Rhabditids Flashcards
True or False:
Most rhabditids are free-living nematodes.
TRUE
Only a few are facultative parasites.
What is the characteristic morphological feature of the rhabditids?
Rhabditiform esophagus
(rhabditiform = barbell-shaped)
3 regions:
corpus, isthmus, bulb
Identify this structure and the regions pointed to by the arrows.
Rhabditiform esophagus
Top arrow: corpus
Middle arrow: isthmus
Bottom arrow: bulb
Name a famous free-living rhabditid nematode.
Caenorhabditis elegans
Where does Rhabditis strongyloides normally live?
Free-living in decaying organic matter
Can Rhabditis strongyloides complete its life cycle in host skin?
NO
List some risk factors for an animal becoming infected with Rhabditis strongyloides.
Wet, dirty bedding
Animal is sick/recumbent (i.e. hanging out close to the ground)
List some of the signs associated with “rhabditic dermatitis”
Alopecia
Serum exudate
Pruritis
Erythema
Pustules
Secondary bacterial infections
This lesion is from an animal that way laying down in moist bedding for a prolonged period.
- What parasite might you suspect?
- How can you confirm your diagnosis?
- Rhabditis strongyloides
- -*Biopsy and histopathology
True or False:
The lesions from Rhabditis strongyloides are typically limited to areas contacting the ground.
TRUE
This is Rhabditis strongyloides found on a biopsy. Where does this worm live in the host?
Skin
This is an adult Rhabditis (Pelodera) strongyloides. How would you characterize its esophagus?
Rhabditiform
*Note: all stages of Rhabditis have a rhabditiform esophagus.
In the skin, where do you usually find R. strongyloides larvae?
Hair follicles
How would you treat an infection with R. strongyloides?
Ivermectin
Antibiotics for secondary bacterial infections
Which host is most often infected by Halicephalobus gingivalis?
Equines
True or False:
Humans usually survive Halicephalobus gingivalis infections
FALSE
Always fatal
Unlike Rhabditis, Halicephalobus probably can’t penetrate skin all on its own. How does it gain access to the host?
Ingestion
Inhalation
Hematogenous spread
(lactogenic transmission?)
Where is Halicephalobus gingivalis usually found in the host?
CNS
Kidneys
Heart
Maxilla
Nasal cavity
Prepuce
Mammary gland
Bone
What kind of host response is elicited by Halicephalobus?
Granulomatous inflammation
Adult Halicephalobus gingivalis females are parthenogenetic. You’ve totally been studying and know what this word means.
Define parthogenetic.
Parthogenetic - eggs develop without fertilization from a male.
Describe the male of Halicephalobus gingivalis.
No male has ever been described.
All infecting Halicephalobus are parthenogenetic females.
You find these nodules in a kidney. On histopath, you find a worm with a rhabditiform esophagus. What species do you suspect?
Halicephalobus gingivalis
Describe the reproductive tract of Halicephalobus gingivalis.
Dorsoflexed ovaries
Single egg in uterus
Describe the treatment for Halicephalobus gingivalis
Surgical resection of affected tissue
Anthelmintics
Low success rate
What is the common name of Strongyloides spp.?
Intestinal or minute thread worm
Which sex of Strongyloides spp. is parasitic?
Only females
Which phase of the life cycle is found inside in freshly-laid Strongyloides spp. eggs?
L1
(Except in Strongyloides stercoralis, in which the eggs hatch in the intestine and the L1 is shed in the feces)
What is unique about the Strongyloides spp. life cycle?
Has both free-living and parasitic generations
Describe the esophagus of an adult parasitic Strongyloides female.
Filariform esophagus
(note that these worms are still rhabditids, but adult parasitic females do not have a rhabditiform esophagus)
What is the term for the parasitic generation of Strongyloides spp.?
Homogonic
In the homogonic phase of Strongyloides spp., where does the adult live within the host?
(Recall that homogonic is the parasitic generation)
Small intestinal mucosa
Parthenogenetic Strongyloides spp. in the host lay eggs, which are deposited in the feces. What life phase is contained within the eggs?
Rhabditiform L1
What happens to the rhabditiform L1 of Strongyloides spp. once it is shed in the feces? (2 options)
Develops into an infective filariform L3, which can infect a host and develop into an adult parasitic female
or
Develops into free-living rhabditiform adult males and females
What is the term for the free-living generation of Strongyloides spp.?
Heterogonic
Is the heterogonic generation of Strongyloides sp. sexual or parthenogenetic?
Sexual
Rhabditiform males and females reproduce sexually to produce eggs with rhabditiform L1’s.
(Recall that adult parasitic females are parthenogenetic)
What are the two sources of infective filariform L3’s in the Strongyloides sp. life cycle?
Eggs from parasitic parthogenetic females
Eggs from sexual free-living adults
This is the egg of Strongyloides sp.
- What phase is present in the egg?
- Which is the infective phase?
- Egg: rhabditiform L1
- Infective: filariform L3
This larva was found in the fresh feces of a dog.
- What kind of larva is it?
- Which species is most likely?
- Rhabditiform L1
- Strongyloides stercoralis
In this species, the egg hatches inside the host, and L1 larvae are shed in the feces.
Describe the tail of the L3 of Strongyloides spp.
Notched tail.
(Looks like something took a bite out of it.)
List the modes of infection for Strongyloides spp.
Skin penetration by L3 in the environment
Ingestion of L3 in environment (minor mode of infection)
Transmammary transmission of L3
Can Strongyloides spp. go hypobiotic in dogs?
NO
Note that Strongyloides spp. can be hypobiotic in other species. This is an important source of transmammary infections.
What will happen to a Strongyloides spp. L3 once it has been swallowed (either from the contaminated environment of from the colostrum)?
Penetrates mucosa, enters blood stream, moves to the lungs.
- Penetrates alveoli, coughed up, swallowed.
- Can also stay in blood to go hypobiotic in the tissues (except in dogs)
Adult parthenogenetic females live in the small intestine.
What will happen to the L3 larva of Strongyloides spp. once it penetrates the skin?
Enters blood stream, moves to lungs.
Penetrates alveoli, coughed up, swallowed.
-Can also stay in blood to go hypobiotic in the tissues (except in dogs)
Adult parthenogenetic females live in the small intestine.
In which Strongyloides species will you see L1 larvae instead of larvated eggs in fresh feces?
Strongyloides stercoralis
Found in humans and dogs
*Note that because the eggs hatch inside the body, autoinfection is possible.
Describe how autoinfection occurs in Strongyloides stercoralis.
- Female lays egg in host small intestine
- Egg hatches in host and releases rhabditiform L1 (unique amongst the Strongyloides species)
- Rhabditiform L1 develops into filariform L3 in host small intestine.
- L3 penetrates mucosa, undergoes blood-lung migration, is swallowed, and develops into an adult female.
In which host demographics are you most likely to find Strongyloides infections?
Young animals (transmammary transmission)
Immunocompromised hosts
What is the name of the feline Strongyloides species?
Where does it live?
- -Strongyloides tumefaciens*
- -*Lives in large intestine
(all other Strongyloides species live in the small intestine)
Which Strongyloides species infects primates, dogs, and rarely cats?
Strongyloides stercoralis
