Diphyllobothrium latum - Introduction, Classification, History, Habitat, Morphology

Introduction of Diphyllobothrium latum

Diphyllobothrium latum is the most common species of tapeworm which infects humans. It is called a fish tapeworm, a broad fish tapeworm because fish is a common source of infection in humans. It is the longest parasite found in the intestine of man and causes diphyllobothriasis.

The tapeworm infects both fish and mammals.

Classification of Diphyllobothrium latum

Phenotypically, Diphyllobothrium latum is classified as:

Kingdom: Animalia

Phylum: Platyhelminthes

Class: Cestoda

Order: Diphyllobothriidea

Family: Diphyllobothriidae

Genus: Diphyllobothrium

Species: D. latum

History of Diphyllobothrium latum

Historically, Diphyllobothrium latum was first described in 1592 from clinical specimens in Switzerland. Centuries later in 1917, Janicke and Rosen described the parasite's life cycle.

Habitat of Diphyllobothrium latum

Adult Diphyllobothrium latum habitats the small intestine- mainly the ileum or jejunum of humans.

Morphology of Diphyllobothrium latum

Morphologically, Diphyllobothrium latum can be adult, proglottids, egg, and infective form.

Adult

The adult Diphyllobothrium latum is composed of three fairly distinct morphological segments- the scolex (head), the neck, and the strobila (lower body). It is ivory in shape and measures 10 meters or more lengthwise. The adult tapeworm can live for 5 years to 13 years and produce about 1 million eggs per day.

Scolex

• Diphyllobothrium latum scolex is elongated and spoon-shaped

• presence of two long, weak grooves or bothria, one ventral, and another dorsal

• lacks suckers and hooks

Neck

• Diphyllobothrium latum neck is thin and unsegmented

• longer than the head

Strobilla

• Diphyllobothrium latum strobilla consists of 3000-4000 proglottids (segments)

• mature/gravid proglottids are broader than long, measuring 2mm to 4mm in length and 10mm-12mm in width

Proglottids

Each mature proglottid of Diphyllobothrium latum contain

• a bilobed ovary near the rear end of the segments

• a central rosette-like uterus

• three genital openings- vas deferens, vagina, and uterus

The vas deferens, vagina, and uterus are present close to each other in that order. The gravid proglottids of Diphyllobothrium latum expel the eggs through their uterine pore.

Egg

• Diphyllobothrium latum eggs are light brown in color which are bile stained

• oval shaped with measurements around 70μm to 45μm in size

• inconspicuous operculum or lid is present at one pole of the egg

• a small knob-like projection is present at the other end which may or may not be visible in the unsegmented ovum

• freshly passed eggs are not infective to humans

Infective form

Plerocercoid

• third stage larva of Diphyllobothrium latum is plerocercoid

• also known as sparganum

• white, unsegmented, and tape-like

• measures 10mm in length

• not encysted or encapsulated

• has a partly invaginated scolex

• found freely in the body cavity, muscles, and connective tissues of the fish host