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Dirofilaria worms produce microfilariae, not eggs.
Dirofilaria worms produce microfilariae, not eggs.
'''Microfilariae''':
'''Microfilariae''':
*in peripheral circualtion
*in peripheral circualtion
*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.
*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 ===
=== Feline Heartworm Disease===
*A canine parasite - see under Dog Nematodes for life-cycle etc.
*Cats are abnormal hosts, and so ''D. immitis'' is not very infective for cats.
*Nevertheless, feline infection is common (up to 25%) in some heavily endemic areas.
*But only small numbers of adult worms (1-3) establish.
*The prepatent period is longer (approximately 8months) than in the dog.
*Few, if any, microfilariae are produced (<20% of cases positive).
*The life-span of the worm is shorter (2-3years).
*However: one dead adult → acute pulmonary crisis (thromboembolism).
*Lung pathology similar to dog, but little heart pathology.
*Coughing starts 4-6months post-infection.
*Antibody-detection ELISA used for diagnosis, but false positives occur (antigen ELISA cannot be used as antigen rarely expressed in cats).
*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.
==Signalment==
==Diagnosis==
'''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.
===Clinical Signs===
'''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)
===Diagnostic Imaging===
===Laboratory Tests===
===Pathology===
'''Worms produce''':
'''Worms produce''':
*substances that are:
*substances that are:
*this is accompanied by increased red blood cell fragility, haemolytic anaemia and haemolobinuria.
*this is accompanied by increased red blood cell fragility, haemolytic anaemia and haemolobinuria.
==Treatment==
'''Chemotherapy''':
'''Chemotherapy''':
*three treatment objectives needing different approaches:
*three treatment objectives needing different approaches:
6) Check for adults (ELISA) 4-6months after adulticide, and before start of each subsequent mosquito season.
6) Check for adults (ELISA) 4-6months after adulticide, and before start of each subsequent mosquito season.
==Prognosis==
==Links==
==References==
==Heart Worm==
==Heart Worm==