"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

February 24, 2010

February 24 - Gnathostoma lamothei

This nematode, with spines and hooks covering its body lives attached inside the stomach of racoons in Southern Mexico. These worms lay their eggs in the host’s stomach and the eggs find their way to outside when the vertabrates poop. If this happens close to freshwater and the parasite is lucky enough, a free-living larva is liberated from each egg. These larvae can live for a few days in the water until it dies or… is swallow by a copepod. The nematode then penetrates the digestive system of the copepod and lives there until the copepod is ingested by a fish. Once in the fish, the nematode again penetrate the intestine and finds its way into the muscles where it encysts. The life cycle of Gnathostoma lamothei comes full circle when a racoon eats fish flesh with the parasite encysted in the muscles. Inside the raccoon, the parasite penetrates the intestine, spends some time there, and then finally enters the stomach to start the cycle again.

The life cycle of G. lamothei is fascinating but in reality is much more complicated. Larvae allocated in the muscle of fish can infect an extraordinary number of animals other that dogs and cats. For example, if a frog or snake eats the infected fish, the nematode penetrates the intestine again to encyst in the muscles. The nematode larvae can move from animal to animal until it reaches a racoon.

Humans can be infected by this parasite or by closely related species while eating raw freshwater fish. Human gnathostomiosis is a common food-borne parasitic disease in several countries of Asia and now is becoming a serious health problem in some areas of Latin America. In most of the cases the larvae of Gnathostoma don’t encyst in humans. On the contrary, the larva migrates erratically throughout the body, most of the cases close to the skin. Remember, the next time you eat sushi, sashimi, ceviche or any kind of raw fish, be sure that is not fresh-water fish!!

You can read more about it here.

Contributed by Alejandro Oceguera-Figueroa.

1 comment:

  1. Thanks for this one! I remember reading Parasite Rex and not being able to eat sushi for almost two years! Now once again the thought of going to Stix our favorite sushi bar, reminds me of going to the ocean after watching Jaws! lol

    Parasites are my second favorite organism, insects being my fav. Last spring my daughter, age 5, and I watched Sir David Attenborough's BBC documentary Life in the Undergrowth. It was a fascinating show. My daughter came away with the knowledge that "wasps are mean!".
    One of species of wasp lays their eggs in the tree's flower, causing a gal (I think that's right) and feeds off the tree as a larva. Later that spring she found a gal on one of our trees. We cut it open and sure enough we found a larva inside. That night she drew a letter for Mr Attenborough, and we sent it off.
    Surprise of surprises that fall she received a hand written reply with a signed picture. Now she is fully fascinated with nature and how the world works.
    Popularizing science is so important. Keeping that wonder of the world going long after childhood has passed is so difficult. It is important to remember WE are a part of the world and not separate from it.

    Thanks for the extra effort it takes to produce a blog like this.

    P.S. my daughter thinks the pictures are icky or scary. lol