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| | *''[[Angiostrongylus vasorum]]'' | | *''[[Angiostrongylus vasorum]]'' |
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| − | *''Dirofilaria immitis'' (not in UK) | + | *''[[Dirofilaria immitis]]'' (not in UK) |
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| − | == Nematodes of Dogs - LUNGWORMS ==
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| | == Treatment of Hookworms, Whipworms and Lungworms in Dogs and Cats == | | == Treatment of Hookworms, Whipworms and Lungworms in Dogs and Cats == |
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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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| − |
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| − | '''''Dirofilaria immitis''''':
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| − | *a filarial worm
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| − | *females: up to 30cm long; males: up to 15cm long
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| − | *life-span 5-7years
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| − | *up to 250 worms may establish in the heart and pulmonary arteries
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| − | *produce microfilariae, not eggs.
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| − |
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| − | '''Microfilariae''':
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| − | *in peripheral circualtion
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| − | *periodicity - maximum numbers in blood evening/night
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| − | *greater than 300µm long
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| − | *life-span 2years
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| − | *present in approximately 60% of infected dogs
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| − | *microfilariae are absent from the circulating blood if:
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| − | **only immature worms present
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| − | **only one worm present
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| − | **only one sex
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| − | **microfilariae killed by immune response (in 15% of dogs)
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| − | **females sterilised by chemotherapy (e.g. ivermectin).
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| − |
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| − | '''Intermediate hosts''':
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| − | *many, but not all, species of mosquito.
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| − |
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| − | '''Local Epidemiology''':
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| − | *determined by feeding preferences of local species, and population density.
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| − | *up to 45% of non-protected dogs infected in some parts of USA.
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| − | '''In mosquito''':
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| − | *microfilariae → L1 → L2 → infective L3
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| − | *this takes 1week at 30°C, or 4weeks at 18°C - there is no development below 14°C.
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| − | *when mosquito next feeds:
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| − | **L3 moves to mouthparts
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| − | **up to 12 L3 deposited on skin
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| − | **enter body via puncture wound.
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| − |
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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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| − | '''Zoonotic hazard''':
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| − | *human infection can occur, but few cases are diagnosed
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| − | *this usually happens when a radio-opaque plaque is detected in the lung, and further investigation shows it to be caused by a trapped ''D. immitis'' larva.
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| − |
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| − | === Pathology ===
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| − | '''Worms produce''':
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| − | *substances that are:
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| − | **antigenic
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| − | **immunomodulatory
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| − | **pharmacologically active.
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| − | '''Lesions are''':
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| − | *'''not''' confined to the location of the worms
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| − | *also caused by shear stress of high blood flow.
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| − | '''Severity''':
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| − | *not associated with the number of worms
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| − | *exacerbated by exercise (i.e. by high blood flow rate)
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| − | *sedentary dogs often asymptomatic - symptoms most commonly associated with racing greyhounds.
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| − | '''Acute prepatent disease''':
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| − | *immature adult worms in caudal distal pulmonary arteries
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| − | *leads to intense diffuse eosinophilic reaction, which in turn leads to coughing.
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| − |
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| − | '''Chronic disease''':
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| − | *mature worms in right heart and pulmonary arteries
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| − | *endothelial swelling and sloughing
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| − | *increased permeability → inflammation → periarteritis
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| − | *platelets/white blood cells activated → thrombosis
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| − | *proliferation of smooth muscle, thickening of media:
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| − | → impairment of blood flow
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| − | → pulmonary hypertension
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| − | → right ventricular strain
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| − | → right ventricular hypertrophy and right-sided heart failure
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| − | *insufficient blood pumped through pulmonary capillary bed → insufficient preload for left ventricle.
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| − |
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| − | '''Post Caval Syndrome (Dirofilarial haemoglobinuria)''':
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| − | *can be acute or chronic
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| − | *heavy heartworm infestation:
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| − | **entangled clumps of worms → impaired closure of tricuspid valve → post-caval stagnation → hepatic congestion and hepatic failure
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| − | *this is accompanied by increased red blood cell fragility, haemolytic anaemia and haemolobinuria.
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| − |
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| − | '''Clinical signs''':
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| − | *often sudden onset severe lethargy and weakness, but:
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| − | *signs variable, reflecting multiple system dysfunction - pulmonary circulation, heart, liver and kidneys:
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| − | **lung damage (severe pulmonary hypertension; thromboembolism)
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| − | **heart failure (right-sided congestive)
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| − | *therefore, '''not''' pathognomonic
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| − | *acute prepatent = coughing
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| − | *chronic = exercise intolerance, sometimes with ascites
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| − | *acute post caval syndrome = collapse (dyspnoea, pale mucous membranes or jaundice, haemoglobinuria)
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| − |
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| − | '''Diagnosis''':
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| − | *Physical examination:
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| − | **signs of heart disease
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| − | **lung involvement
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| − | *Radiography:
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| − | **enlargement of right heart, main pulmonary arteries; arteries in lung lobes with thickening and tortuosity; inflammation in surrounding tissues
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| − | *ECG:
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| − | **right axis deviation → deep S waves
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| − | *Echocardiography:
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| − | **if post caval syndrome suspected - right ventricular enlargement with worms in ventricle appearing as parallel lines.
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| − |
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| − | '''Clinical pathology''':
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| − | *needed alongside physical examination and other tests to determine treatment strategy and prognosis.
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| − |
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| − | '''Parasite detection''':
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| − | *methods for demonstrating microfilariae in blood:
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| − | **wet blood smear (okay for quick look, but insensitive) = ''D. immitis'' not progressively motile
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| − | **Knott's test = red blood cells lysed; stained sediment examined
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| − | **micropore filter = blood forced through; microfilariae held on filter; stained and examined
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| − | **antibody detection ELISA = not reliable in dogs, but it is the best for cats (although some false positives)
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| − | **antigen detection ELISA (using specific antigen from adult female worm) = reliable positives from 5-7months post-infection in dogs; although occasional false negatives occur → '''not''' useful for cats
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| − | *the immunochromatographic test (ICT) uses coloured gold colloidal particles tagged to monoclonal antibodies to visualise the presence of adult worm antigen - performance similar to antigen detection ELISA, but quicker and easier to do (but not as quantitative as some ELISAs are)
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| − | *operator error can give false positives, therefore best to confirm result with another test.
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| − |
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| − | '''Chemotherapy''':
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| − | *three treatment objectives needing different approaches:
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| − | 1) '''Adulticidal'''
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| − | *risk that dead worms → thromboembolism → respiratory failure
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| − | *therefore, hospitalise and strict exercise restriction for at least 3weeks post-treatment
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| − | *organic arsenicals for adulticidal therapy:
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| − | **'''Thiacetarsamide''' (2.2mg/kg IV bid for 2days) - hepatotoxic; skin sloughing
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| − | **'''Melarsomine''' (2.5mg/kg IM sid for 2days) - generally safer, but greater risk of thromboembolism
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| − | NB - Ivermectin preventative doses over 16months reduces adult worm numbers
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| − | 2) '''Microfilaricidal'''
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| − | *start 3-6weeks after adulticidal therapy:
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| − | **'''Ivermectin''' (50µg/kg)
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| − | **'''Milbemycin oxime''' (0.5mg/kg)
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| − | NB - risk of reaction to dead microfilariae in sensitised animals (lethargy, retching, tachycardia, circulatory collapse) - observe for 8hours post-treatment
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| − | 3) '''Preventative (prophylactic)'''
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| − | *objective = kill migrating L4 before they reach the heart
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| − | *monthly treatments are 100% effective and safe if used properly, but often fail because of inadequate owner compliance
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| − | *test for adult infection/microfilarie before start and annually thereafter:
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| − | **'''Ivermectin''' (6µg/kg monthly) - blocks maturation of larvae; these die only after several months
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| − | **'''Selamectin''' (6mg/kg monthly)
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| − | **'''Moxidectin''' (injectable formulation - 0.17mg/kg gives 6months protection)
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| − | **'''Milbemycin oxime''' (0.5mg/kg monthly) - care → kills microfilarie, therefore risk of reaction
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| − | **'''DEC (diethylcarbamazine)''' daily - care → kills microfilarie, therefore severe risk of reaction
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| − |
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| − | '''Treatment of Post Caval Syndrome''':
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| − | *surgical removal with forceps via jugular vein
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| − | *usually very successful, but:
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| − | *do not crush or fragment worms
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| − |
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| − | → massive release of antigen
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| − |
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| − | → cardiac failure and acute respiratory distress
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| − |
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| − | → rapid death
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| − |
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| − | '''A typical therapy protocol''':
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| − | 1) Pre-treatment evaluation
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| − | 2) Adulticide: 4-6weeks restricted exercise
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| − | 3) Microfilaricide: 3weeks after adulticide
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| − | 4) Initiation of monthly preventative treatments
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| − | 5) Check for microfilariae after 2weeks
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| − | 6) Check for adults (ELISA) 4-6months after adulticide, and before start of each subsequent mosquito season.
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| | [[Category:Dog]] | | [[Category:Dog]] |