Heartworms are parasitic filarial worms, Dirofilaria immitis, that can infect dogs and cats. These very long, slender worms cause heartworm disease when they clog the right ventricle and vessels of an animal's heart. The larvae infect mosquitoes, who spread them when they bite pets. These larvae travel through the animal's blood and lodge in the heart, where they grow into adults, who produce more larvae to infect more mosquitoes. Pets can live with the infection for years but the congestion of the heart with worms ultimately leads to death and, in the meantime, to decreased physical activity and overall health. Due to the severity of these infections, most veterinarians suggest monthly preventative medication in mosquito-prone areas.
Heartworm Preventative Medications
Heartworm infection is prevented by medication. The most common drugs in these medications are ivermectin, pyrantel pamoate, praziquantel, milbemycin oxime, and lufeneron. Many pet owners are concerned that use of these drugs may cause serious side effects, including neurological disorders. Use in an infected pet will cause worms to die. As they die, they release toxins which can cause much physical distress, including seizures and death. The dying worms may also migrate into the lungs, causing further complications.
Potential Side Effects
Studies done by the manufacturers suggest these drugs have many potential side effects, though these are reported to be rare. Some side effects are common to most pharmaceuticals, such as nausea and vomiting. However, in some dogs and cats side effects include severe neurological disturbance and loss of muscle control. Pets most at risk for serious side effects are those with underlying medical conditions.
Contraindications
Autoimmune diseases of the nervous system can cause increased drug sensitivity. Observations of German Shepherds (Alsatians) suffering from degenerative myelopathy (a disease where the immune system attacks the nerve sheaths) suggest that use of monthly heartworm drugs may cause stronger symptoms and more rapid disease progression.
Epilepsy is also a contraindication for monthly heartworm drugs, which can cause seizures to become more frequent.
The most frequent cause of severe side effects is drug sensitivity or allergic reaction. If your pet has ever had an allergic reaction to any of the drugs used in heartworm medication, or develops symptoms of allergy, discontinue use.
Non-pharmaceutical Prevention
The holistic viewpoint on these drugs is that taking monthly dosages of pharmaceuticals causes toxins to accumulate leading to effects over time that are not apparent during a single study or early in use. Veterinarians and others who embrace this point of view claim that supporting your pet's overall health will make her or him more resistant to heartworm infection. They recommend a healthy diet and plenty of exercise to keep worm larvae from infesting the heart. Mosquito repellents, keeping pets indoors during mosquito season, and herbal anti-parasite treatments are also recommended as alternatives to pharmaceutical preventatives.
Sources
Centers for Disease Control and Prevention, Guidelines for Veterinarians
Rutgers Center for Veterinary Biology, http://www.rci.rutgers.edu/~insects/disease.htm
American Veterinary Medical Association
University of Florida, http://neuro.vetmed.ufl.edu
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