Every month, lots of dog owners, and a few cat owners, give their pets some form of heartworm prevention. But recent studies show increasing numbers of pets positive for the disease ñ even in Colorado. Some people believe the worms now have the upper hand. Has our trusted protection failed us?Dog owners and a growing number of cat owners understand that once -a-month heartworm preventives keep their pets safe from this very serious vascular parasite. Despite easy-to-use preventive medications, a significant number of dogs are testing positive for heartworms.In some cases, we find the monthly dose of medication was not given on time, opening the door for potential infection. In other cases, medical records and client compliance appears to be complete, yet the pet is positive on the annual heartworm blood test.Heartworm preventive works by killing immature heartworm larvae spread by mosquitoes. In theory, a pet who receives medication each month should be protected and never have a positive heartworm test. So, why does this happen?Many owners are quick to blame the heartworm preventives themselves. They believe continued use of the drugs will create resistant worms and that will lead to an increase in positive cases. On the surface, this theory appears to have merit. After all, we know that improper and excessive use of antibiotics can create resistant bacteria.But according to an article in Veterinary Parasitology, heartworm resistance should not occur. The authors looked at the life cycle of the heartworm, genetic mechanisms of resistance, as well as the timing and dose of the heartworm medications. Their conclusion shows the current medications are unlikely to select for any sort of genetic resistance among the heartworm parasite. In other words, it is doubtful current heartworm preventive practices are causing any resistance. So, what is happening?As unpopular as it sounds, pet owners and veterinarians may have to share the blame. A pet owner who fails to purchase enough preventative medication for a full 12 months is putting their pet at risk. Also, research shows that nearly 50 percent of dog owners who buy heartworm prevention do not give the medication as directed ñ that is a big window of vulnerability!Likewise, veterinary clinics are just not being good enough about reminding their clients about the importance of year-round prevention. In a survey of veterinarians to find out why, researchers found there is simply so many things that the doctor and the pet owner have to discuss at that annual visit, this often gets passed over.Even our pets are not entirely blameless. Pets that take oral medication and ìburyî it or spit it out wonít benefit from its protection. Also, if your pet has an upset stomach the day you give the medication, the complete dose could be lost in a bout of vomiting.In all of this negativity, there is good news. Experts state that the heartworm preventive failure rate is less than 1 in a million; meaning that if your dog takes his medication routinely, the chances of developing heartworm disease is almost non-existent.Additionally, veterinarians have multiple options available to clients for providing protection to their pets. Monthly chewable tablets (the most popular form and easiest to give) are available along with topical formulations for more finicky pets. There used to be an injection that lasted six months, but it has been removed from the market in the U.S.This is an important note: All of the manufacturers of heartworm preventive medication guarantee their products. They will pay for heartworm disease treatments if your dog tests positive. Pretty good insurance and a reason to give the medication year round.Sometimes, itís easier for people to blame the product rather than admit to a very common mistake, but the fact is pet owner compliance problems may be the biggest reason more pets have what appears to be heartworm preventive failure.Finally, what about Colorado? We have it here, and it is increasing and surprising veterinarians at the frequency. Many factors contribute to this increase, but it is safe to say that Colorado dogs should be on heartworm preventive just like their cousins from the Deep South.As always, your family veterinarian will have the best advice. Beware of Internet sites circulating unfounded rumors and opinions from dubious sources. Dr. Jim Humphries is a house call veterinarian in Falcon. He also serves as a visiting professor at the College of Veterinary Medicine at Texas A&M University. He lives in Falcon with his wife, horses and Great Danes. http://www.MobilePetDocs.com
