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