Circulating heartworm antigen appears in the blood as early as five months post-infection in a small percentage of dogs, but most dogs are not antigen positive until seven months post-infection. Yes, contrary to popular belief, a dog infected six months previously can be negative on an antigen test.
No one wants to hear that their dog has heartworm, but the good news is that most infected dogs can be successfully treated. The goal is to first stabilize your dog if he is showing signs of disease, then kill all adult and immature worms while keeping the side effects of treatment to a minimum.
While 100% of adult worms might be dead at the 6-month point, residual heartworm antigen in circulation is detectable for a time and could lead to an invalid test result. Waiting an additional 3 months allows time for the antigen to be cleared from the dog.
Heartworm Positive
False positive tests occasionally occur, so it is important that you consult your veterinarian for follow-up advice. A second test will probably be done. Heartworm is a serious, even life threatening disease, but it can be treated.
Depending on prevalence, the positive predictive value of the heartworm antigen test ranged from 15 to 54% and negative predictive value from 99 to 99.9%. For a hospital testing 1,000 dogs per year, false-positive test results may vary from 24 to 27 dogs.
Known causes of false positive heartworm antigen tests include infection with Spirocerca lupi, Angiostrongylus vasorum and A. odendhali, while related nematodes, such as other Dirofilaria spp., Dracunculus insignis and Onchocerca spp., are also thought to induce false positive results [49,50,51,52,53].
Testing for Microfilariae: Any antigen test that is positive or “weak” positive should be followed up with a test for microfilariae. The presence of microfilariae confirms that mature adult worms are present in the heart and indicates the need for specific treatment to kill microfilariae.
One female worm could survive and cause the test to be positive. If the worm burden was large before treatment then perhaps not all the worms died. n A new infection is possible if the monthly preventive was dosed incorrectly, or a dose was missed or accidently not ingested by the dog.
After treatment, the adult worms die and are carried by the blood to the lungs where they lodge in small blood vessels. There they decompose and are absorbed by the body over a period of several months. Reactions to the drugs are not uncommon, and there is always some risk involved in treating a dog for heartworms.
Approximately 9 months after treatment is completed, your veterinarian will perform a heartworm test to confirm that all heartworms have been eliminated. To avoid the possibility of your dog contracting heartworm disease again, you will want to administer heartworm prevention year-round for the rest of his life.
There is some risk involved in treating dogs with heartworms, although fatalities are rare. "A new drug is available that does not have as many side effects, allowing successful treatment of more than 95% of dogs with heartworms."
Dogs with heartworm disease can live high-quality lives as long as they are given appropriate care. After completing treatment and following your veterinarian's recommenda- tions on heartworm disease testing and prevention, the chances of any long-term effects are very low.
Some dogs live with heartworms for a long time with little to no outside indicators of infection, especially if they don't have many heartworms. That said, heartworms have a lifespan of five to seven years, so unfortunately they have plenty of time to wreak havoc on your dog's system.
Once the microfilariae start circulating through a dog's blood, they have become a host and are able to pass the disease back to mosquitos. The heartworms will continue to live in the heart until they die—typically 5-7 years.
Most dogs can be safely leash-walked during the treatment recovery period and providing appropriate chew toys can help relieve some of that stored up physical energy.
Once treated, the heartworms die slowly and begin to dissolve, taking several weeks. Three to four weeks later, your dog will begin phase two to get rid of the baby heartworms. Following that, continued checkups and testing continues, and your canine pal will be placed on heartworm preventative medication.
With the three-dose adulticide protocol described above, in conjunction with doxycycline and macrocyclic lactones as recommended by the American Heartworm Society, 98% of dogs will be cleared of heartworm infection.
Yes, contrary to popular belief, a dog infected six months previously can be negative on an antigen test. A low worm burden can markedly affect a test's sensitivity. These tests will detect dogs infected with one – two female worms only 60 – 70 percent of the time.
They can be controlled naturally with citrus oils, cedar oils, and diatomaceous earth. Dogs needing conventional treatment may benefit from herbs such as milk thistle and homeopathics such as berberis; these minimize toxicity from the medications and dying heartworms.
If owners can't afford treatment at the time of diagnosis, Dr. Herrin recommended delaying melarsomine therapy but still initiating treatment with both a preventive and doxycycline. This will prevent further infection and remove the dog as a heartworm reservoir.
Unlike intestinal parasites, however, which, once killed, can simply be passed in the animal's stool, heartworms, once dead, do not have an easy way to be eliminated from the body. The dog's immune system must break down the dead worms, an elimination process which is very effective but does take some time.
Signs of heartworm disease may include a mild persistent cough, reluctance to exercise, fatigue after moderate activity, decreased appetite, and weight loss. As heartworm disease progresses, pets may develop heart failure and the appearance of a swollen belly due to excess fluid in the abdomen.
Most of the monthly heartworm medicines have a safety factor of at least 15 days of protection if a dose is missed. This means that if you're just a week or two late, your pet is likely still within that window of protection and would be unlikely to become infected during that time.
Lethargy and reluctance to exercise are also common signs described in dogs with heartworm disease. If your pet loses interest in going for walks or is fatigued after activity, it may be a sign of heartworm disease. Some dogs have a decreased appetite and, as a result, lose weight.