Heartworm Diagnosis Flashcards
Heartworm incidence
Diagnosed in all 50 states
- regionally endemic
- environmental changes created by humans (heat islands, microenvironments that support larvae formation in mosquitoes)
- highest infection rates (45%)
Sensitivity
TP/TP+FN
- proportion of animals with disease that test positive
- 100% Se test recognizes all actual positives (no false negatives)
Specificity
TN/FP+TN
- proportion of animals without disease that test negative
- 100% Sp test recognizes all actual negatives (no false positives)
Canine - disease or infection?
- history
- clinical signs
- diagnostic procedures
- -> serology, microfilariae detection (differentiate from acanthocheilonema reconditum), physical, radiographs, ultrasound, echocardiography
PCR
Sensitive (less likely to have FN)
- accurate
- can discriminate D. immitis microfilariae from other filarial worms
- morphologic abnormalities
- infection with more than one species
Antigen testing - canine
ELISA
- detects hw antigen in patients blood
- more useful than antibody tests
- highly specific, used to confirm disease
- less likely to have FP
- information about worm burden
- most detect mature female HWs (infections with >1 worm and infections that are 7-8 months old)
Antigen testing generally does not detect infections ______
Less than 5 months old
What are possible reasons for a false negative?
Infections are:
- light
- all male
- duration < 5 months
- technical error
Microfilaria tests in regions where HW prevalence is high
Many (20%) of hw infected dogs may not be microfilaremic
- percentage is higher for dogs on a macrocyclic lactone prevention
- most microfilaremic dogs can be detected by blood smear
Microfilaria movement
Cell movement is created by motility of microfilariae
- stationary, rather than migratory pattern, indicative of dirofilaria
- movement beneath buffy coat in micro-hematocrit tube might be visible
Direct smear
Non-concentration test
- giemsa stain
- microfilaria have a wide curved front part and pointed rear
- insensitive method for examining blood in which low numbers of microfilariae are present
Direct smear - pros and cons
Advantages
- used to verify infection
- microfilariae indicate infection with adults
Disadvantages
- must differentiate from acanthocheilonema reconditum microfilariae
- not sensitive enough to rule out heartworms
- not used for screening
- might miss some positives
Modified Knott test or Difil filter test
Preferred method for observing morphology
- recommended minimum volume is 1 ml
- absence or presence of microfilariae
- measurements of microfilarie
- differentiates D. immitis from non-pathogenic species
- more sensitive than direct smear
HARD
Heartworm associated respiratory disease (in cats)
Acute
- collapse, dyspnea, convulsions, diarrhea/vomiting, blindness, tachycardia, syncope, sudden death
Chronic
- vomiting, coughing, dyspnea, lethargy, anorexia, weight loss, chylothorax
Severe disease is associated with _______
Migration of young adult HW in lungs, even without patent infection
