All dogs should undergo a thorough history and physical examination before the start of treatment. Thoracic radiographs provide the best overall assessment of the status of pulmonary arterial and parenchymal disease and are useful for estimating prognosis. The risk of postadulticide pulmonary thromboembolism is increased in dogs with preexisting clinical and radiographic signs of severe pulmonary vascular disease, especially in those with right-sided heart failure or a high worm burden.

In young, asymptomatic dogs the inclusion of a CBC, blood urea nitrogen or creatinine measurement, and urinalysis yields a sufficient database. A more complete serum chemistry profile, in addition to thoracic radiographs and urinalysis is recommended for middle-age and older dogs or those with clinical signs. A platelet count is advised in animals with radiographically severe pulmonary heart disease. Urine protein loss is quantified or a urine/creatinine ratio is calculated if hypoalbuminemia or proteinuria is detected.

Mild-to-moderate increases in liver enzyme activities may be caused by hepatic congestion but do not prelude therapy with melarsomine. Liver enzyme activities usually return to normal within 1 to 2 months of heartworm treatment. Aspirin is not recommended as a routine preadulticide treatment in most dogs because of the lack of convincing evidence of a beneficial antithrombotic effect. It is unclear whether dogs with severe pulmonary arterial disease benefit from aspirin therapy given for 1 to 2 weeks before the start of adulticide treatment.

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Signs and symptoms of heartworm disease in dogs.

Many dogs are asymptomatic when the disease is diagnosed by a positive routine screening test result. Dogs with occult disease or those that have not been routinely tested are more likely to have advanced pulmonary arterial disease and clinical signs. Symptomatic dogs often have a history that includes exertional dyspnea, fatigue, syncope, cough, hemoptysis, shortness of breath, weight loss, or signs of right-sided congestive heart failure.

Heartworm disease in dogs is characterized by a change of a dog's bark and total loss has sometimes been reported. The physical examination findings may be normal in early or mild disease. Severe disease is frequently associated with poor body condition, tachypnea, dyspnea, jugular vein distention or pulsations, ascites, or other evidence of right-sided heart failure. Increased or abnormal lung sounds (wheezes, crackles), a loud and often split second heart sound, an ejection click or murmur at the left base, a murmur of tricuspid insufficiency, or cardiac arrhythmias are variably heard on auscultation. Severe pulmonary arterial disease and thromboembolism can be associated with epistaxis, disseminated intravascular coagulation, thrombocytopenia, and possibly hemoglobinuria; the latter is also a sign of the caval syndrome.

Occasionally, aberrant worm migration to the central nervous system, eye, femoral arteries, subcutis, peritoneal cavity, and other sites occurs and causes related signs. Several cases of systemic arterial migration causing hindlimb lameness, paresthesia, and ischemic necrosis have been described. Worm and thrombus extraction via femoral arteriotomies, along with adulticide therapy, has been successful in some cases, but limb amputation may be necessary.

Canine heartworm disease diagnostic plan:

History
Physical examination
Heartworm check
Blood work
Urinalysis
Chext X-rays
Electrocardiography
Echocardiography

Canine heartworm disease treatment:

Drugs to kill adult worms
Restricted exercise
Aspirin
Corticosteroids
Drugs to kill larvae in the bloodstream
Prevention
Surgery


Canine heartworm disease dietary plan:

A diet with controlled levels of protein, phosphorus and sodium. Consider body conditions.

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The life cycle of the heartworm (Dirofilaria immitis) is as follows: A mosquito ingests microfilariae (first-stage larvae L1) from an infected host animal. The L1 must molt twice within the mosquito in order to mature; therefore microfilariae passed to another dog by blood transfusion or across the placenta do not develop into adult worms. It takes approximately 2 to 2.5 weeks for infective larvae (now L3) to develop within the mosquito. Infective L3 larvae enter the new host when the mosquito takes a blood meal. The L3 larvae travel within the subcutis of the new host, molting into the L4 stage in about 9 to 12 days and into the L5 stage.

The young worms enter the vascular system approximately 100 days after infection, migrating preferentially to the peripheral pulmonary arteries of the caudal lung lobes. It takes at least 5 and usually more than 6 months before an infection becomes patent and gravid female worms release microfilariae. Thus a puppy younger than 6 months with circulating microfilariae most likely received them transplacentally and does not have patent heartworm disease.

Various species of mosquitoes throughout the world can transmit the infection. The disease is widespread in the US but is particularly prevalent along the eastern and gulf coasts and in the Mississipi River Valley. Heartworm disease has been found in animals in all 50 states, although few cases are encountered in other areas of the US and Canada. Heartworm transmission is limited by climatic conditions. For the L1 larvae to mature to the infective stage within a mosquito, the average daily temperature must be more than 64 degrees Farenheit for about 1 month. In most areas of the US heartworm transmission peaks in July and august.

More information on heartworm disease medication here.

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Heartworm prophylaxis is indicated for all dogs living in endemic areas. Because sustained warm, moist conditions are important for heartworm disease transmission, the time of year when infection is possible is limited in most parts of the United States. Transmission is limited to only a few months in the most northern part of the US; year-round transmission is thought possible only in the far southern edge of the continental US. It appears that monthly heartworm preventive therapy is necessary only from June through October or November for dogs in most of the US and from April to November or December for dogs in in the southern one third of the US. Year-round monthly preventive therapy is probably prudent at the southern most edge.

Several macrolide drugs are currently available for preventing heartworm disease; the avermectins (ivermectin, selamectin) and the milbemycins (milbemycin oxime, moxidectin). Diethylcarbamazine (DEC) is also still available as a preventive agent. Preventive therapy can begin at 6 to 8 weeks of age. Before chemoprophylaxis is started for the first time, dogs old enough to have been previously infected should be tested for circulating antigen and (if DEC is to be used) microfilariae. Retesting for circulating antigen should be done periodically; usually every 2 to 3 years is adequate. The avermectins and milbecymins induce neuromuscular paralysis and death in nematode (and arthropod) parasites by interacting with membrane chloride channels. These agents have a wide margin of safety in mammals.

Periodic retesting is an important part of heartworm prophylaxis. After the first year of monthly prophylaxis, a heartworm antigen test should be done to confirm the dog’s negative status. If preventive therapy has been given as scheduled, retest intervals longer than 1 year may be sufficient. When DEC is used as preventive, yearly microfilariae testing is important before DEC is reinstituted. Supplemental antigen testing is also recommended.

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Ivermectin and milbemycin have been used effectively as microfilaricidal medicine drugs, although neither is approved by the U.S. Food and Drug Administration for this purpose. Medicine drug treatment for microfilariae is generally administered 3 to 4 weeks after adulticide therapy. The rapid death of many microfilariae within 3 to 8 (sometimes 12) hours of the first dose can cause systemic effects, including lethargy, inappetence, salivation, retching, defecation, pallor and tachycardia. Usually such adverse effects are mild. However, dogs with high numbers of circulating microfilariae occasionally experience circulatory collapse that responds to glucocorticoid therapy. It is recommended that dogs be closely observed for 8 to 12 hours after initial medicine drug absorption. An additional benefit of both medicine drugs is that they prevent new infection.

Medicine drugs Ivermectin (Ivomec or Heartguard) is an avermectin with efficacy against a variety of nematode and anthropode parasites. Moxidectin and selamectin are also known to be microfilaricidal, but there is inadequate clinical experience with them for this purpose. Other drugs that have been used include levamisole and fenthion; but since they are less effective than ivermectin and milbemycin, must be given for a longer period, and have frequent adverse effects, they are not recommended.

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