
In the decade or so that I’ve been covering tick-borne illnesses, I’ve heard a lot about co-infecting organisms, which are broadly defined as pathogens that can be transmitted to humans (or animals) along with Lyme bacteria when someone is bitten by a blacklegged tick. By far the most common ones I hear about are babesia, bartonella, and Borrelia miyamotoi although it remains unclear what percentage of Lyme disease patients are contracting these infections in Canada.
I’d like to shift focus for a moment to a tick-borne pathogen that tends to get little press and yet is likely to become a significant health problem in the coming years.
That pathogen is Anaplasma phagocytophilum and over the past decade Canadian researchers have been slowly ramping up their surveillance of it, with a few papers appearing in scientific journals each year. Since 2018, the rate at which these papers are being published has increased significantly and all signs point to that trend continuing into the foreseeable future.
Here’s why: Anaplasma phagocytophilum is a bacterium that’s carried by the same blacklegged ticks (Ixodes scapularis, Ixodes pacificus) that carry Lyme disease although it tends to be present at much lower rates. When anaplasma infects someone on its own, it causes human granulocytic anaplasmosis, the symptoms of which include fevers, headaches, chills, and muscle aches. But when someone contracts anaplasmosis along with Lyme disease, they tend to get much sicker than they would if they contracted each pathogen alone and they stay ill for much longer. So it’s important to know what percentage of blacklegged ticks are carrying anaplasma and whether those same ticks are also infected with Lyme bacteria.
In an effort to answer these questions, researchers went looking for anaplasma in companion animals, wildlife, ticks, and humans in 2018 and 2019. Here’s what they found:
In 2018, researchers reported the rates of anaplasma in Canadian dogs ranged from 0.19% to 1.8%, depending on region, with the highest percentages being identified in Manitoba, Saskatchewan, and Ontario. In Quebec, the prevalence of anaplasma in dogs appeared to be quite low, but researchers noted that a survey undertaken a decade earlier had detected the bacterium’s DNA in 15% of ticks collected from hunter-caught deer in the province, suggesting that the percentage of anaplasma in at least some regions of Quebec may be much higher than the 2018 study was able to establish. A separate paper published in 2018 found the number of human granulocytic anaplasmosis cases in Manitoba has steadily increased since 2013.
It’s in 2019 that things really start to get interesting. Earlier this year, public health researchers published the results of a nine year study (2009-2017) during which 65 blacklegged ticks were collected in Saskatchewan. Those ticks were all obtained through passive surveillance efforts since active field surveillance failed to turn up a single one despite widespread searches in classic tick environments. As a result, researchers are confident there are presently no breeding blacklegged tick populations in the province, concluding that all the ticks collected through passive surveillance likely came from adventitious ticks carried into the province by migrating birds. That’s the good news.
The bad news is that anaplasma was discovered in 8% of the blacklegged ticks tested and more than half of those were found to be co-infected with Borrelia burgdorferi. Those aren’t numbers you like to see, but it’s hard to say how problematic that finding is since the total number of blacklegged ticks collected in Saskatchewan over the nine years was so low that 8% may not be representative of what the true rates will be when breeding populations become established.
It’s worth noting there was no identified trend in the rates of anaplasma in Saskatchewan from one year to the next, so we can’t really say the percentages are rising. They’re actually rather random. What we can say is that anaplasma has been found in Saskatchewan dogs as far back as 2009 at a rate similar to what has been seen in Manitoba and higher than the rates identified in Ontario, Quebec, and the Atlantic provinces.
This year also saw the publication of a research paper that looked at seven years (2008-2015) of test results for anaplasma in Canadian dogs. In total, over 750,000 tests were conducted with 3,118 coming up positive. That represents a 100% increase over the seven year study period. That news is somewhat mitigated by the rate itself, which is a relatively low 0.4%. However, it varied between regions with significant increases being seen in Manitoba, Ontario, Quebec and Nova Scotia. One of the notable findings of this study was that 5% of all tick-borne infections in dogs were co-infections involving at least two pathogens. The combination of ehrlichia and anaplasma accounted for 2.2% of infections while anaplasma teamed up with Borrelia burgdorferi in 0.8% of infections. And that’s bad news for our canine friends since, like humans, dogs tend to become significantly ill when battling two tick-borne infections at once.
In 2019, researchers also published a paper looking at human granulocytic anaplasmosis in Ontario residents between 2011 and 2017. In total, 83 patients tested positive for anaplasma exposure. Researchers ultimately concluded that none of these cases met the criteria to be considered confirmed, but five were thought to be probable and 78 were classified as suspected. The highest infection rates were found in eastern and northwestern Ontario.
Another study published in 2019 took a look at the rates of anaplasma in wildlife and companion animals in Ontario. Most of the blacklegged ticks in this study came from raccoons and dogs, but skunks, grey squirrels, groundhogs, coyotes and opossums also yielded their fair share of ticks. Anaplasma was found in 2.3% of these ticks leading researchers to conclude that anaplasma is circulating in nature within the province.
So what does it all mean? It means that anaplasma is present throughout much of eastern Canada. And although it does not appear to be circulating in nature in Saskatchewan, researchers expect the blacklegged ticks that host the bacteria to start forming breeding populations there sometime in the near future.
Nowhere in Canada can the risk of contracting anaplasma be considered high. But there are signs that rates of infection in nature and companion animals is starting to rise and in Ontario alone 83 probable or suspected human cases have been identified, which is concerning.
It bears noting that it’s the belief of all these scientists that the rates of anaplasma will rise over the coming years in Canadian ticks, animals, and humans. It’s only a matter of time.