Tapeworms are parasitic flatworms that live in the intestines of vertebrate animals. There are several different types of tapeworms that can infect humans, with the most common being pork tapeworms, beef tapeworms, dwarf tapeworms, and fish tapeworms. Tapeworms can vary greatly in size and appearance depending on the species.
What do tapeworms look like generally?
In general, tapeworms have long, flat, segmented bodies. Their bodies consist of a head (scolex), a neck, and then a series of segments called proglottids. The scolex attaches to the intestinal wall using suckers or hooks. New proglottids are continuously formed behind the scolex as the tapeworm grows. Mature proglottids containing eggs break off from the back end of the tapeworm and are passed in feces.
Tapeworms lack a digestive system and absorb nutrients through their skin. Their bodies are covered with a tough outer coating that protects them and allows them to survive in the intestines. This coating makes their bodies appear white or yellowish.
The size of tapeworms can range tremendously depending on the species. Most species that infect humans are quite long, ranging from a few inches to over 15 feet in length. However, their bodies are only about 1-4mm thick. The dwarf tapeworm is an exception and only grows to about an inch long.
What does the scolex (head) look like?
The scolex or head of a tapeworm is only about 1mm wide but is specialized for attaching to the intestinal wall. It may have suckers, grooves, or hooks that allow it to firmly latch onto the lining of the intestines. The suckers look like small round cups, while the grooves or hooks may have sharp points or protrusions.
The scolex of different tapeworm species can vary somewhat in appearance:
- Pork tapeworms have a scolex with four suckers and a rostellum (cone-shaped prominence) covered in hooks.
- Beef tapeworms have a scolex with four suckers and no rostellum or hooks.
- Fish tapeworms have a scolex that is oval with two grooves or pits.
- Dwarf tapeworms have a very small scolex with just a simple oval shape.
What do the proglottids and segments look like?
Behind the scolex is the neck region, followed by the proglottids which make up the majority of the tapeworm’s body length. Proglottids are basically the segments that make up the tapeworm. New proglottids are continuously formed by the tapeworm as it grows.
Young proglottids close to the neck are smaller and cube-shaped. As proglottids mature further down the body, they become larger and elongated in shape. Mature proglottids may eventually take on a square-like shape.
Proglottids contain the reproductive organs of the tapeworm. Immature proglottids have no reproductive organs. Mature proglottids contain complete male and female reproductive systems that produce eggs. Fully mature proglottids filled with eggs detach from the end of the tapeworm once they are ready.
The number and size of proglottids can vary between tapeworm species:
- Pork tapeworms have about 1000–2000 proglottids.
- Beef tapeworms have about 1000 proglottids.
- Fish tapeworms have about 3000–4000 proglottids.
- Dwarf tapeworms have only about 100-200 proglottids due to their small size.
What does a mature proglottid look like?
When a proglottid is mature and filled with eggs, it may take on an elongated, rectangular shape up to 1 cm long. The proglottids turn white or yellowish in color and may even appear grainy as they fill with eggs. The eggs are contained in circular packets throughout the proglottid.
As a proglottid fills with more and more eggs, it starts to detach from the end of the tapeworm body. Filled proglottids may start to take on a square-like shape before they fully break off and exit the body in feces.
What do tapeworm eggs look like?
Tapeworm eggs are very small, ranging from about 20-40 microns in size depending on the species. They have an oval shape and a yellow-brown color. The eggs have a protective outer shell with a tiny embryo inside that develops into a larva.
Tapeworm eggs are packaged into groups within the proglottids before being released. In some species like fish tapeworms, the eggs may be contained singly in capsules.
Here is a table comparing the typical size of eggs from different tapeworm species that infect humans:
| Tapeworm Species | Egg Size |
|---|---|
| Pork tapeworm | 30-43 microns |
| Beef tapeworm | 32-36 microns |
| Fish tapeworm | 20-30 microns |
| Dwarf tapeworm | 28-33 microns |
Can you see tapeworms with the naked eye?
Most species of tapeworms that infect humans can reach several feet in length, so long tapeworms are sometimes visible to the naked eye when they exit the body. Segments containing eggs may also be seen in feces.
However, tapeworms inhabiting the intestines cannot be seen without medical imaging tests or examination of surgical specimens. Their thin bodies are difficult to detect during routine medical procedures.
Sometimes proglottids can be observed moving or crawling around the anal area, appearing like pieces of white string or grains of rice. This may prompt someone to seek medical evaluation.
How are tapeworms visually diagnosed?
If tapeworm infection is suspected, the stool may be examined under a microscope to look for eggs. However, eggs may not appear continuously in feces so examination of multiple samples may be needed.
Imaging studies like CT scans, MRIs, and ultrasounds may reveal long tapeworms in the intestines if they are large enough. Endoscopy procedures can also sometimes identify tapeworms attached to the intestinal walls.
Rarely, tapeworms are spotted incidentally during abdominal surgeries and operations. More invasive procedures can provide a definitive diagnosis by obtaining a sample of the worm for identification.
Conclusion
Tapeworms can vary greatly in size and appearance depending on the specific species. All tapeworms have a small head or scolex that attaches to the intestines, followed by a series of proglottid segments that make up the length of the body. Mature proglottids filled with thousands of tiny eggs eventually detach from the tapeworm and exit the body. While tapeworm infections may go unnoticed, some species can grow quite large and their egg-filled proglottids may sometimes be visible to the naked eye.
