Transmission of Nematodes

Question 1

Toxocara Canis

Answer 1

1) Direct transmission
Ingestion of infective embryonated eggs (L2)  release of larvae in GI tract  migrate to liver  to lungs  up trachea  swallowed  go to small intestine where molt to L5  produce eggs in about 1 month (prepatent period)
Called hepatotracheal migration

2) Transplacental transmission:
Primary route of infection for puppies
Encysted larvae in bitch’s tissues become activated at day 42 of gestation and migrate to the fetal liver. Eggs may appear in fecal exams by three weeks of age.

3) Transmammary transmission:
Encysted larvae pass in the bitch’s milk to nursing puppies. No migration occurs.
Relatively unimportant route in puppies, and may not occur.

4) Ingestion of paratenic hosts:
Many animals serve as paratenic hosts
More important method in wild canids.

Question 2

Toxocara Cati

Answer 2

Transmammary transmission
Primary route of infection for kittens

Direct transmission

Ingestion of infective eggs

Ingestion of paratenic hosts
More important in cats, since they are hunters

Transplacental transmission
DOES NOT OCCUR

Question 3

Toxascaris Leonina

Answer 3

Direct Transmission:
Under optimal conditions, eggs embryonate and become infective in 1 week. After ingestion, eggs hatch and larvae migrate into the intestinal wall, where 2 molts occur. No other migration occurs.

Ingestion of paratenic hosts OR intermediate hosts (because a larval molt occurs in them – to L3).
IHs include mice, rabbits and chickens

Question 4

Hookworms

Answer 4

Direct – Ingestion of free-living L3

Develop in small intestine – usually no migration
Percutaneous
Penetrate the skin and migrate through the circulatory system into the lungs, trachea, esophagus, stomach, and small intestine, where they mature
Some larvae encyst in skeletal muscle in dormant stage (hypobiotic larvae)

Transplacental

Transmammary
Via milk for 1st 3 weeks lactation
Primary route for puppies

Question 5

Whipworms

Answer 5

Direct: Eggs become infective in about 2 weeks under ideal conditions  ingested by host  larvae emerge through operculae  mature in intestine  adults live in cecum (appendix) or colon (large intestine)

Question 6

Threadworms

Answer 6

Transmission is percutaneous – L3 enters skin  circulation  lung (L4)  trachea  gut (L5); also occasionally oral ingestion of L3s with same migratory route

Question 7

Capillaria aerophila

Answer 7

Direct transmission by ingestion of infective L3 eggs  adults in trachea and lungs

Question 8

Aelurostrongylus abstrusus

Answer 8

Indirect – Female lays eggs in lung tissue  L1 larvae (kinked tails) in trachea  swallowed and passed in feces  Ingested by mollusk  possible paratenic host  cat ingests mollusk or paratenic host  worms develop into adult in cat

Question 9

Filaroides osleri and F. hirthi

Answer 9

L1 larvae passed in saliva or feces – is directly infective to others by ingestion of feces or lung tissue, or from an infected bitch grooming her puppies

Question 10

Capillaria plica (dogs) ; C. feliscati (cats)

Answer 10

Indirect – Earthworms are IH

Question 11

Dioctophyma renale

Answer 11

Eggs to water environment in FH urine  annelid (Lumbriculus variegatus)  2 molts  FH infected by ingestion of annelid or paratenic host  L3 migrates to liver  kidney (right kidney more commonly infected because of location adjacent to liver)

Question 12

Spirocerca lupi

Answer 12

Live in large (up to golf ball size) fibrous nodules in wall of esophagus and stomach (up to 40 worms/nodule)  small fistulae to lumen of gut  eggs pass through fistulae  out in feces  ingested by IH (beetles)  develop to L3  FH infected by ingestion of IH or paratenic host  L3 released in FH stomach  circulation  aorta, where remain about 3 months  then pass through wall to adjacent esophagus  form nodules

Question 13

Physaloptera rara (dogs) & P. preputialis (cats)

Answer 13

Indirect – IH beetles, cockroaches, crickets, etc

Question 14

Enterobius vermicularis

Answer 14

Reinfection by contamination of hands  ingestion of infective eggs
Contaminated clothing, bedding, etc.
Airborne – eggs survive several days in dry dust; several weeks in high humidity and moderate temperatures
Retroinfection thought possible (eggs hatch and larvae migrate back into rectum)

Question 15

Wuchereria bancrofti

Answer 15

IH – Blackfly

Question 16

Trichostrongylus axei

Answer 16

Ingestion of L3 – non-migratory in host

Question 17

Habronema muscae, Habronema microstoma, Draschia megastoma

Answer 17

Adults attach to wall of stomach  larvated eggs (which soon hatch) or L1 larvae pass in feces  fly larvae feeding in feces ingest L1s  develop to infective L3s  passes from fly to horse —-
If near lips, ingested  L3 to stomach
If on skin wound  L3 invade injured tissues  host reaction to L3  large granulomas called “summer sores”  development arrested at L3

Question 18

Parascaris equorum

Answer 18

Direct – L2 egg ingested  hepatotracheal migration; foal-to-foal transmission

Question 19

Strongyloides westeri

Answer 19

mainly milk-borne

Question 20

Large Strongyles (Red Worms)

Answer 20

All infected by ingestion of L3 larvae

Question 21

Strongylus equinus

Answer 21

Ingestion large intestine  gut mucosa  submucosa – enclosed in nodules (molt to L4)  abdominal cavity  liver  hepatic ligaments  pancreas; kidney; etc.  molt to L5  gut by direct penetration of gut wall

Question 22

Strongylus edentatus

Answer 22

Ingestion  portal circ  liver – form nodules  molt to L4  hepatic ligaments  subperitoneal CTs  mesentery  gut  nodules in gut walls  through to lumen

Question 23

Strongylus vulgaris

Answer 23

Ingestion L3  penetrates gut mucosa  molt  L4 to lumen of submucosal aa.  up mesenteric aa.  remain here 3-4 mo. & grow  molt to L5  down the arteries  small branches on serosal intestinal surface  nodules  rupture through mucosa  gut lumen  mature in 2 ½ - 3 months

Question 24

Small Strongyles

Answer 24

Ingestion of L3  mucosa of colon  nodule formation  molt to L4  mucosa  molt to L5 –L4/L5 feed on mucosa

Question 25

Oxyuris equi

Answer 25

Eggs laid on perineum (grayish smear grossly) – not often seen on fecal exam.
Eggs drop to ground  infective L3  hosts ingest L3 when grazing  cecum/colon  L4  feeds on mucosa  L5 – feeds on gut contents

Question 26

Dictyocaulus arnfeldi

Answer 26

Eggs hatch in air passages, gut, or soon after feces passed  L3  ingested  lymphatics  lungs

Question 27

Setaria equina

Answer 27

IH: Mosquitoes

Question 28

Thelazia lacrimalis

Answer 28

L1 passed by female  ingested by fly  L3  migrate into orbit of new host when fly feeds

Question 29

Gongylonema sp.

Answer 29

IH: Coprophageous beetles, cockroaches

Question 30

Ostertagia sp.

Answer 30

Infection by ingestion of L3  migrate into mucosa  2 molts  young adults emerge on surface
Hypobiosis very important in this species

Question 31

Trichostrongylus axei

Answer 31

infection by ingestion of L3  penetrate mucosa and molt to L4  returns to mucosal surface  L4 begins blood-sucking

Question 32

Nematodirus sp.

Answer 32

Most important feature – doesn’t hatch until L3 in shell – survives freezing extremes very well – found in temperate areas

Question 33

Bunostomum sp.

Answer 33

Ingestion of L3

Percutaneous penetration of L3

Question 34

Strongyloides papillosus

Answer 34

Routes of infection:
Percutaneous
Oral
Prenatal
Milk

Question 35

Toxocara vitulorum

Answer 35

Most important route of infection – thru milk

Direct infection may occur

Question 36

Oesophagostomum sp.

Answer 36

L3 infective  thru mucosa  form nodules  molt to L4  lumen.
Nodules become larger in animals previously infected (greater than 1 cm in animals parasitized over 1 year).

Question 37

Dictyocaulus viviparous – cattleDictyocaulus filaria – sheep, goat

Answer 37

Infection by ingestion of L3
Larvae to lungs by lymphatics
1st molt in mesenteric lymph nodes; 2nd in lungs

Question 38

Ascarops strongylinaPhysocephalus sexalatus

Answer 38

IH: Dung beetle

Eggs in feces – eaten by dung beetles –L3 –ingested by pig

Question 39

Ascaris suum

Answer 39

L2 egg infective – hepatotracheal migration

Question 40

Trichinella spiralis

Answer 40

Life cycle: female in small intestine  large #s active larvae  blood vessels (several weeks in circ.)  encyst in muscle tissue (viable for years)  tissue eaten by another host (rat, man, pig)  (pigs IH or FH)  larvae freed from cysts  mature in intestine  copulate  produce larvae for about 2 weeks

Question 41

Metastrongylus sp.

Answer 41

IH: earthworms

Question 42

Macracanthorhynchus hirudinaceus

Answer 42

IH: larvae of dung beetles, June bugs, water beetles