Categories
Internal Medicine

Diphyllobothriasis

Infection of the small intestine by Diphyllobothrium spp “fish tapeworm” acquired from eating undercooked or raw fish.

Infection of the small intestine by Diphyllobothrium spp “fish tapeworm” acquired from eating undercooked or raw fish.

  • Longest human tapeworm (4-15 m in length) and may remain active in the gut for over 20 years

Parasitology

Dibothriocephalus “broad tapeworms” or “fish tapeworms”:

Tapeworms or cestodes are hermaphroditic parasites, which can live for considerable periods of time in the human gastrointestinal tract. Fish tapeworm (Diphyllobothrium species) are endemic in various parts of the world, the commonest species being Diphyllobothrium latum.
  • D. latus (M/C)
  • Others: D. dendriticum, D. nihonkaiense, etc

Morphology:

  • Longest human tapeworm (4-15 m in length) and may remain active in the gut for over 20 years
  • Anterior end: Scolex with attachment grooves on its dorsal and ventral surfaces
  • Segmented body, each containing sets of male and female reproductive organs, allowing for its high fecundity
(A) A strobila of Diphyllobothrium latum expelled by the patient (about 260 cm). (B) An egg extracted from the uterus of a gravid proglottid. The egg was ovoid and operculated. (C) Tissue section stained with hematoxylin and eosin showing the rosette-shaped uterus of a gravid proglottid. An ovoid cirrus sac is located in the anterior side of the gravid proglottid. Several eggs are observed in the loops of the uterus. (D) Molecular identification of D. latum by PCR. Lanes (1–4) represent the PCR products amplified by using different primers for the most common Diphyllobothrium species. Lane 1, D. pacificum; lane 2, D. latum; lane 3, D. dendriticum; lane 4, D. nihonkaiense. M: marker. | An, Y. C., Sung, C. C., Wang, C. C., Lin, H. C., Chen, K. Y., Ku, F. M., Chen, R. M., Chen, M. L., & Huang, K. Y. (2017). Molecular Identification of Diphyllobothrium latum from a Pediatric Case in Taiwan. The Korean journal of parasitology, 55(4), 425–428. https://doi.org/10.3347/kjp.2017.55.4.425

Life cycle:

  • Infective stage: Plerocercoid larvae (spargana)
  • Definitive hosts: Humans (& other fish eating animals)
  • Intermediate and paratenic hosts: Freshwater and marine fishes (commonly perch, pike, salmon)
Eggs are passed unembryonated in feces (1). Under appropriate conditions, the eggs mature (approximately 18-20 days) (2) and yield oncospheres which develop into a coracidia (3). After ingestion by a suitable crustacean (first intermediate host) the coracidia develop into procercoid larvae (4). 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 (5). 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 (6). 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 (7). 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 (8). 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 5-6 weeks after infection. | (2020) CDC – Diphyllobothriasis. Retrieved November 26, 2020, from https://www.cdc.gov/dpdx/diphyllobothriasis/index.html

Humans infected with D. latum will begin to pass eggs in their stools on average 15 to 45 days after the ingestion of the plerocercoid stage of larvae.


Clinical features

Diphyllobothriasis can be a long-lasting infection, up to 25 years. Most infections are asymptomatic but gastrointestinal symptoms may occur in some patients.

  • Gastrointestinal symptoms: Abdominal pain, vomiting, diarrhea, and dyspepsia
  • Other symptoms: Anemia, fatigue, anorexia, fever, and myalgia

Complications:

  • Aberrant migration of proglottids: Cholecystitis or cholangitis
  • Massive infections: Intestinal obstruction
  • Vitamin B12 deficiency: Pernicious anemia

Case study:


Diagnosis

Diagnosis of the fish tapeworm requires a thorough history with particular attention to the patient’s occupation, hobbies, eating habits, and travel history.

Laboratory workup:

  • Peripheral eosinophilia
  • Megaloblastic anemia
  • Vitamin B12 deficiency (if the worm has attached in the proximal small intestine, it can compete for vitamin B12 absorption)

Stool sample:

  • Eggs/proglottids:
  • Ovoid, yellow-brown, and operculated
  • Display a small knob or ‘abopercular’ on the opposite end of a lid-like opening or ‘operculum’, which may be inconspicuous.
Microscopic image of Diphyllobothrium latum egg, displaying the abopercular (arrow) on the opposite end of the operculum. | Lal, S., & Steinhart, A. H. (2007). Diphyllobothrium latum: a case of an incidental finding. World journal of gastroenterology, 13(12), 1875–1876. https://doi.org/10.3748/wjg.v13.i12.1875

CT scan:

Abdominal computed tomography showed multiple reactive mesenteric lymph nodes (arrows). | Lee, S. H., Park, H., & Yu, S. T. (2015). Diphyllobothrium latum infection in a child with recurrent abdominal pain. Korean journal of pediatrics, 58(11), 451–453. https://doi.org/10.3345/kjp.2015.58.11.451

Colonoscopy:

Colonoscopy can also reveal unexpected findings, including parasitic infection, even in asymptomatic patients.
Colonoscopic images revealing a segmented worm in the ascending colon (A), passing through the ileo-caecal valve into the small intestine (B). | Lal, S., & Steinhart, A. H. (2007). Diphyllobothrium latum: a case of an incidental finding. World journal of gastroenterology, 13(12), 1875–1876. https://doi.org/10.3748/wjg.v13.i12.1875

Management

  • Praziquantel (single dose): Stool culture for ova should be negative a week after treatment; occasionally a second dose might be needed
  • Vitamin B12 supplementation: Return to normal ranges within a period of several months

Leave a Reply