Trichinella spiralis

Trichinella LifeCycle

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If you read Feral Pigs: From Piglets to Problems, you might recall that Trichinella spiralis was one of the parasites mentioned. I was fortunate enough to have an Introductory Parasitology class at Virginia Tech (full of really interesting and disgusting things that induce paranoia) where this and Toxoplasma gondii were discussed, so most of this post will be thanks to notes from Dr. Zajac’s incredible class. Many of the terms included can be found defined here.

– Scientific Classification –

The definitive and intermediate host of Trichinella are in the same animal (in this diagram, a rodent). The parasite is looking for striated muscle, and therefore as a histiotrophic parasite, spends part of its life cycle within a cell or tissue where it waits for the muscle to be eaten. ANY warm-blooded animal can serve as a host.

Trichinella spiralis

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Pigs can get infected by eating garbage, rodents or each other. As pigs are omnivorous, they may eat rats which can be loaded with Trichinella. Once infected, they may not show any sign of disease.

Human infection, on the other hand, can result in enteritis, myalgia, fever, and kidney and respiratory failure if the parasites are prevalent enough. 5 larvae per gram of muscle is fatal.

To prevent infection, cook pork thoroughly or freeze it at -15˚C for 20 days or more, depending on the size.

Parasites like Trichinella have added to the perception that pork is unsafe. In the U.S., it is less of an issue now in confined pigs since they tend to be grain fed instead of fed with raw garbage. Organic and pasture raised operations have brought about concern of the re-emergence in swine. A couple of other hosts from which one can acquire infection are bears and horses. Current Trichinella cases are mostly from undercooked bear meat and the parasites can survive freezing. There have been several outbreaks of the parasite in horse meat in France and even some U.S. horses.

:: Next post: Toxoplasma gondii ::


Parasite Terminology

H. diminuta life cycle.

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:: The image chosen is of the life cycle of a specimen that I actually have a jar full of in my room… ::

Before I dive into aspects about the parasites mentioned in my last post (Trichinella and Toxoplasma gondii), I thought it would be a good idea to post a few definitions of frequently used terms. For future parasite posts, I’ll be sure to try to include a link here to make it easy on new readers, or just in case you’ve forgotten.

  • Life cycle: entire life history including stages and hosts
    • Direct: only one host
    • Indirect: one or more hosts
  • Definitive host: host in which parasite reaches (reproductive) maturity OR sometimes the most important host to us
  • Transport (or paratenic) host: no development occurs, used to get closer to necessary host (eg. marine parasite)
  • Intermediate host: necessary part of life cycle; immature parasite cannot reach maturity without it (eg. heartworms need stage in mosquito before infecting dog)
  • Patent infection: period when parasites are mature and reproduction occurs, parasite produces evidence of infection (eg. eggs)
  • Prepatent period: period following infection before parasites mature; often before infection can detected by microscope
  • Zoonosis: disease transmitted from animal to human
    • Reservoir host: animal carrying infection that can be transmitted to humans
    • Vector: agent (usually arthropod) transmitting disease
  • Helminth: worm
  • Anthelmintic: dewormer
  • Geohelminth: helminth acquired directly from the environment without intermediate hosts or vectors (term used for human intestinal parasites)
:: The information from this post is from my Introductory Parasitology notes taught by Dr. Zajac at Virginia Tech ::

Feral Pigs : From Piglets to Problems

Description: The Wild Boar (Sus scrofa) is the...

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We’ve all gotten the cutesy side of pigs in the media from shows like Winnie the Pooh and his pal Piglet. People also have pigs as pets, not just in a farm environment. Over the years, domestic pigs have escaped their confines leading to feral pigs, also known as wild hogs, wild boars, and razorbacks, among other names. After being introduced to the U.S. by Europe in the 1500s, Sus scrofa hasn’t stuck strictly to captivity. “Within two generations out of captivity, domestic pigs usually lose their pink hue and turn striped and coarse-haired, DePerno said, allowing them to blend in with feral populations” (NG). According to studies, 39 states harbor an estimated 4 million wild pigs.

The hogs can be aggressive both with humans and the environment. Rooting can damage local flora thereby affecting the surrounding fauna and with tusks, usually 3-5″, that have been recorded up to 9″, hogs can easily injure a human. (WDNR) Aside from the dangers their activity poses to agriculture, the environment and humans from physical injuries alone, they also may bring parasites back into the domestic population. The two main parasites of concern are Toxoplasma gondii and Trichinella (which I will address in a later post or two). The parasites can spread through consumption of the meat and can make its way back into domestic populations should the feral pigs come into contact with free range pigs. The consensus seems to be an aggressive approach to eradicating the razorback issue.

Here’s a video about the feral hog issue in one of my very favorite countries, towards the end of which he actually discusses his hunting techniques:


:: I am not big on hunting, nor will I ever be. Sometimes you have to take into account alternative methods in order to put a band-aid on human made problems. ::