Recently, a letter I co-authored called Treponemal infection in nonhuman primates as possible reservoir for human yaws was published in Emerging Infectious Diseases. It’s free if you want to check it out!
Most people I know have never heard of yaws, but at one time it was very, very common in tropical regions across Africa, Asia, and the Americas. It’s a chronic, debilitating infection that is usually contracted during childhood, and it is caused by a bacterium closely related to the one responsible for syphilis. Luckily, it’s easily treated. You can cure it in its early stages with a single shot of penicillin, and recently we have learned that a single course of oral antibiotics appear to work just as well. In short, there is really no reason for anybody to have to suffer from this horrible disease.
Many other people feel the same way. In fact, a huge yaws eradication campaign took place in the mid-20th century. After World War II, this was one of the first big public health campaigns planned by a brand new World Health Organization. More than 40 million people were treated, and the number of new cases fell by as much as 95%. Not bad! The campaign wasn’t successful, though, in that it never achieved its ultimate goal: wiping this disease from the face of the earth.
There are multiple reasons why the first campaign failed. One big reason is that it simply didn’t have the resources to keep on top of things. After a while, the WHO turned over the responsibility for yaws surveillance and treatment to local governments. Unfortunately, the whole reason the campaign was necessary in the first place was that local governments weren’t capable of carrying out these kinds of tasks without support. Not surprisingly, yaws resurged in a number of countries and is still around today.
There is another important reason that the eradication campaign may have run into trouble: a potential animal reservoir. One of the most important criteria for an eradicable disease is that there is no animal reservoir. Otherwise, you can totally eliminate the infection from a population, only to have it re-enter via an infected animal. A single infected person spreads it throughout a newly susceptible population, and all of your hard work is for naught. In this situation, eradication is not an acceptable goal–though control certainly is. In our EID article, we outline all the evidence that supports the hypothesis (around since the 1960s) that (1) African monkeys and apes are infected with yaws and (2) they may be capable of spreading the infection to humans. Infection via animals could help explain the mysterious cases encountered during the first campaign, when infected individuals would turn up in a previously treated population, having had no contact with any infected people as far as anyone could tell.
The WHO announced a second yaws eradication campaign recently, but it doesn’t seem as though much thought has been given to the problem of an animal reservoir. People involved in the first eradication campaign were calling for further research into the potential problem of simian yaws as early as the 1960s, but this history seems to have been largely forgotten. That’s unfortunate. Eradication campaigns are incredibly expensive. In the end, the cost of finding and treating cases skyrockets, because it entails going to remote and dangerous places to treat the very last hidden cases of an infection on earth. The polio eradication campaign has been going on for years and years longer than was originally planned, and we have spent much, much more than was originally budgeted because of these difficulties. Eradication campaigns also put a tremendous financial burden on the countries involved, as well as sponsor organizations such as the WHO. Money spent on yaws eradication (vs. simple yaws control) is money that low income countries cannot spend on other important health problems, like HIV, tuberculosis, and the childhood infections that represent huge sources of mortality. There is a huge opportunity cost involved. (Side note: a great book on the drawbacks of the polio eradication campaign, relevant to eradication campaigns in general, is William Muraskin’s Polio Eradication and its Discontents.) If we decide to launch a new eradication campaign, we need to make sure that we can actually carry it out, so that the resources we expend will have been well spent.
Our argument in this letter in a nutshell: before throwing a massive amount of resources behind another eradication campaign, it makes sense to do our due diligence and make sure that an animal reservoir is not going to torpedo yaws eradication for a second time.