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→Clinical Signs
===Clinical Signs===
===Clinical Signs===
In dogs, historical findings at the time of presentation can vary. Some animals are asymptomatic, or cough only occasionally. In countries where heartworm is endemic, animals may be routinely tested for dirofilariasis at the end of the high-risk season, when weather becomes cooler<sup>3</sup>. Therefore, positive laboratory testing may be the first indication of disease<sup>1</sup>. More obvious signs may be seen depending on the severity of disease. Generally, the onset of heartworm disease is insidious, and clinical signs are related either to a high parasite burden, or to an allergic response to the parasite<sup>2</sup>. Affected dogs most often show coughing, and dyspnoea/tachypnoea, exercise intolerance, loss of condition and syncope may also be seen. In severe cases the pulmonary vessels may rupture, leading to haemoptysis or epistaxis. There is a tendency for signs to only manifest during exercise, and so patients with a sedentary lifestyle may never show overt disease. Right-sided congestive heart failure may ensue when worm burden is high, and signs can include jugular disension, ascites, marked exercise intolerance and hepatomegaly. A systolic murmur is sometimes audible on cardiac auscultation.
In dogs, historical findings at the time of presentation can vary. Some animals are asymptomatic, or cough only occasionally. In countries where heartworm is endemic, animals may be routinely tested for dirofilariasis six months after the end of the high-risk season<sup>3</sup>. Therefore, positive laboratory testing may be the first indication of disease<sup>1</sup>. More obvious signs may be seen depending on the severity of disease. Generally, the onset of heartworm disease is insidious, and clinical signs are related either to a high parasite burden, or to an allergic response to the parasite<sup>2</sup>. Affected dogs most often show coughing, and dyspnoea/tachypnoea, exercise intolerance, loss of condition and syncope may also be seen. In severe cases the pulmonary vessels may rupture, leading to haemoptysis or epistaxis. There is a tendency for signs to only manifest during exercise, and so patients with a sedentary lifestyle may never show overt disease. Right-sided congestive heart failure may ensue when worm burden is high, and signs can include jugular disension, ascites, marked exercise intolerance and hepatomegaly. A systolic murmur is sometimes audible on cardiac auscultation.
A classification system for the presentation of heartworm disease exists<sup>1</sup>, outlined in the table below.
A classification system for the presentation of heartworm disease exists<sup>1</sup>, outlined in the table below.
*Lung sounds may be increasd
*Lung sounds may be increasd
*Radiography may show mild-to-moderate changes, e.g. right ventricular enlargement.
*Radiography may show mild-to-moderate changes, e.g. right ventricular enlargement.
*Anemia and proteinuria may be present.
*Anaemia and proteinuria may be present.
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|<center>'''Class 3'''</center>
|<center>'''Class 3'''</center>
|'''Severe disease'''
|'''Severe disease'''
*Signs are variable but may include weight loss, exercise intolerance, tachypnoea, dyspnoea, severe/persistent coughing, hemoptysis, syncope, or ascites.
*Signs are variable but may include weight loss, exercise intolerance, tachypnoea, dyspnoea, severe/persistent coughing, haemoptysis, syncope, or ascites.
*Radiographs appear abnormal: right ventricular hypertrophy, enlargement of the main pulmonary artery, and diffuse pulmonary densities. ECG often shows right ventricular hypertrophy.
*Radiographs appear abnormal: right ventricular hypertrophy, enlargement of the main pulmonary artery, and diffuse pulmonary densities. ECG often shows right ventricular hypertrophy.
*Anaemia, thrombocytopenia, and proteinuria are seen.
*Anaemia, thrombocytopenia, and proteinuria are seen.
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Caval syndrome is a very severe form of heartworm disease that can occur in dogs and cats. It is characterised by respiratory distress, signs of right-sided heart failur, intravascular haemolysis and haemoglobinuria. Disseminated intravascular coagulation frequently occurs, and the syndrome is often fatal.
Caval syndrome is a very severe form of heartworm disease that can occur in dogs and cats. It is characterised by respiratory distress, signs of right-sided heart failuer, intravascular haemolysis and haemoglobinuria. Disseminated intravascular coagulation frequently occurs, and the syndrome is often fatal.
In cats, most infections are asymptomatic. However, sudden death can occasionally occur. This may be preceded by an acute respiratory crisis, thought to be due to parasitic thromboembolism and obstruction of a major pulmonary artery<sup>1, 2</sup>. When clinical signs are less acute, they are vague and may include anorexia, weight loss and letheargy. Intermittent coughing and dyspnoea can appear similar to feline asthma. Syncope may also occur, and cats may vomit. The cause of this vomiting is undetermined<sup>3</sup>.
In cats, most infections are asymptomatic. However, sudden death can occasionally occur. This may be preceded by an acute respiratory crisis, thought to be due to parasitic thromboembolism and obstruction of a major pulmonary artery<sup>1, 2</sup>. When clinical signs are less acute, they are vague and may include anorexia, weight loss and lethargy. Intermittent coughing and dyspnoea can appear similar to feline asthma. Syncope may also occur, and cats may vomit. The cause of this vomiting is undetermined<sup>3</sup>.
===Radiography===
===Radiography===