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Description:This is a photomicrograph depicting a Trichinella spiralis cyst seen embedded in a muscle tissue specimen, in a case of trichinellosis.

Trichinellosis is acquired by ingesting meat containing cysts (encysted larvae) of Trichinella sp. roundworm (nematode) parasites.
After exposure to gastric acid and pepsin, the larvae are released from the cysts and invade the small bowel mucosa where they develop into adult worms (female 2.2 mm in length, males 1.2 mm; life span in the small bowel: 4 weeks). After 1 week, the females release larvae that migrate to the striated muscles where they encyst. Encystment is completed in 4 to 5 weeks, and the encysted larvae may remain viable for several years. Ingestion of the encysted larvae perpetuates the cycle.

Rats and rodents are primarily responsible for maintaining the endemicity of this infection. Carnivorous/omnivorous animals, such as pigs or bears, feed on infected rodents or meat from other animals. Different animal hosts are implicated in the life cycle of the different species of Trichinella. Humans are accidentally infected when eating improperly processed meat of these carnivorous animals (or eating food contaminated with such meat).

High Resolution: Click here for hi-resolution image (2.88 MB)
Content Providers(s):CDC/ Dr. I. Kagan
Creation Date:1961
Photo Credit:
Links:CDC – Division of Parasitic Diseases, DPDx; Trichinellosis Fact Sheet
CDC – Division of Parasitic Diseases, DPDx; Trichinellosis
CDC Organization
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Copyright Restrictions:None - This image is in the public domain and thus free of any copyright restrictions. As a matter of courtesy we request that the content provider be credited and notified in any public or private usage of this image.