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Dirofilaria immitis (view source)

Revision as of 13:17, 17 May 2010

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*There is no licensed adulticidal therapy, and treatment may be fatal for the cat as well as the worm.
 
*There is no licensed adulticidal therapy, and treatment may be fatal for the cat as well as the worm.
 
*Ivermectin or selamectin can be used for prevention.
 
*Ivermectin or selamectin can be used for prevention.
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==Heart Worm== (Cardiology)
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===Description===
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*Life cycle of [[Dirofilaria immitis|''dirofilaria immitis'']]
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*Dogs, cats, and ferrets can be affected
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*Cats are more resistant to infection compared to dogs, but it only takes one or two worms to cause serious disease in cats.
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*Caval Syndrome is the result of extremely heavy worm burdens and is rarely seen.
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'''Infection with heart worm can affect the following structures:'''
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'''1. Pulmonary arteries
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'''
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e.g. pulmonary thromboembolism of dead worms
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'''2. Pulmonary parenchyma'''
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e.g. allergic pneumonitis
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'''3. Heart'''
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e.g. pulmonary thromboembolism-->pulmonary hypertension-->increased right ventricular afterload-->right ventricular hypertrophy-->myocardial failure-->right heart failure
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'''4. Liver
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'''
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e.g. hepatic congestion from heart failure
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'''5. Kidneys'''
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e.g. antigen-antibody complexes lead to glomerulonephropathies
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===Distribution===
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*Endemic in the United States (especially southeast); South America, Southeast Asia, Middle East, Australia, Japan, Southern Europe
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*Warm weather conditions that support the mosquito population contribute to heart worm disease
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====Transmission====
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*Several types of mosquitoes are the intermediate host to the nematode worm D. imitis
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*Mosquitoes are infected with D. imitis when they bite an infected animal with circulating microfilaria (L1 stage)
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===Signalment===
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Genetics & Breed Predisposition: Large Breeds; Male>Female; 4-8 years old on average; Untreated with prophylactics
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Cats: Outdoor cats; Male>Female; 3-6 years old on average; Untreated with prophylactics
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===Diagnosis===
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====History & Clinical Signs====
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-Asymptomatic +/- (Acute Infections)
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-Symptomatic +/- (Chronic Infection)
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-Exercise Intolerance
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-Haemoptysis
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-Coughing
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-Tachypnea
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-Syncope
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-Right Heart Failure +/-
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-Vomiting (cats)
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-CNS signs (cats)
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-Collapse (cats)
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-Sudden Death (cats)
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====Physical Exam====
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-Signs of right sided heart failure
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-Crackles heard on auscultation
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-Splitting of the S2 heart sound signifies pulmonary hypertension
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====Staging Heartworm Disease====
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{| style="width:75%; height:200px" border="1"
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!'''Class'''
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!'''Description'''
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|-
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| Class 1
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| No physical or clinical signs
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|-
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|Class 2
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| Mild cough, Slight radiographic changes
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|-
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|Class 3
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|Cough, Exercise intolerance, Dyspnoea, Abnormal lung sounds, Enlarged pulmonary artery, Signs of right heart failure 
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|-
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|Class 4
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| Caval Syndrome; Signs of right heart failure, Abnormal lung sounds, Abnormal heart sounds, Death
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|-
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|}
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====Laboratory Findings====
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'''Lab Tests'''
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'''Heartworm Antigen Testing''' (dogs, cats)
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-ELISA test kits test antigens associated with female D. immitis infections
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-False negatives with male only infections (common in cats)
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'''Direct Blood Smear''' (dogs)
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-Detects microfilaria from a blood sample
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-Only works if the infection is very severe
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-Not used on cats because after 6-8 weeks of a heart worm infection the microfilaria disappear.
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'''Modified Knott's Test or Filter Tests''' (dogs)
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-These centrifugal concentration techniques detect small amounts of microfilaria from a direct blood smear
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- (+) test indicates microfilaria production by adults
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-(-) test indicates either no infection or an occult infection (immune system destroys L1)
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-If negative test results, follow up with antigen test to rule out occult infections
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-Not used on cats because after 6-8 weeks of a heart worm infection the microfilaria disappear.
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'''Antibody Testing''' (dogs, cats)
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-(+) test only indicates exposure to D. immitis
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-(-) test rules out D. immitis infection (useful in cats)
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'''Laboratory findings'''
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Biochemistry: increased liver enzymes, azotemia, proteinuria, hypoalbuminemia
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Haematology: eosinophilia, basophilia, thrombocytopenia, neutrophilia with left shift if the animal has a pulmonary thromboembolism, non-regenerative anaemia
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====Radiography====
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-Enlarged right heart
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-Dilation of main pulmonary artery
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-Enlarged peripheral branches of pulmonary arteries (especially diaphragmatic lobes)
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====Electrocardiography (ECG)====
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-Usually normal
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-Right Ventricular Enlargement +/- (deep S waves)
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-Right Atrial Enlargement +/- (tall P waves)
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-Atrial arrhythmias +/-
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====Echocardiography====
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-Right heart enlargement
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-Dilation of the main pulmonary artery
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-Visualization of D. immitis if the infection is severe
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===Treatment===
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*Currently there are few treatment options for cats infected with heart worm except surgical removal in severe cases or the controversal use of thiacetarsamide.
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*In dogs with allergic pneumonitis, give oral corticosteroids before starting heart worm treatment.
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====1. Adulticidal (kills worms slowly)====
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e.g. melarsomine dihydrochloride, Thiacetarsamide
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-Give two doses 24 hours apart or perform a graded-kill protocol (1 dose into epaxial muscles; repeat 1-3 months later; repeat 24 later)
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-Rest animal for up to six weeks after treatment to avoid a thromboemolism (major treatment risk)
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(If thromboembolism develops treat with: prednisolone, heparin, and oxygen)
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-Perform an antigen test 3-6 months after treatment to ensure adult worms have been killed
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====2. Microfilaricidal (kills microfilaria)====
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-Given about 4 weeks after adulticidal treatment
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e.g. milbemycin, ivermectin
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-Modified Knott's test should be performed 3 weeks after microfilaricide treatment.  If it is positive repeat microfilaricidal protocol.  If negative proceed to preventative treatment.
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====3. Prophylaxis====
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-Test animals for heart worm before administering preventative treatment
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-Give dogs a supply of monthly macrocyclic lactones
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e.g. ivermectin, milbemycin, selamectin, moxidectin
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-All year coverage is usually the best way to ensure owner compliance
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===Prognosis===
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-Dependent on the stage at which heart worm has been diagnosed.
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-Caval Syndrome has a 50% survival with surgical removal of the heart worms
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[[Category:Filarioidea]]
 
[[Category:Filarioidea]]
 
[[Category:Dog_Nematodes]]
 
[[Category:Dog_Nematodes]]
 
[[Category:Cat_Nematodes]]
 
[[Category:Cat_Nematodes]]
Bara
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