Nematodes

Question 0

general life cycle of nematodes

Answer 0

• egg/larvae : L1 - L5; L3 is infective stage!
• larvae in IH
• adults in DH

Question 1

all nematodes general characteristics

Answer 1

tubular bodies with body cavity

• dioecious
• cuticle modifications - cervical alae
• males may have a copulatory bursa and/or spicules

Question 2

3 different types of eggs

Answer 2

oviparous - single stage or murula

ovoviviparous: single L1 larva
larviparous: eggs retained in uterus - “gives birth” to live larvae/microfilariae

Question 3

how to diagnose nematodes

Answer 3

• McMaster’s procedure: fecal, egg count, not sensitive
• fecal culture: mature larvae to L3
• fecal sedimentation

Question 4

blood diagnostics for nematodes

Answer 4

• microfilariae
• blood smear
• difil filter technique
• modified knott’s concentration test

Question 5

trichostrongyle : characteristics

Answer 5

superfamily of nematodes

• small, bursate, usually in ruminants
• inhabit abomasum and SI
• all their eggs look the same

Question 6

the HOTC trichostrongyle

Answer 6

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

Question 7

life cycle of trichostrongyle

Answer 7

1. eggs shed in feces
2. L1 - L3 in feces - feed on bacteria
3. L3 ingested while DH grazing - exsheath in rumen
4. enter wall of abomasum or SI - develop to L4. lumen dwelling adult in mucosa of predilection site

Question 8

hypobiosis

Answer 8

larval inhibition - nematodes have ability to arrest development and go dormant at L4 stage

Question 9

paraasitic gastroenteritis (PGE)

Answer 9

• caused by a compex of mainly trichostrongyloid nematodes
• major impediment in cattle
  clinical signs: diarrhea, anemia, “bottle jaw”
  weanlings most susceptible

Question 10

Ostertagia ostertagi - “brown stomach worm” pathogenesis

Answer 10

• larvae destroy gastric glands as they develop

- damages Hcl producing parietal cells

Question 11

ancyclostoma caninum

Answer 11

• 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!

Question 12

toxocara canis

Answer 12

• 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

Question 13

Trichinella spiralis

Answer 13

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

Question 14

dirofilaria immitus

Answer 14

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

Question 15

life cycle of dirofilaria immitis

Answer 15

1. Mff released by female worm - enters circulation, mosquito fees on dog with circulating Mff
2. Mff develop to infective larvae L3
3. infective larvae are deposited at the skin surface when mosquito takes another blood meal - L3s enter DH @ mosquito bite wound
4. larvae undergo several molts during their migration to the heart and lungs
5. adult worms mature in the heart or lungs, mate and produce Mff

Question 16

diagnosing heartworm

Answer 16

• detection of antigen uses point of care tests like SNAP, dirochek, snap 4DX, etc.
• detection of circulating microfilariae
• imaging techniques

Question 17

when dogs become antigen positive for dirofilaria immitis

Answer 17

• with no prophylaxis the earlies is 5m with the usual being 7 months
• with macrocyclic lactone with doses mixed its usually 9 months

Question 18

when dogs become Microfilariae positive for dirofilaria immitis

Answer 18

• 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

Question 19

what is the most sensitive test for dirofilaria immitis

Answer 19

dirocheck (uses serum or plasma)

Question 20

what do the Ab tests for dirofilaria immitis tell you?

Answer 20

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.

Question 21

if a dog is Ag: positive and Mff: negative what could cause this?

Answer 21

• 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

Question 22

if a dog is Ag: negative but Mff: positive what could cause this?

Answer 22

• 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

Question 23

If a dog was Ag: variable and Mff: positive OR negative

Answer 23

• fluctuating Ag level due to number of female worms, ages of worms or quality of sample

Question 24

pathogenicity/clinical signs of dirofilaria immitis

Answer 24

- disease primarily due to adults - right ventricle, pulmonary artery - irritate vessel walls, produce pro-inflammatory molecules that induce inflammation of vessels: "villous endarteritis" - vascular resistance - vessel inflammation increases cardiac workload - decreased cardiac output - decreased organ perfusion, decreased circulation, exercise intolerance - coughing and hemoptysis (blood in sputum) - vena cava syndrome: infect atrium and vena cava, overrun with worms, obstruct blood flow, interfere with tricuspid valve closure, liver congestion, herat murmur

Question 25

canine v. feline heartworm

Answer 25

canine: highly susceptible, many worms, worms long lived, usually Microfilaremic, heart and lungs affected, easily diagnosed, treatment and preventatives available feline: less susceptible, few worms, few worms cause disease, worms short lived, usually amicrofilaremic, lungs most affected, diagnoses difficult, only symptomatic tx available, preventatives available

Question 26

tx of heartworm:

Answer 26

- melarsomine dihydrochloride (immiticide) - greater efficacy of killing adult worms - NO activity against worms < 4months - convenience of administration

Question 27

alternatives to immiticide: "slow kill"

Answer 27

- continuous monthly use of preventatives - currently macrocyclic lactones are NOT APPROVED for this use - requires compliant monthly treatment - may require long periods to remove all worms - view this as a viable alternative when immiticide cannot be used

Question 28

treatment/control of dirofilaria immitis

Answer 28

- treat clinical signs - surgical removal of worms - removal of Mff - year round monthly preventative - annual testing