| Line 203: |
Line 203: |
| | ==Links== | | ==Links== |
| | ==References== | | ==References== |
| − |
| |
| − |
| |
| − |
| |
| − |
| |
| − |
| |
| − |
| |
| − |
| |
| − | ==Heart Worm==
| |
| − |
| |
| − | (Cardiology)
| |
| − | ===Description===
| |
| − |
| |
| − | *Life cycle of [[Dirofilaria immitis|''dirofilaria immitis'']]
| |
| − |
| |
| − | *Dogs, cats, and ferrets can be affected
| |
| − |
| |
| − | *Cats are more resistant to infection compared to dogs, but it only takes one or two worms to cause serious disease in cats.
| |
| − |
| |
| − | *Caval Syndrome is the result of extremely heavy worm burdens and is rarely seen.
| |
| − |
| |
| − |
| |
| − | '''Infection with heart worm can affect the following structures:'''
| |
| − |
| |
| − | '''1. Pulmonary arteries
| |
| − | '''
| |
| − |
| |
| − | e.g. pulmonary thromboembolism of dead worms
| |
| − |
| |
| − |
| |
| − | '''2. Pulmonary parenchyma'''
| |
| − |
| |
| − | e.g. allergic pneumonitis
| |
| − |
| |
| − |
| |
| − | '''3. Heart'''
| |
| − |
| |
| − | e.g. pulmonary thromboembolism-->pulmonary hypertension-->increased right ventricular afterload-->right ventricular hypertrophy-->myocardial failure-->right heart failure
| |
| − |
| |
| − |
| |
| − | '''4. Liver
| |
| − | '''
| |
| − |
| |
| − | e.g. hepatic congestion from heart failure
| |
| − |
| |
| − |
| |
| − | '''5. Kidneys'''
| |
| − |
| |
| − | e.g. antigen-antibody complexes lead to glomerulonephropathies
| |
| − |
| |
| − |
| |
| − | ===Distribution===
| |
| − |
| |
| − | *Endemic in the United States (especially southeast); South America, Southeast Asia, Middle East, Australia, Japan, Southern Europe
| |
| − |
| |
| − | *Warm weather conditions that support the mosquito population contribute to heart worm disease
| |
| − |
| |
| − |
| |
| − | ====Transmission====
| |
| − |
| |
| − | *Several types of mosquitoes are the intermediate host to the nematode worm D. imitis
| |
| − |
| |
| − | *Mosquitoes are infected with D. imitis when they bite an infected animal with circulating microfilaria (L1 stage)
| |
| − |
| |
| − |
| |
| − | ===Signalment===
| |
| − |
| |
| − | Genetics & Breed Predisposition: Large Breeds; Male>Female; 4-8 years old on average; Untreated with prophylactics
| |
| − |
| |
| − | Cats: Outdoor cats; Male>Female; 3-6 years old on average; Untreated with prophylactics
| |
| − |
| |
| − |
| |
| − | ===Diagnosis===
| |
| − |
| |
| − | ====History & Clinical Signs====
| |
| − |
| |
| − | -Asymptomatic +/- (Acute Infections)
| |
| − |
| |
| − | -Symptomatic +/- (Chronic Infection)
| |
| − |
| |
| − | -Exercise Intolerance
| |
| − |
| |
| − | -Haemoptysis
| |
| − |
| |
| − | -Coughing
| |
| − |
| |
| − | -Tachypnea
| |
| − |
| |
| − | -Syncope
| |
| − |
| |
| − | -Right Heart Failure +/-
| |
| − |
| |
| − | -Vomiting (cats)
| |
| − |
| |
| − | -CNS signs (cats)
| |
| − |
| |
| − | -Collapse (cats)
| |
| − |
| |
| − | -Sudden Death (cats)
| |
| − |
| |
| − | ====Physical Exam====
| |
| − |
| |
| − | -Signs of right sided heart failure
| |
| − |
| |
| − | -Crackles heard on auscultation
| |
| − |
| |
| − | -Splitting of the S2 heart sound signifies pulmonary hypertension
| |
| − |
| |
| − |
| |
| − | ====Staging Heartworm Disease====
| |
| − |
| |
| − | {| style="width:75%; height:200px" border="1"
| |
| − |
| |
| − | !'''Class'''
| |
| − | !'''Description'''
| |
| − |
| |
| − | |-
| |
| − | | Class 1
| |
| − | | No physical or clinical signs
| |
| − | |-
| |
| − | |Class 2
| |
| − | | Mild cough, Slight radiographic changes
| |
| − | |-
| |
| − | |Class 3
| |
| − | |Cough, Exercise intolerance, Dyspnoea, Abnormal lung sounds, Enlarged pulmonary artery, Signs of right heart failure
| |
| − |
| |
| − | |-
| |
| − | |Class 4
| |
| − | | Caval Syndrome; Signs of right heart failure, Abnormal lung sounds, Abnormal heart sounds, Death
| |
| − |
| |
| − | |-
| |
| − | |}
| |
| − |
| |
| − |
| |
| − |
| |
| − | ====Laboratory Findings====
| |
| − |
| |
| − | '''Lab Tests'''
| |
| − |
| |
| − | '''Heartworm Antigen Testing''' (dogs, cats)
| |
| − |
| |
| − | -ELISA test kits test antigens associated with female D. immitis infections
| |
| − |
| |
| − | -False negatives with male only infections (common in cats)
| |
| − |
| |
| − |
| |
| − | '''Direct Blood Smear''' (dogs)
| |
| − |
| |
| − | -Detects microfilaria from a blood sample
| |
| − |
| |
| − | -Only works if the infection is very severe
| |
| − |
| |
| − | -Not used on cats because after 6-8 weeks of a heart worm infection the microfilaria disappear.
| |
| − |
| |
| − |
| |
| − | '''Modified Knott's Test or Filter Tests''' (dogs)
| |
| − |
| |
| − | -These centrifugal concentration techniques detect small amounts of microfilaria from a direct blood smear
| |
| − |
| |
| − | - (+) test indicates microfilaria production by adults
| |
| − |
| |
| − | -(-) test indicates either no infection or an occult infection (immune system destroys L1)
| |
| − |
| |
| − | -If negative test results, follow up with antigen test to rule out occult infections
| |
| − |
| |
| − | -Not used on cats because after 6-8 weeks of a heart worm infection the microfilaria disappear.
| |
| − |
| |
| − |
| |
| − | '''Antibody Testing''' (dogs, cats)
| |
| − |
| |
| − | -(+) test only indicates exposure to D. immitis
| |
| − |
| |
| − | -(-) test rules out D. immitis infection (useful in cats)
| |
| − |
| |
| − |
| |
| − | '''Laboratory findings'''
| |
| − |
| |
| − | Biochemistry: increased liver enzymes, azotemia, proteinuria, hypoalbuminemia
| |
| − |
| |
| − | Haematology: eosinophilia, basophilia, thrombocytopenia, neutrophilia with left shift if the animal has a pulmonary thromboembolism, non-regenerative anaemia
| |
| − |
| |
| − |
| |
| − | ====Radiography====
| |
| − |
| |
| − | -Enlarged right heart
| |
| − |
| |
| − | -Dilation of main pulmonary artery
| |
| − |
| |
| − | -Enlarged peripheral branches of pulmonary arteries (especially diaphragmatic lobes)
| |
| − |
| |
| − |
| |
| − | ====Electrocardiography (ECG)====
| |
| − |
| |
| − | -Usually normal
| |
| − |
| |
| − | -Right Ventricular Enlargement +/- (deep S waves)
| |
| − |
| |
| − | -Right Atrial Enlargement +/- (tall P waves)
| |
| − |
| |
| − | -Atrial arrhythmias +/-
| |
| − |
| |
| − |
| |
| − | ====Echocardiography====
| |
| − |
| |
| − | -Right heart enlargement
| |
| − |
| |
| − | -Dilation of the main pulmonary artery
| |
| − |
| |
| − | -Visualization of D. immitis if the infection is severe
| |
| − |
| |
| − |
| |
| − | ===Treatment===
| |
| − |
| |
| − | *Currently there are few treatment options for cats infected with heart worm except surgical removal in severe cases or the controversal use of thiacetarsamide.
| |
| − |
| |
| − | *In dogs with allergic pneumonitis, give oral corticosteroids before starting heart worm treatment.
| |
| − |
| |
| − |
| |
| − | ====1. Adulticidal (kills worms slowly)====
| |
| − |
| |
| − | e.g. melarsomine dihydrochloride, Thiacetarsamide
| |
| − |
| |
| − | -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)
| |
| − |
| |
| − | -Rest animal for up to six weeks after treatment to avoid a thromboemolism (major treatment risk)
| |
| − |
| |
| − | (If thromboembolism develops treat with: prednisolone, heparin, and oxygen)
| |
| − |
| |
| − | -Perform an antigen test 3-6 months after treatment to ensure adult worms have been killed
| |
| − |
| |
| − |
| |
| − | ====2. Microfilaricidal (kills microfilaria)====
| |
| − |
| |
| − | -Given about 4 weeks after adulticidal treatment
| |
| − |
| |
| − | e.g. milbemycin, ivermectin
| |
| − |
| |
| − | -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.
| |
| − |
| |
| − |
| |
| − | ====3. Prophylaxis====
| |
| − |
| |
| − | -Test animals for heart worm before administering preventative treatment
| |
| − |
| |
| − | -Give dogs a supply of monthly macrocyclic lactones
| |
| − |
| |
| − | e.g. ivermectin, milbemycin, selamectin, moxidectin
| |
| − |
| |
| − | -All year coverage is usually the best way to ensure owner compliance
| |
| − |
| |
| − |
| |
| − | ===Prognosis===
| |
| − |
| |
| − | -Dependent on the stage at which heart worm has been diagnosed.
| |
| − |
| |
| − | -Caval Syndrome has a 50% survival with surgical removal of the heart worms
| |
| − |
| |
| − |
| |
| − | *Establish in '''heart''' and [[Lungs Circulatory - Pathology|pulmonary arteries]]
| |
| − | *Larvae migrate through connective tissue
| |
| − | *Immature adults move to caudal distal pulmonary arteries causing diffuse eosinophilic reaction in lung parenchyma, then migrate back to right ventricle
| |
| − | *May cause [[Lungs Circulatory - Pathology#Embolism, thrombosis and infarction|pulmonary thromboembolism]]
| |
| − |
| |
| − | ==cat==
| |
| − |
| |
| − | *As in dogs above
| |
| − | *Not very infective in cats but one dead adult causes acute pulmonary crisis - [[Lungs Circulatory - Pathology#Embolism, thrombosis and infarction|thromboembolism]]
| |
| − | == Nematodes of Dogs - CANINE HEARTWORM ==
| |
| − | *''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.
| |
| − | *The presenting signs are usually those of heart failure, but sudden collapse may occur in heavily infected dogs.
| |
| − | *The endemic zone for canine heartworm disease is spreading as people increasingly travel with their pets.
| |
| − | *Strains of ''D. immitis'' are adapting to cooler climates.
| |
| − | *It is not endemic in the UK, but more infected dogs are likely to be imported now that the quarantine regulations have been relaxed.
| |
| − | *It has a very long prepatent period, so clinical signs may not appear for many months after importation.
| |
| − | *Although primarily a canine parasite, cats and ferrets can become infected.
| |
| − | *Owners taking their pets into endemic regions require advice on how the disease can be prevented.
| |
| − | '''In dog''':
| |
| − | *larvae migrate through connective tissues and moult twice
| |
| − | *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
| |
| − | *start producing microfilariae 6-7months post-infection.
| |
| | | | |
| | | | |