Nematodes I: Heartworm Diagnosis Flashcards
Where is heartworm disease endemic?
All contiguous 48 states Hawaii Puerto Rico US Virgin Islands Guam
What is the sensitivity of tests?
TP/TP+FN
Proportion of animals with disease that test positive
100% Se test recognizes all actual positive (no false negatives)
What is the specificity of tests?
TN/FP+TN
Proportion of animals without disease that test negative
100% Sp test recognizes all actual negatives (no false positives)
How can you diagnose heartworms in dogs?
History Clinical signs Diagnostic procedures ---Serology (Ag testing) ---Microfilariae detection ---Physical exam ---Radiographs ---Ultrasound ---Echocardiography
Why is microfilariae detection important in diagnosing canine heartworms?
Differentiation from Acanthocheilonema reconditum
Describe PCR used in the diagnosis of canine heartworms
Sensitive (less likely to have FN) Accurate Can discriminate D. immitis microfilarie from other filarial worms that infects dogs Morphologic abnormalities Infection with more than one species
What does antigen testing do in canine heartworms?
Detects heartworm antigen in patient’s blood
Highly specific
What is the antigen source for an antigen test in canine heartworms?
Adult female heartworm uterus
What are possible reasons for a false negative in an antigen test for canine heartworms?
Light infection
All male
Duration is less than 5 months
Technical error
Where should microfilaria tests be performed?
In regions where heartworm prevalence is high
What is a direct smear test used for in canine heartworms?
Insensitive methods for examining in blood in which low numbers of microfilariae are present
What are advantages to microfilariae detection with direct smear?
May be used to verify infection
Microfilariae indicate infection with adult heartworms
What are disadvantages to microfilariae detection with direct smear?
Must differentiate from Acanthocheilonema reconditum microfilariae
Not sensitive enough to rule out hearworms (might have some FN)
Not used for screening
Might miss some positives
What is the preferred emthod for observing morphology of heartworms in dogs?
Modified Knott test or Difil filter test
What is the recommended minimum of blood volume for the modified Knott test and Difil filter test?
1 ml
