Thursday, May 26, 2016

There Are Worms In My Heart

Ok, not technically right in the heart itself, but more on that later. And not technically my heart, at least probably not, but more on that later too.

It is "Heartworm Season" in Manitoba. Yes it is. If you work in a veterinary clinic it is unmissable, unmistakable, unforgettable. It's not that our wards are packed full of dogs sick with heartworm disease, rather it's that the testing for and prevention of has to occur in a fairly narrow calendar window. Compounding this, for most people it's convenient to get all the other annual stuff done at the same time since they've dragged Fido in anyway (incidentally, no actual dogs are named Fido, or Rover, or Rex, or Spot; some cats are though). Consequently most of us see as many patients in a week in the spring as during a month in the winter.

I don't want to waste time spewing Basic Heartworm Facts. You can get those from, gulp, the internet (try or, better still, from your friendly neighbourhood veterinarian. Some of you even are "your friendly neighbourhood veterinarian", in which case said spewing would be even more time wasting. Instead I want to touch on a few of the more unusual Cool Heartworm Facts (ok, some of you will consider these Gross Heartworm Facts, but I think they're cool).

Cool Heartworm Fact #1
Heartworm has probably been around forever (or a very long time that may as well be forever) with possible reports in the 1500s. It was first positively identified as such in 1847 in South America and then 1856 in the southeast USA. It has gradually been spreading north and west since, arriving in Manitoba in the 1980s.

Cool Heartworm Fact #2
However, despite that spread, large areas such as Saskatchewan, the Arctic and the West Coast do not have it. Not necessarily because of a lack of mosquitoes, but because of a lack of positive dogs already there. Mosquitoes are just flying syringes moving heartworm from one dog to another. This is why the mosquito paradise of northern Manitoba is heartworm free.

Cool Heartworm Fact #3
Heartworms can be huge, up to 35 cm / 14 inches. And they can be numerous, with infestations of over 100 worms reported.

Cool Heartworm Fact #4
The above reported size and numbers are very rare, so most of the time "heartworm" is a misnomer. Most of the time the worms are hanging out in the pulmonary arteries leading away from the heart. Only if there are more than about 25 do they actually back up into the heart. But pulmonaryarteryworm is so much more unwieldly. Unless you are German like me, in which case you prefer more accurate long unwieldly words.

Cool Heartworm Fact #5
Wildlife can get heartworm. Logically foxes, coyotes and wolves are most at risk, but it has also been reported in bears, raccoons, leopards, sea lions and, oddly enough, beavers. Cats and ferrets are at some potential risk as well depending on where you live, but that is a big subject best addressed separately.

Cool Heartworm Fact #6
Perhaps the coolest fact. Humans can also get heartworm. Heartworm positive mosquitoes bite us all the time and release microfilaria (baby heartworms) into our bloodstream all the time, but fortunately we are not good hosts so 99.9%  (and probably a few more 9s after that) of the time they die. However, there have been at least 80 cases reported in humans in the US, mostly in the lungs but occasionally - shield your eyes if you are squeamish - the eyes and the testicles (!). These have mostly been mild infections. The main problem is that on lung x-rays a heartworm lesion looks very much like a tumour, prompting further invasive tests. Radiologist call it a "coin lesion". So if you overhear the interns whispering about this while they shoot sideways glances at you, ask about heartworm...

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