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| ==Links== | | ==Links== |
| ==References== | | ==References== |
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− | ==Heart Worm==
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− | (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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− | |Class 2
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− | | Mild cough, Slight radiographic changes
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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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− | |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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− | *Establish in '''heart''' and [[Lungs Circulatory - Pathology|pulmonary arteries]]
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− | *Larvae migrate through connective tissue
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− | *Immature adults move to caudal distal pulmonary arteries causing diffuse eosinophilic reaction in lung parenchyma, then migrate back to right ventricle
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− | *May cause [[Lungs Circulatory - Pathology#Embolism, thrombosis and infarction|pulmonary thromboembolism]]
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− | ==cat==
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− | *As in dogs above
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− | *Not very infective in cats but one dead adult causes acute pulmonary crisis - [[Lungs Circulatory - Pathology#Embolism, thrombosis and infarction|thromboembolism]]
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− | == Nematodes of Dogs - CANINE HEARTWORM ==
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− | *''Dirofilaria immitis'' is one of the most important causes of morbidity and mortality in dogs in many regions of the world that have a warm, humid climate, including parts of southern Europe, USA and Australia.
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− | *The presenting signs are usually those of heart failure, but sudden collapse may occur in heavily infected dogs.
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− | *The endemic zone for canine heartworm disease is spreading as people increasingly travel with their pets.
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− | *Strains of ''D. immitis'' are adapting to cooler climates.
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− | *It is not endemic in the UK, but more infected dogs are likely to be imported now that the quarantine regulations have been relaxed.
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− | *It has a very long prepatent period, so clinical signs may not appear for many months after importation.
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− | *Although primarily a canine parasite, cats and ferrets can become infected.
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− | *Owners taking their pets into endemic regions require advice on how the disease can be prevented.
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− | '''In dog''':
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− | *larvae migrate through connective tissues and moult twice
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− | *immature adults (L5) are 1-5cm long → caudal distal pulmonary arteries in 4months → diffuse eosinophilic reaction in lung parenchyma, then migrate back towards right ventricle
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− | *start producing microfilariae 6-7months post-infection.
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