Canine & Feline Heartworm Flashcards
(48 cards)
what is the nematode that causes heartworm infection
dirofilaria immitis
how is dirofilaria transmitted to dogs and cats
mosquito vector
what species are more commonly affected by heartworm disease
dogs > cats
cats are atypical hosts
where is heartworm endemic
all lower 48 states
where is heartworm hyperendemic
SE states and mississippi river valley
what drugs are used for heartworm prevention in dogs and cats
macrocyclic lactones (ML)
ivermectin, selamectin, moxidectin, milbemycin
what life stage of the heartworm lifecycle do macrocyclic lactones target
kills L3 and early L4 larvae
does NOT kill adults
when should a puppy start using prevention
6 to 8 weeks old
use year round
heartworm life cycle in a dog
- mosquito ingests microfilaria from a HW infected host
- in the mosquito - dirofilaria grow to L3 larvae in 10 days
- mosquito bites a new dog and transmitted L3 larvae into the dog tissues
- L3 larvae grows into L4 and resides in tissues (45-65 days)
- L4 enters the bloodstream and develops into an adult (4-5 months)
- adults in the blood start producing microfilaria
how long post-infection does microfilaria production begin in dogs
6 to 7 months
how long do adult HWs and microfilaria live in dogs
adults - 5-7 years
microfilaria - 1-2 years
heartworm lifecycle in a cat
- mosquito ingests microfilaria from a HW infected host
- in the mosquito - dirofilaria grow to L3 larvae in 10 days
- mosquito bites a new cat and transmits L3 larvae into the cat tissues
- L3 larvae grows into L4 and resides in tissues (2 months)
- cat immune system kills majority of larvae and developing adults - L4 enters the bloodstream and develops into an adult (4-6 months)
- adults in the blood start producing microfilaria
how long post-infection does microfilaria production begin in cats
7-8 months
do microfilaria circulate in cats
rarely
where do adult heartworms reside in dogs
pulmonary arteries
majority in the caudal pulmonary vascular tree
what does the severity of clinical signs depend on
- relative # of worms
- duration of infection
- host-parasite interaction
how does the cat immune system respond to heartworm
many immature adults die once they reach the pulmonary arteries
infection is typically cleared at the L4/early L5 stage
even if cleared - can still cause inflammation in the pulmonary parenchyma and bronchioles –> cough, tachypnea
what is the typical worm burden in cats
1-3 worms
causes many false negatives on antigen tests (threshold is 3 worms)
what is wolbachia
gram negative bacteria
gets released in large numbers during worm death and exacerbate acute inflammatory response + increased bronchoreactivity
what can occur in feline HW infections that doesn’t occur in canine infections
aberrant migrations - neurologic, ocular, arterial
what heartworm test is used in dogs
antigen testing
high sensitivity and specificity - good screening test
what does the antigen test detect and how early can it detect it after infection
adult females
must be at least 3 worms
detects antigen 6 months after infection
- earliest detectable time for puppies - 8 months old
if a dog has a lapse in prevention for > 6 months, when should they be tested
now and again in 6 months
if a dog has a lapse in prevention for <6 months, when should they be tested
6 months after re-starting prevention
