Diphyllobothrium Latum

the largest tapeworm known to infect humans.

"the fish" or "broad tapeworm."

It is also known by the name Diphyllobothrium

Port of Entry : By Mouth

Part of Body Infected : Small Intestine

Site of Parasite in the Host : Small Intestine

Immature eggs are passed in feces of the mammal host (the definitive host, where the worms

reproduce). When a human eats an undercooked fish that is infected, the human becomes

infected by the plerocercoid, which then develops into an adult inside the small intestines. The

tapeworm attaches to the mucous membrane of the small intestine. The adult tapeworm has

proglottids, which are sections of its body. The proglottids release immature eggs, which end up

in the feces and starts the life cycle all over. A tapeworm can grow to be 10 meters long and

produce over 1 million eggs per day.

Disease : Diphyllobothriasis - is an infection caused by a fish tapeworm.

Alternative Names : Fish tapeworm infection

Symptoms The vast majority of infected individuals have no symptoms. Symptoms may

include:

Vague abdominal discomfort

Nausea, vomiting, or diarrhea

Loss of appetite and weight loss

Abdominal pain

Weight loss, fatigue, constipation

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 anemia 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 B-12 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.

Causes

The fish tapeworm, scientifically named Diphyllobothrium latum, represents one of the giant

tapeworm species. Humans become infected when they eat raw or undercooked fish that contain

tape worm larvae (sparganum).

The infection is seen in many areas where humans consume uncooked or undercooked fish from

rivers or lakes. Diphyllobothriasis is seen in Eastern Europe, North and South America, African

countries in which freshwater fish are eaten, and in some Asian countries.

After a person has eaten infected fish, the larva begin to grow in the intestine. The adult worm,

which is segmented, may attain a length of 30 feet. Eggs are formed in each segment (proglottid)

of the worm and are passed in the stool. Occasionally, a string of proglottids may be passed in

the stool.

Fish tapeworm infection may lead to Vitamin B12 deficiency and the subsequent development of

megaloblastic anemia.

Exams and Tests

Infected individuals sometimes pass visible segments of worm in their stools.

Tests may include:

Complete blood count

Stool smear

Treatment

Praziquantel - 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.

Niclosamide - An alternative treatment is Niclosamide, 2 g PO once for adults or 50 mg/kg PO

once.

Gastrografin - 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.

Medicines to fight the parasites are given in a single dose to treat the tapeworm infection.

Vitamin B12 injections or supplements may be needed to treat megaloblastic anemia.

Possible Complications

Megaloblastic anemia

Intestinal blockage

Clinical Manifestations

Infection with Diphyllobothrium latum is usually asymptomatic, although occasional

diarrhea, abdominal pain, fatigue, vomiting, dizziness, or numbness of fingers and toes

may be present. Eosinophilia develops during the early stages of worm growth.

1. Immature eggs are passed in feces . 

2. Under appropriate conditions, the eggs mature (approximately 18 to 20 days)

and yield oncospheres which develop into a coracidia

3. After ingestion by a suitable freshwater crustacean (the copepod first

ntermediate host) the coracidia develop into procercoid larvae

4. Following ingestion of the copepod by a suitable second intermediate host,

typically minnows and other small freshwater fish, the procercoid larvae are

released from the crustacean and migrate into the fish flesh where they

develop into a plerocercoid larvae (sparganum).

 

5. The plerocercoid larvae are the infective stage for 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, e.g.,

trout, perch, walleyed pike. 

6. In this case, the sparganum can migrate to the musculature of the larger

predator fish and humans can acquire the disease by eating these later

intermediate infected host fish raw or undercooked .

7.  After ingestion of the infected fish, the plerocercoid develop into immature

adults and then into mature adult tapeworms which will reside in the small

intestine.  The adults of D. latum attach to the intestinal mucosa by means of the

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)

9. and are passed in the feces.  Eggs appear in the feces 5 to 6 weeks after

infection.  In addition to humans, many other mammals can also serve as

definitive hosts for D. latum.

How Can I Prevent Getting Broad Tapeworm?

Do not eat raw or undercooked fish from infected lakes. Freeze fish at -10°C for 24 hours. Cook fish to 54 to 56°C for 5 minutes or until cooked throughout. Clean fish immediately after catching; do not feed fresh fish or viscera to your dog or

other pets. Marinating or lightly pickling fish will not kill all the plerocercoid.