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What is a heartworm?
What is the definitive host for heartworms?
What are alternate hosts for heartworms?
- wild canids
- sea lion
What are the aberrant hosts for heartworms?
Describe the life cycle of heartworms.!
- mosquiteo infected by 1st stage larvae (L1, circulating microfilaria) when takes a blood meal
- transforms to L2 then L3 in mosquito (infective within 2 - 21/2 weeks)
- mosquito bites dog and L3's infect
- L3's migrate around in dog's SQ tissue for 100 days and molts from L3 to L4 to L5
- L5 (immature adult) enters vasculature and travels to pulmonary arteries and matures to adult
- Adults reproduce and release L1's (microfilaria) (takes about 6 months)
Describe right sided heart failure.
- plaque formation in pulmonary arteries
- atherosclerosis occurs (hardening of arteries)
- pulmonary hypertension (narrow arteries increases pressure)
- right ventricular enlargement
What are the clinical signs of right-sided heart failure?
- hepatic congestion
Describe pulmonary pathology.
- pulmonary thromboembolism (usually dead worms or inflammation surrounding worms) in pulmonary vasculature and lungs
- worms are allergenic and cause eosinophilia when present
What are the clinical signs of heartworms?
- Early: none
- coughing (moist, worse after rest)
- signs of heart failure (exercise intolerance, hepatomegaly, ascites, syncope)
What is ascites?
accumulation of fluid in the peritoneal cavity
How do we diagnose heartworms?
- clinical signs
- look for microfilaria
What kind of tests do we use to look for microfilaria?
- direct wet mount of whole blood (works if there is a whole lot of them)
- concentration tests
What are the different concentration tests we use to diagnose heartworms?
- modified knott's test
- membrane filtration test
- HCT tube
Do all these tests detect occult infections?
What are occult infections?
What can heart worms be confused with?
Describe Modified Knott's Test.
- concentration method
- more accurate than direct
- mix whole blood with formalin
- pour off supernatant
- stain sediment and examine
Describe how to do filter testing.
- concentration method
- mix blood (1cc) with 2% formalin (or water) (about 10cc)
- squirt through filter
- look at stained filter under scope
What is another name for dipetalonema reconditum?
What are dipetalonema reconditum?
nonpathogenic nematodes that resemble heartworms
How are Dipetalonema reconditum transmitted?
Where do Dipetalonema reconditum live?
in SQ tissue
How do we differentiate between Dirofilaria and Dipetalonema?
- Dirofilaria undulates in place on a direct smear and Dipetalonema makes headway
- Dirofilaria are larger with taper head and a straight tail
Describe what Dipetalonema looks like.
- moves across
- blunt head
- curly tail
- smaller than Dirofilaria
Describe what Dirofilaria looks like.
- wiggles in place
- taper head
- straight tail
- larger than Dipetalonema
What type of serological testing do we do for heartworms?
- Antibody tests (ELISA test) - we don't use them
- Antigen tests
What type of antigen tests do we use?
- ELISA test for antigen
What are the different kinds of Immunochromatographic tests?
- Rapid ImmunoMigration
- Lateral flow immunochromatography
- Immunochromatographic staining
Why do we do serological testing?
if an animal is on any of the macrolide (once-a-month) preventatives there will be no circulating microfilaria (L1's)
The ELISA antibody tests are more reliable in what animal?
What do the antigen tests detect?
adult female Dirofilaria
What do the antibody tests test?
- detect antibodies
- detects exposure, but not actual infection
What do ELISA antigen tests detect?
detect surface antigen of adult female Dirofilaria
Are ELISA Antigen tests specific?
yes very specific
What are Hemagglutination tests not approved for?
What does Hemagglutination tests use to test?
How long does it take to get results from Hemagglutination tests?
Are Hemagglutination tests specific and sensitive?
- less specific
- less sensitive
What does sensitivity mean?
- can the test pick up animals who have the disease?
- what are the chances of false negatives?
What does specificity mean?
- how likely is it that an animal with a positive test is really positive?
- what are the chances of false positives?
What are the different types of Immunochromatographic tests?
- Heska Solo Step
- Witness HW
- ICT Gold
What test is lateral flow immunochromatography?
Heska Solo Step (K9)
Do you have to mix solutions for the Heska Solo Step test?
Does the Heska Solo Step test required refrigeration?
Are results slow or fast for the Heska Solo Step test?
What test is the rapid immunomigration test?
Does Witness HW test require refrigeration?
Are the results slow or fast for the Witness HW test?
Which test is the immunochromatographic staining test?
ICT Gold HW
How accurate is the ICT Gold HW test?
Does the ICT Gold HW test have false positive results?
When do we get the results for the ICT Gold HW test?
What usually causes a false negative in a antigen test?
- infections less than 6 months old (not adults yet)
- less than 3 adult females present
- all male infection
What are the 4 parts to treating heartworms?
- Kill the adults worms
- Resting period (wait for body to reabsorb them)
- Kill the circulating L1's
- Keep the dog from becoming infected again
What are the different adulticide arsenic compounds?
- old treatment
- IV only (perivascular sloughing)
- toxicity common
- vomiting, diarrhea, anorexia, jaundice
- Lumbar epacial muscles only
- small gauge needle (inflammation common)
- if there is a mild/new infection then give 2 deep IM injections 24 hours apart on alternate sides
Describe step 1 for treatment of heartworms.
older or more serious infection: split schedule (1 injections now, followed by 2 24 hours apart in a month)
Describe step 2 for treatment of heartworms.
- 4 - 6 week rest period
- risk of dead worms floating into the lungs (emboli) - coughing and respiratory difficulty
- keep animal as quiet as possible
Describe step 3 for treatment of heartworms.
- microfilaricide treatment (kill babies)
- kill circulating microfilaria (L1s)
- life-threatening allergic reaction to the dead microfilaria possible
- hospitalize for the day and observe for signs of anaphylaxis
What are the signs of anaphylaxis?
- signs of shock (pale, weak rapid pulse, prolonged CRT)
- sometimes see vomiting
- don't usually see urticaria, pruritus, but it is possible
What microfilaricide treatment do we use?
- Ivermectin (high dose)
- Milbemycin (regular monthly preventative dose)
What is step 4 for heartworm treatment?
Which types of dogs do we avoid the use of Ivermectin in?
collie or collie mixes
What are the different heartworm preventatives?
- Diethylcarbamazine (DEC)
What kind of host is a cat?
How long do worms live in cats?
16 - 24 months
How many adults are in cats?
average about 2 - 3 adults
What percent of infections are occult in cats?
How are feline heartworms diagnosed?
What is the pathology for feline heartworm disease?
- can mimic feline asthma
- lung damage and anaphylaxis due to larvae (heartworm associated respiratory disease - HARD)
- chronic vomiting
How do we treat feline heartworms?
- no safe treatment for worms (adults)
- symptomatic treatment
- preventatives available
How do we test for feline heartworms?
Because there is a shortage of immiticide, what are our goals?
- reduce potential pathology from infection
- maintain health of dog until it can be appropriately treated
- prevent additional heartworm infection of the dog
What are the steps to reaching this goal while there is a shortage of immiticides?
- limit activity of dog
- place non-protected dog on heartworm prevention
- administer doxycycline to reduce pathology
What is this?
Which one is on the left and which one is on the right?
- left: dipetalonema
- right: dirofilaria
What is this?
dirofilaria in diff quik
What is this?