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Parasites and Diseases

A Field Guide

SARCOCYSTOSIS (“ricebreast” of ducks)

caption follows
Sarcocysts in breast muscle of duck.

What causes sarcocystosis?
  • Sarcocystosis is caused by the cyst stage of a single-celled parasite.
  • Lifecycle: The parasite needs a waterfowl host and a carnivore host. The parasite multiplies in the waterfowl forming cysts in the muscles. The carnivore becomes infected when it eats meat from a duck with cysts. The parasite reproduces in the carnivore’s intestine without harming the carnivore. It comes out in the carnivore’s droppings and contaminates vegetation, which is eaten by ducks.

Where does sarcocystosis occur?
  • Sarcocystosis occurs in many species of ducks throughout Alaska.

What are the signs of sarcocystosis?
  • Waterfowl and carnivore hosts usually appear healthy.
  • When butchering infected ducks, cysts may be observed in the breast muscle.
  • Cysts may look like grains of rice (whitish streaks) running in the direction of the muscle fibers.

How can I protect myself?
  • Humans cannot be infected by the cysts of Sarcocystis spp. in meat.

Can I eat the meat? [can infect dogs]  [cook well]
  • Meat from an infected duck is suitable for human consumption.
  • Cooking will kill the parasite.
  • Do not feed infected meat to dogs.

Samples to collect
  • Breast muscle of ducks.
  • To report an occurrence or to submit a sample for identification/analysis, contact the DWC Wildlife Disease Surveillance reporting hotline 907-328-8354, send an email to or visit your local ADF&G office.