Cercaria

Definition

Cercaria is a larval stage in the life cycle of certain parasitic flatworms, particularly those that cause diseases such as schistosomiasis. This free-swimming, tailed larva is the infective stage that emerges from the snail intermediate host and seeks to penetrate the skin of the definitive human host.

5 Must Know Facts For Your Next Test

1. The cercaria larva is equipped with a forked tail that propels it through water to facilitate finding and penetrating the human host's skin.
2. After penetrating the skin, the cercaria larva sheds its tail and transforms into a juvenile worm that migrates to the blood vessels.
3. Schistosomiasis, caused by Schistosoma parasites, is one of the most widespread parasitic diseases, infecting over 200 million people worldwide.
4. Exposure to contaminated freshwater where snail intermediate hosts live is the primary risk factor for contracting schistosomiasis and encountering the cercaria larva.
5. Control of schistosomiasis involves breaking the life cycle by targeting the snail intermediate hosts and providing access to clean water and sanitation to reduce human exposure to cercaria.

Review Questions

• Describe the role of the cercaria larva in the life cycle of parasitic flatworms that cause schistosomiasis.
  • The cercaria is the free-swimming, tailed larval stage of parasitic flatworms that emerges from the snail intermediate host. This larva is the infective stage that actively seeks to penetrate the human skin, the definitive host. After successful skin penetration, the cercaria sheds its tail and transforms into a juvenile worm that migrates to the blood vessels, where it matures into the adult stage and reproduces, completing the life cycle of the parasite.
• Explain how the characteristics of the cercaria larva contribute to its ability to infect human hosts.
  • The cercaria larva is well-adapted to locate and infect human hosts. Its forked tail allows it to propel itself through water, increasing its chances of encountering and penetrating human skin. Additionally, the cercaria is equipped with specialized structures and enzymes that facilitate skin penetration, enabling it to shed its tail and transform into the juvenile worm stage that can migrate to the blood vessels. These adaptations are crucial for the cercaria to successfully transition from the snail intermediate host to the human definitive host, where the parasitic flatworm can complete its life cycle and reproduce.
• Evaluate the importance of controlling the snail intermediate host in the prevention and management of schistosomiasis, a disease caused by parasitic flatworms with the cercaria as the infective stage.
  • Controlling the snail intermediate host is a crucial strategy in the prevention and management of schistosomiasis, as it targets a critical step in the life cycle of the parasitic flatworms. Since the cercaria larva emerges from the snail, reducing the snail population or eliminating their habitats can effectively break the transmission cycle and limit the availability of the infective stage. This approach, combined with providing access to clean water and sanitation to reduce human exposure to the cercaria, is an important part of comprehensive schistosomiasis control programs. By addressing the snail intermediate host, the production and spread of the cercaria larva can be significantly reduced, ultimately preventing the infection of human hosts and the continued transmission of this parasitic disease.

Related terms

Schistosomiasis:

A parasitic disease caused by blood flukes of the genus Schistosoma, which has the cercaria as the infective stage that can penetrate human skin.

Snail Intermediate Host: Certain species of freshwater snails that serve as the intermediate host for the parasitic flatworms, harboring the larval stages including the cercaria.

Definitive Host:

The primary host, in this case humans, where the adult worm stage of the parasitic flatworm lives and reproduces, after the cercaria larva has successfully penetrated the skin.