Comment by capableweb | Hacker News Reader

Comment by capableweb | Hacker News Reader

It's mentioned that "GWD is spread by drinking water containing Guinea worm larvae" (https://www.cdc.gov/parasites/guineaworm/gen_info/faqs.html) but also that "There was no chance for the disease to return after the last human case occurs", how does that fit together? Are people getting it from drinking from the same infected water sources as others, and by not seeing anyone getting it means there is no more infected water sources?

Edit: Apropos nothing, it sounds terrible to get infected:

> Guinea worm disease is usually contracted when people consume water contaminated with tiny crustaceans (called copepods) that eat Guinea worm (Dracunculus medinensis) larvae. The larvae develop into adults within the human host. After about a year, a meter-long pregnant female worm emerges slowly through a painful blister in the skin, often of the legs or feet. A sufferer may seek relief by dipping the affected limb in water. However, contact with water stimulates the emerging worm to release its larvae and start the cycle anew.

Edit: Which, I think answered my question. Leaving my comment rather than deleting it as maybe others had the same question.

One phase of the lifecycle only happens in humans and dogs. Once no one (or their dog) has it, then the cycle is done. The out-of-human part is three phases of larva which take a few weeks, although I didn’t see how long the phase 3 larva could persist without a human or dog host to proceed to adulthood.

https://www.cdc.gov/parasites/guineaworm/biology.html

While tragic, it is beyond hilarious that "everyone and their dog" is a thing here.

I still don't understand how getting rid of the last human case will resolve the issue. Presumably these crustaceans & worms still exist in the wild? Isn't there always a chance for a new flareup to occur?

The parasite only effects humans and dogs. I guess that the worms in the water go away after a while. Prevention breaks the cycle.

The worms themselves don't live in the water at all. Its larvae are released into the water, and can only grow to maturity and reproduce if they're consumed by a host.

And, then consume some of the host (I guess?)

From wikipedia,

"In 2020, Guinea worm was found in 1507 domestic dogs in Chad, 15 in Ethiopia, and eight in Mali, as well as in 61 domestic cats in Chad and three in Ethiopia. Small numbers have also been found in wildcats and baboons.[9] These findings are a potential problem for the eradication program. "

Now I'm making things up, but it may be that eradication from human water sources is enough to break the cycle, if maybe the other mammals in the area are more migratory and cannot provide a consistent reservoir.

As I understand it, they rely on human hosts, so if no humans get infected for a while, the rest will die out. After that, there is none of them left, so no one can get infected again.

It appears to not be known for sure as of 2019 if dogs are a main host or not.

https://www.nature.com/articles/d41586-019-02921-w

The parasite has a life cycle that passes through several stages.

One of the stages involves infecting a mammal (and apparently mostly human) host.

If you disrupt that stage, you disrupt the life cycle of the parasite. If you disrupt that stage completely, no parasite continues to the next cycle and after a bit of time there isn't any more parasite.

The larvae don’t live forever and need a human or dog to procreate.

Also, we’ll only be reasonably sure no human or dog cases exist over a year after the last human was infected because that’s how long it takes for symptoms to become obvious.

I expect the life expectancy of the larvae to be much shorter, but can’t find that online (https://en.wikipedia.org/wiki/Dracunculus_medinensis#Life_cy... says* “Within the copepod, the D. medinensis larvae develop to an infective stage within 14 days”*, but doesn’t mention how long they stay infective or how long they can spend in the water before being eaten by the copepod)

They probably also will be careful of declaring victory too early because of the existence of animal reservoirs (https://en.wikipedia.org/wiki/Dracunculus_medinensis#Animal_...)

It is a cultural thing of educating fisherman to stop feeding fish entrails to dogs, and keeping infected dogs and people from entering the waterways once infected to break the reproductive cycle.

We have an American version of the Guinea work that affects raccoons and other wildlife, but hasn’t crossed over. https://www.michigan.gov/dnr/managing-resources/wildlife/wil...

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