Why Ticks Are Looming Large for Dogs and Cats

The spread of parasites won’t be slowing this year.


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Originally published in the March 2015 issue of Veterinary Practice News

Ticks have been steadily spreading across the United States in recent years, their incidence growing rapidly right along with the white-tail deer population.

It’s still a bit early to say for sure, but it doesn’t look like that spread will be slowing this year.

A parasite forecast published each spring by the Companion Animal Parasite Council gives veterinarians and pet owners a good idea of what they can expect in the way of tick, intestinal parasite and heartworm prevalence.

“We expect to see—unless intervention is increased—continued spread of the tick-transmitted diseases and some continued small climb in heartworms,” said Dwight Bowman, MS, Ph.D., a Cornell University veterinary parasitology professor and CAPC board member.

Tick-transmitted agents that test (Lyme, Anaplasma, Ehrlichia) are increasing in the percentage of animals positive within an area—and the current ranges are expanding too, he said.

It’s always hard to tell what a year will hold in terms of parasites. Extreme cold and dry weather have a significant negative effect on flea and tick populations, and while much of the northern half of the U.S. has experienced cold and snowy weather, it has not been prolonged.

“It does not appear that ticks should be greatly affected by the weather to date,” said Michael W. Dryden, DVM, Ph.D., Dipl. ACVM, a professor of diagnostic medicine and pathobiology at Kansas State University widely known as Dr. Flea. He spoke to Veterinary Practice News in February.

“So my best guess right now is we are going to have a bad tick season. Weather in February and March will play a major role yet and could alter this forecast.”

What kind of weather we’ll be having is a secondary factor when it comes to parasite predictions in the eyes of Stephen Jones, DVM, president of the American Heartworm Society.

“Making predictions about heartworm disease is challenging, because by far the most significant contributing factor is human behavior: pet-owner compliance in administering heartworm preventives,” Dr. Jones said.

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The group has been conducting surveys to monitor the incidence of heartworm disease in the U.S. since 2001. The most recent survey was in 2014 and was based on data from 4,500 veterinary practices and shelters during the 2013 calendar year.

Similar to previous years, the latest survey shows that heartworm disease was diagnosed in all 50 states and that heartworm rates held steady.

The steady rates seem to support Jones’ assertion about weather as a secondary factor in heartworm incidence.

“Because mosquitoes spread heartworm disease, weather patterns that affect mosquito proliferation certainly play a role,” Jones said. “However, veterinarians responding to our latest survey were clear in stating that compliance trends are much more significant than weather.”


Veterinarians who reported increased incidence in their geographic areas credited the rise to poor compliance (61 percent), while more than seven in 10 who saw incidence drop directly attributed the improvement to a rise in preventive use.

Additional factors that indicate that heartworm cases could rise in 2015, according to the group, include:

Heartworm disease is now endemic in areas of the country that previously were less well known for heartworm risk. In the latest AHS survey, these areas included the upper Midwest—especially the states of Michigan, Illinois, Indiana and Ohio—and the western states of Arizona and California.

The number of mosquito species that transmit heartworm disease in the U.S. may be increasing. More than 70 species worldwide transmit heartworm, and more than 20 of these species have been identified in the U.S. The influx of new species to the U.S. is an ongoing threat.

Recently Los Angeles Vector Control announced that a mosquito species from Australia has been found in Southern California. The species is the Aedes notoscriptus, also known as the “Aussie Mozzie.” While it is the leading heartworm vector in Australia, it was previously undocumented in the U.S.
Bowman, too, sees heartworm incidence trending upwards in some areas, but he said the news isn’t all bad.

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“Florida remains a bright spot, where seemingly heartworm prevention is embraced as the prevalence is staying near 1.3 percent—about 60 percent of dogs before the launch of the monthlies were positive for heartworms back in the late 1980s,” he said. “It seems that it might be increasing in the panhandle, but it is going down even more in southern Florida.”

Southern Texas also seems to be doing a good job at heartworm prevention, as the area has lowered the prevalence infection, Bowman said. “Unfortunately, the Midwest and Northeastern U.S. seem to have let their guard down, and more heartworm prevention is needed.”

As for intestinal parasites, Bowman said the trend for Toxocara canis (roundworm) has been going down slightly, Ancylostoma caninum (hookworm) has stayed roughly the same and Trichuris vulpis (whipworm) has bounced around.


Bowman encouraged veterinarians to use local data to motivate their clients to take preventive measures.

“CAPC has provided tools that readily show local data, and we have recently completed a consumer survey that shows that people find an awareness of local disease prevalence an incentive to visit the veterinarian,” he said. “Thus, veterinary practices should maximize their use of the data we present that is shown at the county level.”

The survey, sponsored by Bayer HealthCare Animal Health, is titled “The Importance of Local, Timely Parasite Information.”

It found that pet owners want to know about parasite risks. The survey shows nine of 10 pet owners want to be notified if there’s a high incidence of parasites in their county, and two-thirds of survey respondents want to be notified immediately.

Eighty percent preferred to be notified of this incidence by email, while 55 percent prefer a phone call and nearly 40 percent want a postcard. Social media (16 percent) and newsletter (13 percent) were the least preferred mediums.

According to the survey, more than one-half of pet owners have never discussed the potential impact of parasites with their veterinarian, and only 9 percent have discussed parasites in detail.

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Dr. Dryden advised veterinarians to start tick control early and often.

“It seems there are always new tick-vectored pathogens being discovered,” Dryden said. “Right now is not too early to start. We now have a good array of effective flea and tick products. The key is to get clients to use them year round and lifelong.”

Step 1 in that process, Dryden said, is educating clients about the consequences of flea and tick infestations on their pets.

To make this message more effective, he suggests appealing to clients’ feelings that their dogs and cats are not just pets, but members of the family.

“Not only do fleas and ticks suck blood, but they can transmit or cause significant disease,” is Dryden’s message for clients. “Protection is acquired through diligent use of effective veterinary prescribed products.”

Beyond that, he advised making parasite prevention part of an overall preventive medicine program.

“Why should vaccinations, other than rabies, take precedence over parasite control?” he said. “Both are equally important. Now that we have effective, easy-to-administer and safe parasiticides, we have to think about them as preventives just like vaccines.”

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