Parasite prevention can save your dog or cat
The Companion Animal Parasite Council has rated Dover the number two metropolitan area in the nation for percentage increase in heartworm in dogs and cats.
“The prevalence has increased,” said veterinarian Jennifer Shonts, of Duck Creek Animal Hospital in Smyrna. “We used to see two a year … now we’re up to one or two a month. Mosquitoes are definitely not taking it easy on our canine friends.”
The CAPC Top 10 Cities Heartworm Report for May considered positive heartworm test results from the preceding 30 to 45 days. Out of 15,558 Delaware dogs tested, 74 had heartworm, or about 0.5 percent.
Nationally, heartworm rates have risen over the last five years and are up 20% from 2013.
The council’s data comes from IDEXX Laboratories and Antech Diagnostics, labs that process samples from veterinarians. Since not all pets get tested, the number of heartworm positive animals is likely higher.
“In some areas, like Houston, Texas, the number of heartworm cases is endemic,” said Dr. Craig Prior, a Nashville veterinarian and CAPC board member. “But in places like Delaware, where we don’t have a lot of cases and suddenly see an increase, that tells you something is going on locally.”
Reasons for the rise
Heartworm is on the rise here for at least two reasons. First, climate change has caused an increase in the mosquito population, and mosquitoes are heartworm carriers.
“The direct effects of temperature increase are an increase in immature mosquito development, virus development and mosquito biting rates,” Yale School of Public Health’s Maria Diuk-Wasser told Scientific American.
Second, pets are being transported at a higher rate than ever, and heartworm goes along for the ride.
“We’re bringing heartworm positive dogs and our mosquitoes are biting them, then they’re infected and passing it to our dogs here,” Shonts said.
According to a 2017-18 American Pet Products Association survey, 37 percent of pet owners travel with their pets, or roughly 20 percent more than a decade ago. Pets are also traveling to them.
“Hurricane Katrina [caused] the largest transportation of animals in the history of the world,” said Dr. Janice Sosnowski, owner of Governor’s Avenue Animal Hospital in Dover. “There were tons of animals who were displaced or lost in a hot, mosquito driven area. We don’t see a lot of dogs with heartworm … unless we’re getting a rescue in from South Carolina, or Louisiana or Alabama. Most of the time, it’s recently adopted dogs.”
Most states, including Delaware, require only a rabies test for pets to cross state lines.
Following Hurricane Harvey in 2017, Brandywine Valley SPCA, the state’s contracted shelter partner, transported at least 80 dogs and cats from Houston.
“If we transfer in from another shelter or rescue, the animal is tested beforehand and we test again here as confirmation,” said marketing director Linda Torelli. “If we have a heartworm positive dog, we treat the dog here and allow them to be adopted during that time, with the treatment completed at our clinic and the cost included in the adoption fee.”
However, heartworm tests are far from error-proof. American Veterinarian estimates that between six and 38.7 percent of all negative antigen tests are false. Antigen tests are the most commonly used heartworm tests.
The CAPC’s Prior urged adopters to be cautious.
“When you get a dog from shelter or rescue, get it tested again to make sure it’s healthy and not carrying anything,” he said.
What are heartworms?
According to the American Heartworm Society, heartworm parasites live in the hearts and lungs of dogs and cats, wolves, foxes, raccoons, sea lions and, occasionally, humans.
One infected animal can greatly increase the number of mosquitoes carrying the parasite in an area, thereby increasing the chance of infection.
Canine heartworm causes severe lung disease, heart failure and other organ damage. Dogs can host hundreds of worms before the parasites kill them, in a very slow and painful manner.
“It’s horrible,” said Grass Roots Rescue’s Karli Crenshaw. “Their chests enlarge to two to three times the normal size. Their chests and abdomens fill with fluid. They struggle to breathe and essentially drown.”
Grass Roots, based in Milton, deals with heartworm frequently. They recently took Brienne, about seven, from a North Carolina shelter, with her puppies.
“They pulled 12 bowls of fluid out of her abdomen. She’s still not out of the woods but she’s stable for now,” Crenshaw said.
Heartworm in cats is much rarer. They don’t normally develop adult heartworms, and if they do, it’s usually one to three worms. However, infected cats can develop heartworm associated respiratory disease, which can be fatal. There is no treatment for heartworm in cats.
Rarer still is heartworm in humans. According to the Centers for Disease Control and Prevention, the larvae usually don’t survive transmittal from mosquito to human and, when they do, they do not reach sexual maturity and therefore cannot reproduce or spread to new hosts.
Protecting your pet
“Heartworm preventatives are affordable, safe and effective,” Prior said. “This is why CAPC recommends all pets, no matter where they live, be tested annually and placed on heartworm preventatives 12 months of the year.”
Ivermectin is the most popular heartworm preventative for dogs, sold as Heartgard or Sentinel. They require a veterinary prescription, and vets will require your dog be tested first.
It costs from $20-$60 for a six month supply, depending on the dog’s size. Prices for common cat heartworm preventatives like Revolution are comparable.
Treatment for heartworm can cost over $1,000.
“It’s very expensive to treat, the damage it does to animals’ hearts and lungs is horrific and it is long term and in many cases fatal,” Prior said. “It is much easier to prevent than treat.”
If your dog tests positive for heartworm, treatment typically begins with a round of antibiotics and steroids. A heartworm preventative is then administered to kill larvae in the bloodstream. Finally, over a period of about a month, three injections of melarsomine are administered by a veterinarian to kill the adults.
Exercise restriction during treatment is necessary because activity increases the rate at which heartworms damage organs.
As the adult worms die, complications can occur. Owners of dogs being treated for heartworm must watch closely for coughing or gagging, difficulty breathing, lack of appetite, excessive drooling, vomiting and/or diarrhea. Unfortunately, some dogs do not survive treatment.
For more, visit capcvet.org.