Parasitology: heartworms

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jill.hinton
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Parasitology: heartworms
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2015-07-11 17:09:49
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parasitology lecture on heartworms
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  1. Heart worm taxonomy
  2. Survey in _(year)_, by American Heartworm Society, revealed _______ dogs were diagnosed with hearworm disease across the US. This number has more than doubled in recent years.
    • 2004
    • 255,000
  3. The first case of heartworms was found in a ______ in the _____.
    • feline
    • 1920's
  4. Heartworm disease means the animal 
    1.
    2.
    • 1. has heartworms (etiological agent) AND 
    • 2. animal suffers from the debilitating symptoms associated with the infection of hearworms
  5. Applies to 1st stage larva of Dirofilaria immitis. Only talking about first stage larva and only when referring to heartworms in the definitive host.
    Microfilaria
  6. Dirofilaria immitis found in its definitive host the canidae is found in 3 primary regions in the United States:
    • 1st - Gulf coast
    • 2nd - East Coast
    • 3rd - Great Lakes
  7. Concern that a subpopulation of heartworms in certain areas has developed resistance to heartworm preventative medications. What is this new strain?
    MP3 strain
  8. This new subspecies of heartworms _______, this identified as subspecies to D. immitis and showed resistance to __________
    • MP3
    • Fipranil
  9. The strain was isolated from a naturally infected dog in __________. It was placed in a Beagle to test the efficacy of four commercially available heartworm preventatives. Which one tested at 100% efficacy?
    • Northeast Georgia in 2006
    • Immidicloprid
  10. This heartworm is most commonly found in large cats of Africa
    Dirofilaria ripens
  11. A parasite that is infecting an animal that is not its definitive host will have differences, making it_______.
    1.
    2.
    3.
    • less pathogenic
    • 1. parasite will not be as big
    • 2. will not reproduce as well
    • 3. life span will be shorter
  12. What makes heartworms spread so easily?
    • 1. pet owners can't afford heartworm preventatives
    • 2. confusing as to when they should start and stop giving preventatives
    • 3. unwillingness to accept the possibility of heartworm transmission
  13. Heart worm epidemiology:
    Diagnosed Dirofilaria immitis all States including world wide from ______ to _______. 
    However there has been no recorded transmission to occur in _________ although it has been diagnosed here.
    • Europe to Asia
    • Alaska
  14. Most important factor contributing to further dissemination of Dirofilaria immitis disease (heart worms)
    Relocation of infected, microfilaremic dogs
  15. First appearance of heartworms in the United States:
    Hennepin County, Minnesota in 1937
  16. Stages of the Heartworm
    include where each stage is found
    • Stage 1 - Microfilaria - 1st adult and mosquito
    • Stage 2 - No name - mosquito only
    • Stage 3 - Infective stage - mosquito and 2nd adult (under skin 1week)
    • Stage 4 - Pre-adult Stage - 2nd adult only (migrate under skin 100 days)
    • Stage 5a - Immature Adult Stage - 2nd adult only (in pulmonary artery 80 days)
    • Stage 5 - Mature Adult Stage - 2nd adult only
  17. Heart worm Transmission
    _____ is common in homes of US and effects both dogs and cats
    Culex mosquito
  18. 50% of all dogs positive on occult test for Dirofilaria immitis, are known to be negative for microfilaria. Why?
    • 1. All adult HW are same sex
    • 2. WBC have attacked and engulfed the foreign proteins of the microfilaria
  19. There is another filarid other than D. immitis that is transmitted by the flea. What is this filarid and the name of the flea?
    • Acanthochelonema reconditum
    • Ctenocephalis felis "the cat flea"
  20. Stage 1 of this blood filarid will appear almost identical in a direct smear to that of Dirofilaria immitis.
    Acanthochelonema reconditum
  21. Why is it important to know the difference between D. immitis and A. reconditum?
    Both filarids produce 1st stage larva that will appear in the blood. A. reconditum is not pathogenic and does not need treatment although it can be treated
  22. History for diagnosis of heartworms, symptoms of a HW (+) dog:
    • "not doing well" - ususally reason owner brings animal in
    • coughing
    • loss of stamina
    • ascites - fluid in abdomen
    • front legs bowed out - due to stress, elbows will rotate out
  23. Diagnosis of Heartworm Disease:
    1.
    2. 
    3.
    4.
    • 1. blood samples
    • 2. history - usually reason dog is in clinic
    • 3. radiology
    • 4. echocardiography
  24. Best and worst Diagnosis for microfilaria:
    • Direct smear
    • modified knots test
    • Hematocrit tube - worst for microfilaria
    • difil test - best for microfilaria
  25. Best diagnosis test for Heartworms
    Occult Test - antibody or antigen test
  26. Why is the modified Knots test no longer used to diagnose HW?
    A filtration test that used formaldehyde - this is a cancer producer
  27. When diagnosing HW, radiology diagnosis is used to________
    confirm severity of infection
  28. Blood sample - Microfilaria
    Fresh blood is taken from the vein and a drop is placed on the slide. Cover and observe for microfilaria in motion (____)
    Direct Smear 64%
  29. Blood sample - Microfilaria
    Utilizes formaldehyde 2% and a centrifuge method to localize the microfilaria at the bottom of a tube (____)
    Modified Knot's Method 84%
  30. Signs of caval syndrome
    Heart will appear as an inverted D shape on echochardiogram and a cap over pulmonary artery
  31. Blood sample - Microfilaria
    1mL of blood mixed with 1mL of lysing solution and filtered through difil paper. Paper is stained and viewed.
    Difil (Millipore filtration test) test - most reliable in detecting microfilaria
  32. Blood sample - Microfilaria
    blood is spun down for a PCV check. View above the buffy coat to see the microfilaria moving around. Efficacy?
    • Microhematocrit Tube test
    • Poorest of the diagnostic blood test
  33. Poorest method for diagnosing microfilaria
    Microhematocrit tube
  34. When differentiating D. immitis from A. reconditum in a difil test we look at the anterior end. What difference is visible to us?
    • A. reconditum anterior end is blunt
    • D. immitis anterior end is tapered
  35. Blood Sample Occult tests
    Two types of Occult test:
    1.
    2.
    • 1. Antibody Test - MAT (microfilaria antibody test) and DAT (dirofilaria antibody test)
    • 2. Antigen test
  36. Occult test of choice and the most diagnostic test on the market
    Antigen test
  37. These Occult tests are no longer used since the antigen test is considered far superior in diagnosing Heart Worms
    • Antibody Test
    • MAT - microfilaria antibody test
    • DAT - dirofilaria antibody test
  38. 3 medications that will react to the microfilaria resulting in anophylactic chock and death
    • 1. milbemycin oxime (Interceptor - Novartis)
    • 2. organophosphates (Diclorvus)
    • 3. Diethylcarbamazine citrate (DEC)
  39. What are reasons as to why we would get a false negative heartworm (1)antibody test and a false negative heartworm (2)antigen test:
    1.
    2.
    • 1. antibody - Will get a positive if there are ANY foreign worms in the body. Other parasitic worms are detected other than D. immitis
    • 2. antigen - some animals have developed immune complexes against the antigen test giving a false negative
  40. Any test that detects antigens or antibodies is considered an _______
    Occult Test
  41. Companion Animal Parasite Control (CAPC) recommends what testing to veterinarians?
    Microfilaria and antigen tests annually on dogs including those on HW preventatives
  42. Why can't we use the antigen test to detect HW in cats?
    There are not enough adults present to get a (+) antigen test. We use the antibody test instead
  43. Two Antigen test available for detecting circulating HW antigens.
    ELISA (Enzyme Linked Immunosorbent Assay Test) and immunochromatographic test
  44. We can reconcile unexpected negative results by simply __________
    retesting with a different test
  45. Was once written that all antigen test required at least _______ to get a positive antigen occult test. This is not held as absolute today.
    three mature females
  46. A graded test reaction can be recognized by __________ but quantitative results are not displayed by ___________.
    • ELISA test systems
    • immunochromatographic tests
  47. This antigen or ELISA test can be run individually or as a group of tests, which is called ________.
    batch testing
  48. Other causes of false negatives on a Heartworm test
    (1)blood sample not warmed up to room temperature, (2)infection is light, (3)female worms have yet to mature, or (4)they are only males in this infection
  49. Before starting heart worm treatment the American Heartworm Society recommends ________
    confirming all positive ELISA test
  50. Largest test labs in United States.
    These labs checked over _________ in 2010 using exclusively antigen and not antibody tests.
    • Idexx and Antech
    • 63,000
  51. Why aren't more dogsprotected from HW each year?
    1. 
    2.
    3.
    4.
    5.
    • 1. 24% of pet owners don't spend money at clinics, instead they get their info and products from Wal-Mart or Petco
    • 2. Clients have no understanding of HW
    • 3. Prices of treatment and prevention deter clients
    • 4. 1/3 of all pet owners only go to the vet for vaccines
    • 5. 1/3 only go when animals are sick
  52. According to research, the two items critical in persuading clients to further health care are _________ and _________.
    communication and consistency
  53. Why are ELISA test not as sensitive to Heartworms in cats?
    • 1. due to low heartworm burden
    • 2. immature female heartworms in the early stages of development
    • 3. strictly male infection
  54. Overall, the most useful tests to confirm heartworm infection in cats are _________ or ________ or __________
    • Serology (antibody levels or antibody test)
    • thoracic radiographs - still not useful
    • echocardiography - still not useful
  55. Best heartworm testing for cats is _________ not thoracic radiographs or echocardiography, why?
    • serology (antibody) - antibody levels or antibody testing
    • why? because there are not enough heartworms present to get a positive test
  56. Clinical picture of heartworms in cats. (What causes death)
    If cats have a male and female they will attach to chardi tendani on tricuspid and mitral valves and release when the cat breathes taking them to the pulmonary artery and then to the lungs. Adults caught in the Pulmonary artery and block the flow. Cat will die in minutes due to hypoxia
  57. _____ - lack of oxygen to the tissues
    hypoxia
  58. After treating animal for a heart worm infection you must wait to retest with an antibody test or you can get a false positive. Explain.
    antibody test will only show whether an infection occured. It will detect antibodies still present from a previous infection even when no adults are present. It will detect the hormones still present in the blood
  59. This test is most useful in testing for heart worms in cats; checks for the antibodies produced by the immune system when the body is fighting a heart worm infection.
    antibody test
  60. An immune response can be produced by both male and female heart worms and the response is seen as early as ____________.
    2 months post infection
  61. When testing for heart worms this is the most logical test to run on asymptomatic cats.
    antibody test
  62. What is the downside of the antibody test?
    antibody test can only show whether an infection occurred. It cannot show if the animal is still infected
  63. Changes typically seen in a positive heart worm canine radiograph
    • 1. enlargement of the pulmonary artery at 1 o'clock 
    • 2. enlargement of the right side of the heart commonly called the "inverted D"
  64. Which 2 views do we use when diagnosing heart worms via radiograph? If positive what can be seen with each view?
    • 1. lateral view - heart is enlarged more than 5 ribs in length
    • 2. ventral dorsal view - heart sits on sternum (inverted D)
  65. Changes that can be seen in a heart worm positive cat:
    What can not be seen due to the low HW burden?
    • 1. enlargement of the main lobar and peripheral pulmonary arteries
    • 2. the pulmonary artery is greater than 1.6xs the width of the ninth rib
    • no "inverted D"
  66. The body wall of an adult heart worm is highly echogenic, therefore a positive echocardiograph will show the worms appearing as _________ where the imaging plane cuts across loops of the parasite.
    "equal signs"
  67. These are novel parasiticides and insecticides that are produced through fermentation by soil-dwelling microorganisms
    Macrocyclic lactones
  68. Macrocyclic lactones includes the following preventative medications
    • Ivermectin
    • Milbemycin oxime
    • Selametin
    • Moxidectin
  69. Macrocyclic lactones are highly therapeutic possessing anthelmintic activity against _____, ______, and in some instances ______________.
    microfilaria, 3rd and 4th stage larvae, young adult heartworms (S5a)
  70. Prevention of heartworm disease medications
    1. This is an oral medication to be given daily as a HW preventative by Pfizer (now called _____) would kill stage 3 HW and came in the proprietary name of Filarabits, Nemacide, Dirocide
    • Zoetis
    • DEC diethylcarbamazine citrate
  71. HW preventatives
    2. An oral manufactured by Bayer, came in the proprietary name of Heartgard. For dogs and cats
    Ivermectin
  72. HW preventatives 
    3. Oral by Novartis - Interceptor
    Milbemycin oxime
  73. HW preventatives
    4. Oral by Novartis that would kill other parasites as well as being a HW preventative - Sentinel
    Milbemycin oxme + Lufenuron
  74. HW preventatives
    5. 1st topical HW preventative by Pfizer (____), also took care of other parasites such as intestinal parasites, mange mites, etc. - Revolution for dogs and cats
    • Zoetis
    • Selamectin
  75. HW preventatives
    6. 1st inject-able HW preventative by Ft Dodge - Proheart 6
    Moxidectin
  76. HW preventative
    7. Topical by Bayer - Advantage Multi for dogs only
    Imidacloprid + Moxidectin
  77. Liquid Diethylcarbamazine Phosphate is
    Styrylpyridium chloride
  78. A non-macrocyclic lactone that was the first oral heart worm preventative. To be given daily, would kill only S3 larva and would react with S1 microfilaria.
    DIC - diethylcarbamazine citrate
  79. Before starting prophylaxis with DlC __________ is mandatory
    testing for microfilariae
  80. This product was dispensed as a liquid in the food of dogs in the early 70s, for dogs that would not take a pill or for owner with many dogs. A non-macrocyclic lactone, Styride Caricide - last of this product was "Dirocide"
    Styrylpyridium chloride diethylcarbamazine phosphate
  81. DIC may be started on dogs with _____ infections only.
    adult heart worm
  82. Oral heart worm preventatives of importance:
    • DEC
    • Ivermectin
    • Milbemycin oxime
  83. Heartworm preventatives that will react with S1 larvae, microfilaria
    • Diethylcarbamazine citrate
    • Organophosphates - Diclorvus (Task)
    • Milbemycin oxime
  84. Protocol for heartworm prevention concerning Ivermectin and Milbemycin oxime (this is no longer considered effective in places like Houston)
    recommended to be given one month before heartworm season up until one month after heartworm season
  85. Ivermectin:
    • 1st alternative to DEC
    • "heartgard" by Merial
    • killed L3 and L4
    • oral (chewable), every 30 days
    • 1st heartworm preventative made for the feline
  86. Ivermectin dosage for dogs
    6mg/kg
  87. Ivermectin also came as Heartgard Plus when __________ was added
    Pyrantel Pamoate - added for intestinal parasite control
  88. 50% of dogs with heartworms will be negative for microfilaria, why?
    • wbc are doing their job and engulfing the microfilaria
    • all adult heartworms are the same sex and cannot reproduce
  89. Family Avermectins include:
    • Ivermectin
    • Selamectin
    • Doramectin
    • Eprinomectin
  90. Warning with Ivermectin. What dogs are unusually sensitive to high doses of ivermectin
    • Collie dogs have autosomal recessive inheritance 
    • and other glycoprotein deficient dogs
  91. Milbemycin oxime
    • Interceptor - Novartis 
    • Oral 
    • L3, L4, hooks, rounds, and whips 
    • given once a month 
    • * used off label - sterilize M HW and lessen life expectancy if given 3-4 months
  92. Milbemycin oxime + lufenuron
    • Sentinel - Novartis 
    • Oral ovitrol effect - prevents formation of chitin 
    • L3, L4, hooks, rounds, and whips 
    • flea must bite the dog. does not kill the adult
  93. Mechanism of action of avermectin and Milbemycin oxime
    • Suffocates the parasite. 
    • Behind the neuron transmitter glutamate chloride channel between a nerve and the muscle. This interrupts communication from CNS and does not allow the muscle to activate. Prevents breathing, suffocate and die
  94. To topical products for heartworm prevention on the market today:
    1.
    2.
    • 1. Selamectin 
    • 2. Moxidectin + imidacloprid
  95. Selamectin
    • Revolution - Pfizer 
    • dogs 6-7 wks and older 
    • 1st topical to protect against heartworms and fleas
    • in cats: hw prevention, kills fleas, ovitrol, ear mites, rounds, hooks, 
    • in dogs: hw prevention, kills fleas, ovitrol, ear mites, sarcoptic mites
  96. Moxidectin + Imidacloprid
    • Advantage Multi - Bayer 
    • Dogs and cats topical
    • Prevent heartworms
    • imidacloprid will stay on the surface primarily
    • Moxidectin will go to the bloodstream systemically
  97. Moxidectin injectable
    • Proheart 6 - Ft. Dodge 
    • injectable once every 6 months to prevent microfilaria development

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