Heartworm Disease Flashcards
1
Q
describe dirofilaria immitis
A
- agent of heartworm disease, potentially fatal CP pathogen
- DH: domestic dogs and wild canids
-IH mosquito (vector)
-accidental/aberrant hosts: cats, ferrets, humans, >30 mammals - adults reside in pulmonary arteries!!!, microfilaria in blood
- all life cycle stages can cause pathology
- prevent: L3/L4 with macrocyclic lactones
-treat: adults with melarsomine
2
Q
describe acanthocheilonema reconditum
A
- DH: canids
-IH: fleas and lice - adults in SQ, Mf in blood
- low pathogenicity: need to ID versus dirofilaria immitis (look very similar!!)
- prevent: flea control
-treat: N/A
3
Q
describe canine heartworm disease
A
- endemic in every state in continental USA
- prevalence ranges 1-10%
-cats usually 5-20% of dog prevalence
4
Q
describe the heartworm life cycle
A
- microfilaria live in blood
- mosquito takes blood meal
- 10-14d later, heartworm will go through 2 molts within the mosquito until it gets to L3 (infective stage)
-heartworm has made its way from mosquito kidneys to mosquito head - mosquito takes another blood meal and deposits L3
-due to capillary/hemolymph effect, mosquitoes get sucked into the one who was bit - in a few days, the first molt happens within the dog (L3-L4 stage)
-this stage is the target of preventative drugs!!!!
-these stages are making their way through tissues trying to access the bloodstream
-L4 stage is shorter in cats, this and the developing stages are very immunostimulating to cats! usually killed earlier than adulthood - L4 develops into developing and then mature adults (sexual maturity) 6-7 months post infection
-can only detect adults via antigen!! so need 6-7 months before detection post infection!! - adults can live 5-7 years (microfilaria can live 1-2 years)
5
Q
describe the microfilaria, larval, and adult stages of heartworms
A
microfilariae: 300um, lifespan 1-2 years, live in blood of domestic host
larval: 1mm (L3),
-IH: microfilaria to L3, 10-14d
-DH: L3-L4: 3-10d
adults:
male: 15cm
-female: 20-30cm
-5-7 year lifespan
-location: pulmonary vessels by day 70
-sexually mature at 6 months
6
Q
describe the pathology caused by migrating larvae, juvenile and adult worms, and dead adults and microfilariae
A
- inflammatory and mechanical damage
-stippling almost pathognomonic for HWD - immune mediated reactions
-complexes love to deposit in kidneys: glomerulonephritis, leads to proteinuria we see in HWD dogs - thromboemboli
- severity of cardiopulmonary pathology determined by multiple factors!
-worm numbers
-host immune response
-duration of infection
-host activity level (active dogs = worse pathology, blood is moving faster through heart, rubbing worms even more)
7
Q
describe wolbachia
A
- most species of filarioid nematodes harbour bacterial endosymbionts names wolbachia
-wolbachia live in the lateral cords under the cuticle of the worms, transmitted vertically from female to her microfilaria - wolbachia-associated proteins induce inflammatory responses by macrophages and neutrophils
8
Q
describe the classifications of canine HWD
A
- early infection/class 1: no signs
- mild disease/class 1: cough
- moderate disease/class 2: cough, exercise intolerance, abnormal lung sounds
- severe disease/class 3:
-cough, exercise intolerance,
-abnormal heart and lung sounds
-enlarged liver
-syncope
-ascites
-death - caval syndrome/class 4:
-worms get stuck in tricuspid valve somehow
-sudden onset of severe lethargy and weakness accompanied by hemoglobinemia and hemoglobinuria
-an EMERGENCY! must surgically remove worms or dog will die!!!
9
Q
describe acute HWD signs/caval syndrome
A
- large numbers of worms
-obstruct blood flow of tricuspid valve
-hemolytic anemia - rapid onset
- HEMOGLOBINURIA
- dx confirmed by echo
- death usually within 12-72 hours unless surgically removed
-treatment of choice: surgical removal of worms via jugular vein - poor candidates for treatment
10
Q
can a dog ever transmit heartworms directly to another dog?
A
NOOOOO
11
Q
describe assessment of a patient with HWD
A
- history, PE, exercise intolerance
- immunodiagnosis +/- test for microfilaria
- serum chemistry/hematology
-liver function assessment - UA
- radiography
-enlarged right heart (reverse D)
-enlarged pulmonary artery
-congested dorsal lung lobe - cardiac US and ECG
12
Q
describe macrocyclic lactones
A
- affect microfilaria, L3, L4, and adult stages
-do NOT prevent initial infection via mosquitoes, prevent development of disease!! (target L3, L4)
-strategy is to allow dogs to become infected but then prevent those worms from developing to adult form - routes:
-oral: ivermectin, milbemycin oxime, moxidectin
-topical: moxidectin, selamectin, eprinomectin
-injectable: moxidectin
13
Q
describe HWD diagnosis
A
- antigen testing
-preferred method: approx 20% may be microfilaria negative (thanks to macrocyclic lactones)
-detects female uterine antigen (ELISA and immunochromatographic test): earliest detection about 5 months post infection, at least 90% of dogs harboring at least 3 adult females will test positive - microfilariae testing:
-in TANDEM WITH antigen testing ALWAYS: testing for microfilariae alone is not recommended
-concentrate Mf (modified Knott’s/filtration test): earliest detection about 6 months post infection, microfilariae reduction assay
–using this test, length, width, and shape of head are most useful to ID dirofilaria versus acanthocheilonema
14
Q
describe CHWD treatment
A
- adulticidal drugs:
-organic arsenical (melarsomine dihydrochloride- immiticide or diroban) IM injections
-affects rapidly multiplying digestive cells
-worms starve to death in 7-10 days, then embolize to lungs for up to 4 weeks
-3 dose regiment recommended - microfilaricidal drugs:
-some macrocylic lactones at preventative dose rates kill Mf +/- sterilize uterus of females within 1 month - 1 year
-ivermectine, milbemycin
-topical moxidectin/imidicloprid labelled microfilaricide - adjunct therapy:
-doxycycline: prior to treatment for 4 weeks, reduces wolbachia, reducing pulmonary pathology associated with death of heartworms AND blocks further transmission to new hosts
15
Q
describe heartworm disease in cats
A
- a few worms can cause life threatening disease
-cats usually infected with less than 5 worms
-diagnosis more difficult (may be only 1-2 female worms present, if any) - cats only have a transient microfilaremia
- <5% of infected cats are microfilaria positive at time of exam
-become infected from mosquitoes that have fed on infected dogs
