It’s everywhere.

The north woods of Maine. The mountains of Utah. The ‘burbs of Chicago. All of those places, previously thought out-of-reach and safe, are in fact suffering the ravages of the insidious march. Or, more precisely, the pets living there are.

Heartworm disease, the nasty, strength-sapping, potentially deadly assault on animals limited mostly to the South up until the last decade, has surged its way throughout the nation, according to recently released results from the American Heartworm Society (AHS). The every-three-years survey, which tracks heartworm incidence from data supplied by more than 5,000 veterinary clinics, has documented cases in every state, says Wallace Graham, a veterinarian in Corpus Christi, Texas, and president of the AHS.

“It’s troubling,” this relentless spread, says Graham, “especially when prevention is so simple.”

That simple thing to which he refers is heartworm prevention medication, which generally runs about $50 to $100 a year, depending on the brand and weight of the dog.

The case for taking the prevention route, regardless of where you live, is pretty simple: Any dog (or cat, for that matter, it’s now known) that isn’t on a preventive protocol can be infected when bitten by a mosquito carrying the parasite — which the mosquito picked up when it bit another infected animal. The parasite takes up residence in the animal’s pulmonary arteries and heart, ultimately leading to awful trouble breathing, lung disease, issues with other organs and heart failure. Treatment to rid dogs of heartworm (there isn’t one for cats) is harsh: an arsenic-based drug kills the parasite, costs $600 to $1,200, and the dog must be confined in a crate for a month or more while the heartworms die off and dissolve (because exercise or excitement can prompt embolism).

Another argument for the preventive protocol: An infected animal is a virtual Petri dish for spreading the disease to others near and far.

There was a time when vets in areas where mosquitoes disappear for six or more months a year — places such as New England, the mountains of the West, and the Northern tier states, for example — recommended six-month, summer-only schedules of preventive meds. Some of them still do (and some have shifted to nine-month protocols).

But AHS says that less than year-round prevention everywhere is bad because:

•Many areas are experiencing warm weather earlier in spring and later in fall than in years past, meaning mosquitoes can emerge unexpectedly.

There are warm micro-climates that support mosquitoes even in cold regions.

Owners increasingly take their pets on vacation, often to areas where mosquitoes are active.

Companies that produce heartworm prevention will pay for a good chunk of the treatment in the rare case that a dog develops heartworm disease if vet records show drug purchases indicate the animal was on the preventive year-round.

So even though many owners and some vets still don’t follow the year-round recommendation, “thinking that the cold or dry climate they live in makes such vigilance unnecessary,” says Graham, “we can cite case after case of heartworm-positive pets living in areas assumed to be low-risk for heartworm.”

For both dogs and cats, heartworm disease may not be obvious early on. But eventually, dogs will develop a persistent cough, fatigue and weight loss, the AHS says, as the worms grow to the point that they literally strangle dogs’ ability to breathe and pump blood and survive.

Cats, when invaded by the parasite, may vomit, gag, have difficult or rapid breathing, and show lethargy and weight loss. The respiratory symptoms are often mistaken for feline asthma or allergic bronchitis, when they’re actually the result of a syndrome defined quite recently as heartworm-associated respiratory disease.

“This is a much different disease in cats,” says Graham.

Most cats spontaneously cure themselves over a period of months (though sudden death occurs in a few), but significant lung damage often occurs, and supportive therapy as they heal can be necessary, including prednisone, IV fluids, oxygen therapy and cardiovascular drugs.

The heartworm society — which since 1974 has been tracking the disease, advancing the study and treatment of it, and making information available to vets and consumers — is funded in part by the many companies that make heartworm-prevention medications. This could be regarded, of course, as a moderator as folks process how risky one’s particular situation is and what steps should be taken, especially when living outside the South (where dogs die of the disease in huge numbers, and 70% of some shelters’ animals are heartworm positive).

Graham knows the funding can raise skepticism. But, he says, it’s from many companies, not one; they exert no pressure regarding how the society goes about educating the public and the veterinarian community; and AHS’ recommendations are based on “peer-reviewed scientifically documented research.”

AHS’ website, www.heartwormsociety.org, has a wealth of information.