Lecture 11 2/16/24 Flashcards
What are the general characteristics of Dirofilaria immitis?
-IH is mosquitoes
-DH is dogs/wild canidae, marine mammals, ferrets, cats
-males 12-22 cm
-females 25-31 cm
-mf 300 x 7 um
-PPP 6 months
What are the characteristics of the Dirofilaria immitis life cycle?
-juvenile worm matures to adult over 3 month period
-microfilaria produced by young adults 6 months post-infection
-lifespan of 5 to 7 years for adults; 2 years for mf
-average infection of 14 worms
What clinical signs are associated with heartworm infection?
-potentially asymptomatic
-cough
-dyspnea
-exercise intolerance
-weight loss
-ascites
-anemia
-eosinophilia
-thrombocytopenia
-glomerulonephritis
-proteinuria
What causes the clinical signs associated with heartworm?
-pulmonary arterial disease with inflammation and arteritis
-pulmonary thromboemboli
-pulmonary hypertension
-prolonged severe pulmonary hypertension/potential right heart failure
What is the gold standard for heartworm diagnosis?
-Knott’s/filter test
-antigen test
What is important about the timing of heartworm testing?
-earliest possible detection of heartworm antigen is 5 months
-low worm burden and and preventatives can delay antigen detection
What can lead to a dog being AG positive and Knott’s negative?
-5 month old worms
-all female worms
-immunological occult
-prophylaxis induced
-few mf present
What can lead to a dog being Ag negative and mf positive?
-dead adults with mf circulating
-antibody sequestration/antigen-antibody complexes
How can radiographs be used to diagnose heartworm?
-right-sided heart enlargement
-“reverse D shape”
Why is monthly heartworm preventative considered to be retroactive?
the monthly dose kills what has accrued in the animal in the past month
Why does transplacental transmission of heartworm not lead to adult worms in puppies?
the microfilaria must go through the mosquito IH to become an adult
Which drug is used to treat adult heartworms?
melarsomine dihydrochloride
Why is it important to separate out heartworm treatment into multiple doses?
killing fewer worms per treatment reduces the cumulative impact of worm emboli
What should be done during month one of heartworm treatment?
-start monthly heartworm prev.
-prescribe doxycycline to kill Wolbachia
-prescribe pred. to reduce symptoms
-begin exercise restriction
How does Wolbachia contribute to heartworm pathogenesis?
-surface proteins contribute to pulmonary/renal inflammation
-bacteria releases endotoxin
What should be done during month two of heartworm treatment?
give second dose of heartworm prev.
What should be done during month three of heartworm treatment?
-give third dose of heartworm prev.
-give first melarsomine inj.
-prescribe pred. to control symptoms
-further decrease activity level
Why is exercise restriction important during heartworm treatment?
aids in minimizing pulmonary emboli and thrombosis
What should be done during month four of heartworm treatment?
-give fourth dose of heartworm prev.
-give second and third melarsomine inj.
-prescribe pred. to control symptoms
-continue exercise restriction for 6-8 weeks post last injection
What should be done after completing heartworm treatment?
performing both an antigen test and a Knott’s test 6 months after completing treatment
What are the main treatment principles that apply to heartworm?
-three melarsomine dose protocol kills 98% of adults (100% clearance)
-thromboembolism WILL occur - exercise restriction important
-prednisone is treatment of choice for inflammation associated with embolism
-doxycycline reduces Wolbachia
What are the characteristics of caval syndrome?
-occurs when animal has so many worms that they enter right atrium and vena cavae
-life threatening
-requires immediate surgery
-adult chemotherapy only after animal is stable post-op
What are the characteristics of Acanthocheilonema?
-IH is fleas/lice/ticks
-DH is dogs/cats/primates/raccoons/marine mammals
-males 9-17 mm
-females 20-32 mm
-mf 270 x 5 um
-PPP 2 months
How do dogs and cats differ in terms of worm burden?
when exposed to 100 L3:
-dogs will develop approx. 75 adult worms
-cats will develop approx. 5-10 adult worms
What are the characteristics of Dirofilaria in cats?
-adults have shorter lifespans
-often no microfilaria
-ectopic infection more common
-often in the lungs instead of heart
What clinical signs are associated with heartworm in cats?
-dyspnea
-coughing
-vomiting
-neurologic signs
-sudden death
-may be asymptomatic
Why is it more likely to get a false neg. heartworm test in cats?
-antigen tests only detect antigens from female worms; cats typically only have male worms
-cats do not typically have microfilaria for detection via Knott’s test
When is disease most likely to occur in cats with heartworm?
-immature worms enter pulmonary arteries
-worms die within pulmonary arteries
How does heartworm treatment differ between dogs and cats?
-no recommended adulticidal treatment in cats
-focus instead on relieving clinical signs in cats
-provide supportive care and prophylaxis
