Chain of Infection

Review the attached schematic for the life-cycle and transmission of Guinea Worm.

• What is the infectious agent for Guinea Worm?  Please name it and describe (is it a virus, bacteria etc.). Briefly describe it’s life-cycle.

• Outline the chain of infection by identifying the reservoir(s), portal(s) of exit, mode(s) of transmission, portal(s) of entry, and factors in host susceptibility.

1. Reservoirs:
2. Portals of exit:
3. Modes of transmission:
4. Portals of entry:
5. Factors in host susceptibility:

• Can the infectious agent continue without a human host? Why or Why not?  What else is required for the infectious agent to complete its life-cycle?

• Develop public health strategies to prevent Guinea Worm Disease in the human population. Hint – look at each link in the chain of transmission and see if you can break the chain!  Provide one strategy for a-e above, or explain why there is no strategy for that link in the chain.

Dracunculiasis (guinea worm disease) is caused by the nematode (roundworm) Dracunculus medinensis.

Life Cycle:

Humans become infected by drinking unfiltered water containing copepods (small crustaceans) which are infected with larvae of D. medinensis . Following ingestion, the copepods die and release the larvae, which penetrate the host stomach and intestinal wall and enter the abdominal cavity and retroperitoneal space . After maturation into adults and copulation, the male worms die and the females (length: 70 to 120 cm) migrate in the subcutaneous tissues towards the skin surface . Approximately one year after infection, the female worm induces a blister on the skin, generally on the distal lower extremity, which ruptures. When this lesion comes into contact with water, a contact that the patient seeks to relieve the local discomfort, the female worm emerges and releases larvae . The larvae are ingested by a copepod  and after two weeks (and two molts) have developed into infective larvae . Ingestion of the copepods closes the cycle .