Heartworms- Parasitology

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Heartworms- Parasitology
2014-05-14 13:07:40

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  1. life cycle of dirofilaria immitis
    • 1. dog 1 has S5 (adults) and S1 (microfilaria)
    • 2. mosquito takes blood and picks up S1
    • 3. S1 molts to S3 in mosquito (time depends on the temp)
    • 4. mosquito inserts S3 and saliva into dog 2
    • 5. S3 molts to S4 in SQ tissue
    • 6. S4 stays in SQ tissue for 100 days
    • 7. S4 molts to S5 (pre-adult) and moves to PA
    • 8. S5 stays in PA for 80 days then molts to adult S5
  2. oral preventatives
    • DEC
    • Heartgard
    • Interceptor
    • Sentinel
  3. topical preventatives
    • Revolution
    • Advantage Multi
  4. Injectable preventatives
    Proheart 6
  5. "Nemacide" "Dirocide" Filaribits"
    Diethycarbamazine citrate "DEC"

    • Pfizer
    • oral
  6. "Heartgard"

    • Merial
    • oral
  7. "Interceptor"
    Milbemycin oxime

    • Novartis
    • oral
  8. "Sentinel"
    Milbemycin oxime & Lufenuron

    • Novartis
    • oral
  9. "Revolution"

    • Pfizer
    • topical
  10. "Proheart 6"

    • Ft. Dodge
    • injectable
  11. "Advantage Multi"
    Moxidectin & Imidacloprid

    • Bayer
    • topical
  12. Diethylcarbamazine citrate "DEC"
    Nemacide, Dirocide, Filaribits
  13. Ivermectin
  14. Milbemycin oxime
  15. Milbemycin oxime & Lufenuron
  16. Selamectin
  17. Moxidectin
    Proheart 6
  18. Moxidectin & Imidacloprid
    Advantage Multi
  19. "Heartgard Plus"
    Ivermectin & Pyrantel pamoate

    (pyrantel added for intestinal parasite control)
  20. etiology of heartworm
    Dirofilaria immitis
  21. heartworm disease means the animal:
    • has heartworms
    • suffers from the debilitating symptoms
  22. heartworm family
  23. new strain
  24. first appearance 
    Hennepin County, Minnesota- 1937
  25. DEC only killed
    stage 3 infective larvae (so had to give every day)
  26. stages of heartworm
    • stage 1- microfilaria (dog 1&mosquito)
    • stage 2- no name stage (in mosquito only)
    • stage 3- infective stage (mosquito & dog 2)
    • stage 4- pre-adult stage (dog 2 only)
    • stage 5a- immature adult stage (dog 2 only)
    • stage 5- mature adult stage (dog 2 only)
  27. most common transmission
    Culex mosquito (common in homes of people)
  28. causes for the 50% of dogs positive on occult test for Dirofilaria immitis but negative for microfilaria
    • same sex (all male or all female so cannot reproduce microfilaria to be present in blood)
    • WBC attacks
  29. need at least __ females to get positive results on antigen test
  30. filarid that may be mistake for Dirofilaria immitis
    Acanthochelonem reconditum 

    (transmitted by the flea, Ctenocephalis felis/canis)
  31. D. immitis vs. A. reconditum
    • D. immitis
    • shape: tapered head, straight
    • movement: undulate in one spot
    • body cells: homogenous

    • A. reconditum
    • shape: blunt head, button hooked tail
    • movement: foward, quickly!
    • body cells: salt&pepper
  32. diagnosis
    • blood samples:
    • direct smear (only 50% dogs have microfilaria)
    • modified knot's test 
    • difil test (best microfilaria test)
    • hematocrit tube (PCV- poorest test)
    • occult test (2 types: antibody or antigen)
    • history
    • radiology
    • echocardiography
  33. heartworm symptoms noted by owner
    • coughing (hw die and go to lungs)
    • loss of stamina
    • ascites (blood backs up into liver to abdomen)
    • front legs bowed outward (to take pressure off ribcage to breathe easier)
  34. blood samples- microfilaria
    direct smear: fresh blood taken from vein, a drop places on slide, cover and observe for microfilaria in motion (64%)

    modified knot's method: formaldehyde 2% and centrifuge to localize the microfilaria at the bottom of a tube (84%)

    difil (milipore filtration) test: 1 mL of blood mixed with 1 mL lysing solution and filtered through difil paper. paper is stained, viewed under 4X or 10X. (concentrates the microfilaria) *most reliable microfilaria test*

    microhematocrit tube: blood spun down for PCV check. view the buffy coat to see microfilaria moving around. (poorest for microfilaria)
  35. best test for dogs
  36. best test for cats and why?

    need at least 3 female worms for a positive antigen test and cats are not likely to have that because not a definitive host so do not have many heart worms to began with.
  37. heart worm symptoms noted by owner
    • coughing (HW die and go to lungs)
    • loss of stamina
    • ascites (blood backs up into liver to abdomen)
    • front legs bowed outward (to take pressure of rib cage to breathe easier)
  38. 2 types of occult tests
    • antibody: MAT (microfilariae antibody test)
    • DAT: (dirofilariae anitbody test)

    • antigen: ELISA, immunochromatographic test systems 
    • occult of choice/most diagnostic
  39. ELISA
    Enzyme Linked Immunosorbent Assay test

    (can give weak/strong positives)
  40. any test that detects antigens or antibodies
    occult test
  41. changes typically seen in canine radiograph with HW
    • enlargement of pulmonary artery at 1 o'clock
    • enlargement of ride side of heart ("inverted D")
  42. macrocylic lactones
    • Ivermectin
    • Milbemycin oxime
    • Selamectin
    • Moxidectin

    (anthelmintic activity against microfilaria, 3&4th stage larvae)
  43. 7 methods of HW prevention
    • Diethylcarbamazine citrate (Filaribits)
    • Ivermectin (Heartgard)
    • Milbemycin oxime (Interceptor)
    • Milbemycin oxime&Lufenuron (Sentinel)
    • Selamectin (Revolution)
    • Moxidectin (Proheart 6)
    • Moxidectin&Imidacloprid (Advantage Multi)
  44. Ivermectin kills
  45. How does Sentinel work?
    does not kill the adult flea but breaks the life cycle by inhibiting egg development: added Lufenuron prevents the formation of chitin, a substance needed for the egg shell formation
  46. first topical to protect against heartworms and fleas
    Revolution (Selamectin)

    safe for cats, and dogs including collies
  47. macrocylclic lactones (ivermectin, milbemycin oxime, selamectin, moxidectin) will:
    • clear microfilaria
    • sterilize adults
    • shorten lifespan of adults

    (usually complete with in 6-12 months of oral dosing monthly)
  48. treatment for adult heartworms
    Immiticide (Melarsomine dihydrochloride)

    • Merial
    • IM injections of 2, 24 hr interval
    • (dogs with greater risk, 3 injection protocol of one initial dose, followed in 4-6 wks with a 2 dose treatment: treatment of choice of American Heartworm Society)
    • do this to gradually kill the adults rather than killing them all at once and clogging the pulmonary artery.

    kidney&liver function necessary because it is an arsenic
  49. where is Immiticide (Melarsomine dihydrochloride) administered?
    deep epaxial lumbar muscles
  50. if dog is pathogenically unable to receive treatment with immiticide, what is the alternative?
    • put them on macrocyclic lactones to:
    • deplete microfilaria
    • sterilize adults
    • shorten lifespan of adults

    will take months-yrs but safer than insulting the liver
  51. all macrocyclic lactones have a "reach back" of
    2 months
  52. old/dangerous adulticide
    Caparsolate (Thiacetarsamide sodium)

    • 4-6 injections given IV
    • dogs died after being used as a preventative every 6 months from liver failure
  53. adulticides not in use today
    • Levamisole HCl
    • Fenthion (Talodex) once sold through black market in Tx
  54. microfilaricide treatment
    • Ivermectin (drug of choice)
    • Selamectin (Revolution)
    • Milbemycin (Interceptor)
    • Dithiazine Iodine (Dizan)
    • Levamisole HCl- no longer used
    • Fenthion- can be damaging to liver bc it is an organophosphate
  55. adult worms when treated with adulticide will die in
    10-14 days

    they are swept to the lungs where they become lodged in the alveoli and are decomposed by neutrophils, macrophages, and lymphocytes. the lungs are very susceptible to internal hemorrhage and tissue abuse, thus the dogs MUST NOT excersize for at least 6 weeks.
  56. classification of HW disease
    • class 1- asymptomatic to mild hw disease
    • no radiographic signs/anemia signs
    • occasional cough
    • no laboratory problems
    • (treatment!)

    • class 2- moderate
    • radiographic signs present
    • anemia is obvious with PCV less than 30%
    • mild proteinuria
    • mild elevation of laboratory data
    • some loss of condition
    • cough
    • (treatment! must stabilize prior to)

    • class 3- severe
    • radiographic signs
    • significant anemia
    • (no treatment! stabilize&alternate dosage)
  57. Caval Syndrome
    condition that develops in heavily infected dogs

    large numbers of adult hws in the right atrium&right ventricle cause the tricuspid valve to close improperly&obstruct blood flow through the tricuspid valve, extra hws back up through the vena cavas as far as the liver and right jugular vein

    produces lethargy, weakness, hemoglobinuria, hemoglobinemia, tricuspid valvular insufficiency, noticeable jugular pulsations (veins do not usually thump like arteries do-this is caused from back up of blood flow) 

    confirmation can be made with echocardiograph/radiographs
  58. Caval Syndrome also known as
    Dirofilarial Hemoglobinuria (since microfilaria are seen in the urine)

    vena cava syndrome
  59. Wolbachia
    most filarial nematodes, including Dirofilaria immitis, harbor obligate intracellular, gram negative bacteria belonging to the Genus Wolbachia (Rickettsiales)

    contribute to pulmonary and renal inflammation through its surface protein Wolbachia Specific Protein (WSP) producing endotoxins

    pretreatment with doxycyline (clindamycin) (antiobiotic) may help to kill Wolbachia
  60. heartworms are usually attached to the 
    chordae tendineae
  61. convert C to F
    9/5 x C+32= F
  62. number of HW develop in the heart normally
    • dog: 8
    • cat: 0-2
  63. Immune Recognition
    previously infected dogs less HW will survive due to antibody production
  64. why treat microfilaria?
    • potential threat to other dogs, cats, ferrets
    • pathological changes make treatment of adults more difficult (brain infarcts, heart infarcts, renal problems)
    • anaphylactic shock/death if given prevention
  65. common mistake for diagnosing Dirofilaria immitis
    Acanthocheilonema reconditum
  66. anaphylactic shock reactions in HW positive dogs
    causes: DEC, Interceptor, Dichlorvos

    • Type 1 hypersensitivity (anaphylactic):
    • mast cells (basophils) release histamines that dilate blood vessels
    • hypotension ensues, resulting in reduced cardiac output
    • loss of tone in all peripheral vessels
    • blood cannot get back to heart and lungs to receive O2
    • animal goes into coma and dies from hypoxia (deficiency in amount of oxygen reaching the tissues)
  67. symptoms of anaphylactic shock
    (occurs within 20 min time frame)

    • dilated pupils, diarrhea, vomiting
    • WBC goes down in 1 hr, alkaline phosphatase increases rapidly, platelets decrease instantly by as much as 10,000
  68. most common symptom of toxicity, such as acidosis, resulting from increase CO2
  69. final symptom of shock (animal has gone through compensatory, progressive, and irreversible stages)
    dilated pupils
  70. what type of name is "Immiticide"?
  71. non-proprietary name for Immiticide
    Melarsomine dihydrochloride
  72. class 1 HW treatment
    two injections 24 hrs apart

    • each side of lumbar area, 22 gauge
    • recheck in 6 months
  73. class 2 and 3 treatments
    • one injection
    • 30 days later give 2 injections 24 hrs apart

    this allows for slower kill time, reducing possibility of thromboembolisms from the dead worms passing into the lungs 
  74. following treatment of HW
    restricted exercise for at least 6 wks to decrease possibility of thromboembolisms in the lungs as adult hw start dying from the adulticide and become dislodged and travel to the lungs to be reabsorbed by neutrophils and macrophages

    (phagocytosis continues 6-9 months)
  75. life span in dog/cat
    • dog: up to 7 ys
    • cat: 2-5 yrs
  76. signs of hw disease in cats usually develop during one of two stages
    • arrival of immature S5 in pulmonary artery
    • death of adult hw
  77. HARD
    heartworm-associated respiratory disease

    go to lungs to be reabsorbed and cause cat to cough/gag

    often mis-diagnosed as asthma or allergic bronchitis
  78. cat unable to breathe all of a sudden..
    • hw copulate, release grip from chordae tendineae, and block pulmonary artery
    • blockage=no blood/air to lungs

    die w/in 15 min
  79. PTE
    Pulmonary Thromboembolism

    thrombus:clot  embolus: moving clot
  80. gold standard test for dog
    antigen test
  81. antibody test advantages for cat
    can detect antibodies in both male&female worms 

    antigen test not helpful since cats usually only have 1-2 hw
  82. hw prevention for cats
    • Revolution (Selamectin)
    • Heartgard (Ivermectin)
    • Interceptor (Milbemycin oxime)
    • Advantage-multi (Moxidectin, Imidacloprid)
  83. first oral hw preventative, Heartgard (Ivermectin), released by Merial in
  84. Heartgard Plus released in
  85. Sentinel (addition of Lufenuron to Milbemycin oxime to control fleas) in
  86. first topical, Revolution released in
  87. first injection, Proheart 6, released in