Todayโs path rounds are on ๐ก๐๐๐ซ๐ญ๐ฐ๐จ๐ซ๐ฆ!
๐๐ก๐๐ญ ๐ข๐ฌ ๐ข๐ญ?
๐๐๐๐ซ๐ญ๐ฐ๐จ๐ซ๐ฆ is a parasitic disease caused by a roundworm called ๐๐ข๐ซ๐จ๐๐ข๐ฅ๐๐ซ๐ข๐ฌ ๐ข๐ฆ๐ฆ๐ข๐ญ๐ข๐ฌ. These worms like to live in the heart (hence the name of the disease) and in the ๐ฉ๐ฎ๐ฅ๐ฆ๐จ๐ง๐๐ซ๐ฒ ๐๐ซ๐ญ๐๐ซ๐ฒ (major vessel going from the heart to the lungs), and can get up to 30cm long!
๐๐ก๐จ ๐ ๐๐ญ๐ฌ ๐ข๐ญ?
We typically think of this disease in dogs, however technically many different mammals can get infected. Most importantly, cats and ferrets can get infected, which can be fatal in these species.
๐๐ก๐๐ญ ๐๐๐ฎ๐ฌ๐๐ฌ ๐ข๐ญ?
Heartworms are a round worm that can be found in tropical and subtropical regions primarily, although they are starting to be found more commonly in temperate areas of North America. Dogs are considered the ๐ซ๐๐ฌ๐๐ซ๐ฏ๐จ๐ข๐ซ of this disease, meaning that they are the source of essentially every infection!
It is the adult stage of these worms that actually lives in the heart and pulmonary artery, where they produce ๐ฆ๐ข๐๐ซ๐จ๐๐ข๐ฅ๐๐ซ๐ข๐๐ (larvae) that are released into the bloodstream. A mosquito feeding on the animal will pick up these microfilariae and transmit them to the next animal they feed on, spreading the infection.
๐๐ก๐ฒ ๐ข๐ฌ ๐ญ๐ก๐ข๐ฌ ๐ ๐ฉ๐ซ๐จ๐๐ฅ๐๐ฆ?
This may come as a surprise, but your heart isnโt really meant to have worms living in it! The valves that the worms snake through donโt close properly, causing the heartโs chambers to become leaky, and the mass of worms blocks normal blood flow through the pulmonary artery, causing ๐ก๐ฒ๐ฉ๐๐ซ๐ญ๐๐ง๐ฌ๐ข๐จ๐ง (high blood pressure) in that vessel. Typically these severely affected dogs will develop signs of cardiac dysfunction, and this dysfunction can progress to congestive heart failure.
These worms can also form ๐ญ๐ก๐ซ๐จ๐ฆ๐๐จ๐๐ฆ๐๐จ๐ฅ๐ข, where their attachment to the heart wall fails and they end up in the bloodstream. Once they are in the vessels, they will be pushed along until they reach a vessel they are too large to pass through, causing a blockage. Tissues downstream of that vessel will no longer receive nutrients and oxygen, causing ๐ง๐๐๐ซ๐จ๐ฌ๐ข๐ฌ (cell death). Not good!
๐๐ก๐ฒ ๐ข๐ฌ ๐ญ๐ก๐ข๐ฌ ๐๐ข๐ฌ๐๐๐ฌ๐ ๐ฌ๐จ ๐๐จ๐ง๐๐๐ซ๐ง๐ข๐ง๐ ๐ข๐ง ๐๐๐ญ๐ฌ ๐๐ง๐ ๐๐๐ซ๐ซ๐๐ญ๐ฌ?
Because these worms are quite large, and these critters (and their hearts!) are quite small, even small numbers of worms can cause heart failure.
Additionally, the consequences of a worm thromboembolus are even more severe, because these worms will block โlargerโ, more important vessels in these species than they normally would in a dog. For example, in cats, even one adult heartworm forming an embolus can block off major vessels in the lungs, causing severe respiratory stress and potentially even death.
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐๐ข๐๐ ๐ง๐จ๐ฌ๐๐?
This disease can be diagnosed in a couple of ways, such as detecting ๐๐ง๐ญ๐ข๐ ๐๐ง (parts of the worm) or antibodies against the worm in the blood. But probably the most interesting way is doing a ๐๐ฅ๐จ๐จ๐ ๐ฌ๐ฆ๐๐๐ซ, where a drop of blood is looked at under a microscope. On this smear, you can actually see the little microfilariae swimming around in the blood! Wild.
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐ญ๐ซ๐๐๐ญ๐๐?
This disease is treated using ๐๐๐ฎ๐ฅ๐ญ๐ข๐๐ข๐๐๐ฌ (adult-killing drugs) that specifically target the worms hanging out in the heart. This treatment can be risky however, because dying adults can form thromboemboli as mentioned previously. In very severe infections, surgical removal of the worms is ideal to hopefully reduce this potential complication of treatment.
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐ฉ๐ซ๐๐ฏ๐๐ง๐ญ๐๐?
Prevention is key for this condition! Giving routing doses of antiparasitic medications, recommended by your veterinarian, can kill the adult and microfilarial stages to prevent them from developing into adults. If you live in an area where heartworm is present, it is absolutely crucial to have your dog (and cat!) on a preventative plan to keep these nasty worms at bay.
๐๐ก๐จ๐ญ๐จ๐ฌ
1) An example of a microfilaria in a blood smear! The purple dots nearby are blood cells, to give you a sense of how big these larvae are!
2-6) Adult heartworms in their favourite location. Anybody want some spaghetti? 
๐๐จ๐ฎ๐ซ๐๐๐ฌ
Maxie, G. Jubb, Kennedy and Palmerโs Pathology of Domestic Animals, Volume 3. Sixth Edition.
Atkins, C. Heartworm disease in dogs, cats and ferrets. Merck Vet Manual 2014.
Photos 1-7 ยฉ Noahโs Arkive contributors Leathers, Niyo, Cho, Jakowski, Crowell, Rech, Kesdangsakonwut licensed under CC BY-SA 4.0.
