New approach to preventing infection in dogs may stem tide of resistance

If you’ve heard that heartworm, a dangerous parasite that can cause serious disease and death in dogs as well as cats, is becoming resistant to the drugs we’ve long relied on to protect our pets, you’ve heard correctly.

“Failure of oral preventive drugs is reported most often from the Mississippi Delta area, where transmission rates are very high and resistance to preventive drugs has been confirmed,” said Dr. John McCall, professor emeritus in the Department of Infectious Diseases at the University of Georgia College of Veterinary Medicine. “But the spreading of resistance to other parts of the country is just a matter of time.”

The threat of heartworm that can’t be prevented with our present drugs is not a minor one. Infection with heartworm, a parasite spread by mosquitos, can cause life-threatening immune system reactions, respiratory distress, kidney failure, heart failure and other symptoms in both cats and dogs. However, there’s some good news, too. McCall recently published a study of a new two-step approach to fighting heartworm infection in dogs, one that targets both the heartworm and the mosquito that carries it.

“Heartworm is a two-parasite system,” said Dr. Elizabeth Hodgkins, director of veterinary relations for Ceva Animal Health, which makes Vectra 3D, a topical mosquito repellent and insecticide for dogs that also fights fleas and ticks. “Until now, we have not targeted one of these parasites, the mosquito. We’ve relied on preventive drugs against the worm to do the ‘heavy lifting’ alone.”

This flies in the face of how human public health programs fight mosquito-carried diseases like Zika virus, where the mosquito is always the primary target. Not only that, but putting all your health eggs in one prevention basket will always be less effective than protecting against disease with more than one strategy.

“When you get a flu vaccine, you still take other precautions, don’t you?” asked Hodgkins. “You still wash your hands and avoid standing in the air space of someone who’s coughing. You know there are other things you need to do to give that vaccine the best chance to keep you from getting sick.” It’s the same, she said, with heartworm.

When it comes to preventing the spread of resistant heartworm outside the South, or protecting dogs in areas where resistance is already present, targeting the mosquito is a valuable extra layer of prevention.

Resistance is thwarted because the topical medication stops more than 95 percent of mosquitos from biting protected dogs. As a result, the dog has a greatly reduced risk of getting infected -- and so does an uninfected mosquito, who might bite an infected dog later. That stops the transmission of both resistant and non-resistant heartworm.

On top of that, the repellent and insecticide killed 98 percent of the mosquitos exposed to a protected dog. That’s good news for everyone, including humans, cats and other pets, who would benefit from a reduced mosquito population. “In areas where mosquitoes are abundant, hundreds, and possibly thousands, of mosquitoes can bite a dog in in a 24-hour period,” said McCall. “The use of a repellent and insecticide could reduce this by 95 percent or more for an entire month.”

While there’s no such thing as 100 percent protection when it comes to living creatures, this double-defense of topical repellent and oral preventive medication is about as close as you can get.

Although cats also suffer from heartworm infection, there is currently no repellent safe for use on them. Owners of both cats and dogs should keep the treated dog away from the cat until the topical repellent is fully dry, usually a few hours after application.

Dog owners can learn more at fightheartwormnow.com, and should consult their veterinarian about how to best protect their pets from heartworm infection.

Feline liver mass usually benign

Q: My 8-year-old cat has been diagnosed with a biliary cyst. Can you tell me anything about this condition?

A: That’s an interesting question. A biliary cyst is a large, fluid-filled growth on the bile duct system of the liver. It’s the most common type of liver mass seen in cats, but the incidence isn’t very high -- about 5.5 percent. Biliary cysts usually affect senior cats older than 10 years.

Cats with biliary cysts may have a decreased appetite and lose weight. If the mass is large enough -- some can be the size of a softball -- it may put pressure on the stomach and cause discomfort. The condition is usually diagnosed with an abdominal ultrasound exam.

The good news is that the cysts are benign and don’t spread elsewhere in the body. The bad news is that they often require surgical removal, the sooner the better. Fortunately, they don’t typically invade the liver, so the surgery tends to be uncomplicated.

One potential risk, though, is excessive bleeding, which sometimes occurs when tumors are removed from the liver. Another is if cats refuse to eat after surgery, especially if those cats are overweight. It might seem like a good way for the cat to lose some weight, but lack of appetite is downright dangerous for fat cats because it puts them at risk for a serious condition called hepatic lipidosis. These cats may need to have a feeding tube placed to make sure they take in enough nutrition until they recover.

Generally, the prognosis is good for cats with biliary cysts. Once the mass is removed, it usually doesn’t return quickly. Depending on location and whether a cat has complications, the cost of surgery and aftercare can approach $6,000, but a good pet health insurance policy will cover most of the expense.

This story was originally published October 21, 2016 at 7:13 PM with the headline "New approach to preventing infection in dogs may stem tide of resistance."