Changes

Also known as: heartworm disease.

[[Image:Dirofilaria immitus.jpg|thumb|right|250px|''Dirofilaria immitis'' - Courtesy of the Laboratory of Parasitology, University of Pennsylvania School of Veterinary Medicine]]

Do not confuse with: ''Angiostrongylus vasorum'', angiostrongylosis.

Also known as: '''Heartworm Disease — Dirofilariasis

Beware confusing with: ''[[Angiostrongylus vasorum]]'', [[angiostrongylosis]].

[[Image:Dirofilaria immitus.jpg|thumb|right|150px|''Dirofilaria immitus'' - Courtesy of the Laboratory of Parasitology, University of Pennsylvania School of Veterinary Medicine]]

''Dirofilaria immitis'' is a nematode parasite that causes heartworm disease in dogs, cats and ferrets. Heartworm

disease is transmitted by mosquito bites and there are more than 70 species of mosquito that are able to transmit infection; Aedes, Anopheles and Culex are the most common vector species. Heartwoem disease has been reported in many countries with temperate and is particularly prevalent in the USA, Canada, and southern Europe. The introduction of the PETS travel scheme has increased the concern over Dirofilariasis in the UK.

''Dirofilaria immitis'' is a nematode parasite that causes heartworm disease in dogs, cats and ferrets. Heartworm disease is transmitted by [[Culicidae|mosquito]] bites and there are more than 70 species of mosquito that are able to transmit infection; ''Aedes, Anopheles'' and ''Culex'' are the most common vector species. Heartworm disease has been reported in many countries with temperate climate and is particularly prevalent in the USA, Canada, and southern Europe. The introduction of the PETS travel scheme has increased the concern over Dirofilariasis in the UK.

Dirofilarias does have zoonotic potential: infected mosquitos can transmit ''Dirofilaria immitis'' to humans, but the infection does not become patent. The infective larvae instead reach the lungs, become encapsulated, and die causing granulomatous reactions called "coin lesions" in the process. These are only imporant because they may be confused with neoplastic metastasis to the lungs on radiography¹.

''Dirofilaria'' does have zoonotic potential: infected mosquitos can transmit ''D. immitis'' to humans, but the infection does not become patent. The infective larvae instead reach the lungs, become encapsulated, and die causing granulomatous reactions called "coin lesions" in the process. These are only important because they may be confused with neoplastic metastasis to the lungs on radiography¹.

==Life Cycle==

==Life Cycle==

 

''Dirofilaria immitis'' adults reach maturity and sexually reproduce in the '''pulmonary arteries''' and '''right ventricle'''. Adult males are around 15cm in length, and females are around 25cm¹. After mating, female worms release larvae known as microfilariae (or L1) into the circulation. When a mosquito takes a blood meal from the infected dog or cat, microfilariae are ingested. Mosquitoes are true intermediate hosts for ''Dirofilaria immitis'', since microfilariae require a period of maturation to L2 then L3 in the vector. The duration of this development depends upon environmental conditions. For example, maturation at 30°C takes around 8 days, but when temperatures are down to 18°C, this takes around one month². Below 14°C, development is halted and resumes when temperatures rise. In cooler climates, this means that transmission of heartworm disease to new canine or feline hosts can only occur in warmer months.  

''Dirofilaria immitis'' adults reach maturity and sexually reproduce in the pulmonary arteries and right ventricle. Adult males are around 15cm in length, and females are around 25cm¹. After mating, female worms release larvae known as microfilariae (or L1) into the circulation. When a mosquito takes a blood meal from the infected dog or cat, microfilariae are ingested. Mosquitos are true intermediate hosts for ''Dirofilaria immitis'', since microfilariae require a period of maturation to L2 then L3 in the vector. The duration of this development depends upon environmental conditions. For example, maturation at 30°C takes around 8 days, but when temperatures are down to 18°C, this takes around one month². Below 14°C, development is halted and resumes when temperatures rise. In cooler climates, this means that transmission of heartworm disease to new canine or feline hosts can only occur in warmer months.  

Once matured, L3 in the mosquito migrate to the labium, from which they erupt onto the host's skin as the mosquito feeds. Larvae then migrate into the bite wound and, as most dogs are highly susceptible to heartworm disease, most L3 then establish infection. It takes 2-3 days for L3 to moult to L4, which remain in the subcutaneous tissues for up to two months before becoming young adults (L5) and migrating to the pulmonary arteries.  

Once matured, L3 in the mosquito migrate to the labium, from which they erupt onto the host's skin as the mosquito feeds. Larvae then migrate into the bite wound and, as most dogs are highly susceptible to heartworm disease, most L3 then establish infection. It takes 2-3 days for L3 to moult to L4, which remain in the subcutaneous tissues for up to two months before becoming young adults (L5) and migrating to the pulmonary arteries.  

==Pathogenesis==

==Pathogenesis==

Sequelae to heartworm infection include pulmonary thromboembolism, which can either occur due to the death and metastasis of adult worms, or due to platelet aggregation induced by the parasite. In severe cases, live nematodes can migrate to the right ventricle, right atrium and caudal vena cava. The resulting incompetence of the tricuspid valve, augmented by concurrent pulmonary hypertension, leads to signs of right-sided heart failure. Flow of erythrocytes through the mass of parasites formed can also cause haemolysis and thus haemoglobinaemia. This combination of acute right-sided heart failure and intravascular haemolysis is referred to as "caval syndrome", which in severe cases can also be characterised by thromboembolic events and [[Disseminated Intravascular Coagulation|disseminated intravascular coagulation]]. Due to the smaller numbers of adult worms, caval syndrome is less common in cats².

 

Sequelae to heartworm infection include pulmonary thromboembolism, which can either occur due to the death and metastasis of adult worms, or due to platelet aggregation induced by the parasite. In severe cases, live nematodes can migrate to the right ventricle, right atrium and caudal vena cava. The resulting incompetence of the tricuspid valve, augmented by concurrent pulmonary hypertension, leads to signs of right-sided heart failure. Flow of erythrocytes through the mass of parasites formed can also cause haemolysis and thus haemoglobinaemia. This combination of acute right-sided heart failure and intravascular haemolysis is referred to as "caval syndrome", which in severe cases can also be characterised by thromboembolic events and disseminated intravascular coagulation. Due to the smaller numbers of adult worms, caval syndrome is less common in cats².

In cats, heartworm disease generally causes a diffuse pulmonary infiltrate and an eosinophilic pneumonia². Adult worms may die and embolise to the lungs, resulting in severe haemorrhage and oedema of the affected lobe. Immature nematodes have also been known to migrate to sites other than the pulmonary arteries and heart such as the CNS, eye and subcutaneous tissues. These ectopic infections are far more common in cats than in dogs, suggesting that ''D. immitis'' is not well adapted to feline hosts.

In cats, heartworm disease generally causes a diffuse pulmonary infiltrate and an eosinophilic pneumonia². Adult worms may die and embolise to the lungs, resulting in severe haemorrhage and oedema of the affected lobe. Immature nematodes have also been known to migrate to sites other than the pulmonary arteries and heart such as the CNS, eye and subcutaneous tissues. These ectopic infections are far more common in cats than in dogs, suggesting that ''D. immitis'' is not well adapted to feline hosts.

==Signalment==

==Signalment==

''Dirofilaria immitis'' infection affects dogs more commonly than cats, and risk is greatest in outdoor animals. Dogs of any age may be affected, but infections are most common in 3 to 8 year old dogs, and medium and large breeds are over-represented^{1, 3}. In cats, there are no breed or age predispositions, but males are more frequently affected³. Ferrets may also contract dirofilariasis; there are no age or sex predilections¹.

''Dirofilaria immitis'' infection affects dogs more commonly than cats, and risk is greatest in outdoor animals. Dogs of any age may be affected, but infections are most common in 3 to 8 year old dogs, and medium and large breeds are over-represented^{1, 3}. In cats, there are no breed or age predispositions, but males are more frequently affected³. Ferrets may also contract dirofilariasis; there are no age or sex predilections¹.

===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 cooler³. Therefore, positive laboratory testing may be the first indication of disease¹. 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 parasite². 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 season³. Therefore, positive laboratory testing may be the first indication of disease¹. 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 parasite². 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 distension, ascites, marked exercise intolerance and hepatomegaly. A systolic murmur is sometimes audible on cardiac auscultation.

A classification system for the presentation of heartworm disease exists¹, outlined in the table below.

A classification system for the presentation of heartworm disease exists¹, outlined in the table below.

  !width="92%"|<center><u>'''Clinical Signs'''</u></center>  

  !width="92%"|<center><u>'''Clinical Signs'''</u></center>  

  |-

  |-

  |<center>'''Class 1'''</center>   

  |<center>'''Class I'''</center>   

  |'''Asymptomatic or mild disease'''  

  |'''Asymptomatic or mild disease'''  

*Weight loss, reduced exercise tolerance or an occasional cough may be seen.  

*Weight loss, reduced exercise tolerance or an occasional cough may be seen.  

*No radiographic signs or laboratory abnormalities.

*No radiographic signs or laboratory abnormalities.

  |-

  |-

  |<center>'''Class 2'''</center>  

  |<center>'''Class II'''</center>  

  |'''Moderate disease'''

  |'''Moderate disease'''

*Animal coughs occasionally and shows mild-to-moderate exercise intolerance.  

*Animal coughs occasionally and shows mild-to-moderate exercise intolerance.  

*Lung sounds may be increasd

*Lung sounds may be increased

*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.  

  |-

  |-

  |<center>'''Class 3'''</center>  

  |<center>'''Class III'''</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.

  |-

  |-

  |<center>'''Class 4'''</center>  

  |<center>'''Class IV'''</center>  

  |'''Caval syndrome'''

  |'''Caval syndrome'''

*Sudden onset of collapse, haemoglobinuria, and respiratory distress.  

*Sudden onset of collapse, haemoglobinuria, and respiratory distress.  

  |}

  |}

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 failure, 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^{1, 2}. 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 undetermined³.

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^{1, 2}. 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 undetermined³.

===Radiography===

===Radiography===

In dogs, thoracic radiography provides good information on disease severity and is useful for screening dogs showing clinical signs compatible with ''D. immitis'' infection¹. However, thoracic radiograph do not neccessarily reflect the current worm burden: radiographic signs of advanced disease can persist long after an infection has run its course⁴. Conversely, dogs with high burdens may be inactive and thus show few clinical signs or radiographic changes. Radiographic signs are mild-to-moderate in class II disease, but become more obvious in class III infections. The main pulmonary artery is enlarged,sup>1, 4</sup>, and the caudal lobar vessels appear tortuous¹ Ill-defined, fluffy infiltrates are apparent, and often surroung in the caudal lobar vessels. Right-sided cardiomegaly may be appreciated, and pleural and peritoneal effusions can be noted if right-sided congestive heart failure occurs⁴.

In dogs, thoracic radiography provides good information on disease severity and is useful for screening dogs showing clinical signs compatible with ''D. immitis'' infection¹. However, thoracic radiograph do not necessarily reflect the current worm burden: radiographic signs of advanced disease can persist long after an infection has run its course⁴. Conversely, dogs with high burdens may be inactive and thus show few clinical signs or radiographic changes. Radiographic signs are mild-to-moderate in class II disease, but become more obvious in class III infections. The main pulmonary artery is enlarged^{1, 4}, and the caudal lobar vessels appear tortuous¹. Ill-defined, fluffy infiltrates are apparent, and often surround the caudal lobar vessels. Right-sided cardiomegaly may be appreciated, and pleural and peritoneal effusions can be noted in right-sided congestive heart failure⁴.

Cardiac changes on thoracic radiography are less common in cats than dogs. The caudal lobar veins are enlarged (greater than 1.5 times the width of the ninth ribe), and the pulmonary arteries are blunted and tortuous^{3, 5}. Patchy parenchymal infiltrates may be seen in the region of vessels in animals showing respiratory signs^{1, 3}. Enlargement of the main pulmonary artery cannot normally be seen in cats, as it is has a relatively midline position and is thus obscured by the cardiac silhouette^{1, 5}. Right-sided cardiomegaly is not considered a typical finding in the cat⁵.

Cardiac changes on thoracic radiography are less common in cats than dogs. The caudal lobar veins are enlarged (greater than 1.5 times the width of the ninth rib), and the pulmonary arteries are blunted and tortuous^{3, 5}. Patchy parenchymal infiltrates may be seen in the region of vessels in animals showing respiratory signs^{1, 3}. Enlargement of the main pulmonary artery cannot normally be seen in cats, as it has a relatively midline position and is thus obscured by the cardiac silhouette^{1, 5}. Right-sided cardiomegaly is not considered a typical finding in the cat⁵.

===Echocardiography===

===Echocardiography===

Echocardiography is more important in cats than dogs because of the increased difficulty of diagnosis and the fact that this test can have a high sensitivity depending on operator experience¹. Specificity is 100%⁵, and the test can help exclude or confirm other primary cardiac diseases such as hypertrophic cardiomyopathy³. Worms can be visualised as parallel hyperechoic lines¹, and are seen in the right atrium and ventricle and main pulmonary artery^{1, 3, 5}.

 

Echocardiography is more important in cats than dogs because of the increased difficulty of diagnosis and the fact that this test can have a high sensitivity depending on operater experience¹. Specificity is 100%⁵, and the test can help exclude or confirm other primary cardiac diseases such as hypertrophic cardiomyopathy³. Worms can usually be visualised as parallel hyperechoic lines¹, and are seen in the right atrium and ventricle and main pulmonary artery^{1, 3, 5}.

===Electrocardiography===

===Electrocardiography===

The ECG of infected dogs is usually normal. Right ventricular hypertrophy patterns are seen when there is severe, chronic pulmonary hypertension and are associated with overt or impending right-sided CHF (ascites). Heart rhythm disturbances are usually absent or mild, but atrial fibrillation is an occasional complication in dogs with Class III disease.

Electrocardiography is less useful in the cat, as involvement of the heart chambers does not occur as frequently as in the dog⁵.

===Laboratory Tests===

===Laboratory Tests===

In both dogs and cats, routine haematology, biochemistry and urinalysis should be performed. Most parameters are usually within normal limits, but an anaemia can often be seen. Eosinophilia and basophilia are also common, and when seen together suggests occult dirofilariasis or allergic lung disease ^{1, 3}. Eosinophilia peaks as L5 enter the pulmonary arteries and subsequently varies. An inflammatory leukogram is also possible³. Hyperglobulinemia due to antigenic stimulation is an inconsistent finding^{1, 3}. Right-sided heart failure or immune-complex glomerulonephritis can lead to hypoalbuminaemia and, very occasionally, nephrotic syndrome¹. Because of this, it is possible for urinalysis to reveal proteiunuria^{1, 3}. Haemoglobinaemia and haemoglobinuria are associated with caval syndrome³.  

[[Image:dirofilariasis.jpg|right|thumb|200px|Dirofilariasis. Courtesy of T. Scase]]

There are several methods for the specific demonstration of ''Dirofilaria immitis'' in the animal. Firstly, direct '''microscopic examination''' allows rapid identification of microfilariae in a drop of fresh blood, as their movements can vigorously displace the surrounding red blood cells². Despite being quick, simple and inexpensive, this test is not sufficiently sensitive to provide a definitive diagnosis, particularly when there is a low concentration of microfilariae in the bloodstream. '''Filtration methods''' therefore exist to facilitate the microscopic demonstration of microfilariae^{2, 3}. These include the '''modified Knott's test''', which involves haemolysis, centrifugation and staining with methylene blue before direct examination. Tests such as this are more sensitive than merely examining a drop of blood, and the morphology of microfilariae can be clearly seen. However, sensitivity in comparison to other methods is still low and so microfilarial identification tests are often reserved for confirmation of weak positive antigen tests and determination of microfilarial status prior to treatment with a microfilaricide³. Cats frequently lack circulating microfilariae, and so direct microscopic examination is of little use in this species.

Tests exist to detect ''D. immitis'' antigens. '''ELISAs''' specific for proteins released from the reproductive tract of adult female worms are available for in-house use². Sensitivity and specificity are excellent, but small worm burdens and the presence of immature female- or male-only infections can give low antigen titres hence false negatives. This is especially common in cats. '''Specific agglutination and immunochromatography''' techniques are also available for use in dogs. Any antigen test performed in the first six months of infection may give false negative results as levels of circulating antigen are initially low while female worms mature. '''In-house tests''' are also available to detect antibody against ''Dirofilaria immitis''. The presence of antibodies confirms exposure, but does not necessarily provide information about current infection. These tests are therefore most useful for ruling out infection. ''D. immitis'' antibody tests have a low specificity² and so have largely been superceded by tests for antigen.

'''PCR-based tests''' are highly sensitive and specific for the diagnosis of immature and adult heartworms, and are especially useful in unconventional (e.g. wildlife) hosts². At present, these tests are not widely available for the diagnosis of ''Dirofilaria immitis''.

Difil-test; EVSCO Pharmaceuticals, Buena, New Jersey,USA) and the modified Knott's test (haemolysis, centrifugation

and staining with methylene blue) are more

sensitive and allow morphological examination of the

ELISA antigen tests detect specific circulating proteins

when re-screening for heartworm disease or evaluating

the response to treatment. Small worm burdens, the

presence of immature females or male-only infections

are common causes of low antigen titres and false

negative results, especially in cats, where these circumstances

occur more frequently. In dogs, specific agglutination and immunochromatography techniques are also

results because of the low antigen levels in the circulating

laboratory tests (see table below). The presence of antibodies

but not necessarily current infection. Consequently, antibody

Polymerase chain reaction (PCR)-based tests offer a very

in unconventional hosts. However, at present, these tests

are not widely available.

 

he antigen detection test is the preferred diagnostic method for asymptomatic dogs or when seeking verification of a suspected HW infection. This is the most sensitive diagnostic method available to veterinary practitioners. Even in areas where the prevalence of HW infection is high, ~20% of infected dogs may not be microfilaremic. Also, monthly macrolide prophylaxis induces embryo stasis in female dirofilariae.

Available antigen detection tests are very sensitive and specific. To determine when testing might become useful, it is advisable to add a predetection period to the approximate date on which infection may have been possible. A reasonable interval is 7 mo. There is generally no need to test a dog for antigen or microfilariae prior to ~7 mo of age. The level of antigenemia is directly related to the number of mature female worms present. At least 90% of dogs harboring ≥3 adult females will test positive. In general, strong-quick positive reactions correlate with relatively high worm burdens. For low-burden suspects, commercial laboratory-based microwell titer tests are the most sensitive.

===Pathology===

===Pathology===

On post-mortem examination, the right side of the heart is found to be enlarged. There is proliferation of the pulmonary arterial myointima, as well as pulmonary thromboembolism and haemorrhage. If right-sided congestive heart failure was present in life, the hepatomegaly and hepatic congestion will be seen.

On post-mortem examination, ''Dirofilaria immitis'' worms are apparent in the pulmonary artery and possibly the right side of the heart. The right side of the heart is found to be enlarged and there is proliferation of the pulmonary arterial myointima. Pulmonary thromboembolism and haemorrhage may be seen. If right-sided congestive heart failure was present in life, hepatomegaly and hepatic congestion will be apparent.

==Treatment==

==Treatment==

Decisions in the treatment of heartworm disease are dependent on the severity of infection. A scheme exists to classify patients in terms of disease severity². Class one patients have subclinical heartworm disease, and carry an excellent prognosis following treatment wiht adulticidal drugs. Class two animals show mild to moderate clinical signs and similar radiographic changes. These animals may respond positively to treatment. Dogs with class 3 disease have severe clinical signs, such as persistent coughing, dyspnoea, right-sided heart failure or haemoptysis, and these are reflected by severe radiographic signs. These cases have a high risk of pulmonary thromboembolism and so prognosis is guarded and the benefits of adulticidal treatment should be considered carefully.  

Adulticidal treatment may be declined by the owner, owing to the risk of thromboembolism. Alternatively, it may not be possible to implement adulticidal treatment if the patient is suffering renal or hepatic failure³. In these cases, monthly administration of prophylactic doses of ivermectin is a reasonable treatment option, as it prevents further infection and may kill some adult nematodes².

Even low grade infections in cats may result in pulmonary thromboembolism with adulticidal treatment, and spontaneous remission is seen in some cats. Because of this, symptomatic treatment (cage rest, oxygen supplementation, fluid therapy, bronchodilators and dexamethasone) may be more appropriate in sick cats, and clinically well cats can merely be monitored regularly for remission. Adulticidal treatment should only be considered in cats that fail to respond to supportive treatments but are in a stable condition.

Even low grade infections in cats may result in pulmonary thromboembolism with adulticidal treatment. Because of this, symptomatic treatment of sick cats may be followed by surgical or catheter-based extraction of nematodes once the patient is stable³. Stablisation is similar to that for feline asthma, and can include cage rest, oxygen supplementation, bronchodilators (e.g. theophylline), tapering doses of prednisolone, and balanced fluid therapy if indicated³. Heartworms have a much shorter life-span in cats, and spontaneous remission is seen in some cases. Regular monitoring may therefore be the best course of action in clinically well cats.

In '''caval syndrome''', surgery is the treatment of choice. Worms are removed from the right side of the heart and the main pulmonary artery using flexible crocodile or basket-type retrieval forceps². This procedure is complex and requires general anaesthesia and fluoroscopic imaging, but reduces the risk of thromboembolism following subsequent adulticidal treatment. Symptomatic and supportive therapy to stabilise the patient should be continued for around one month after surgery before adulticidal treatment is administered³.

and hepatotoxic than its predecessor thiacetarsamide,

and has a higher efficacy. Melarsomine is injected

administration of melarsomine, the likelihood of pulmonary

If adulticidal treatment is declined by the owner,

monthly administration of prophylactic doses of ivermectin

further infection and may kill some adult nematodes.

physical removal of worms from the right side of the

heart and the main pulmonary artery using flexible crocodile

or basket-type retrieval forceps. This procedure is

complex, requires general anaesthesia and fluoroscopic

imaging, but may reduce the risk of thromboembolism

following subsequent adulticidal treatment.

Heartworm prophylaxis should be implemented in all cats and dogs living in or visiting areas in which ''Dirofilaria immitis'' is endemic. In the UK, milbemycin oxime and selamectin are licensed for the prevention of heartworm disease and should be administered on a monthly basis as they are capable of killing migrating larvae up to week six post-infection. In the event of non-compliance or a missed dose, it may be necessary to test the animal for ''Dirofilaria immitis'' six months later if they are likely to have been exposed to infection during the time they were unprotected. Drugs that persist in the long term, such as injectable moxidectin, can help overcome this issue.

|full text = [http://www.cabi.org/cabdirect/FullTextPDF/2010/20103181752.pdf '''A review of American heartworm society guidelines for the management of heartworm infections in cats.''' Guerrero, J.; The North American Veterinary Conference, Gainesville, USA, Small animal and exotics. Proceedings of the North American Veterinary Conference, Orlando, Florida, USA, 16-20 January 2010, 2010, pp 1173-1176, 1 ref.]

 

[http://www.cabi.org/cabdirect/FullTextPDF/2008/20083097550.pdf '''Epidemiology and prevention of ''Dirofilaria'' infections in dogs and cats.''' Genchi, C.; Guerrero, J.; McCall, J. W.; Venco, L.; Veterinary Parasitology and Parasitic Diseases, Naples, Italy, Mappe Parassitologiche, 2007, 8, pp 145-161, many ref.]

 

[http://www.cabi.org/cabdirect/FullTextPDF/2006/20063226177.pdf ''' Heartworm of dog - its aetiopathogenesis, diagnosis, treatment and prevention.''' Kundu, P.; Intas Pharmaceuticals Ltd, Ahmedabad, India, Intas Polivet, 2006, 7, 1, pp 106-110, 16 ref.]

 

[http://www.cabi.org/cabdirect/FullTextPDF/2005/20053201370.pdf ''' The utility of echocardiography in the diagnosis of feline heartworm disease: a review of published reports.''' Defrancesco, T. C.; Atkins, C. E.; Seward, R. L.; Knight, D. H.; American Heartworm Society, Batavia, USA, Recent advances in heartworm disease: Symposium '98, Tampa, Florida, USA, 1-3 May, 1998, 1998, pp 103-106, 20 ref.]

 

|Vetstream = [https://www.vetstream.com/canis/search?s=nematode Nematodes]

In mildly symptomatic  or asymptomatic animals, the course of dirofilariasis is usually uneventful following treatment and the prognosis is excellent³. Animals with severe infection carry a guarded prognosis with a higher risk of complications.

|book = Arthropod-borne Infectious Diseases of the Dog and Cat

|author = Susan E. Shaw, Michael J. Day

==Links==

==Links==

==References==

==References==

#Venco, L (2007) Heartworm (Dirofilaria immitis) disease in cats. ''Dirofilaria immitis and D. repens in dog and cat and human infections'', 126-132.

#Venco, L (2007) Heartworm (Dirofilaria immitis) disease in cats. ''Dirofilaria immitis and D. repens in dog and cat and human infections'', 126-132.

#Ridyard, A (2005) Heartworm and lungworm in dogs and cats in the UK, ''In Practice'', '''27(3)''', 147-153.

#Ridyard, A (2005) Heartworm and lungworm in dogs and cats in the UK, ''In Practice'', '''27(3)''', 147-153.

[[Category:Filarioidea]]

[[Category:Filarioidea]]

[[Category:Dog_Nematodes]]

[[Category:Dog_Nematodes]]

[[Category:Cat_Nematodes]]

[[Category:Cat_Nematodes]]

[[Category:To_Do_-_Parasites]]

[[Category:Zoonoses]]

[[Category:Cardiovascular Diseases - Dog]]

[[Category:Respiratory Parasitic Infections]]

 

[[Category:Expert_Review]]

[[Category:Respiratory Parasitic Infections]]

[[Category:Cardiology Section]]

[[Category:To_Do_-_Lizzie]]