Morphology, Life cycle and Lab diagnosis of Taenia solium (Pork Tapeworm)

Morphology of Taenia solium (Pork tapeworm or Armed tapeworm of man)

There are two types of tapeworms. These are Taenia solium (Pork Tapeworm) and Taenia saginata (Beef Tapeworm). Here we will discuss only Taenia solium. Taenia saginata will be discussed in another slide. Tapeworms are parasitic worms to infect humans and cause the disease taeniasis. It is a flatworm or platyhelminth belonging to class Cestoda. It exists as an adult worm and eggs.

Morphology of adult Taenia solium (Adult pork tapeworm)

• General characteristics: It is a flatworm or platyhelminth. It has a ribbon-like body. Its length may be up to several meters. Its body consists of multiple segments. Each segment is called proglottis. Its body is divided into the follwoing three segments

• 1. Scolex: Scolex is an anterior end of Pork Tapeworm. It is a knob-like structure considered as the head of Taenia solium. The scolex has typically four suckers called acetabula. Acetabula attach the Taenia solium to the wall of the host intestine. Tapeworm has two circular rows of hooks called rostellum. Hooks in anterior rows are larger than hooks in posterior rows. The acetabula and Rostellum are specialized organs of Taenia solium to attach to the intestine wall of the host.

• 2. Neck: It is an unsegmented narrow part of the Tapeworm in between scolex, and proglottids. It produces proglottids.

• 3. Strobila: It is the main body of the Pork Tapeworm consisting of 800 to 900 segments. Each segment is called Proglottid. Each segment (proglottid) is formed from the neck of the Tapeworm. There are three types of proglottids in the strobila of Pork Tapeworm. These are immature proglotids, mature proglotids and gravid proglotids.

  • Immature proglottids: Proglottids near the neck are smaller and immature. Its male and female reproductive parts cannot be differentiated.

  • Mature proglottids: Proglottids away from the neck are larger than immature proglottids. Both male and female reproductive organs are present in each proglottids. These reproductive organs in proglottids can be easily differentiated.

  • Gravid proglottids: Mature proglottids towards the posterior end of adult tapeworm are gravid proglottids. These proglottids have eggs. They release eggs into the environment with the stool of the human host.

Morphology of Taenia solium egg ( Pork Tapeworm eggs)

Eggs are spherical in shape and golden brown in color. The golden brown color of eggs is due to THE staining of eggs with human bile. Eggs are covered with transparent film and found in clumps. Eggs have embryos thus also called Onchosphere. The life span of the oncosphere is 8 weeks. It does not float on a saturated saline solution. They can infect cattle but not human

The life cycle of Taenia solium ( Pork Tapeworm)

The life cycle of Tapeworm is complex and involves multiple hosts. Human and carnivorous animals are the definitive hosts (primary hosts) of the Taenia solium. Pigs and herbivorous animals are the Intermediate hosts (Secondary hosts) of the Taenia solium.

• 1. Egg: The life cycle of  Pork Tapeworm begins with the egg. These eggs are excreted from the host body with stool.

• 2. Intermediate host: Herbivorous animals such as pigs are the intermediate hosts of the Taenia solium. Tapeworm eggs enter their body with the contaminated water and vegetation.

• 3. Larva development:  Pork Tapeworm eggs release larvae inside the intermediate host's body. These larvae are called Oncospheres. Oncospheres penetrate the intestinal wall of the intermediate host and migrate to various tissues of the heart, lungs, and muscular tissues. Inside tissue, they form fluid-filled cysts called cysticerci.

• 4. Definitive host infection: Infected intermediate hosts are eaten by the definitive host. Carnivorous animals and humans are the definitive hosts of the Tapeworm. Definitive hosts get an infection after consuming raw or undercooked meat (intermediate host) containing cycticerci. Cysticerci can survive up to six months.

• 5. Adult Tapeworm: Cysticerci develop into adult Pork Tapeworms inside the intestine of the definitive hosts. It takes 2 to 3 months. They attach to the intestine wall by using a scolex (Head). They grow and develop segmented bodies. Each segment is called proglottids. Tapeworm is hermaphrodite. Both sexes are in the same body. Each proglottid has both sex organs. Proglottids continuously produce eggs.

• 6. Eggs release: Mature proglottids (Gravid proglottids) containing eggs are at the end of the  Pork Tapeworm body. Pork

Lab diagnosis of Taenia solium ( Pork Tapeworm)

The laboratory diagnosis of Pork Tapeworm is carried out by detection and identification of Taenia solium eggs and proglottids in morning stool samples. Administration of anthelmintic drugs at bedtime and collection of stool samples in the morning is the most suitable technique to detect and identify parasites. Laboratory diagnosis should be interpreted in conjunction with clinical symptoms of infection. The following are the most commonly used techniques to detect and identify eggs and proglottids of Tapeworm.

• 1. Microscopic examination: Eggs and proglottids of the Pork Tapeworm are not visible to the naked eye. They are detected by microscopic examination of stool samples. Stool samples without dilution or without concentration or concentrated stool samples or peri-anal swabs are used to detect PorkTapeworm eggs and proglottids.

  • Stool examination (Egg detection): It is the most common and reliable method to detect and identify worms

  • Direct wet method: A small amount of fresh stool sample is mixed with saline solution and examined under the microscope for the presence of eggs and proglottids in the sample.

  • Concentration techniques such as sedimentation method, floating method, or formalin ether sedimentation techniques are used to concentrate the sample. Concentration techniques increase the chance of detection of eggs and proglottids in the sample.

• 2. Serological tests: Enzyme-linked immunosorbent assay (ELISAs) is commonly used as serological tests to detect and diagnose Tapeworm. It is not used in routine clinical practice.

• 3. Imaging technique: Imaging techniques such as computed tomography (CT) or magnetic resonance imaging (MRI) are used to detect cysticerci in tissues of muscles, brain, and eyes. It is used in serious cases such as neurocysticercosis.

Dr Pramila Singh