Parasite Risks Are Expanding. Here’s Why Year-Round Protection Should, Too

A dog stands outside with a leash in its mouth.

Parasites are expanding beyond their typical seasons and geographies. Host populations are growing, and their ranges are expanding. These changes, when combined with rising temperatures and other environmental factors, are opening new paths for parasitic diseases to reach new areas, making year-round protection more important than ever. 


Parasites and Parasite-transmitted Diseases Are Spreading 

Across the US, parasites and the diseases they transmit are arriving in areas where they haven’t been before. From deer to coyotes to birds, the populations of hosts that carry disease-causing parasites have expanded.  Seasonal boundaries are blurring. New threats are emerging. 

These changes, when combined with rising temperatures and other environmental factors, are opening routes for parasitic diseases to invade new areas. This is why year-round parasite protection for pets is now more important than ever. 

“Parasites are a risk for all pets, even those that don’t spend much time outside. Pets can be infected or infested even if they play in our gardens and our homes. It’s critical to make sure people are aware of new risks that may not have been there historically where they live,” said Jaime Kline, DVM, Senior Professional Services Veterinarian at Boehringer Ingelheim Animal Health. “The good news is that this awareness is increasing. Pet owners have been more and more confident to embrace responsible parasitic protection.”  

Looking Inside: Heartworms in Dogs and Cats 
Mosquitoes aren’t just pesky, they can be vectors of several pathogens, including those that cause heartworm disease in dogs and cats. With their expanded ranges, heartworm disease is more prevalent in dogs than it was 20 years ago. In both dogs and cats, heartworm disease is a growing concern beyond just the south.  

“Veterinarians in states with historically lower prevalence should be vigilant about the increasing risk of heartworm infection and are encouraged to have a discussion with their clients about the increased risks. More than a million dogs in the US have heartworms, but heartworm disease is preventable,” said Kline. “Year-round use of heartworm disease preventive products remains the best means of providing protection against this devastating disease.  Annual testing is also recommended in our canine patients to monitor compliance and preventive efficacy.”  

“Year-round, broad-spectrum parasite prevention is crucial for several reasons,” says Michael Dryden, DVM, Professor Emeritus of Veterinary Parasitology at Kansas State University. “First, it eliminates the guesswork involved in determining when to start and stop seasonal treatments. Second, it addresses the overlapping ecological patterns of various parasites.” 

Dr. Dryden has presented more than 1,000 invited seminars on clinical veterinary parasitology at local, regional, national, and international meetings. In recent meetings, a question he’s been hearing lately is around the optimal oral dose of moxidectin needed to be 100 percent effective in preventing heartworm disease in dogs.  

“The scientific fact is that three micrograms per kilogram with one oral dose is 100 percent effective against all susceptible isolates,” says Dryden. “There are a small group of resistant isolates in a narrow part of the US, but moxidectin is the one molecule that has been more successful against these isolates than other molecules have been. What's been clearly shown in laboratory studies is increasing the oral moxidectin dose a little and giving multiple monthly doses maximizes efficacy against those rare resistant isolates. Year-round protection gives every pet the best protection and that is the recommendation for all pets in the US.” 

Tick Trouble 

Ticks are also spreading into new geographies, bringing tick-borne diseases with them. The lone star tick is one of the more common ticks found to parasitize dogs, cats and people in the US. You may have heard of the so-called red-meat allergy in the news. The lone star tick is the culprit. It also can transmit Cytauxzoon felis, causing an often-deadly disease, to cats.  

Lyme disease is transmitted by the black-legged tick, sometimes called the deer tick. The range of this tick is also expanding, and the risks of Lyme transmission, as well as other diseases transmitted by this tick, are increasing in places where it was not historically a significant problem.   

Although ectoparasites like ticks don’t move around much on their own, they can travel long distances with vertebrate hosts. For lone star ticks and black-legged ticks, their population explosion and range expansion are directly linked to the white-tailed deer population. Birds are another common host that can act to transport these parasites from one area to another. The shifting scope of animals and organisms that can act as parasite hosts means that some of these threats might be present now around every household — even in urban areas.  
In addition to expanding ranges, new invasive tick species have become established in the US. For example, Asian Longhorned ticks were reported for the first time in the United States in 2017 and have been found on pets, livestock, wildlife, and people in the US. There are even reports of livestock having heavy infestations with high tick burdens resulting in weight loss, anemia, and even death due to exsanguination (severe blood loss).  
Veterinarians are the best counselor for responsible parasite control for pets 

Parasites are everywhere. They are as old as their hosts, living together in a coevolution of millions of years. Yet the risks caused by changes in the environment necessitate changes in behavior. Embracing responsible parasite protection is imperative to help keep animals healthy. 

The good news is that the damage that parasites cause can be prevented, ensuring animal health and welfare through the prevention of regular infestations/infections and the treatment of clinical parasitosis. Pet owners should always talk to their veterinarian to discuss the best individual options to keep their pets safe.  

“By working together, pet owners and the veterinary community can keep animals protected from parasites no matter where they live,” said Dryden.