Heartworms are spread by Mosquitos. Mosquito species capable of transmitting heartworm disease can be found in most geographical areas. More than 70 species of mosquitoes are capable of transmitting the disease.
Transmission can occur anytime infected mosquitoes are active and feeding.
Rare instances of transmission of microfilaria from infected bitches to fetuses via the placenta and from dog to dog via blood transfusion can occur. However, these microfilariae will not develop into adult worms. Presence of these microfilariae can confound a diagnosis and may serve as a potential source of microfilaria that could be transmitted by feeding mosquitoes.
Heartworm infection in the dog induces or may induce pulmonary endothelial damage, villous proliferation, and activation and attraction of leukocytes and platelets due to live worms as well as thrombosis, granulomatous, and villous inflammation due to dead and/or dying worms.
Pulmonary vessels may become thickened and tortuous.
Cardiac output may be reduced. Pulmonary hypertension may lead to compensatory right heart enlargement and right heart failure. Clinical signs include cough, dyspnea, weight loss, ascites and jugular venous distension, exercise intolerance, and arrhythmias.
Heartworm may induce glomerulonephritis and proteinuria secondary to antigen-antibody complexes.
Rarely, ectopic infections of the eye, central nervous system, peritoneal cavity, systemic circulation, or skin have been reported.
Caval syndrome has been reported.
In a small number of cases; worms may be found in the post cava and right atrium, causing interference of tricuspid valve function. This results in a peracute life-threatening hemolytic anemia and right heart failure.
Associated findings include:
pallor, weak pulses, tachycardia, and sudden collapse
hemoglobinemia and hemoglobinuria
disseminated intravascular coagulopathy (DIC)
murmur caused by tricuspid regurgitation auscultated best on right side of thorax.
Courtesy of CAPC Vet – Read much more about Hearworm disease HERE.
