Parasit - Heartworms

drraythe's version from 2015-05-10 21:48


Question Answer
How do you get HW?Mosquitos
Is resistance in HW is common/uncommon?COMMON!!
Infective stage of HW?L3
Genus+spp of HW?Dirofilaria immitis (True Heartworm)
How is HW Dx?Antigen-ELISA snap test
HW is usually found in Dogs, what other species has it been found in?HOOMINS!! Cats, horses, California sea lions, harbor seals, black bears, ferrets, beaver, wolverine, red panda & clouded leopard (Several species are zoonotic)
What are the CS of heartworms in hoomins?Fever, cough, chest pains, mild eosinophilia.
What are some consequences of HW in Hoomins?Focal pulmonary infarction w/ granuloma formation (lesions containing calcified worms), SQ lesions & (rarely) adult worms in the great vessels & heart
What test can you use to differentiate between species?High resolution melting analysis coupled to RT PCR (RT PCR-HRMA)
Animal not playing Frisbee like usual/ no HW prevention. What is an easy cheap test to confirm HW?SNAP test (Antigen ELISA)
How can you diff. Dipetalonema reconditum from Dirofilaria immitis? Bent body, more slender in the mid-body (less that the width of RBCs), skinnier/more tapered tail
Path of HW in hoomins?Focal pulmonary infarcts from granulomas
Cat w/ inflammatory response in lung?HW
Life cycle of HW?Females are viviparous → produce microfilariae (pre-larval stage) which travel in the blood stream. L1 is taken up when mosquito feeds L1 → L3 development in the mosquito (IH) approx. 8-17 days. Mosquito feeds again on a new animal → L3’s have only minutes to get into new host from inside Mosquito
Why is xmission via Mosquitoes so effective?Mosquitoes may live up to 600 days & can overwinter in rodent burrows
What is the PPP of heartworms?PPP = Approx. 5 - 6 mos
How long is the Patent period inside the hosts (Dog & Cat)?Approx. 5 to 6 yrs (dog); Approx. 4 yrs (cat)
Where do HWs like to hang out in the cat/dog?In the caudal pulmonary arteries (arteries of the lower lung lobes) (cats & sometimes dogs) & the Rt ventricle (dogs)
Some cases of _ xmission have been reported in the _?Tranplacental xmission; DOG
What does Stage 1 HW infection look like in a dog?Early infection (no abnormal clinical signs observed except for a slight cough). This is a mild stage, & dogs will appear happy & healthy may not show up on test
What does Stage 2 HW infection look like in a dog?Moderate Dz, lingering cough or fatigue after exercise (exercise intolerance). Heartworms may show in tests.
What does Stage 3 HW infection look like in a dog?More severe & noticeable. Dogs continue to cough, exercise intolerance, dyspnea; the Dz is quite evident on x-rays
What does Stage 4 HW infection look like in a dog?Severe Dz, Hepatomegaly, syncope (temporary loss of consciousness due to poor blood flow to the brain), ascites (fluid in the abdominal cavity), death if untreated
In cats clinical signs of HW infection may be?NOTHING ((Asymptomatic), Respiratory distress (HARD), Intermittent vomiting unrelated to eating, Death
In cats what stage of HW is causing CS?L4
What is HARD?Heartworm Assoc. Resp. Disease = vascular & airway disease caused by early death of immature worms
What would you NOT want to give a cat with HWs? Melarsomine!! NOT recommended for cats
What is the pathology of D. immitis? (5)1) Obstructive pulmonary arterial dz
2) Endarteritis (the presence of worms causes turbidity in vessels & proliferation of the intima)
3) Thrombus formation (sequelae of chronic obstructive Dz)
4) Cats - Interstitial pneumonitis (Heartworm Associated Respiratory Dz) – allergic bronchitis due to the death of immature worms
5) (Vena) Caval syndrome (in the dog there may be obstruction of the tricuspid valve, very serious) → hepatic & renal pathology which leads to congestive heart failure (CHF)
What is caused by the physical presence of adult worms in the pulmonary artery? (4)1) Adult worms denude the endothelium resulting in thrombosis & proliferation
2) Pulmonary arteries dilate become tortuous & lose their normal tapering & arborizing pattern
3) Pulmonary artery obstruction, pulmonary hypertension & cor pulmonale develops (Rt ventricular concentric hypertrophy)
Besides CHF, what are other lesions that HW can cause?Renal lesions → Glomerulonephritis (Common) Renal Amyloidosis (very rare); Granulomatous nodules/inflammation (due to Immune mediated microfilarial destruction) (High antibody level results in the destruction of microfilaria within the pulmonary capillaries as they are released from the adult)
If you have found Granulomatous nodules/inflammation in a lung biopsy what does it mean?
the Dz has progressed to the greatest degree of pulmonary pathology & you are probably seeing other severe clinical signs
You have a canine you KNOW is HW+, but the SNAP test came back negative, how could you explain this?The canine is hosting HWs that are <5 mo old (less than the PPP) or the canine is a puppy who is >6 mo old.
How old do HWs have to be before the SNAP Antigen ELISA will detect them? Why?>7-8 mo old; the antigen the ELISA tests for is produced by MATURE females
Why do we use the SNAP Antigen ELISA vs other tests?This test is fast & easy to use, they are most sensitive method to screen an asymptomatic population or verify a suspected heartworm infection & the specificity HIGH
The amount of mature female antigen detects is?Directly, but imprecisely related to the # of mature female HWs present
How will you test for HW in cats?Feline Triple SNAP test = tests for FIV, FeLV & HW antigen
How should you document the results of a "negative" HW test? Why?No Antigen Detected You should NEVER put down the result NEGATIVE the results of the test are not 100% accurate, false positives & user errors can occur
What other ways can you detect HW microfilaria?Modified Knott's test which fixes & stains the microfilaria,
or place blood in capillary tube, spin it down & observe the buffy coat for microfilaria
What other ways can you detect adult HW infection?X-RAYS, look for the 'Reverse D'
Torturous enlarged vessels (prune effect), inflammation, & bronchiole interstitial pattern (in cats & dogs)
What method is often used to confirm HW Dz in cats? Ultrasound
You have a dog who tested + for HW, you think it might be a mod/severe case & you want to see if there is RT ventricular enlargement, How might you do that?ECG & ultrasound
What is the Tx for HW? Where & how is it given?Melarsomine dihydrochloride (Immiticide)is the only FDA approved drug! 2 doses are given via the deep IM injection into Lumbar Muscles, 24 hrs apart
During HW Tx & recovery, what must be strictly restricted?Exercise
HW Tx is very painful & dangerous, what are the likely complications of Tx? (3)1) Severe pulmonary thromboembolism
2) Obstruction of blood flow through pulmonary arteries due to the presence of dead heartworms and lesions in the arteries and capillaries of the lungs
3) Fever, cough, hemoptysis (blood in the sputum) & sudden death.
Your client being Tx for HW is showing CS of Pulmonary embolism, what can you give to reduce the CS?Diminishing doses of glucocorticosteroids can help to control clinical signs of pulmonary thromboembolism, which can be severe after adulticide therapy if infection is heavy and pulmonary arterial disease is extensive.
What steroid would give to lessen the CS of Pulmonary embolism? How would you give it?Prednisone; dosed at 0.5 mg/kg BID for the 1st week & 0.5 mg/kg 1 daily for the 2nd week, followed by 0.5 mg/kg every other day for 1 to 2 weeks.
What zoonotic obligate intracellular bacteria do filarial nematodes carry?G(-) bacteria; genus Wolbachia (Rickettsiales)
What complications does Wolbachia add to animals w/ HW infxn?The major surface protein of Wolbachia (WSP), induces a specific IgG response in dogs infected with D. immitis; WSP may contribute to pulmonary & renal inflammation (production of endotoxins)
What condition can an immune response to Wolbachia cause in humans?Elephantitis
How will you Tx your patient who has HWs & Wolbachia infxn?Give Doxycycline 10 mg/kg twice daily for 4 weeks before administration of melarsomine for HW Tx, to reduce Wolbachia numbers in all stages
What bonus thing does Doxycycline do?Works on heartworms by causing infertility in female worms, 3rd & 4th stage larvae
Why is the slow-kill method of the HW Tx not recommended?RESISTANCE
How will you know if your HW Tx worked?HW antigen undetectable 6 mos post-Tx
What is Caval syndrome?It acutely in some heavily infected dogs when large numbers of adult HW that partially obstruct blood flow through the tricuspid valve & also interfere with valve closure.
What will you see in a dog with Caval Syndrome? (4)1) Congestion of the liver
2) Sudden onset of lethargy & weakness
3) Coarse systolic murmur
4) +/- hemoglobinuria & hemoglobinemia.


Question Answer
5 month old puppy in your clinic came in b/c of a wound. You collect blood from the wound & see microfilaria in the microscope. Likely suspect?Dipetalonema reconditum = HW mimic that DOES NOT cross react w/ HW test (SNAP test will be negative)
If you do a Knotts test on Dipetalonema reconditum what will the result be?Positive (but the ELISA SNAP test will be negative!)
Dipetalonema reconditum is _ in dogs?Non-Pathogenic!
Dipetalonema reconditum is xmitted byFleas
What is Stephanofilaria?A Very tiny filarid found in dermal lesions on the ventral abdomen of cattle
What is the IH for Stephanofilaria?Haematobia (horn fly)
“Humpsore” is causes by what species of Stephanofilaria? Where do lesions appear?S. assamensis; lesions occur on the hump, neck & legs of cattle