New freeze-resistant trichinella species discovered

Kim Kaplan of USDA’s Agricultural Research Service writes a new freeze-resistant Trichinella species has been discovered in wolverines by Agricultural Research Service scientists and their colleagues. Trichinella are parasites that cause the disease trichinosis (formally referred to as trichinellosis), which people can get by eating raw or undercooked meat from infected animals. 

Before the advent of modern biosafety practices, Americans risked infection from Trichinella spiralis from contaminated pork. Residual risk exists when consuming wild game infected with this, or other species of Trichinella.

Freezing pork for three days generally kills T. spiralis but will not kill freeze-resistant varieties endemic to the Arctic. This study indicates freeze-resistance in this newly discovered species.

This is the first species of Trichinella discovered since 2012, and the 13th species identified since the genus was discovered in 1835.

The new species, now named Trichinella chanchalensis (and nicknamed “oddball”), was found in 14 of 338 wolverine samples tested. About 70 percent of the wolverine samples were infected by some Trichinella species. The samples were all provided by Canadian authorities that oversee trappers and/or game meat food safety in that country.

Wolverines, the largest member of the weasel family, are found mostly in northern Canada, Alaska, Nordic countries in Europe and throughout western Russia and Siberia.

“They make an excellent sentinel species to help us understand the scope of Trichinella in the environment,” said ARS research zoologist Peter Thompson who led the study. “A wolverine can have a home range of about 1,000 miles and will eat just about anything it can kill or scavenge, including caribou, moose, ground squirrels and other rodents as well as carnivores such as foxes and even other wolverines.” Thompson is with the ARS Animal Parasitic Diseases Laboratory in Beltsville, Maryland.

When the researchers first saw the new freeze-resistant Trichinella, they sought to understand if there had been interbreeding between T. nativa and T6, another freeze-resistant variety that is closely related to T. nativa.

By sequencing the newly discovered Trichinella species’ complete genome, it was shown that its DNA is about 10 percent different from any other Trichinella. By comparison, human and chimpanzee DNA only differ by 1 percent.

“Evolutionarily, the evidence shows that Trichinella chanchalensis split off from the other known Trichinella species about 6 million years ago, making it a very old species among Trichinella,” Thompson said. “That brings up the question of how T. nativa and T6 got their freeze resistance. Did the trait evolve more than once or is there some other mechanism at work?”

The ARS Animal Parasitic Diseases Laboratory, which is part of the Beltsville Agricultural Research Center, has a long history of helping provide the scientific basis for regulations that in the past ensured cured and cooked pork products were safe and reliable. Some of the lab’s accomplishments include:

Discovered that Trichinella can be reduced in pork by proper freeze methods, leading to new, effective meat inspection control measures in the first decade of the 20th century.

Established the standards for using salt, moisture, pH and temperature to effectively treat fermented, dry-cured pork sausage for Trichinella.

Assisted in the development of the best management practices for raising pigs to essentially eliminate the chances of domestic pork being infected with Trichinella.

Created the Polymerase Chain Reaction (PCR) test to specifically identify Trichinella species using a small DNA sample.

This research was published in the International Journal for Parasitology (

The Agricultural Research Service is the U.S. Department of Agriculture’s chief scientific in-house research agency. Daily, ARS focuses on solutions to agricultural problems affecting America. Each dollar invested in agricultural research results in $20 of economic impact.

Careful with that boar: 90 sick with trichinosis after eating raw sausage in Italy

ProMed reports 90 persons presented to the Infectious Diseases Hospital Amedeo di Savoia, Torino, North-West Italy between 24 Dec 2019 and 10 Jan 2020 after consuming raw sausages from a wild boar hunted in the area of Susa Valley, 50 km [31.1 mi] away from Torino, in late November 2019.

All of them either were symptomatic (fever, muscle and/or abdominal pain, nausea) or had peripheral blood eosinophilia over 500/cmm, or both. IgG serology for trichinella was performed by immunoblot (Trichinella E/S IgG kit, EFFEGIEMME, Milan, Italy) and resulted positive in 48/90 (53.3%), allowing a diagnosis of confirmed trichinella infection.

Otherwise, a diagnosis of suspected trichinella infection was made with a negative serology, probably due to performing the test too early, before the development of antibodies or possibly a false negative result. In a few cases (under 10 cases) an alternative diagnosis was considered.

All patients were treated with oral albendazole 400 mg twice daily for 10 days and prednisone 50 mg/day.

Most likely, all patients were infected after eating meat from a single animal, given the low prevalence of the infection in this area: no human case has ever been detected in Torino province, and only one wild boar has been found positive for trichinella at microscopy in Susa valley in the last 10 years.