Non-GI Nematodes Flashcards
Where do non GI nematodes live?
- heart
- lungs
- urinary tract
Which species get Dirofilaria immitis?
- DOGS
- rarely CATS (rarely patent)
- v rarely PEOPLE (not patent; sub q & lung nodules)
how do we identify adult Dirofilaria immitis?
- identification of adult parasites is usually based primarily on their location w/in host
how do we identify microfilariae Dirofilaria immitis?
- tapered anterior end & long, thin, pointed tail
- can be distinguished from microfilaria of skin dwelling nematode Dipetalonema reconditum, which have a blunt head
How do you distinguish Dirofilaria immitis from Dipetalonema (or Acanthocheilonema) reconditum?
“5 Rs of Reconditum”
- Round head
- rare
- reduced size & #
- recurved tail
- rapid movement
Reconditum is non-pathogenic & the adults live in sub q tissues
What is the life cycle of Dirofilaria immitis?
- in Ca DH, adults are located in the pulmonary artery & R ventricle
- microfilariae (L1) are released into the blood
- following ingestion by a suitable female mosquito during blood-feeding, microfilariae undergo 2 moults to become infective L3 which move to mouthparts of mosquito
- under ideal conditions (constant 27 C), approx 14 days are required for dev of infective larvae in mosquitoes
- @ constant 18 C, larvae require approximately 1 month to become infective
- during subsequent blood meal, infective L3 escape from mouthparts & penetrate skin of Ca, often through wound made by mosquito’s probiscis
- in Ca, newly introduced larvae migrate in sub q CT
- by ~ 3-4 m after infection immature adults are present in heart & pulmonary artery
- PPP in Ca is 6-7 months
- adult parasites can survive for 5-7 yrs
- microfilariae can survive in Ca for up to 2 yrs in absence of adult heartworm
- in Fe, it rarely completes dev to adult stage
- infection is usually not patent
- immature parasites may be present in heart & pulmonary arteries, but they are also common in other sites
Pathogenesis & clinical signs of heartworm:
- often asymptomatic
- decreased exercise tolerance, coughing, anorexia, weight loss
- severe cases: R sided heart failure, hepatic congestion, ascites, syncope, death
- parasite Ag/Ab complex deposition can cause glomerulonephritis & proteinuria
- caval syndrome (sm dogs, rarely cats): worms block caudal vena cava/tricuspid valve (requires immediate surgical removal of worms)
How is Dirofilaria immitis diagnosed?
- Hx (geographic location, travel)
- clinical signs
- radiographs/ultrasound (enlarged pulmonary arteries & R heart; may see worms, check for caval syndrome)
- diagnostic tests (microfilarial concentration test (modified Knotts); immunodiagnosis (adult female Ag detection (DOGS) & Ab detection (CATS)) - AHS recommends to do both dog tests annually
What are the testing recommendations for heartworm? (questions)
- who? pets living in or travelling from endemic regions
- what test(s)? Ag, Knotts, or Ab (Fe)
- where? annually in endemic areas
- when? @ least 6 months after last possible exposure (spring in Canada)
- why test? (prior to starting preventatives (anaphylaxis, masking); if suspect non-compliance in endemic regions; to monitor success of treatment; many drug companies will not cover cost of adulticidal treatments if pets are not tested annually)
why would a dog who is positive on Ag test be negative on Knotts test for microfilaria?
- could be false positive
- could have tested too early in day (microfilariae are out in blood when they are most likely to be sucked up by a mosquito)
- if you only have females (so no microfilariae)
- only adults present
- on monthly preventatives that can kill off microfilaria but not adults
Why would a dog who was negative on an antigen test have microfilaria in buffy coat of PCV tube?
- could be blocked Ag (Ag-Ab complex)
- adults all dead but microfilaria still present (tail end of infection)
- could be a different microfilaria
- could have treated & killed adult heartworms but not microfilaria (2 different treatments)
How do you interpret heart worm tests?
- false positives on antigen test are possible, esp. in low prevalence regions like Western Canada (if suspect false positive, try a different test, then retest in 3 months if still not convinced)
- false negatives on antigen & microfilaria tests (recent infections - immature females, PPP; single sex infections)
- false negatives on Ag test (blocked Ag; Ag/Ab complexes)
- false negatives on microfilaria tests (senescent infections - L1 may disappear after 9 months; Ca on monthly preventatives - masking; diurnal patterns in microfilarial activity in blood)
What are monthly preventatives for L3 & L4 heartworm larvae?
- ivermectin
- milbemectin
- selamectin
- moxidectin
resistance is developing to these
What is the adulticide for heartworm?
- melarsomine (immiticide)
- NOT IN FE (toxic, need to be removed surgically)
What are the microfilaricides for L1 heartworm larvae?
- ivermectin
- moxidectin
What antibiotic is used to kill Wollbachia & why?
Doxycycline
- kills gut bacteria inside of heartworm, starving them
In cases where adulticide treatment is not possible, what might be considered a salvage procedure?
- use of monthly oral ivermectin or topical moxidectin heartworm preventative along w/ doxycycline
how do you treat for heartworm?
- PREVENTATIVES: START ONE MONTH FOLLOWING THE FIRST POSSIBILITY OF EXPOSURE & CONTINUE UNTIL ONE MONTH AFTER THE LAST POSSIBILITY OF EXPOSURE (MAY-OCT IN CANADA)
- in Ca that are confirmed positives: if symptomatic stabilize w/ glucocorticoids, diuretics, vasodilators, fluids, oxygen; treat infection w/ macrocyclic lactones, doxycycline, melarsomine, prednisone, & cage rest
- risk of pulmonary thromboembolism depends on activity level of dog, & intensity & extent of disease
What is the ecology/epidemiology of heartworm?
- domestic & wild canids normal DH
- mosquito vectors (culicidae): Aedes spp, Anopheles spp., Culex spp
- endo-symbiotic bact Wolbachia
- seasonal transmission
- patchy geographic distribution
- low test positivity in Ca in Canada
Public health significance of Dirofilaria immitis?
- human inf has been reported from many of countries in which parasite occurs in Ca (including USA, but only 1 case has been reported in Canada (in Ontario, in a woman who had recently traveled in several areas outside Canada that are endemic))
- usually parasite doesn’t complete its dev in people, & causes a sm “coin” lesion in lung, which may be symptomatic
Where is Angiostrongylus vasorum found?
- Dogs, wild canids, & mustelids
- In Canada: Newfoundland & NS
- transmitted by gastropod intermediate hosts
Life cycle of Angiostrongylus vasorum?
- like most metastrongyloid nematodes, it undergoes indirect life cycle w/ gastropod IH
- adult parasites live in the R ventricle & pulmonary arteries of DH (canid)
- they produce eggs which dev into L1 which are coughed up, swallowed, & passed in feces of canid DH
- L1 from feces enter gastropod IH where they dev into L3
- canid DH become infected when they consume gastropod containing infective L3 or L# that have emerged spontaneously from gastropods
- frogs & Av may serve as paratenic hosts, but their role in transmission is not clear
- PPP from ingestion of L3 to production of L1 in feces is 6-8 wks
Public health significance of Angiostrongylus vasorum?
- not known to be zoonotic
- other spp of genus are zoonotic, but are not found in Canada
How is Angiostrongylus vasorum diagnosed?
- clinical signs similar to Dirofilaria immitis
- can be more severe: disseminated intravascular coagulation; rarely CNS
- L1 detected on Baermann or in bronchoalveolar lavage (BAL)
- ELISA for Ag of adult nematode (Europe)
how is Angiostrongylus vasorum treated?
- monthly prophylaxis ML (moxidectin or mibemycin) - apr-nov
- ML or fenbendazole for adults
Where does Aelurostrongylus abstrusus live?
Lung parenchyma
Life cycle of Aelurostrongylus abstrusus?
- L1 in feces of Fe -> (in gastropod IH: L1 -> L2 -> L3) -> ingested by Fe OR ingested by paratenic host (rodent, frogs, birds) & then that is ingested by Fe
- In Fe, GI tract -> blood -> lungs
what is the ecology/epidemiology of Aelurostrongylus abstrusus?
- Fe in BC & Atlantic Canada
- often asymptomatic, may cause coughing, even death
- ML, fenbendazole
What is important about Crenosoma vulpis?
- Ca & wild canids as DHs
- adults live in bronchi/bronchioles
- shed larvae in feces
- L1 -> L3 in gastropod intermediate hosts
- Dx: L1 in Baermann or BAL (Ddx Angiostrongylus)
- Tx: ML, fenbendazole
Where does Filaroides (Oslerus) osleri live & who are its hosts?
- Airways, more in trachea, right before they bifurcate
- wild canids & Ca who hunt them
Where does Filaroides hirthi live & who are its hosts?
- lung parenchyma
- dogs in kennels, often immunosuppressed
how are Filaroides (Oslerus) osleri often diagnosed?
via bronchoscopy
What is the life cycle of Filaroides (Oslerus) osleri & Filaroides hirthi?
- L1 in feces or bal OR internal autoinfection possible OR L1 are shed in saliva & vomit, & may be transmitted to pups via regurgitation feeding -> ingested by another dog
- atypical life cycle
- direct
- ovoviviparous
- L1 is shed & infective stage
What is the pathogenesis of Filaroides (Oslerus) osleri?
- often asymptomatic
- pathognomonic cough/retch triggered by exercise, cold
- nodules may obstruct air, cyanosis, & collapse in pups
What is the pathogenesis of Filaroides hirthi?
- often asymptomatic
- clinical only in immunosuppressed (hyperinfection due to autoinfection)
- occasionally fatal bronchopneumonia
How to manage Filaroides?
- decontaminate environment, break vertical transmission (hand rear pups), repeated treatments w/ ML or fenbendazole (label in UK)
Which spp are in the subfamily Capillariinae (capillarids)?
- Capillaria aerophila (Eucoleus aerophilus)
- Capillaria (Eucoleus) boehmi
- Capillaria (Pearsonema) plica
Facts about the Capillariinae (capillarids):
- direct or indirect life cycles (earthworm IH)
- eggs are the shed stage (have polar plugs)
- L1 develops in eggs (infective stage like in Trichuris vulpis)
Where do Capillaria aerophila (Eucoleus aerophilus) live?
- in Ca & Fe, wild canids
- adults live in trachea & bronchi, shed eggs in feces
Where do Capillaria (Eucoleus) boehmi live?
- Ca & wild canids
- adults live in nasal & sinus cavities (shed eggs in feces)
Where do Capillaria (Pearsonema) plica live?
- Ca & Fe, wild canids
- adults live in bladder (shed eggs in urine, w/ or w/o cystitis)
Facts about Dioctophyme renale:
- DH: Ca, wild canids, mustelids, very rarely people
- adults can be over 1 m long
- live in the renal pelvis (generally of the right kidney, but sometimes free in the peritoneum)
- destroy kidney parenchyma but usually subclinical (unilateral)
- incidental finding on spay
- relatively common in MB & Northern ON
What is the life cycle of Dioctophyme renale?
- eggs in urine -> (in Oligochaete IH, L1 -> L2 -> L3) -> L3 ingested by Ca OR paratenic hosts which are then ingested by the dog -> become adults in dog
- LONG PPP - 4-5 months
