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Alaria americanus?

William Reeder "wmr-60 at ix.netcom.com" at popd.ix.netcom.com
Tue Aug 25 22:54:54 EST 1998

Bert/Marie Tallant wrote:
> Friends in Oklahoma (a father and two grown children) are in the
> University Med Center
> in Oklahoma City infected with ?Alaraia americanus?  The CDC is there as
> this seems to be extremely rare.  They contracted the parasite from
> wading in a farm pond.  I have been unable to find any information on
> this organism/disease.  Can anyone out there shed any light?
> Many thanks,
> Bert Tallant

Alaria americana is trematode worm (trematodes are parasitic flatworms) 
which normally live in the intestines of wild canines such as foxes.  
This worm has a very complex life cycle.  First a aquatic snail is 
infected from the worm eggs which have been passed in the foxes stool.  
The eggs hatch a small swimming stage known as a miracidium. The 
miracidium burrows into the flesh of the snail. After further development 
the parasite leaves the snail and infects a tadpole. This feat is 
performed by another swimming stage known as a cercaria, this stage 
burrows into the flesh of the tadepole. The parasite stays in the 
tadepole as it develops into a frog.  When the fox eats the frog, the 
young worm, now known as a mesocercaria, burrows into the body cavity of 
the fox and finds its way into the lungs of the fox.  After a few weeks 
development in the lungs the worm crawls up the windpipe and down the 
esophagus back into the intestinal tract where the adult worms live.  If 
another animal such as a snake or rat eats the frog the worm remains 
immature waiting for its normal host the fox.
Human infections with Alaria are very rare (I have read of only 3 cases). 
 Human infections have been reported from the United States (1 case in 
Louisiana) and Canada (2 cases). But man is not the natural host for this 
worm so the immature worm (mesocercaria) migrate and can wind up almost 
anywhere.  Two of the cases were acquired from eating undercooked frog 
legs the other from "small game".  One of the cases was fatal.  The 
mesocercaria are extremely small, they are just visible as tiny specks 
(300 to 800 microns).  In the fatal case thousands of these tiny worms in 
the lungs caused hemorrhage and swelling blocking the air passages,  the 
patient died from asphyxiation nine days after eating frog legs.
Acquiring the infection from wading seems unlikely given what is known of 
the life cycle and other human infections.
I hope this information has been helpful.

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