Superfamily Ascaroidea Flashcards
(33 cards)
Two families within the superfamily Ascaroidea
- Ascarididae (ascarids)
- -Terrestrial mammals, reptiles, and birds - Anisakidae (anisakids)
- -Marine mammals and fish-eating birds (larval stage is present in birds)
Important Ascarids
- Ascaris suum (pig) - 15-40 cm
- Parascaris equorum (horse) - 15-50 cm
- Toxocara canis (dog) - 10-18 cm
- Toxocara cati (cat) - 3-10 cm
- Toxascaris leonina (dog and cat) - 7-10 cm
- Baylisascaris procyonis (raccoon and dog) - 10-24 cm
Adult Ascarid morphology
- Large, thick bodied
- Females are larger than males
- Have three well-developed lips around the stoma
- Cervical alae (present in T. leonina and Toxocara spp.)
Ascarid life-cycle
- Adult ascarids present in the small intestine
- Lays eggs, found in fresh feces (non-infective)
- After 2-3 weeks, eggs containing larvae are found in the soil (infective) - appears to be coiled inside the egg
- Ingestion (fecal-oral or paratenic host)
- Transmission to the definitive host
- Migration in the definitive host (hepato-pulmonary-tracheal migration)
- Adult ascarids present in the small intestine
Life-cycle and transmission types
Direct: Ascaris suum and Parascaris equorum
–Ingestion of larvated eggs from contaminated environment
Direct/Indirect: Toxocara, Toxascaris, and Baylisascaris
–Paratenic host (T. canis and T. cati)
–Prenatal or transplacental (T. canis)
–Transmammary (T. canis and T. cati)
Development in the environment
- Ascarids are prolific egg producers –> shed millions of eggs per day
- Eggs are extremely resistant
- -Last for years in the soil
- –Single most important factor in epidemiology!
- Eggs are very sticky
- -Adhere to surfaces and objects (need to clean with chlorine or bleach, not just soap)
- Development is temperature dependent
- -Optimal temp is 25-30 degrees Celsius
- -Takes ~2-4 weeks to become infective (embryonated) in the environment (exception: T. leonina, 3-5 days)
Direct life-cycle
- Ascaris suum and Parascaris equorum
- Eggs are shed in the feces –> develop infective larva within the egg –> ingested –> larvae hatch –> penetrate the intestine –> migrate through the liver, lungs (L4), trachea, then intestine (adult)
- Prepatent period:
- –Ascaris suum = 60-62 days
- –Parascaris equorum = 72-94 days
Clinical disease: Ascaris suum and Parascaris equorum
Common to both:
-Infective egg - polluted soil or stuck to mammary skin
-Hepatic migration - mechanical damage, eosinophilic inflammation, scarring (possible)
-Migration in the lung - verminous pneumonitis
-Immature adults return to the intestine - no significant clinical disease
-Small intestine - catarrhal enteritis, interference with nutrient absorption and growth (stunting growth), economic losses, GI obstruction, aberrant migration, GI perforation
Ascaris suum only:
–ZOONOTIC (will migrate and develop in humans)
—Often seen in children who are around swine in many parts of the world (occasional reports in US)
–Swine lung: petechial hemorrhage (respiratory distress, rapid and shallow, audible expiration (thumps))
–Liver: milk spots (fibrotic areas - migration of the larvae)
Toxascaris leonina general info
- Host = dogs, cats, foxes, wolves, and big cats
- Not zoonotic
- Clinical disease is rarely observed
- Prevalent in geographical regions with cooler climates
Toxascaris leonina life-cycle
- Adult in small intestine
- Eggs containing one single cell are shed in the feces
- Takes 3-5 days to become egg containing infective larva in the soil
- From there, can go down two different routes
1. Eggs ingested by definitive host (dog or cat) and travel via mucosal migration - -Prepatent period = 2-2.5 months
- -Adult in small intestine
2. Eggs are ingested by a paratenic host (rodent) and travel via lymphatics or contiguity of tissues - -Larvae are arrested in the tissues
- -Dog or cat eats the paratenic host
- -Adult in small intestine
Toxocara canis adult morphology
- Host = dogs and wild canids
- Robust adults (10-15 cm long)
- Cervical alae present on anterior end
- Digitiform appendage on male worm
- Spicules found on male worm
T. canis routes of transmission
- Ingestion of infective egg
- Transplacental
- -MOST important route of transmission
- -Ensures that most puppies (90%) are infected at birth
- Transmammary
- -Can be passed at larval stage
- Paratenic host
Toxocara canis life-cycle
- Adult in small intestine
- Eggs containing one cell shed in feces
- After four weeks, the eggs contain infective larvae, present in the soil
- From there, can go down two different routes
1. Eggs ingested by the dog - -From there, can go down two different routes
- –1. Tracheal migration in puppies < 3 months of age (prepatent period is 4-5 weeks)
- —Adult in small intestine
- –2. Somatic migration in puppies > 3 months of age (prepatent period is 4-5 weeks)
- —Infective larvae is arrested in the tissues of the bitch
- —Larvae are reactivated during pregnancy
- —From there, can go down two different routes
- —-1. Larvae enter the pups in utero during the third trimester
- —–Larvae in lungs of pups
- —–Pups born, larvae mature, patent at 3 weeks post partum
- —–Adult in small intestine
- —-2. Larvae shed in the milk, if mother infected during lactation, ingested by the pups
- —–Adult in small intestine
2. Eggs ingested by the paratenic host - -Somatic migration (liver –> lung –> tissue)
- -Infective larvae arrested in tissues of paratenic host
- -Dog eats paratenic host
- -Adult in small intestine
T. canis general info
- Complex life-cycle
- Clinical disease may be absent in adult dogs
- Most patent infections occur in puppies < 6 months of age
T. canis clinical disease
- Pot-bellied appearance
- Unthriftiness
- Rough hair coat
- Poor appetite
- Abdominal discomfort with vocalization
- Hepatic migration damage, verminous pneumonitis, kidney scarring, catarrhal enteritis, obstruction of gut, perforation of gut, interference with absorption, diarrhea, vomiting, aberrant migration of worms
Toxocara cati general info
- Found in cats
- Arrow-headed worm
- Similar clinical disease as T. canis
T. cati life-cycle
- Adult in small intestine
- Eggs containing one cell found in feces
- Eggs containing infective larvae found in soil after four weeks
- From there, can go down two different routes
- -1. Eggs ingested by cat
- –From there, can go down two different routes
- —1. Tracheal migration (prepatent period = 2 months)
- —-Adult in small intestine
- —2. Somatic migration
- —-Infective larvae arrested in tissues of queen
- —-Larvae shed in milk, if mother infected during lactation, ingested by kittens
- —-Mucosal migration
- —-Adult in small intestine
- -2. Eggs ingested by paratenic host
- –Infective larvae arrested in tissues of paratenic host
- –Cat eats paratenic host
- –Mucosal migration
- –Adult in small intestine
Differences of transmission between T. cati and T. canis
T. cati
-No transplacental transmission
-Transmammary transmission does occur
–Does not occur in chronically infected queens
–Might occur if acute infection present during late-pregnancy
-Tracheal or somatic migration occurs
–But host age related differential migration does not
–Prepatent period is ~8 weeks
-Paratenic host ingestion occurs
–Prepatent period is ~3 weeks
T. canis
-Transplacental transmission does occur
-Transmammary transmission does occur
-Tracheal or somatic migration does occur
-Host age related differential migration is present
-Paratenic host ingestion does occur
Comparison of T. cati, T. canis, and T. leonina
Cervical alae
- T. canis and T. leonina have thinner alae
- T. cati has a much thicker alae
Ascarid infection characteristics
- Acute to chronic clinical disease
- Always worse in young animals
- Varies with intensity of infection and frequency of reinfection
- Pathology is related to location of adults and migration paths of larvae
- Larval migration causes:
- -Mechanical damage and hemorrhages
- -Edema and marked eosinophilic inflammation
- Immunopathological responses may also occur
Diagnosis of ascarid infections
- Clinical signs (adult animals rarely show clinical signs)
- Necropsy lesions
- Adult recovery at necropsy (or surgery)
- Eggs in feces
- Adult and immature worm recovery from vomitus or feces (often in T. canis and T. cati infections)
- Ultrasound
- Endoscopy
How to ID eggs
- Size
- Shape
- Color
- Internal structures
- Surface features
Baylisascaris procyonis
- Found in raccoons and dogs (definitive hosts)
- Adult worms are present in the small intestine
- Eggs are shed in the feces
- Dogs can also be accidental hosts
Accidental host
- Presence of migrating larvae in the body tissues of the host
- This host is not involved in the completion of the life cycle
