Heartworm Epidemic
Heartworms were first identified in the United States in 1847 and occurred most frequently on the seacoast in the southeastern United States. In recent years, heartworm disease has been found throughout the United States. The movement of infected animals that could serve as sources of infection for others is probably a significant contributing factor to heartworms spreading across North America. The actual number of infected dogs and cats in the United States is unknown. Heartworms are found in dogs, cats, and ferrets. They also occur in wild animals such as California sea lions, foxes and wolves. They have rarely been found in people.
What are heartworms? How do animals become infected with heartworms?
Heartworms are passed from an infected mosquito to a host animal. There are more than 60 different species of mosquitoes that can transmit heartworms.After biting an infected animal, the mosquito bites another animal, the larvae enter the animal's skin. The larvae grow and after about three months finish their migration to the heart, where they grow into adults, sometimes reaching a length of 14 inches. The time from when an animal was bitten by an infected mosquito until adult heartworms develop, mate, and lay microfilariae is about 6-7 months in dogs and 8 months in cats.
Severely infected dogs can have up to several hundred heartworms in their hearts and vessels. Adult worms in dogs usually live up to 5-7 years. Thirty to eighty percent of infected dogs have microfilariae, and the microfilariae can live up to 2 years. Microfilariae cannot mature into adult heartworms unless they pass through a mosquito. For more details, watch the following video: For a better idea of how this infection takes place view this video. How dogs and cats become infected with heartworm
What damage do heartworms cause?
Clinical Signs
Heartworm disease may cause a combination of medical problems in the same dog including dysfunction of the lungs, heart, liver and kidneys. The disease may have an acute onset but usually begins with barely detectable signs resulting from a chronic infection and a combination of physiologic changes. Dogs that are not exercised strenuously that have a low number of adult worms may never have apparent signs of heartworm disease. However, in most dogs, the heart and lungs are the major organs affected by heartworms with varying degrees of clinical signs.Clinical Signs Associated with Canine Heartworm Disease
Early Infection No abnormal clinical signs observed
Mild Disease Cough
Moderate Disease Cough, exercise intolerance, abnormal lung sounds
Severe Disease Cough, exercise intolerance, dyspnea (difficulty breathing), abnormal lung sounds, hepatomegaly (enlargement of the liver), syncope (temporary loss of consciousness due to poor blood flow to the brain), ascites (fluid accumulation in the abdominal cavity), abnormal heart sounds, death
Diagnosis
The diagnosis of canine heartworm disease depends upon the following:
* an accurate patient history
* the recognition of varied clinical signs
* the use of several diagnostic procedures that may include:
o blood (serological) testing
o microfilarial detection and differentiation
o physical exam and clinical laboratory tests X-ray (radiology)
o angiography and
o ultrasound (echocardiography)
o in the worst case scenario, examination after death (necropsy).
What is included in a good heartworm prevention program?
The best program for prevention of heartworm infection includes using preventives, performing routine heartworm testing, and reducing exposure to mosquitoes.Heartworm preventives
Every dog , whether indoor or outdoor, should be on a heartworm preventive.
Medications used to prevent heartworm infections are called preventives. The first thing to remember is that preventives are NOT used to kill the adult worms. Some preventives can cause severe problems if given to animals with adult heartworms or microfilariae. Follow the recommendations of your veterinarian and the manufacturer of your preventive in regard to testing prior to giving the preventive.
A number of monthly heartworm preventives for dogs are on the market. Some heartworm preventives, or drugs that are combined with them, will control other parasites. Preventive products should be used year-round, even in areas where mosquitoes only occur seasonally. Even if doses are accidentally skipped, preventive products are still beneficial to the pet. If given consistently over a 12-month period, it's possible to actually stop worms from developing into adults. Also, monthly heartworm preventives have activity against intestinal parasites, which inadvertently infect three to six million people every year. These preventives protect pets and people. Consult your veterinarian before using these products in a collie or herding breed.
Remember that mosquitoes can get indoors, so even though your dog may not go outside, your dog is still susceptible.
How is heartworm infection treated?
Melarsomine (ImmiticideŽ), the medication currently used to treat heartworm infection, also contains arsenic. It is given by injection deep in the muscles of the back. After treatment, your vet will give you a detailed heartworm rehab protocol. It usually means a long "rest" period.
In very severe infestations, adult worms are removed from the heart surgically. See the following video.
Surgical Removal of Heartworms
