Trichinella spiralis

Trichinella spiralis, sometimes known as the pork worm, is a parasite within the Nematoda class. It can be found in pigs, rats, humans, and bears. This worm causes trichinosis in humans, most often from consuming undercooked pork. This species is the smallest within its class, reaching an average body length of .16 centimeters. Females are twice as large as males, displaying a sexual dimorphism. The reproductive organs of females are unique to the species in that the front end holds developed juveniles, while the back end, where the uterus is found, holds undeveloped eggs. The genome of this species was completed in 2011.

Trichinella spiralis requires one host to mature and survive, because it spends its entire life within the one host. When a human ingests the larvae, which are protected by a cyst like formation, the PH of the stomach allows them to hatch and travel into the intestines. After reaching this area, the larvae dig into the mucosa to grow and breed. Females can live for up to six weeks, laying up to 1,500 larvae. Females are released from the body once they die, but the larvae will travel and grow throughout the circulatory system of their host, causing severe pain and fever. Occasionally, if the larvae enter specific tissues, the host can experience encephalitis or myocarditis that can cause death.

The lifecycle of Trichinella spiralis, although similar to other nematodes, is unique to the species. It lives within one cell in a muscle, modifying it to fit different needs during its life cycle. The nurse cell formations are controlled by the hypoxic environment surrounding the tissue. This environment stimulates the cells in order to regulate and release angiogenic cytokines, such as VEGF, which allows newly hatched T. spinalis larvae to enter the cells and grow.

The symptoms of a Trichinella spiralis infection can first appear between twelve hours and two days after ingestion. These symptoms include immunological reaction and intestinal tissue damage. These can cause vomiting, sweating, nausea, and diarrhea. After five to seven days of infection fever and edema of the face, and after ten days, the host may experience loss of breath, a weakened pulse, lowered blood pressure, severe muscle pain, damage of the heart, and other nervous disorders. These more severe symptoms often lead to death due to heart failure, kidney failure, or respiratory issues. This infection is worse in humans than in pigs, although it can cause death in pigs.

In order to diagnose a Trichinella spiralis infection, experts can perform a muscle biopsy or a number of immunodiagnostic tests. Most hosts are treated with medicines like albendazole or mebendazole, which are commonly used to treat worm infection, but the efficiency of these drugs is not known. Pigs are typically treated with anthelmintics, a drug that also prevents infection.

In the United States, the national trichinellosis surveillance system noted an average number of 393 cases between the years of 1947 and 1951 and an average of twelve cases between 1997 and 2001. These changes are thought to have occurred due to stricter standards in the pork industry. These efforts included the Federal Swine Health Protection Act, which prevented the use of uncooked foods as food for pigs. This legislature also helped create the Trichinae Herd Certification Program, a voluntary program that documents the care and health status of pigs in order to reduce the numbers of trichinellosis infections. Preparation methods have also been changed in order to prevent infection. The USDA used the U.S. Code of Federal Regulations to enhance the processing procedures involved in freezing and cooking pork. Pork that meets the proper standards is known as “certified pork.”

Image Caption: Trichinella spiralis larvae in pressed bear meat, partially digested with pepsin. Credit: DPDx Image Library/Wikipedia