A veterinarian generally cannot determine the exact date or duration a dog has been infected with heartworms, as the disease progresses slowly and is often "silent" for many months. However, they can estimate the minimum time frame based on the heartworm life cycle and the dog's clinical signs and test results.
It usually takes several years before dogs show clinical signs of infection. Dogs of any age, breed or sex may be affected. The disease is rare in dogs less than one year of age, however, because the microfilariae take 5 to 7 months to mature into adult heartworms after infection.
Heartworm disease in dogs
When the infected mosquito bites another dog, the mosquito spreads the infective larvae to the dog through the bite wound. In the newly infected dog, it takes about 6 to 7 months for the infective larvae to mature into adult heartworms.
Symptoms and Side Effects of Heartworms in Dogs. Heartworm side effects can include coughing, diarrhea, weight loss, fatigue, and much more. If you suspect your dog has heartworms, please contact your vet immediately.
Recovery is possible — but it takes time, commitment, and close monitoring. Treating heartworm is a multi-step process, typically lasting several months. The goal is to kill the adult worms without causing dangerous complications and to minimize permanent damage to your dog's heart and lungs.
Coughing or Asthma-like Attacks: Respiratory issues are a common sign of heartworm disease in cats, often mistaken for feline asthma.
Additionally, even though melarsomine is highly effective, a single course of treatment may not completely clear all dogs of infection (the American Heartworm Society protocol calls for three separate injections of melarsomine.
The cough associated with heartworm disease in dogs is often likened to the sound of a goose honking. If your dog tends to get into coughing fits after activity or eating, and if those coughs sound harsh and honk-like, then she may have heartworm disease or another heart related concern.
It takes several months for the body to absorb the decomposed heartworms. Most problems after treatment occur due to these decomposing fragments. To reduce the risk, your dog should avoid exercise and be kept calm for the first month after treatment.
Another clear indicator of heartworm disease is lethargy. If your dog normally has a lot of energy but is now spending a lot more time sleeping or avoiding interacting with you, this may be due to their heart having to work harder to pump blood.
Monthly preventatives are labeled and proven to kill baby heartworms, but they will not kill the adult heartworms that are living in your dog's heart. So while it may kill the baby heartworms and prevent more adults, you're allowing the adult heartworms that are already in there to continue causing more damage.
Treatment for stages 1-2:
Then a 4-week course of both prednisone and doxycycline will be prescribed. Prednisone is a corticosteroid that will help reduce blood clots in the lungs, and doxycycline is an antibiotic that will kill the bacteria living inside the heartworms.
Lethargy and reluctance to exercise are common signs described in dogs with advanced heartworm disease. If your pet loses interest in going for walks or is fatigued after activity, it may be a sign of heartworm disease.
Moxidectin-doxycycline (moxi-doxy) provides a viable alternative to no treatment at all, in cases where arsenical treatment is not possible. Based on current evidence, the most effective non-arsenical treatment regimen is doxycycline 10 mg/kg PO q 12 or 24 h for 28 days, combined with topical moxidectin at label dose.
Anecdotal evidence suggests that herbs such as garlic, black walnut and wormwood, and the homeopathic heartworm nosode, may actually prevent as well as treat infection. Unfortunately, I have not yet been able to find substantive proof that these therapies can reliably and safely prevent or treat infection or disease.
Early Symptoms of Lungworm in Dogs
Stage 4: Severe Disease and Life-Threatening Complications
The most serious stage of heartworm disease can be life-threatening. In severe cases, worms can block blood flow, leading to a sudden emergency known as caval syndrome. Immediate surgical intervention is often required to save the pet's life.
Myth #3: If my pet has heartworms, I will see them in her feces. Although many worm types, such as roundworms and tiny hookworms, are shed in your pet's feces, heartworms do not live in the gastrointestinal (GI) tract, and are not found in feces.
The 3-3-3 rule for dogs is a guideline for the adjustment period after adoption, outlining three phases: 3 Days (decompression, feeling overwhelmed/scared), 3 Weeks (starting to settle in, learning routine, personality emerges), and 3 Months (feeling secure, bonded, and truly at home). It helps new owners manage expectations and be patient as their rescue dog transitions, emphasizing calm energy, routine, and space in the early days to build trust.
Many dogs treated for heartworm have close to a normal life expectancy, depending on how quickly the disease was found. Without treatment, heartworm disease will shorten a dog's natural life expectancy.
Myth 6: Heartworm Disease Is Rarely Fatal in Dogs
Fortunately, heartworms in dogs can be treated. If diagnosed and treated early, before signs that the disease has progressed—such as cough, fatigue, difficulty breathing, and weight loss—many dogs can go on to live normal lives.
The states with the highest density of diagnosed heartworm cases in the latest survey were Mississippi, Louisiana, Texas, Alabama, and Arkansas, said Dr. Jennifer Rizzo, AHS president, in a press release.
Dewormer medicine kills intestinal parasites such as hookworms and roundworms. But they do not kill heartworms. In fact, heartworms live in the blood vessels and not the intestines, so dewormers have no effect on them. Heartworm preventative is the only medicine that can prevent heartworms.