Heartworm Flashcards
What’s the lifecycle of Dirofilaria immitis?
- mature adult heartworm lives in the pulmonary arteries
- mates, release microfilaria in the circulation
- mosquito takes a bloodmeal –> goes in, molts 2 more times with the appropriate ambient temperature & Wolbachia pipientis
- mosquito feeds again, L3 goes back to a host
- molts to L4 in the skin, adipose tissue, muscles within 2 weeks, then to S5 (immature adult) in 2-3m
- immature adult enters to vascular system, goes to the heart and lungs –> final maturation & mating
How long can a dog be infective for?
- Adult worms can live for 5-7y
- microfilaria up to 30m
- disease starts as soon as S5 is reached –> once in circulation, can cause inflammation and respiratory signs, etc
What’s the pathophysiology of heartworm disease?
- worm-induced inflammation, pulmonary hypertension, vasculitis, thromboembolism
- loss of vascular integrity, fibrosis, physical occlusion
- R sided heart failure
- arrhythmia
- glomerulonephritis from antigen-antibody complex
What are the clinical signs of heartworm disease in dogs?
Majority of the patients are asymptomatic
- weight loss, decreased exercise tolerance, cough, dyspnea, lethargy, poor condition
- split 2nd heart sound, right sided heart murmur
- R sided heart failure –> distended jugular, ascites
How is heartworm diagnosed in dogs?
- direct microfilaria detection
- immunodiagnostic antigen test
- CXR
- ECG
- Echo
How does modified Knott’s test work? What’s the limitation?
- it’s basically blood smear evaluation looking for microfilaria, using fresh blood, formaldehyde and methylene blue
- can ddx between D immitis and A reconditum
- A reconditum is not detected on the heartworm antigen test
- not useful in cats, or dogs with no or low numbers of circulating microfilaria, amicrofilaria
What diagnostic tests are available for direct detection of microfilaria?
- modified Knott’s test
- millipore filtration
- wet mount
How is amicrofilaria produced?
immune mediated destruction of the microfilaria in the lungs (eosinophilic pneumonitis)
How does immunodiagnostic antigen tests work for HWI? What are the limitations?
- detects antigens produced by adult female heart worms
- false negative if happens to be all male worms, low number of female worms
- also has a latent period of about 6m for first infection (S5 needs time to mature into adults)
- some provide quantitative data to reflect tumour burden
What’s the overall sensitivity and specificity of ELISA snap tests for HWI?
Sensitivity = 79%
Specificity = 97%
How can CXR be useful for HWI?
Not used as a screening tool
- but can assess the severity of infection, and pulmonary changes
CXR signs:
- R sided hypertrophy
- prominent main pulmonary artery segment
- increased size and density of pulmonary arteries
- pulmonary artery tortuosity and pruning
- interstitial pattern with pulmonary infiltration
What ECG abnormalities would be noted in HWI?
- patterns associated with R ventricular enlargement
How does echo help with HWI diagnosis?
- sensitive in finding R sided heart enlargement (deep S wave, prolonged QRS interval)
How common is HWI in cats?
not common
- generally not the preferred target host for the feeding mosquitoes
- they will have to feed on a canid to be an effective vector’
- cats are inherently resistant to HWI
- life cycle takes longer in the cat
- however, can still have pulmonary and pulmonary vascular pathology even if an infection never matures
What’s HARD?
heartworm associated respiratory disease
- seen in cats
- disease develops even though the heartworm never develops to mature adult
