Title: Parasitic Helminths | Microbiology
Headings: Parasitic Helminths
Parasitic Helminths
Learning Objectives
Nematoda (Roundworms)
Clinical Focus: Anthony, Part 2
Think about It
Platyhelminths (Flatworms)
Think about It
Food for Worms?
Eradicating the Guinea Worm
Key Concepts and Summary
Multiple Choice
Fill in the Blank
Think about It

Content: credit: modification of work by Centers for Disease Control and Prevention)
Phylum Nematoda (the roundworms) is a diverse group containing more than 15,000 species, of which several are important human parasites (Figure 1). These unsegmented worms have a full digestive system even when parasitic. Some are common intestinal parasites, and their eggs can sometimes be identified in feces or around the anus of infected individuals. Ascaris lumbricoides is the largest nematode intestinal parasite found in humans; females may reach lengths greater than 1 meter. A. lumbricoides is also very widespread, even in developed nations, although it is now a relatively uncommon problem in the United States. It may cause symptoms ranging from relatively mild (such as a cough and mild abdominal pain) to severe (such as intestinal blockage and impaired growth). Of all nematode infections in the United States, pinworm (caused by Enterobius vermicularis) is the most common. Pinworm causes sleeplessness and itching around the anus, where the female worms lay their eggs during the night.