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| Dirofilaria worms produce microfilariae, not eggs. | | Dirofilaria worms produce microfilariae, not eggs. |
| | | |
− | ==Signalment==
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− |
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− | ==Diagnosis==
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− | ===Clinical Signs===
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− |
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− | ===Diagnostic Imaging===
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− |
| |
− | ===Laboratory Tests===
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− |
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− | ===Pathology===
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| '''Microfilariae''': | | '''Microfilariae''': |
| *in peripheral circualtion | | *in peripheral circualtion |
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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. | | *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: |
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| *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. |
| | | |
− | '''Clinical signs''':
| + | ==Treatment== |
− | *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''': | | '''Chemotherapy''': |
| *three treatment objectives needing different approaches: | | *three treatment objectives needing different approaches: |
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| | | |
| 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== |
| + | |
| + | |
| | | |
| | | |
− | ==Cat==
| |
− | *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).
| |
| | | |
| | | |
− | === Feline Heartworm Disease ===
| |
− | *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.
| |
| | | |
| ==Heart Worm== | | ==Heart Worm== |