general life cycle of nematodes
- egg/larvae : L1 - L5; L3 is infective stage!
- larvae in IH
- adults in DH
all nematodes general characteristics
tubular bodies with body cavity
- dioecious
- cuticle modifications - cervical alae
- males may have a copulatory bursa and/or spicules
3 different types of eggs
oviparous - single stage or murula
ovoviviparous: single L1 larva
larviparous: eggs retained in uterus - “gives birth” to live larvae/microfilariae
how to diagnose nematodes
- McMaster’s procedure: fecal, egg count, not sensitive
- fecal culture: mature larvae to L3
- fecal sedimentation
blood diagnostics for nematodes
- microfilariae
- blood smear
- difil filter technique
- modified knott’s concentration test
trichostrongyle : characteristics
superfamily of nematodes
- small, bursate, usually in ruminants
- inhabit abomasum and SI
- all their eggs look the same
the HOTC trichostrongyle
H - Haemonchus = barberpole worm = small lacet tooth at base
O - Ostertagia = brown stomach worm = small mouth
T - Trichostrongylus = hair worm = no mouth
C - Cooperia = cooper’s worm = head has swollen bulbous appearance
life cycle of trichostrongyle
- eggs shed in feces
- L1 - L3 in feces - feed on bacteria
- L3 ingested while DH grazing - exsheath in rumen
- enter wall of abomasum or SI - develop to L4. lumen dwelling adult in mucosa of predilection site
hypobiosis
larval inhibition - nematodes have ability to arrest development and go dormant at L4 stage
paraasitic gastroenteritis (PGE)
- caused by a compex of mainly trichostrongyloid nematodes
- major impediment in cattle
clinical signs: diarrhea, anemia, “bottle jaw”
weanlings most susceptible
Ostertagia ostertagi - “brown stomach worm” pathogenesis
- larvae destroy gastric glands as they develop
- damages Hcl producing parietal cells
ancyclostoma caninum
- hookworms w/ deep buccal teeth, curved anterior end
- found in dogs and cats
- habitat = SI
- life cycle is direct
- egg characteristics: 8-cell morula
- dx: float
- disease: young animals, anemia, diarrhea, zoonotic!
toxocara canis
- roundworms: large worms, lateral anterior alae
- found in all mammals
- SI, lungs, liver,
- life cycle = direct
- float
- found in young animals, diarrhea, coughing, pot belly
Trichinella spiralis
trichina worm, small and slender
- found in mammals
- uses IH and DH via consumption
- adults = SI, larvae = striated muscle
- life cycle indirect
- eggs hatch in utero, birth to live larvae
- dx: serum, muscle biopsy
- zoonotic, severe disease in humans
dirofilaria immitus
heartworm, long slender, white, tapered anteiror ends
- cats, dogs, ferrets
- IH = mosquitoes
- found in pulmonary artery, right ventrical, circulating blood
- life cycle = indirect
- egg characteristics = live larvae
- dx = microfilara in blood, antigen test, radiographs
- disease = heart failure, pulmonary disease
life cycle of dirofilaria immitis
- Mff released by female worm - enters circulation, mosquito fees on dog with circulating Mff
- Mff develop to infective larvae L3
- infective larvae are deposited at the skin surface when mosquito takes another blood meal - L3s enter DH @ mosquito bite wound
- larvae undergo several molts during their migration to the heart and lungs
- adult worms mature in the heart or lungs, mate and produce Mff
diagnosing heartworm
- detection of antigen uses point of care tests like SNAP, dirochek, snap 4DX, etc.
- detection of circulating microfilariae
- imaging techniques
when dogs become antigen positive for dirofilaria immitis
- with no prophylaxis the earlies is 5m with the usual being 7 months
- with macrocyclic lactone with doses mixed its usually 9 months
when dogs become Microfilariae positive for dirofilaria immitis
- the earliest with no prophylaxis is 6.5months
- with missed macrocyclic lactone doses they may never develop mff or they may appear transiently in small numbers
what is the most sensitive test for dirofilaria immitis
dirocheck (uses serum or plasma)
what do the Ab tests for dirofilaria immitis tell you?
they tell you if the dog WAS an infection. so if the animal had L3s n the system and the monthly preventative killed them off, the AB test will still come up positive. so it will tell you if you were positive at any point.
if a dog is Ag: positive and Mff: negative what could cause this?
- maturing infection; Mff not yet in circulation
- use of preventative without removing adult worms
- use of microfilaricide w/o removal of adult worms
- unisex (female) infection; males not present
- dog is a true immune -mediated occult
- failure to use microfilaria concentration test
if a dog is Ag: negative but Mff: positive what could cause this?
- Mff are those of another species
- Mff were acquired transplacentally
- adult worms were removed or have died but Mff persist
- contamination of test materials from previous sample
If a dog was Ag: variable and Mff: positive OR negative
- fluctuating Ag level due to number of female worms, ages of worms or quality of sample
