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Heartworm basics

Description

Brief overview of D. immitis infection in dogs and cats.
Cassie Bowling
Flashcards by Cassie Bowling, updated more than 1 year ago
Cassie Bowling
Created by Cassie Bowling over 3 years ago
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Resource summary

Question Answer
Distribution North America (and parts of Canada)
Prevalance (rate in endemic area, sex, age, breed, % in Alabama) In 40-60% of outdoor dogs in endemic areas. Males infected 4x more 5x more common in outdoor dogs Most infections between 3 and 15 years More common in large breeds 3.73% in Alabama
Potential Hosts and habitats Canids, felids, ferrets, sea lions, humans, others Adult worms found in right ventricle, pulmonary arteries, sometimes in right atrium, vena cava, eye, skin, and central nervous system Microfilariae in circulating blood
Dirofilaria immitis (long, slender, white) Males are smaller and have a corkscrew tail Females are about twice as big Bigger than Dipetalonema reconditum
Microfilariae (tapered at anterior end, visible cellularity at head, tail straight or hooked) More numerous in hosts that other filariids May move in place
What is microfilarial periodicity? It is the variation in the number of microfilariae that appear in circulation over time. D. immitis microfilarial have nocturnal and incomplete periodicity, meaning more are present in the evening hours, but they never disappear completely. Diurnal=daytime activity Complete=complete disappearance for a certain amount of time
What is Heartworm Development Unitss (HDUs)? Every degree above 57 degrees (unlikely to develop below)
Life Cycle in dogs 1) Mosquito feeds on dog with circulating microfilariae 2)develop to infective larvae 3) Larvae deposited at skin surface when mosquito feeds 4) 2 molts on way to heart and lungs 5) Worms mature in heart or lungs, mate, and produce microfilariae
What is disease a result of? Primarily the presence of adult worms in the right ventricle and pulmonary arteries. Worms irritate the vessel walls and create inflammation (villous endarteritis). Fragments of dead worms (emboli) lodge in vessels.
Clinical signs Villous endarteritis, right ventricular hypertrophy, exercise intolerance, liver and kidney disease, coughing, blood in sputum, condition lost, anemia, proteinuria
Vena Cava Syndrome or Caval Syndrome Worms present in vena cava partially obstruct blood flow through tricuspid valve and interfere with valve closure. Results in severe congestion of the liver, heart murmur, sudden onset of severe lethargy and weakness followed by hemoglobinuria
Diagnostics HIstory/Clinical signs Microfilariae in direct smear, modified Knott's test, and filter test Antigen test ECG Rads, angiography, echo CBC and Chemistry
What is antigen blocking, why is it an issue, and how can it be taken care of. It is when the D. immitis antigen is completely bound by anti-D. immitis antibodies, preventing it from binding to the capture antibody. This results in false negatives. It can be remedied with heat treatment or acid treatment. Heat: 1 mL of plasma/serum in tube, place in a dry heat block for 10 minutes) centrifuge for 5 minutes, remove supernatant, use to perform test. Acid: Treat with TCA followed by Tris buffer
Treatment Removal of adult worms (immiticide, 2.5 mg/kg) Surgical extraction Removal of microfilariae Place of prevention (slow kill)
What is Wolbachia? Gram negative bacteria Related to Ehrlichia and Anaplasma spp. Endosymbiote Located in hypodermis, ovaries, oocytes, and embryonic D. immitis Important for biological and reproductive function of host Can be treated with doxycycline or minocycline
Life cycle in cats 1) L3 deposited by mosquitos 2)L3 molts to L4 in subcue tissue 3) L4 molts to L5 during migration to heart 4) Arrive in heart, carried to lungs. Most die, few mature.
What is HARD? Heartworm Associated Respiratory Disease in cats. Treat with symptomatic therapy and removal/slow kill.
Acanthocheilonema reconditum Host Location Structure Life Cycle Treatment Significance Found in canids In subcue tissue or abdominal cavity Males .5 inch, females 1 inch Microfilariae taken up by fleas or lice, mature to infective stage, deposited at feeding, words mature. No treatment required Can be confused with D. immitis
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