Cestodes Flashcards
1
Q
What are the species and common names of relevant tapeworms?
A
- Taenia solium - pork tapeworm
- Taenia saginata - beef tapeworm
- Diphyllobothrium latum - fish tapeworm
- Hymenolepis nana - dwarf tapeworm
2
Q
Which tapeworm does not require an intermediate host for its lifecycle?
A
Hymenolepis nana
Capable of auto-infection
3
Q
What is the typical size of:
* Taenia solium
* Taenia saginata
* Diphyllobothrium latum
* Hymenolepis nana
A
- Taenia solium - 2-7 m
- Taenia saginata - 5-25 m
- Diphyllobothrium latum - 2-15 m
- Hymenolpis nana - 15-40 mm
4
Q
Describe the Taeniasis lifecycle for Taenia solium & saginata
A
- Taeniasis is the infection of humans with the adult tapeworm of Taenia saginata, T. solium or T. asiatica. Humans are the only definitive hosts for these three species. Eggs or gravid proglottids are passed with feces; the eggs can survive for days to months in the environment.
- Cattle (T. saginata) and pigs (T. solium and T. asiatica) become infected by ingesting vegetation contaminated with eggs or gravid proglottids.
- In the animal’s intestine, the oncospheres hatch, invade the intestinal wall, and migrate to the striated muscles, where they develop into cysticerci. A cysticercus can survive for several years in the animal.
- Humans become infected by ingesting raw or undercooked infected meat. In the human intestine, the cysticercus develops over 2 months into an adult tapeworm, which can survive for years.
- The adult tapeworms attach to the small intestine by their scolex
- and reside in the small intestine. Length of adult worms is usually 5 m or less for T. saginata (however it may reach up to 25 m) and 2 to 7 m for T. solium. The adults produce proglottids which mature, become gravid, detach from the tapeworm, and migrate to the anus or are passed in the stool (approximately 6 per day). T. saginata adults usually have 1,000 to 2,000 proglottids, while T. solium adults have an average of 1,000 proglottids. The eggs contained in the gravid proglottids are released after the proglottids are passed with the feces. T. saginata may produce up to 100,000 and T. solium may produce 50,000 eggs per proglottid respectively.
5
Q
What are the clinical presentations of taeniasis?
A
- Passage of proglottids in feces most common presentation
- Largely asymptomatic
- May have some abdominal discomfort/diarrhea
Eggs: 30-35 um
6
Q
How are Taenia spp. infections diagnosed?
A
- Identification of characteristic proglottids in stool
- Identification of eggs - solium and saginata are identical
7
Q
What is the treatment for Taenia spp. infection?
A
- Praziquantel – 5 to 10 mg/kg orally (single dose)
- Niclosamide
Eggs: 30-35 um
8
Q
How do you differentiate between Taenia solium and saginata proglottids?
A
- Gravid proglottids are longer than wide (as opposed to D. latum)
- T. solium and T. saginata differ in the number of primary lateral uterine branches:
- T. solium contains 7-13 lateral branches
- T. saginata 12-30 lateral branches.
- Proglottids of T. asiatica are similar to T. saginata and possess more than 12 primary uterine branches.
9
Q
Describe the eggs of Taenia spp.
A
- The eggs of Taenia spp. are indistinguishable from each other, as well as from other members of the Taeniidae
- The eggs measure 30-35 micrometers in diameter
- Are radially-striated
- The internal oncosphere contains six refractile hooks.
10
Q
Describe the lifecycle of Diphyllobothrium latum
A
- Eggs are passed unembryonated in feces.
- Under appropriate conditions, the eggs mature (approximately 18 to 20 days)
- And yield oncospheres which develop into a coracidia.
- After ingestion by a suitable crustacean (first intermediate host) the coracidia develop into procercoid larvae.
- Procercoid larvae are released from the crustacean upon predation by the second intermediate host (usually a small fish) and migrate into the deeper tissues where they develop into a plerocercoid larvae (spargana), which is the infectious stage for the definitive host.
- Because humans do not generally eat these small fish species raw, the second intermediate host probably does not represent an important source of human infection.
- However, these small second intermediate hosts can be eaten by larger predator species that then serve as paratenic hosts. In this case, the plerocercoid migrates to the musculature of the larger predator fish; humans (and other definitive host species) acquire the parasite via consumption of undercooked paratenic host fish.
- In the definitive host, the plerocercoid develops into adult tapeworms in the small intestine. Adult diphyllobothriids attach to the intestinal mucosa by means of two bilateral groves (bothria) of their scolex. The adults can reach more than 10 m in length, with more than 3,000 proglottids. Immature eggs are discharged from the proglottids (up to 1,000,000 eggs per day per worm) and are passed in the feces. Eggs appear in the feces 5 to 6 weeks after infection.
11
Q
What are the possible clinical presentations with D. latum
A
- Most infections are asymptomatic
- Gastrointestinal symptoms may occur in some patients.
- Aberrant migration of proglottids can cause cholecystitis or cholangitis.
- Rarely, massive infections may cause intestinal obstruction
- Megaloblastic anemia
Egg: 55 to 75 µm by 40 to 50 µm
12
Q
How is D. latum infection treated?
A
Praziquantel (10 mg/kg)
Egg: 55 to 75 µm by 40 to 50 µm
13
Q
How is D. latum infection diagnosed?
A
- Microscopic identification of eggs in the stool is the basis of family level diagnosis;
- genus level identification based on eggs is difficult due to overlap in morphological features.
- Eggs are usually numerous and can be demonstrated without concentration techniques.
- Identification of proglottids passed in the stool is also of diagnostic value, but often degenerate within the host and only eggs are visible in stool
14
Q
Describe the eggs of D. latum
A
- Diphyllobothriid eggs are oval or ellipsoidal and range in size from 55 to 75 µm by 40 to 50 µm
- There is an operculum at one end that can be inconspicuous, and at the opposite (abopercular) end is a small knob that can be barely discernible
- The eggs are passed in the stool unembryonated
15
Q
Describe adult D. latum and the proglottids
A
- Mature diphyllobothriids are large tapeworms reaching 2—15 meters in length, with occasional larger specimens.
- The scolex always has two bothria (grooves).
- Proglottids are broader than long, with a single genital pore that opens in the middle of the ventral surface;
- Fully mature specimens may be comprised of a 2,000—5,000 proglottids.
- The ovaries are characteristically rosette-shaped.
16
Q
Describe the lifecycle of Hymenelopis nana
A
- Eggs of Hymenolepis nana are immediately infective when passed with the stool and cannot survive more than 10 days in the external environment.
- When eggs are ingested by an arthropod intermediate host (various species of beetles and fleas may serve as intermediate hosts)
- They develop into cysticercoids, which can infect humans or rodents upon ingestion and develop into adults in the small intestine. A morphologically identical variant, H. nana var. fraterna, infects rodents and uses arthropods as intermediate hosts.
- When eggs are ingested (in contaminated food or water or from hands contaminated with feces), the oncospheres contained in the eggs are released.
- The oncospheres (hexacanth larvae) penetrate the intestinal villus and develop into cysticercoid larvae.
- Upon rupture of the villus, the cysticercoids return to the intestinal lumen, evaginate their scoleces, attach to the intestinal mucosa and
- Develop into adults that reside in the ileal portion of the small intestine producing gravid proglottids.
- Eggs are passed in the stool when released from proglottids through its genital atrium or when proglottids disintegrate in the small intestine.
- An alternate mode of infection consists of internal autoinfection, where the eggs release their hexacanth embryo, which penetrates the villus continuing the infective cycle without passage through the external environment. The life span of adult worms is 4 to 6 weeks, but internal autoinfection allows the infection to persist for years.
17
Q
What are the common clinical presentations of H. nana infection?
A
- Hymenolepis nana infections are most often asymptomatic
Heavy infections with H. nana can cause
* weakness
* headaches
* anorexia
* abdominal pain
* diarrhea.
18
Q
Describe the eggs of H. nana
A
- Eggs of Hymenolepis nana oval and smaller than those of H. diminuta
- Size range of 30 to 50 µm
- On the inner membrane are two poles, from which 4-8 polar filaments spread out between the two membranes.
- The oncosphere has six hooks.
19
Q
How are H. nana infections diagnosed?
A
- The diagnosis depends on the demonstration of eggs in stool specimens.
- Concentration techniques and repeated examinations will increase the likelihood of detecting light infections.
20
Q
What is the treatment for H. nana infection?
A
Praziquantel repetead in 10 days
21
Q
Describe the adults of H. nana
A
- ~0.2-0.5 cm long
- ~200 proglottids each with 100-200 eggs
22
Q
Describe the lifecyle leading to development of cysticercosis
A
- Cysticercosis is an infection of both humans and pigs with the larval stages of the parasitic cestode, Taenia solium. This infection is caused by ingestion of eggs shed in the feces of a human tapeworm carrier. These eggs are immediately infectious and do not require a developmental period outside the host.
- Pigs and humans become infected by ingesting eggs or gravid proglottids image. Humans are usually exposed to eggs by ingestion of food/water contaminated with feces containing these eggs or proglottids or by person-to-person spread. Tapeworm carriers can also infect themselves through fecal-oral transmission (e.g. caused by poor hand hygiene).
- Once eggs or proglottids are ingested, oncospheres hatch in the intestine, invade the intestinal wall, enter the bloodstream, and migrate to multiple tissues and organs where they mature into cysticerci over 60–70 days. Some cysticerci will migrate to the central nervous system, causing serious sequellae (neurocysticercosis).
This differs from taeniasis, which is an intestinal infection with the adult tapeworm. Humans acquire intestinal infections with T. solium after eating undercooked pork containing cysticerci. Cysts evaginate and attach to the small intestine by their scolices. Adult tapeworms develop to maturity and may reside in the small intestine for years.
24
Q
Describe the lifecycle of Dipylidium caninum
A
- Gravid proglottids are passed intact in the feces or emerge from the perianal region of the host.
- In the environment, the proglottids disintegrate and release egg packets, which are also occasionally found free in the feces.
- The intermediate host (most often larval stages of the dog or cat flea Ctenocephalides spp.) ingests egg packets, and the oncosphere within is released into the larval flea’s intestine. The oncosphere penetrates the intestinal wall, invades the insect’s hemocoel (body cavity), and develops into a cysticercoid.
- The cysticercoid remains in the flea as it matures from a larva into an adult.
- The vertebrate host becomes infected by ingesting the adult flea containing the cysticercoid. In the small intestine of the vertebrate host, the cysticercoid develops into the adult tapeworm after about one month.
- The adult tapeworms (measuring up to 60 cm in length and 3 mm in width) reside in the small intestine of the host, where they each attach by their scolex. Gravid, double-pored proglottids detach from the strobila (body) and are shed in the feces.
- Humans also acquire infection by ingesting the cysticercoid contaminated flea. Children are most frequently infected, possibly due to close contact with flea-infested pets image .
25
Q
Describe the eggs of Dipylidium caninum
A
- D. caninum eggs are round to oval
- Average size 35 to 40 µm
- Contain an oncosphere that has 6 hooklets
- Proglottids of D. caninum contain characteristic egg packets that are round to ovoid and contain 5 to 15 or more eggs each.
