Parasitology lecture: Heartworms

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Parasitology lecture: Heartworms
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2015-07-11 18:36:42
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Heartworms
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Heartworms
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  1. Taxonomy of heartworms
    • Phylum: Nematoda
    • Class: Nematode
    • Order: Spirurida
    • Superfamily: Filarloidea
    • Genus: Dirofilaria
  2. First case of heartworms
    1937 in Hennepin Country Minnesota (dog)
  3. Heartworms can affect which species?
    Cat, dog, wolves, ferrets, foxes, sea lions and humans
  4. Having heartworm DISEASE means
    • Animal has HW
    • Animal suffers from debilitating symptoms
  5. Dirofilaria immitis definitive host
    Canidae
  6. Distribution of HW
    • Gulf coast
    • East coast
    • Great lakes
  7. Sub species of heartworms
    • MP3 strain (Auburn study)
    • Dirofilaria ripens (Diagnosed in northeast, large cats are definitive host)
  8. Most important contributing factor for spreading HW
    Relocation of infected dogs
  9. Life cycle of HW
    • 1) Dog #1 has adults (S5) and microfilaria (S1)
    • 2) Mosquito takes blood and picks up S1
    • 3) S1 molts to S3 in mosquito, incubation time depends on temperature
    • 4) Mosquito inserts S3 & saliva in Dog#2.
    • 5) S3 molts to S4 in subcutaneous tissue
    • 6) S4 stays in subcutaneous tissue for 100 days.
    • 7) S4 molts to S5a (pre-adult) and it moves to pulmonary artery
    • 8) S5 stays in pulmonary artery for 80 days and then molts to adult S5.
  10. Most common vector for transmission of HW
    • Culex mosquito 
    • 3,000 species known to transmit D. immitis
  11. Why do 50% of dogs test positive on occult test for D. immitis but are negative for microfilaria?
    • Same sex worms
    • WBC attacks microfilaria
  12. HW symptoms that are noted by the owner
    • Coughing
    • Loss of stamina
    • Ascites
    • Front legs bowed outward
  13. Diagnosis for HW
    • Blood tests
    • History
    • Radiology
    • Echocardiography
  14. Blood tests for HW
    • Direct smear
    • Modified knots method
    • Difil test (best microfilaria test) 
    • Hematocrit tube
    • Occult test (best HW test)
  15. Difil HW test
    1 mL bloos mixed with 1 mL lysing solution and filtered through difil paper. Paper stained and viewed under microscope 4X or10X
  16. Microhematocrit tube HW test
    View above the buffy coat line after centrifuging
  17. Is the antigen HW test reliable in cats?
    No due to not enough adult HW
  18. 2 types of occult HW tests
    • Antibody test
    • Antigen test
  19. 2 types of antibody occult HW tests
    • MAT: Microfilariae antibody test
    • DAT: Dirofilariae antibody test
  20. How many female adult HW needed to get a positive antigen occult test
    2-3
  21. 2 largest vet labs in US
    • Idexx
    • Antech
  22. Why more dogs arent protected from HW
    • 24% of pet owners dont spend money at vet
    • Clients dont understand HW disease
    • Pricing of treatment to high
  23. Running group of tests
    Batch testing
  24. Causes for false negative HW tests
    • Blood not room temperature
    • Light infection
    • Female worms not mature
    • Only male worms
  25. Why ELISA not as sensitive in cats
    • Low adult count 
    • Immature females in early stages on life cycle
    • Only males
  26. Most useful HW test in cats
    • Antibody test
    • Thoracic radiographs 
    • Echocardiography
  27. Antibody test for HW in cats
    Checks for antibodies formed by immune system, immune response produced by male and female HW and response seen as early as 2 months post infection. Downside is it can only tell if cat has been infected and not if still is.
  28. Radiographs for dogs HW positive usually see
    • Enlargement of pulmonary artery
    • Enlargement of right side called "inverted D"
  29. Radiographs for cats HW positive usually see
    • Enlargement of main lobar and peripheral pulmonary arteries
    • Pulmonary artery greater than 1.6 times width of 9th rib
  30. 2 radiograph views that are a must for determining HW
    • Lateral view: heart more than 5 ribs in length and sits on sternum 
    • Ventral Dorsal view: Enlarged pulmonary artery and inverted D
  31. Macrolytic lactones
    • Ivermectin
    • Milbemycin oxime
    • Selamectin
    • Moxidectin
  32. Diethylcarbamazine citrate (DEC)
    • Oral, daily
    • Company: Zoetis
    • Proprietary name: Nemacide, Dirocide, Filaribits
  33. Ivermectin
    • Oral, monthly
    • Company: Merial
    • Proprietary name: Heartgard
  34. Heartgard plus has...
    Ivermectin plus Pyrantel pamoate
  35. Milbemycin oxime
    • Oral, monthly
    • Company: Novartis
    • Proprietary name: Interceptor
  36. Off label use for interceptor
    Will make male HW sterile if given 3-4 months and lessen life expectancy of adult HW
  37. Milbemycin oxime and Lufenuron
    • Oral, monthly
    • Company: Novartis
    • Proprietary name: Sentinel
  38. Selamectin
    • Topical, monthly
    • Company name: Zoetis
    • Proprietary name: Revolution
  39. DEC facts
    • Only kills S3
    • Can produce anaphylactic shock
  40. Ivermectin facts
    • Kills S3 and S4
    • First preventative that made one for cats
    • Collies and glycoprotein deficient dogs are sensitive to high doses
  41. Milbemycin oxime kills what
    S3 and S4 HW, toxocara, ancylostoma, and trichuris
  42. Milbemycin oxime and Lufenuron facts
    • Breaks flea life cycle by inhibiting egg development, prevents chitin formation 
    • Now called Sentinel spectrum
  43. Selamectin facts
    • First topical that protects against HW and fleas
    • Used on Dogs/cats
    • Prevents eggs from hatching 
    • Treats/controls ear mites in dogs/cats
    • Treats rounds/hooks in cats
    • Controls sarcoptic mites on dogs 
    • Safe for use in young 6 weeks of age
  44. Moxidectin with Imidacloprid
    • Topical, monthly
    • Company: Bayer
    • Proprietary name: Advantage multi
  45. Moxidectin with Imidacloprid facts
    Prevents HW and other parasites in dogs and cats
  46. Moxidectin
    • Injectable every 6 months 
    • Company: Ft. Dodge
    • Proprietary name: Proheart 6
  47. Moxidectin facts
    • Dogs were dying so it was taken off the market but is now back
    • Bayer bought the rights to moxidectin
  48. Avermectins
    • Ivermectin
    • Selamectin
    • Doramectin
    • Eprinomectin
  49. Milbemycins
    • Milbemycin oxime
    • Moxidectin
  50. Why can an animal on HW treatment not exercise for 6 weeks?
    Adult HW die from adulticide and dislodge in chordi tendinae and travel to lungs to be absorbed by neutrophils and macrophages. Prevents thrombo-embolism
  51. Macrocylic lactones properties
    • 1) Deplete microfilaria, with uninterrupted doses will eliminate within 6-12 months with moxidectin injection 
    • 2) Sterilize adults
    • 3) Shorten life span of adults
  52. Most reliable method for testing for microfilaria
    Antigen testing
  53. Treatment products for adult HW
    • 1) Melarsomine dihydrochloride
    • 2) Thiacetarsamide sodium
    • 3) Levamisole HCl
    • 4) Fenthion
  54. Melarsomine dihydrochloride
    • Proprietary name: Immiticide
    • Only med available in US
    • IM injection
    • Standard protocol: 2 injections 24 hours apart 
    • Alternative protocol: 3 injections with one initially then 4-6 weeks later a 2 dose treatment 
    • Given in lumbar muscles
    • Doesnt kill worms under 4 months of age
  55. Thiacetarsamide sodium
    • Proprietary name: Caparsolate
    • Given 4-6 injections, 1 ml/lb twice a day for 2 days
    • If given outside the vein will eat bone
    • Once used every 6 months to kill adults but dogs were dying at age 6 from liver failure
  56. Fenthion
    • Proprietary name: Talodex
    • Effective against microfilaria 
    • Once sold in TX on black market with peanut oil 
    • 1 mL/7lbs SUB Q
  57. Microfilaria treatment
    • 1) Ivermectin: 1/4 ml/40lbs, oral
    • 2) Selamectin
    • 3) Milbemycin 
    • 4) Dithiazine Iodine "Dizan" FDA approved
    • 5) Levamisole HCl
    • 6) Fenthion
  58. Class 1 HW disease
    Asymptomatic to mild, no radiographic signs, no anemia, may have lose of condition and occasional cough
  59. Class 2 HW disease
    Moderate, radiographic signs present, obvious anemia with PCV less than 30%, mild proteinuria, loss of condition and coughing
  60. Class 3 HW disease
    Severe, radiographic signs significant, anemia
  61. Caval syndrome AKA
    Dirofilaria Hemoglobinurea
  62. Caval syndrome facts
    • Large numbers of adults obstruct blood flow through tricuspid valve and interfere with valve closure, right side heart failure. 
    • Severe congestion of liver with right jugular pulsations
    • Conformation made with ECG and radiographs
    • Ascites seen in abdomen
  63. Wolbachia is what type of organism
    Rickettsia
  64. Wolbachia facts
    • Contributes to pulmonary and renal inflammation through surface protein (WSP) producing endotoxins
    • Use doxycycline prior to adult HW therapy
  65. Doxycycline for wolbachia prior to HW therapy used to
    • 1) Microfilaria become non-infective
    • 2) Easier to kill adult HW
    • 3) Reduces post treatment side effects from dying worms in pulmonary arteries
  66. How many adult heartworms will the pulmonary artery hold?
    25
  67. How to convert C to F
    1.8 X C + 32= F
  68. S1 molts to S3 inside the mosquito dependent on temperature, if its warmer then...?
    The shorter the incubation period
  69. What happens to a dog that has been treated for HW and becomes infected again?
    Immune recognition, less HW survive due to antibody production
  70. Milbemycin products
    • Interceptor
    • Sentinel spectrum
    • Confortis
    • Trifexis
  71. Why treat microfilaria
    • 1) Potential threat to other animals
    • 2) High numbers make adult HW treatment more complex (renal disease)
    • 3) If HW positive and owner buys DEC animal can go into anaphylactic shock and die
  72. What can Dirofilaria immitis be confused with visually?
    Acanthocheilonema reconditum
  73. What products can cause anaphylactic shock in HW dogs
    • DEC
    • Interceptor
    • Dichlorvos
  74. Type 1 Hypersensitivity (anaphylactic) facts
    • Basophil release histamine dilating blood vessels
    • Hypotension results in reduced cardiac output
    • Loss of tone in capillary walls and sphincters 
    • Blood pools in peripheral vessels 
    • Hypoxia occurs
  75. Most common symptom of anaphylactic
    Vomiting
  76. Final symptom of anaphylactic shock before death
    Dilated pupils
  77. Slow kill method of HW
    • Relies on monthly preventative to treat
    • Cheaper than treating properly
    • Not endorsed by AHS
  78. AHS
    American heartworm society
  79. Traditional treatment recommendations for HW
    • Exam to make sure no microfilara and no liver/kidney damage
    • Pre-treat any existing diseases
    • Treat microfilaria with Ivomec or Revolution 
    • 1st injection of melarsomine dihydrochloride 
    • One month later give 2nd shot
    • One month later check for microfilaria again
    • Check occult test 4 months later
    • Can also give aspirin once a day
  80. How long do adult HW live in cats
    2-5 yrs
  81. How long do adult HW live in dogs
    • 4-5 yrs 
    • 7 yrs
  82. How do HW migrate in cats?
    In body cavities, systemic arteries, and CNS due to not being definitive host
  83. Patho-physiology of HW disease in cats
    • Arrival of S5a in pulmonary artery 
    • Death of adult HW, coughing occurs known as HARD
    • Unlike in dogs HW dont need to reach maturity to cause disease
  84. HARD stands for...
    Heartworm associated respiratory disease
  85. PTE stands for...
    Pulmonary Thrombo-embolism
  86. Signs of HW in cats
    Coughing, rapid breathing, if in PA hypoxia, ataxia, seizures and sudden death
  87. HW prevention for cats
    • Selamection 
    • Ivermectin
    • Milbemycin 
    • Imidacloprid moxidectin

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