It certainly was a formidable scene – one of those that’s too icky to look at but yet too fascinatingly awful NOT to look at.

The bottle I stared into contained a dog heart in which the right ventricle had been shot through with hundreds of slender white threads – finer than angel hair pasta and some up to 12 inches long – that wound their way in and around the muscle.

Heartworms.

The culprit who spreads this disease is that vicious little bloodsucker, the mosquito. When one of these nasty buggers looking for a meal lands on a dog (the most common victim, although cats are by no means immune) who already harbors the disease, it picks up numerous microfilariae, the heartworm’s microscopic larval stage. The mosquito carries these larvae in its system for several days, after which the microfilariae move into the mosquito’s salivary glands. When the mosquito then dips its nose into a dog or cat for its next meal, it transfers these larvae to the new animal, beginning a new infection.

Once in the host’s bloodstream, the larvae spend the next six to seven months undergoing changes. Between 70 and 90 days after entering the host, they cease their free floating and head straight to the right side of the host animal’s heart, where, for about three more months, they grow and wait for just the right moment to start reproducing. While the adults stay put, their newly created microfilariae move into the bloodstream to be picked up by the next mosquito that comes along.

Heartworms sign a roughly seven-year rental agreement if their host is a dog (two to three years if they’re in a cat) The worms continue to grow in size and length during this time, taking up more and more room in the heart muscle and valves. Cats and small dogs need only a few of these worms before they start showing physical strain; larger dogs are able to tolerate more, but in either case, the presence of worms creates great pressure and forces the heart to work harder. Much of the initial damage in the animal is in the arteries of the lungs; owners may notice that their pet begins coughing. Exercise becomes more difficult, and the animal may experience shortness of breath, nosebleeds, or a form of pneumonia.

Continuing worm growth further increases pressure around the heart, causing hypertension. Fluid continues to accumulate in the lungs. The animal’s immune system kicks into higher gear, forming proteins that settle in the joints, kidneys, blood vessels and eyes. The resulting inflammation and tissue damage cause a great deal of pain.

When sufficient heartworm mass all but completely blocks blood flow, fainting and collapse occur, and death usually follows in a day or two.

The disease is difficult to cure. Untreated, it’s a terrible one for the animal to suffer through.

And the sad part is, for most pets it’s all preventable with some basic care early on.

Dog owners need only request a simple blood test to determine whether their pet is infected. If not, most veterinarians recommend that dogs be kept on a heartworm preventative year-round. The treatment, given once a month, is apparently quite the tasty treat: my dogs take theirs readily and look for more. Never give your pet treatment without prior testing.

Tests on cats can be a bit less conclusive, because for some reason felines commonly show single-sex infestations (usually male worms), and fewer worms are present. The need for regular preventatives for cats is still being debated in the veterinary community, although such medicines are available. If your cats run outdoors, you might want to consider these oral preventatives to protect them.

Warm weather brings other problems as well. Fleas and ticks can be the bane of your animals’ existence. Besides causing nearly unbearable itching and discomfort to your pet, some animals are allergic to flea bites and break out with terrible skin problems. In addition, these tiny little highjumpers are happy to ride their four-legged taxicabs inside, where they set up house in your furniture, rugs and bedding. Here they burrow in, mate, lay eggs and start a whole new family tree. They can be difficult to eliminate, and massive infestations on animals actually can cause anemia.

Ticks, too, not only make themselves at home on your pets but will gladly venture from pet fur to human skin. These little guys clamp on literally for dear life, not only looking disgusting but imparting such illnesses as Lyme disease and ehrlichiosis. One dog I know contracted the latter disease from a tick bite and ended up with his underside sutured from stem to stern where the vet went in to remove the resulting softball-sized blood clot. Fortunately, his problem was caught and cured in time.

Yet these problems, too, can be avoided with an ounce of prevention. Your vet can recommend a good flea-and-tick topical. Start early in the season-these parasites often come out sooner than we expect.

A word of caution, however: one brand of flea and tick drops commonly found in discount stores was recently determined to be related to a significant number of severe illnesses, and sometimes death, primarily in cats. Resulting legal action produced restrictions on this product. Always check with your veterinarian before you choose a preventative.

Have fun with your pets this summer, but please be wise about keeping them healthy and safe.

And if you need a pet to share the summer with, come out for a visit to the Lawrence Humane Society. Our hours are on our wonderful new Web site at www.lawrencehumane.org.