Diphyllobothrium

style="background:#Template:Taxobox colour;"|Diphyllobothrium
Proglottids of D. latum
style="background:#Template:Taxobox colour;" | Scientific classification
Kingdom: Animalia Phylum: Platyhelminthes Class: Cestoda Subclass: Eucestoda Order: Pseudophyllidea Family: Diphyllobothriidae Genus: Diphyllobothrium
Species
D. latum D. pacificum D. cordatum D. ursi D. dendriticum D. lanceolatum D. dalliae D. yonagoensis

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

For details about infections caused by Diphyllobothrium, click here.

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Overview

Diphyllobothrium is a genus of tapeworm which can cause Diphyllobothriasis in humans through consumption of raw or undercooked fish. The principal species causing diphyllobothriosis is Diphyllobothrium latum, known as the broad or fish tapeworm, or broad fish tapeworm. D. latum is a pseudophyllid cestode that infects fish and mammals. D. latum is native to Scandinavia, western Russia, and the Baltics, though it is now also present in North America, especially the Pacific Northwest. Other members of the genus Diphyllobothrium include Diphyllobothrium dendriticum (the salmon tapeworm), which has a much larger range (the whole northern hemisphere), D. pacificum, D. cordatum, D. ursi, D. lanceolatum, D. dalliae, and D. yonagoensis, all of which infect humans only infrequently. In Japan, the most common species in human infection is D. nihonkaiense, which was only identified as a separate species from D. latum in 1989.

History

The fish tapeworm has a long documented history of infecting people who regularly consume fish and especially those whose customs include the consumption of raw or undercooked fish. In the 1970’s, most of the known cases of diphyllobothriasis came from Europe (5 million cases), and Asia (4 million cases) with fewer cases coming from North America and South America, and no reliable data on cases from Africa or Australia . Interestingly, despite the relatively small number of cases seen today in South America, some of the earliest archeological evidence of diphyllobothriasis comes from sites in South America. Evidence of Diphyllobothrium spp. has been found in 4,000-10,000 year old human remains on the western coast of South America . There is no clear point in time when Diphyllobothrium latum and related species were “discovered” in humans, but it is clear that diphyllobothriasis has been endemic in human populations for a very long time. Due to the changing dietary habits in many parts of the world, autochthonous, or locally-acquired, cases of diphyllobothriasis have recently been documented in previously non-endemic areas, such as Brazil . In this way, diphyllobothriasis represents an emerging infectious disease in certain parts of the world where cultural practices involving eating raw or undercooked fish are being introduced

Morphology

The adult worm is comprised of three fairly distinct morphological segments; the scolex, the neck and the lower body. The scolex is the head portion of the worm, and is equipped with a slit-like groove (the bothrium) for attachment to the intestine. The scolex attaches to the neck, or proliferative region. From the neck, grows many proglottid segments which contain the reproductive organs of the worm. D. latum is the longest tapeworm in humans, averaging ten meters long. Adults can shed up to a million eggs a day. In adults, proglottids are wider than they are long (hence the name broad tapeworm). As in all pseudophyllid cestodes, the genital pores open mid-ventrally.

Various other species of Diphyllobothrium include:

• Diphyllobothrium nihonkaiense
• Diphyllobothrium dendriticum
• Diphyllobothrium cameroni
• Diphyllobothrium cordatum
• Diphyllobothrium hians
• Diphyllobothrium lanceolatum
• Diphyllobothrium orcini
• Diphyllobothrium pacificum
• Diphyllobothrium stemmacephalum
• Diphyllobothrium scoticum

Life cycle

Life cycle of D. latum. Click the image to see full-size. - Source: https://www.cdc.gov/

Adult tapeworms may infect humans, canids, felines, bears, pinnipeds, and mustelids, though the accuracy of the records for some of the nonhuman species is disputed. Immature eggs are passed in feces of the mammal host (the definitive host, where the worms reproduce). After ingestion by a suitable freshwater crustacean such as a copepod (the first intermediate host) the coracidia develop into procercoid larvae. Following ingestion of the copepod by a suitable second intermediate host, typically a minnow or other small freshwater fish, the procercoid larvae are released from the crustacean and migrate into the fish's flesh where they develop into a plerocercoid larvae (sparganum). The plerocercoid larvae are the infective stage for the definitive host (including humans).

Because humans do not generally eat undercooked minnows and similar small freshwater fish, these do not represent an important source of infection. Nevertheless, these small second intermediate hosts can be eaten by larger predator species, for example, trout, perch, and walleyed pike. In this case, the sparganum can migrate to the musculature of the larger predator fish and mammals can acquire the disease by eating these later intermediate infected host fish raw or undercooked. After ingestion of the infected fish, the plerocercoids develop into immature adults and then into mature adult tapeworms which will reside in the small intestine. The adults attach to the intestinal mucosa by means of the two bilateral grooves (bothria) of their scolex. The adults can reach more than 10 m (up to 30 ft) in length in some species such as D. latum, with more than 3,000 proglottids. One or several of the tape-like proglottid segments (hence the name tape-worm) regularly detach from the main body of the worm and release immature eggs in fresh water to start the cycle over again. Immature eggs are discharged from the proglottids (up to 1,000,000 eggs per day per worm) and are passed in the feces. The incubation period in humans, after which eggs begin to appear in the feces is typically 4-6 weeks, but can vary from as short as 2 weeks to as long as 2 years. The tapeworm can live up to 20 years.

Clinical Symptoms

Symptoms of diphyllobothriasis are generally mild, and can include diarrhea, abdominal pain, vomiting, weight loss, fatigue, constipation and discomfort. Approximately four out of five cases are asymptomatic and may go many years without being detected. In a small number of cases, this leads to severe vitamin B12 deficiency due to the parasite absorbing 80% or more of the host’s B12 intake, and a megaloblastic anemia indistinguishable from pernicious anemia. The anemica can also lead to subtle demyelinative neurological symptoms (subacute combined degeneration of spinal cord). Infection for many years is ordinarily required to deplete the human body of vitamin B12 to the point that neurological symptoms appear.

Diagnosis

Diagnosis is usually made by identifying proglottid segments, or characteristic eggs in the feces. These simple diagnostic techniques are able to identify the nature of the infection to the genus level, which is usually sufficient in a clinical setting . However, when the species needs to be determined (in epidemiological studies, for example), restriction fragment length polymorphisms can be effectively used. PCR can be performed on samples of purified eggs, or native fecal samples following sonication of the eggs to release their contents .

Differential diagnosis

Diphyllobothrium infection must be differentiated from other causes of viral, bacterial, and parasitic gastroentritis.

Organism			Age predilection	Travel History	Incubation Size (cell)	Incubation Time	History and Symptoms			Diarrhea type8				Food source	Specific consideration
							Fever	N/V	Cramping Abd Pain	Small Bowel	Large Bowel	Inflammatory	Non-inflammatory
Viral	Rotavirus		<2 y	-	<102	<48 h	+	+	-	+			+	-	Mostly in day cares, most common in winter.
	Norovirus		Any age	-	10 -103	24-48 h	+	+	+	+			+	-	Most common cause of gastroenteritis, abdominal tenderness,
	Adenovirus		<2 y	-	105 -106	8-10 d	+	+	+	+			+	-	No seasonality
	Astrovirus		<5 y	-		72-96 h	+	+	+	+			+	Seafood	Mostly during winter
Bacterial	Escherichia coli	ETEC	Any age	+	108 -1010	24 h	-	+	+	+			+	-	Causes travelers diarrhea, contains heat-labile toxins (LT) and heat-stable toxins (ST)
		EPEC	<1 y	-	10†	6-12 h	-	+	+	+			+	Raw beef and chicken	-
		EIEC	Any ages	-	10†	24 h	+	+	+		+		+	Hamburger meat and unpasteurized milk	Similar to shigellosis, can cause bloody diarrhea
		EHEC	Any ages	-	10	3-4 d	-	+	+		+	+		Undercooked or raw hamburger (ground beef)	Known as E. coli O157:H7, can cause HUS/TTP.
		EAEC	Any ages	+	1010	8-18 h	-	-	+		+		+	-	May cause prolonged or persistent diarrhea in children
	Salmonella sp.		Any ages	+	1	6 to 72 h	+	+	+		+	+		Meats, poultry, eggs, milk and dairy products, fish, shrimp, spices, yeast, coconut, sauces, freshly prepared salad.	Can cause salmonellosis or typhoid fever.
	Shigella sp.		Any ages	-	10 - 200	8-48 h	+	+	+		+	+		Raw foods, for example, lettuce, salads (potato, tuna, shrimp, macaroni, and chicken)	Some strains produce enterotoxin and Shiga toxin similar to those produced by E. coli O157:H7
	Campylobacter sp.		<5 y, 15-29 y	-	104	2-5 d	+	+	+		+	+		Undercooked poultry products, unpasteurized milk and cheeses made from unpasteurized milk, vegetables, seafood and contaminated water.	May cause bacteremia, Guillain-Barré syndrome (GBS), hemolytic uremic syndrome (HUS) and recurrent colitis
	Yersinia enterocolitica		<10 y	-	104 -106	1-11 d	+	+	+		+	+		Meats (pork, beef, lamb, etc.), oysters, fish, crabs, and raw milk.	May cause reactive arthritis; glomerulonephritis; endocarditis; erythema nodosum. can mimic appendicitis and mesenteric lymphadenitis.
	Clostridium perfringens		Any ages		> 106	16 h	-	-	+		+		+	Meats (especially beef and poultry), meat-containing products (e.g., gravies and stews), and Mexican foods.	Can survive high heat,
	Vibrio cholerae		Any ages	-	106-1010	24-48 h	-	+	+	+			+	Seafoods, including molluscan shellfish (oysters, mussels, and clams), crab, lobster, shrimp, squid, and finfish.	Hypotension, tachycardia, decreased skin turgor. Rice-water stools
Parasites	Protozoa	Giardia lamblia	2-5 y	+	1 cyst	1-2 we	-	-	+	+			+	Contaminated water	May cause malabsorption syndrome and severe weight loss
		Entamoeba histolytica	4-11 y	+	<10 cysts	2-4 we	-	+	+		+	+		Contaminated water and raw foods	May cause intestinal amebiasis and amebic liver abscess
		Cryptosporidium parvum	Any ages	-	10-100 oocysts	7-10 d	+	+	+	+			+	Juices and milk	May cause copious diarrhea and dehydration in patients with AIDS especially with 180 > CD4
		Cyclospora cayetanensis	Any ages	+	10-100 oocysts	7-10 d	-	+	+	+			+	Fresh produce, such as raspberries, basil, and several varieties of lettuce.	More common in rainy areas
	Helminths	Trichinella spp	Any ages	-	Two viable larvae (male and female)	1-4 we	-	+	+		+		+	Undercooked meats	More common in hunters or people who eat traditionally uncooked meats
		Taenia spp	Any ages	-	1 larva or egg	2-4 m	-	+	+	+			+	Undercooked beef and pork	Neurocysticercosis: Cysts located in the brain may be asymptomatic or seizures, increased intracranial pressure, headache.
		Diphyllobothrium latum	Any ages	-	1 larva	15 d	-	-	-	+			+	Raw or undercooked fish.	May cause vitamin B12 deficiency

8Small bowel diarrhea: watery, voluminous with less than 5 WBC/high power field

Large bowel diarrhea: Mucousy and/or bloody with less volume and more than 10 WBC/high power field
† It could be as high as 1000 based on patient's immunity system.

The table below summarizes the findings that differentiate inflammatory causes of chronic diarrhea

Cause	History	Laboratory findings	Diagnosis	Treatment
Diverticulitis	Bloody diarrhea Left lower quadrant abdominal pain Abdominal tenderness on physical examination Low grade fever	Leukocytosis Elevated serum amylase and lipase Sterile pyuria on urinalysis	Abdominal CT scan with oral and intravenous (IV) contrast	bowel rest, IV fluid resuscitation, and broad-spectrum antimicrobial therapy which covers anaerobic bacteria and gram-negative rods
Ulcerative colitis	Diarrhea mixed with blood and mucus, of gradual onset. Signs of weight loss Rectal urgency Tenesmus Blood is often noticed on underwear Different degrees of abdominal pain	Anemia Thrombocytosis A high platelet count Elevated ESR (>30mm/hr) Low albumin	Endoscopy	Induction of remission with mesalamine and corticosteroids followed by the administration of sulfasalazine and 6-Mercaptopurine depending on the severity of the disease.
Entamoeba histolytica	Abdominal cramps Diarrhea Passage of 3 - 8 semiformed stools per day Passage of soft stools with mucus and occasional blood Fatigue Intestinal gas (excessive flatus) Rectal pain while having a bowel movement (tenesmus) Unintentional weight loss	cysts shed with the stool	detects ameba DNA in feces	Amebic dysentery Metronidazole 500-750mg three times a day for 5-10 days Tinidazole 2g once a day for 3 days is an alternative to metronidazole Luminal amebicides for E. histolytica in the colon: Paromomycin 500mg three times a day for 10 days Diloxanide furoate 500mg three times a day for 10 days Iodoquinol 650mg three times a day for 20 days For amebic liver abscess: Metronidazole 400mg three times a day for 10 days Tinidazole 2g once a day for 6 days is an alternative to metronidazole Diloxanide furoate 500mg three times a day for 10 days must always be given afterwards.

Treatment

Upon diagnosis, treatment is quite simple and effective. The standard treatment for diphyllobothriasis, as well as many other tapeworm infections is a single dose of Praziquantel, 5-10 mg/kg PO once for both adults and children. An alternative treatment is Niclosamide, 2 g PO once for adults or 50 mg/kg PO once . Another interesting potential diagnostic tool and treatment is the contrast medium, Gastrografin, introduced into the duodenum, which allows both visualization of the parasite, and has also been shown to cause detachment and passing of the whole worm .

Side Effects of Treatment

Praziquantel has few side effects, many of which are similar to the symptoms of diphyllobothriasis. They include malaise, headache, dizziness, abdominal discomfort, nausea, rise in temperature and occasionally allergic skin reactions . The side effects of Niclosamide are very rare, due to the fact that it is not absorbed in the gastrointestinal tract .

Epidemiology

People at high risk for infection have traditionally been those who regularly consume raw fish, including fishermen who eat the raw liver or roe of their catches and women preparing and tasting foods that contain raw fish . Many regional cuisines include raw or undercooked food, including sushi and sashimi in Japanese cuisine, carpaccio di persico in Italian, tartare maison in French-speaking populations, gefilte fish in Jewish populations, ceviche in Latin American cuisine. With emigration and globalization, the practice of eating raw fish in these and other dishes has brought diphyllobothriasis to new parts of the world and created new endemic foci of disease.

Public Health Strategies

The most viable interventions include: prevention of water contamination both by raising public awareness of the dangers of defecating in recreational bodies of water and by implementation of basic sanitation measures; screening and successful treatment of people infected with the parasite; and prevention of infection of humans via consumption of raw, infected fish . The last of these can most easily be changed via education about proper preparation of fish. Fish that is thoroughly cooked, brined, or frozen at -10˚C for 24-48 hours can be consumed without risk of D. latum infection.

See also

• List of parasites (human)

http://www.stanford.edu/class/humbio103/parasites.htm

References

• "DPDx - Diphyllobothriasis". CDC Division of Parasitic Diseases.
• "UDiphyllobothrium spp". S FDA/CFSAN - Bad Bug Book.
• Janovy, John; Roberts, Larry S. (2005). Foundations of Parasitology (7th ed.). McGraw-Hill Education (ISE Editions). ISBN 0-07-111271-5.CS1 maint: Multiple names: authors list (link)