Test 2

Question 1

what are the two important filarid nematodes

Answer 1

-dirofilaria immitis (dogs and cats)
-acanthocheilonema reconditum (dipetalonema, dogs)

Question 2

why do we need to differentiate between the two filarid nematodes

Answer 2

one of them doesnt require treatment so you can get sued if you treat wrong

Question 3

lifecycle of filarid nematodes (general)

Answer 3

female -> mocrofilariae (pre-L1) -> blood sucking insect -> L3 -> definitive host -> predilection site

Question 4

general characteristics of acanthocheilonema reconditum (microfilariae, adults, intermediate host)

Answer 4

microfilariae
-no taper at anterior end
-shorter and narrower than dirofilaria immitis

adults
-slender, 5cm long
-within CT
-not pathogenic

intermediate host
-fleas (lice)

Question 5

lifecycle of acanthocheilonema reconditum

Answer 5

flea feeds on dog and transmits infective larvae -> adult nematodes in SQ and perirenal tissues release microfilariae -> flea bites dog and ingests microfilariae with blood meal -> microfilariae develop in flea to infective larvar

Question 6

dirofilaria immitis (definitive host, predilection site, intermediate host)

Answer 6

definitive host
-dogs, cats, ferrets, wild canids

predilection site
-right caudal lobar artery

intermediate host
-mosquitoes

Question 7

adult and microfilariae morphology of dirofilaria immitis

Answer 7

adult
-female = 20-30cm long
-male = smaller, tail has loose spiral
-size and site = diagnostic

microfilariae
-tapered anterior end
-longer and wider than A reconditum

Question 8

cycle of dirofilaria immitis

Answer 8

1. a mosquito bites an infected animal, ingesting heartworm microfilariae (pre-L1)
2. microfilariae mature into heartworm larvae (L3) inside mosquito (10-14)
3. infected mosquito bites a dog, transmitting the larvae (L3)
4. larvae enter the dogs bloodstream, migrate to the heart and lungs, grow to a foot long and become sexually mature (7-9 months)
5. adult heartworms can live within the heart and lungs for 5-7 years

Question 9

lifecycle of dirofilaria immitis

Answer 9

-larvae in pulmonary arterioles (d70)
-pre-patent period (~7-9m)
-parasites live 5-7 years (dogs)

Question 10

maturation time of dirofilaria immitis in mosquitoes

Answer 10

18C = 29d
26C = 12d
30C = 8 days

Question 11

what is the general timeframe for the ability to transmit L3 to dogs in southern ontario

Answer 11

starts = june 1
ends = oct 8

Question 12

is there higher prevalence of heartworm disease north or south of the 400 series highways

Answer 12

south

Question 13

dirofilaria immitis in cats

Answer 13

-prevalence < dogs
-often very few parasites
-adult parasites live 1-2 years
-microfilaremic ~1m

Question 14

dirofilaria immitis pathogenesis (3)

Answer 14

-obstruction of blood flow

-parasite excretory products mechanical activity = proliferative pulmonary endarteritis

-dead/dying parasites —> pulmonary embolism

Question 15

dirofilaria immitis large parasite burden pathogenesis

Answer 15

same changes -> pulmonary hypertension -> right ventricular hypertrophy -> heart failure

Question 16

dirofilaria immitis clinical signs; what does it depend on?

Answer 16

-number of adult parasites
-size of dog
-exercise level

Question 17

dirofilaria immitis clinical signs; usual vs severe signs

Answer 17

usual
-exercise intolerance
-coughing, dyspnea

severe signs
-loss of condition, hemoptysis
-ascites, hydrothorax, etc

Question 18

what are the seven dirofilaria immitis tests

Answer 18

1. examination of blood for microfilariae
2. heartworm antigen tests
3. DNA test
4. thoracic rads
5. ultrasound
6. clinical signs
7. history

Question 19

concentration methods for exam of blood for microfilariae

Answer 19

-knotts test
-filter techniques (e.g. difil)

Question 20

what is the primary diagnostic and screening method for heartworm

Answer 20

heartworm antigen tests

Question 21

most common heartworm antigen test

Answer 21

snap 4DX

Question 22

is the DNA test for HW useful

Answer 22

not presently, Sn and Sp not described

Question 23

what do you expect to see in HW positive dogs in thoracic rads

Answer 23

-enlargement of pulmonary vessels
-tortuosity
-right ventricular hypertrophy

Question 24

when is ultrasound useful for HW

Answer 24

if there are a large number of parasites

Question 25

aspects of history that are important for HW (4)

Answer 25

-location
-travel hx
-use of preventive meds
-compliance of meds

Question 26

what is sensitivity

Answer 26

proportion of infected animals that are test positive

Question 27

what is specificity

Answer 27

proportion of uninfected animals that are test negative

Question 28

what do you need to know for using tests for medical decision making

Answer 28

-Sn/Sp
-Prevalence

Question 29

why do we screen dogs in ontario (6)

Answer 29

-to confirm that a dog is HW free before putting it on preventive medication (rule out)

-label recommendation

-required for safety reasons when using diethylcarbamazine (decacide)

-concern about rxns in microfilaremic dogs

-to remove reservois of infection at beginning of the transmission season

-annual testing of all dogs is rec. by the american HW association

Question 30

what is the positive predictive value

Answer 30

if the dog tests positive, how likely is it that the animal is truly infected

Question 31

what is the negative predictive value

Answer 31

if the dog tests negative, how likely is it that the animal is truly uninfected

Question 32

purpose of screening healthy dogs in a low risk area (2)

Answer 32

-want a benchmark negative test before initially starting on heartworm preventive program

-evaluate the need for annual testing for dogs on preventive programs (risk based assessment)