Diphylobotrioza

Epidemiology

Epidemiology The fish tapeworm occurs worldwide (Europe, northern Siberia, North America, western Africa, South-East Asia, Japan, Australia) Humans become infected by eating raw or undercooked fish (e.g. pike, perch, salmon) Besides humans, as an important final host, wild and domestic carnivore animals serve as reservoir hosts

Life cycle of Diphyllobothrium latum

Life cycle of Diphyllobothrium latum

Pathology Pathology – provoked in most cases by a single worm – is light Hosts might be depleted of vitamin B12, resulting in rare cases in a macrocytic anaemia (especially in Scandinavia)

 Scolex of D. latum.

Diphyllobothrium latum morphology A. Scolex

The fish tapeworm of humans has a world-wide distribution The fish tapeworm of humans has a world-wide distribution. Infected persons are usually asymptomatic but may have diarrhea or abdominal pain. Prolonged infection results in vitamin B 12 deficiency. C. Egg. B. Proglottid.

Close-up of a few of the proglottids, showing the rosette-shaped uterus at the center of each proglottid. Section of an adult D. latum containing many proglottids.

Proglottids of Diphyllobothrium latum Proglottids of Diphyllobothrium latum.  These proglottids tend to be passed in strands of variable length in the stool.  The proglottids tend to be broader than long. 

Proglottids of Diphyllobothrium latum Proglottids of Diphyllobothrium latum.  The species characteristics are: the proglottid is broader than it is long; size 2 to 4 mm long by 10 to 12 mm wide; uterus coiled in rosette appearance; genital pore at the center of the proglottid.

Carmine-stained proglottids of D Carmine-stained proglottids of D. latum, showing the rosette-shaped ovaries.

The main body of the worm is virtually filled with male and female reproductive organs allowing it to produce an incredible number of eggs, often more than 1,000,000 a day.

Diphyllobothrium latum in human intestine.

It is the longest tapeworm invading humans with as many as 4,000 segments (proglottids).

The adult is ivory or grayish-yellow in color and can live in humans for 20 years.

Some people are constantly hungry because the tapeworms are eating most of the food. There are times when the worm gets so large that it will cause a colon blockage.

In some people a severe anemia may develop, because of this tapeworm's ability to consume most of its host's vitamin B12.

Diagnostic methods Parasitological diagnosis Patients often observe short segments of the tapeworm (chain of proglottids) in their stools. It is not difficult to confirm diagnosis by detecting the numerous eggs by microscopy.

Treatment 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 (8). 

Prevention and Control Cestode larvae in fish are killed by heat or after freezing The control of transmission is difficult due to many reservoir hosts