Canine Heartworm Cases in Washington State Quadrupled Since 2012
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The number of canine heartworm cases reported in Washington state last year was more than four times higher than the number of cases reported in 2012 according to the Companion Animal Parasite Council (CAPC).
And in King County, the number of heartworm cases reported in 2019 was almost ten time higher than the number reported in 2012.
Seattle DogSpot obtained the data from CAPC’s Parasite Prevalence Maps.
The maps show that the number of cases for various parasites Washington counties reported to CAPC for every year from 2012-2019. Here are some of the highlights:
- Washington counties reported 461 heartworm cases to CAPC in 2019 vs. 94 cases in 2012, an increase of 390%.
- King County reported 242 heartworm cases last year. That’s twice as many as 2017 and a 764% increase since 2012 when the county reported only 28 heartworm cases.
- Clark County had a 307% increase in the number of heartworm cases reported from 2017 (14) to 2019 (57), the highest percentage increase of any Washington county.
- Snohomish County only had 6 heartworm cases reported in 2012 compared to 35 in 2019, an increase of 483%.
A chart showing the changes in heartworm cases for all Washington counties from 2012-2019 is at the end of this post.
Heartworm Can Be Fatal
Mosquitos transmit the heartworm parasite by biting an infected dog and ingesting its blood which contains microscopic worms called microfilaria.
Once inside the mosquito, the worms change into larvae after about 2 weeks. The mosquito transmits the larvae when it bites an uninfected dog and leaves them on its skin.
The larvae enter the dog’s bloodstream through the bite and migrate through its circulatory system. About 6 months later they mature into adult worms.
These adults will eventually end up in a the dog’s heart, lungs and associated blood vessels where they can live 5-7 years.
A dog may not show any signs of heartworm in the early stages of the disease. Eventually, it will develop one or more of these symptoms:
Adult heartworms after they develop from larvae. Photo from American Heartworm Society.
- a mild persistent cough
- reluctance to exercise
- fatigue
- decreased appetite
- weight loss
Left untreated, heartworms can multiply to the point where they cause inflammation in a dog’s arteries and around its lungs.
The inflammation is more severe in dogs with higher numbers of heartworms.
As heartworm progresses, excess fluid in a dog’s abdomen can cause heart failure. It can also cause sudden blockages of blood flow within the heart leading to a life-threatening form of cardiovascular collapse called caval syndrome.
Heartworm can be fatal if it isn’t identified and treated in its early stages.
Why Have Heartworm Cases in Washington State Increased So Significantly?
When we got our first dog in 2002, our vet told us we didn’t need to give him heartworm prevention medication because so few cases were ever reported in Washington.
But last month she told me that due to the increase in heartworm cases in Washington she will most likely start recommending heartworm preventative treatments for all the dogs in her practice.
In 2017 Dr. Brian Joseph, the State Veterinarian at the Washington State Department of Agriculture confirmed that heartworm cases have risen in Washington over the last few years due to:
- climate change
- lack of prevention
- rescue groups that bring heartworm positive dogs in that state with inaccurate, fake or no certificates of veterinary inspection (health certificates)
And last week, Dr. Joseph told me that at a recent United States Animal Health Association meeting, people from the US Department of Agriculture said that “there may be as many as one million dogs brought into the United States every year from foreign countries, but as few as 10,000 may have appropriate health documentation.“
That means that approximately 99% of the dogs brought into the United States from other countries don’t have proper health documents.
This doesn’t mean all dogs brought to the United States from other countries have heartworms or other parasites. Still, you can’t ignore the fact that the increasing number of heartworm cases in Washington have occurred as more rescues import dogs from other countries.
Climate Change and Lack of Prevention
Mosquitos need a warm climate to reproduce. The warmer the weather, the faster they propagate.
Hot weather increases the rate at which mosquitos reproduce. Temperatures in Washington have been above historical norms since 2012, and 2015 was the hottest year on record. Image from the National Centers for Environmental Information.
In an interview with KUOW in 2014, Washington State University entomologist Sharon Collman said, “In hot weather, it can take a mosquito egg four to five days to mature to adulthood. In cool weather, it takes two to three weeks.”
Data from the National Oceanic Atmospheric Administration shows that annual temperatures in Washington from 2000-2019 have been well above the mean for 1901-2000.
Since the beginning of the 20th century, average annual temperatures in Washington “have risen approximately 1.5°F and temperatures over the past three decades have been warmer than any other historical period.”
Average annual temperatures in Washington have increase significantly over the last few decades. Image from American Heartworm Society.
Based on this information, it’s reasonable to assume that above normal average temperature in Washington for the last few decades created a more favorable environment for mosquitos to reproduce quickly.
Hot weather = More mosquitos = Greater Potential for Heartworm to Thrive
I think the explanation is straightforward regarding the lack of prevention.
For years, Washington veterinarians told their clients they didn’t need to use a preventative because heartworm was so rare here.
Veterinarians embedded this mantra into the minds of Washington dog owners for years; as a result, we checked heartworm off our list of potential threats to our dogs’ health and didn’t worry about taking steps to prevent it.
Dog Rescues Bring Heartworm Positive Dogs to Washington
In the last 10-15 years, dog rescues, municipal shelters, and animal transporters created a massive network to move dogs from states with overcrowded, high kill shelters to areas like the Pacific Northwest “where euthanasia rates are lower and pets are in greater demand.”
Rescuers built this infrastructure in 2005 “when Hurricane Katrina left more than 250,000 pets stranded.”
Although Mexico is a hotbed for heartworms, some rescues bring dogs from there to Washington without heartworm testing.
Their effort showed dog rescues “a new way to find placements for unwanted dogs.”
Western Washington is a popular destination for these dogs.
Our shelters often have space for them due to our high spay/neuter rates and a greater demand for adopting shelter dogs.
This transportation network saved the lives of tens of thousands of dogs. It also created the opportunity for people to start fake rescues that bring dogs to Washington from other areas and sell them for hundreds of dollars.
Many of these dogs come from states with high rates of heartworm infections like Texas. And overcrowded shelters there eagerly give dogs to rescues that will take them.
Others come from Mexico where these fake rescues have people who snatch dogs off the streets send them to Washington.
According to this 2016 study on the National Center for Biotechnology Information website, Mexican heartworm rate was 5.3%.
However, the heartworm rate was much higher in areas that border the United States. The Northeastern region, which borders Texas, had a rate of 8.9%, the highest in the country.
The Northwestern region had a rate of 6.1%, the third highest in the country. It borders Texas, New Mexico, Arizona, and California.
Unscrupulous Rescues Skirt Health Testing Rules
Washington requires that all dogs must be “tested negative for heartworm or are currently on a heartworm preventative” before they can come into the state (they must also have a current rabies vaccination).
The Washington Department of Agriculture cited Furever Homes Rescue earlier this year for bringing dogs in Washington without health certificates. The rescue also had a violation in 2015.
Since the primary objective of fake rescues is to make as much money as possible, they often import the dogs here without paying for heartworm testing.
Inevitably, some of these dogs have heartworm, and every one of the growing number of mosquitos in Washington that bites one of them can potentially infect other dogs here.
Furever Homes Rescue in Tumwater is one of the rescues that bring dogs from Mexico to Washington without the required health certificates.
In 2018 the Washington Department of Agriculture citied them for bringing dogs into Washington without health certificates. Another dog had a health certificate without the heartworm testing requirement.
When you adopt a dog brought to Washington from another state or county, ask the rescue to see its health certificate. If it doesn’t have one, then the dog you want to adopt could potentially have heartworms.
How to Protect Your Dog from Heartworm
While the number of heartworm cases in Washington increased significantly since 2012, the percentage of heartworm cases vs. the number of dogs tested is still much lower than other states.
In 2019, 0.6% of the dogs in Washington checked for heartworm tested positive (461 out of 76,816).
Compare that to the percentages of positive cases in the 5 states with the highest incidences of heartworm in 2019 according to the American Heartworm Society:
Mississippi 8.41%
Louisiana 6.53%
Arkansas 4.25%
Texas 3.18%
Tennessee 2.36%
However, just because Washington’s heartworm rate is much lower than these states doesn’t mean you shouldn’t have your dog tested for heartworm or put it on a preventative.
The upward trend in Washington shown on the Parasite Prevalence Maps indicates our heartworm rates will continue to increase.
That’s why Washington dog owners should do the following to protect their dogs from heartworm:
- Ask your vet to test your dog for heartworm annually.
- Ask your vet if your dog should be on a heartworm preventative.
- Find out if the dog you want to adopt from a rescue came from another state. If it did, ask to see the its health certificate to see if a vet tested it for heartworm. If they can’t provide it, don’t adopt from that organization.
For more information on heartworm, please visit the Companion Animal Parasite Council website or the American Heartworm Society’s website.
About the Numbers
CAPC notes that the data in the map “is statistically significant and it serves as a strong representation of the parasite activity for each area. However, it does not represent the total number of positive tests. Instead, we estimate it represents less than 30% of the activity in the geographic regions.”
The numbers are underreported because not all veterinarians send the results of their heartworm testing to CAPC. The blank spaces in the chart means CAPC had no information from that county.
These counties didn’t send any test results to CAPC from 2012-2019 : Douglas, Columbia, Pacific, Skamania, Wahkiakum, Okanogan, Ferry, Pend Oreille, Lincoln, and Garfield.
Some counties like Whitman didn’t send test information for one or more years, but did send it for other years. A zero means a county did heartworm testing but had no positive results.
These numbers don’t include every heartworm test for every dog in every county. But they affirm the that the number of heartworm cases reported in Washington has spiked dramatically since 2012.
* = There is no formula for calculating the percent change if the value for 2012 is 0.
Heartworm cases in Washington state counties ranked by percentage increase from 2012-2019
| County |
2012 |
2013 |
2014 |
2015 |
2016 |
2017 |
2018 |
2019 |
% increase from 2017 |
% increase from 2012 |
| King |
28 |
30 |
36 |
61 |
71 |
121 |
119 |
242 |
100.0% |
764.3% |
| Spokane |
2 |
6 |
3 |
4 |
4 |
11 |
11 |
16 |
45.5% |
700.0% |
| Benton |
1 |
0 |
3 |
1 |
3 |
6 |
4 |
7 |
16.7% |
600.0% |
| Snohomish |
6 |
0 |
5 |
13 |
8 |
32 |
24 |
35 |
9.4% |
483.3% |
| Skagit |
1 |
3 |
6 |
2 |
6 |
8 |
11 |
5 |
-37.5% |
400.0% |
| Clark |
12 |
11 |
19 |
17 |
8 |
14 |
38 |
57 |
307.1% |
375.0% |
| Whatcom |
3 |
5 |
1 |
7 |
5 |
4 |
7 |
14 |
250.0% |
366.7% |
| Kitsap |
4 |
13 |
4 |
7 |
17 |
13 |
23 |
16 |
23.1% |
300.0% |
| Thurston |
6 |
6 |
7 |
12 |
11 |
10 |
24 |
18 |
80.0% |
200.0% |
| San Juan |
1 |
0 |
0 |
0 |
0 |
0 |
0 |
2 |
100.0% |
|
| Walla Walla |
3 |
0 |
0 |
0 |
0 |
0 |
0 |
4 |
33.3% |
|
| Pierce |
16 |
8 |
11 |
14 |
13 |
26 |
27 |
21 |
-19.2% |
31.3% |
| Cowlitz |
2 |
0 |
3 |
0 |
1 |
3 |
6 |
2 |
-33.3% |
0.0% |
| Lewis |
3 |
2 |
0 |
0 |
0 |
1 |
1 |
1 |
0.0% |
-66.7% |
| Stevens |
3 |
0 |
0 |
0 |
1 |
2 |
0 |
0 |
-100.0% |
-100.0% |
| Grant |
1 |
1 |
0 |
0 |
0 |
1 |
0 |
0 |
-100.0% |
-100.0% |
| Mason |
2 |
0 |
1 |
0 |
1 |
0 |
0 |
0 |
-100.0% |
|
| Clickitat |
0 |
0 |
0 |
1 |
0 |
2 |
2 |
0 |
-100.0% |
|
| Kittitas |
0 |
0 |
0 |
1 |
0 |
1 |
0 |
0 |
-100.0% |
|
| Asotin |
0 |
0 |
0 |
0 |
1 |
2 |
0 |
-100.0% |
||
| Chelan |
0 |
0 |
2 |
0 |
2 |
6 |
2 |
6 |
0.0% |
|
| Clallam |
1 |
1 |
0 |
1 |
0 |
1 |
0.0% |
|||
| Island |
0 |
0 |
2 |
1 |
0 |
3 |
1 |
9 |
200.0% |
|
| Whitman |
0 |
0 |
0 |
0 |
0 |
2 |
||||
| Yakima |
0 |
0 |
1 |
0 |
2 |
0 |
2 |
1 |
||
| Jefferson |
0 |
0 |
0 |
1 |
0 |
0 |
1 |
|||
| Franklin |
0 |
0 |
0 |
0 |
0 |
0 |
2 |
1 |
||
| Adams |
0 |
2 |
1 |
1 |
1 |
0 |
0 |
|||
| Douglas |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
||
| Pend Oreille |
0 |
0 |
0 |
|||||||
| Gray’s Harbor |
1 |
2 |
0 |
0 |
0 |
1 |
0 |
|||
| Columbia |
0 |
0 |
||||||||
| Pacific |
0 |
|||||||||
| Wahkiekum | ||||||||||
| Skamania |
0 |
|||||||||
| Okanogan | ||||||||||
| Ferry | ||||||||||
| Lincoln | ||||||||||
| Garfield | ||||||||||
| Total |
94 |
88 |
108 |
143 |
155 |
266 |
307 |
461 |
73.3% |
390.4% |
The post Canine Heartworm Cases in Washington State Quadrupled Since 2012 appeared first on Seattle DogSpot.
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