Ten years ago I was spending a lot of time searching through the "junk box" at my local coin shop.  I had not been married too many years, had a mortgage, had two kids in school, and didn't have much money to spend on hobbies; so I was looking for items to enjoy at prices that wouldn't cause trouble with our household budget.  World coins and currency, tokens, and "junk box" finds can provide a lot of enjoyment for little cost.  I learned a lot about world history, geography, international trade, and international monetary systems through poking around a "junk box" for items I didn't recognize.
I came across what I thought was a coin in the foreign coin box.  It was denominated in centavos and had the word "lazareto" on it.  It was nowhere near mint state, but it wasn't in bad condition either.  I bought it with several other foreign coins and took it home to look it up.
What I discovered later was that it wasn't really a coin in the strictest sense of the word, but rather a token:  a coin-like object used to facilitate a restricted form of exchange or commerce.  It was spent and accepted like money, but only had transactional value within certain establishments or between certain people; it was not universally used for all debts within the jurisdiction of the issuing governing body.  In fact, few people outside of this token's intended circulation would want to even touch it.  The token turned out to be a leper colony coin.
If you don't know more than the average person about leprosy (and at the time I did not), your first reaction might be, "What have I just touched!?"  Leprosy is an ancient disease.  Leprosy caused bumps to appear under the skin; patches of skin turned a deathly whitish color.  Hands would lose feeling and movement, and fingers would shorten, making hands look claw-like.  Leprosy also affected the feet, causing the sufferer to walk stiffly and shuffle, like an old-time movie monster.  The nasal membranes would be affected, making it hard to breathe through the nose, or causing nosebleeds or even disfigurement.  Due to the loss of feeling, cuts and burns would go unnoticed, which would then get infected, causing awful-looking wounds and potentially gangrene, sepsis, and death.  For much of history there was no known cure and little known to treat the symptoms.  An advanced case of leprosy was horrible to the sufferer, and unsettling to those around.

Leprosy has been socially stigmatized at least since Biblical times.  Some saw the disease as a curse from God, possibly for some evil you or your parents had committed.  As medical science advanced and people began learning how diseases were spread, people feared catching leprosy from an affected person.  Whether people feared being cursed by association, catching the disease through proximity, or simply witnessing its awful effects, ancient (and not so ancient) societies did not want to be around anyone suffering from leprosy.  People with the disease were cast out of society and isolated.  Laws were enacted to keep lepers from coming close to people who didn't have the disease. 

Yet, leprosy sufferers often lived quite awhile, and would need care and community.  Therefore, as social outcasts with a common plight, they would often band together and form their own separate communities... and in more modern times, governments would often enforce such an arrangement by creating a separate space for them... what would become known as a "leper colony".  As with most societies, commerce would form, and a means of facilitating commerce would become necessary.  In the case of colonies formed by governments to control the interactions of lepers with the rest of society, special currency for these colonies was created and issued.
"Leper colony money" served more than one purpose.  For those confined to the colony, it provided an ability to conduct commerce within the colony.  People would have jobs, for which they would be paid.  They could purchase things they needed without having to barter.  Having money to spend would lend some sort of feeling of normalcy.  However, it also made escaping more difficult.  A sufferer might decide to sneak out of the colony... but with no money that would be acceptable outside the colony's walls, it would be hard to get very far.  One could send money to family outside the colony, but only by exchanging leper colony money for local currency through the colony's administration.  I'm sure this was often less than useless, as a corrupt administrator could simply pocket the local currency.
As science made further advances, the cause of leprosy was isolated to a slow-growing bacterial infection.  In the mid-20th century, a cure for leprosy (now known as "Hansen's Disease") was discovered.  The Center for Disease Control states that although it is thought that leprosy can spread through aerosolized respiratory droplets (i.e. coughing and sneezing), it is not as successfully contagious as viral diseases such as the flu:  "Prolonged, close contact with someone with untreated leprosy over many months is needed to catch the disease."  The disease has not been totally eradicated, but it is rare.  Even so, 180,000 cases exist worldwide annually, 100 of which are in the United States. 

No transmissions of leprosy have ever been known to occur through handling of coins or currency used by sufferers of the disease.  In spite of this, some people are wary of these numismatic items.  Once a cure and treatment became widespread, the need for leper colony money disappeared.  Like so many other items of currency that were no longer required, many of the coins and notes were destroyed.  Having come from a limited production run in the first place, the destruction of large quantities of these items increases their rarity.  Some, like the "lazareto" type I found, are more common, while others are extremely rare.  Collector value is driven primarily by market, however; a leper colony token is only worth what someone else is willing to pay for it.  Stigma and paranoia regarding leprosy has contributed to keeping the market cool for these items.
For more information on leper colony money, please see this February 13, 2018 article from Atlas Obscura, which includes some information obtained from the ANA's Money Museum Curator Douglas Mudd.
I have no photos of the coin I found, but to see an example, click here.