Hydatid fluid

In the tooltip for today's xkcd, Randall Munroe mentions "hydatid fluid" as one of the bodily by-products that can be offered for a war effort besides "blood, toil, tears, and sweat".  But what is that stuff?  Wikipedia mentions it as an aside in an entry on hepatic tapeworm infection.  They say that if the cyst ruptures and the hydatid fluid mixes with the rest of your body, the result is likely to be anaphylactic shock.  So how is this useful for a war effort?

Here is an article on "the usefulness of hydatid cyst fluid".  Apparently it is of some use in creating a blood test to see whether people have liver-tapeworm infections without lots of expensive CT and MRI scans.

Mr. Munroe's comics are very educational!