and ear mites.
Some pet owners believe that they only need to give their pets heartworm medicine for six months out of the year, when mosquitos are active. But remember - it can take six months for the immature heartworms to grow into reproducing adults. You'll want your pet protected throughout the year to ensure no juveniles have the opportunity to mature into reproducing adults.
Also, the other maladies that the heartworm medicine can prevent are best treated all year long.
Although the preventative medicines work well, there are still factors that can leave your pet at risk. Your pet may discreetly cough up their oral medication without your knowledge. Or they may vomit. Topical medications may rub off or be washed away. Talk to your vet to see if there is a need for an additional treatment.
These possible administration complications are yet another reason to be sure to administer monthly treatments to be sure that there is a smaller window of possible infection.
Because symptoms of heartworm infections are initially mild, it is important to get yearly screenings for the disease. The earlier the disease is detected, the easier it will be to treat.
The heartworm test is done by taking a small sample of blood from your pet. The blood will then be screened for a specific protein (antigen) that the female heartworm releases. If your dog tests positive, your vet will guide you through the process of treatment.
For cats, it is much more difficult to determine if they are infected than in dogs. Two tests will be done including the antigen screen as well as an antibody test that will show if a cat's immune system is reacting to the presence of the heartworm larvae. Vets may need to use an ultrasound or x-ray of the heart to see how the disease has progressed. Confirming the disease in cats is imperative as using heartworm prevention meds in infected cats could be fatal.
As stated above, heartworm infection has to be ruled out in cats before they can receive the preventative medicine. This is because the cat will react to the toxins released when the larvae die from the treatment.
As far as heartworm-positive dogs, your veterinarian may use preventative medicines to kill the microscopic worms and larvae living in the bloodstream. This has to be done with careful veterinary supervision as the toxins released from the dying organisms can also affect dogs, but the risk is not as extreme as it is in cats.
By using the prevention medications in already-infected dogs, a new heartworm infection will not occur while being treated for the existing infection. This makes the treatment for the original infection more effective.
Also, by eliminating the tiny pathogens from your dog's bloodstream, your dog will not be facilitating the further spread of the disease, should they be bitten by another mosquito.
Treatment for Heartworm Disease
For cats, there is no treatment available to eradicate the disease. Palliative care of the secondary symptoms may help. As cats are not very good hosts of the heartworms, they will usually only harbor about six adult worms. Hopefully, by giving the cat good medical care, the kitty will outlive the heartworms (which is only two to three years in felines.)
It is still a good idea to keep heartworm-positive cats indoors on the rare chance an adult heartworm is successful in reproducing and releasing microscopic worms into the bloodstream. Another mosquito bite will start the heartworm lifecycle in another animal.
Despite the gloomy information about heartworm disease, the good news is that 95% of heartworm-infected dogs can be successfully treated. Here is what you can expect should your dog be diagnosed with heartworm:
For more information on heartworm, visit the American Heartworm Society, which also provided the graphic for this article.
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