Matters of the heart(worm)

The other night, I received a call in the wee hours of the morning from a distraught family who asked me to perform a necropsy examination (the animal analog of an autopsy) on a young cat that had died suddenly before its owners could get her to the emergency room.As a veterinary pathologist, part of my job is to perform these examinations in order to answer questions regarding sudden death and to give owners closure, as well as peace of mind, particularly in cases where there is concern for other animals in the household. Often, the patients I see are elderly or very young. This was a 4-year-old cat with no previous health complaints. I was uncertain as to what I would end up finding.My examination yielded only one finding: a single, adult female heartworm in the heart of the cat.Heartworm disease in the dog is bad, but in the cat it can be devastating. The death of a single adult worm can result in a severe anaphylactic immune reaction in a critical area of the body, and this was all that it took to prematurely end the life of this young cat. Finding this disease was surprising, not because her case didnít fit the profile of the disease ñ- it did. Rather, because I, like many of my Colorado veterinary colleagues, had slipped into the quiet assumption that while Colorado technically ìhadî heartworm disease ó it wasnít something that I would necessarily be seeing, particularly in a cat.My wife and I are Colorado transplants from North Carolina, where we both received our veterinary training. The bug-infested North Carolina summers (and spring and fall) mean that every veterinarian there is highly attuned to mosquito-transmitted diseases, most notably heartworm disease, in our small animal companions. Even over the winter season, itís considered best practice for us to recommend our clients continue to use heartworm prevention. This isnít to pad the pockets of our clinics or the drug makers, but our winters werenít reliably cold; and the financial, emotional and physical strain of acquiring heartworm disease is so much worse than the prevention.But here in Colorado, where we often have a much drier climate, the droning buzz of mosquitoes isnít the incessant annoyance that it is for many of our lowlander friends and family. So weíve historically been less stringent with our recommendations regarding heartworm prevention, because the disease prevalence here has been so low in the past. But nothing lasts forever and the times they are ìa changiníî According to the Companion Animal Parasite Council, a nonprofit veterinary organization that monitors parasite disease throughout North America, Colorado has seen a 70 percent increase in heartworm positive cases over the past five years ó and we expect these numbers will continue to rise.Adult heartworms finish their life cycles within the large blood vessels that send blood from the heart to the lungs, where they subsist off of a steady diet of blood. During their stay, fertilized female worms within those vessels have lots and lots of microscopic babies (microfilariae) that circulate through the body in the blood. Itís these worm babies that are sucked up by those pesky mosquitoes to be transplanted to the next host.Cold winters that send the cold-blooded mosquito population into dormancy are nice because they hit the pause button on the insectís feeding, which, in turn, halts new infections. That is the reason some people question whether they need preventive measures over the winter. However, cold winters arenít sufficient to eradicate the disease from an area. Freezing temperatures do not kill mosquitoes or their eggs; the adult heartworms reside, snug as a bug (excusing the pun), within their warm canine (and feline) hosts over the winter and can live for up to five years. This establishes what is referred to as a natural reservoir for the parasite population, which can continue to act as an infection pool once environmental conditions become more favorable to the filthy little insects. This phenomenon has been accelerated by the explosive population growth that Colorado has seen over the past decade, which has introduced more heartworm-positive animals, as well as susceptible hosts into the region.So what can we do about it? As they say, knowing is half the battle. If your veterinarian hasnít had a conversation with you about heartworm prevention, ask about it during your next visit.Understanding the risk factors facing our dogs AND our cats, both outside and in (the kitty who began this conversation was a mostly indoor cat, by the way), will help you be the best advocate for your animal. Meanwhile, there are numerous free resources available to those seeking to get a head start on that conversation.For more information, I highly recommend visiting both the Companion Animal Parasite Council website (http://capcvet.org) and the American Heartworm Society website (http://heartwormsociety.org) to get started.