Heartworm

Happy Valentine's day! Here's a lovely heart mask, unfortunately infested with the nematodes known as heartworms. Heartworms mostly infect dogs and cats, though they've also been found in animals like foxes and sea lions. They aren't considered a health risk to humans, though. We catch them once in a while, but our bodies are good at fighting them off, and they're usually destroyed before they can cause a serious infection.

Creatures like heartworms that live inside of another organism, or 'host', and cause problems for it are called parasites. Heartworms produce thousands of tiny babies (microfilariae) every day, which swim happily around in the host animal's bloodstream—It'd almost be cute if it weren't so gross. The way that they infect other animals is pretty clever: if a mosquito bites the host, it sucks up some blood containing the baby heartworms. When the mosquito bites another animal, the babies are injected into its bloodstream, and over a few months they move to the heart and lungs, burrow in, and start to grow into adults. A full-size heartworm can be more than 30 centimetres long!

Having all those big worms in its heart can be really bad for an animal, since a healthy heart needs to function properly to pump blood around the body. If the disease isn't treated, it can eventually lead to heart failure and death. In warm climates with lots of mosquitos vets usually do blood tests on animals to check for the nematodes from time to time. They can usually catch the disease early and use heartworm pills to kill off the worms, much to the relief of pet owners. Though your pet might get heartworms if you take it on holiday to Spain, Italy, or other places in Southern Europe, it's still not a common disease in the UK.