TUESDAY, 27 OCTOBER 2020While Treponema pallidum is commonly associated with syphilis, certain subspecies are usually spread through direct skin contact, causing bejel and yaws. In all cases, a lesion initially develops at the site of infection, followed by more sores developing over the course of a few weeks to months as the bacterium spreads in the lymphatic system. It can then either lay dormant, or reactivate, forming disfiguring sores and causing damage to the heart, joints and potentially the nervous system as well. Although this means that treponemal infections are highly debilitating if left untreated, they are nevertheless easily treated with either a single injection of penicillin or a single tablet of erythromycin. In fact, a large-scale eradication campaign was initiated by the WHO in the 1950s soon after the mass production of penicillin made such a campaign possible.
Despite initial successes, this eradication campaign was not far reaching enough to eliminate yaws completely, and within several decades a resurgence was seen. Part of the reason for this is because the large, swollen boils that characterise yaws represent only a small proportion of cases. In the earliest stages of the disease, there are often a lack of obvious clinical signs despite already being highly contagious at this point, and in the latent phase, there is often no noticeable physical disease to screen for. In this regard, eradication campaigns can provide a false sense of security, as despite treatment of the active cases, a large pool of latent disease would still remain in a community.
Hence, more recent approaches to eradication have focused on mass treatment regardless of symptoms. In fact, the eradication campaign in Papua New Guinea represents one of six pilot studies being run to test the feasibility of this approach. In this campaign, residents of Lihir Island were each given a dose of azithromycin over the course of three years, with each resident then being followed up to the present date using a variety of means. Here, the authors report the outcome of this eradication campaign in Papua New Guinea. To a certain extent, it proved highly effective, with active yaws being almost completely eradicated (reduced by a factor of 20), and there was a similar reduction in the prevalence of latent yaws in the population. However, the incidence of active yaws began to creep up within 2 years after the end of the eradication campaign, mainly among those who were missed by the campaign, but also due to reinfections amongst the treated population. More concerningly, a cluster of infections resistant to azithromycin were recorded, although it should be noted that these cases were successfully treated with penicillin.
On the whole, this research suggests that yaws may not be as easy to eliminate as previously thought. Any eradication program would need to be globally synchronised and cover as many people as possible, with very few exceptions. This is needed in order to eradicate the disease as thoroughly as possible, to prevent untreated populations from reintroducing the bacterium to treated populations, as seen from this study. Alternatively, a more targeted follow up to the initial eradication programme that combines population surveillance with contact tracing might be more feasible, although such an approach may prove difficult to implement in practice. It also shows that a single oral dose of azithromycin is insufficient, and that multiple doses or the inclusion of other antibiotics, such as penicillin, may prove necessary to mitigate the risk of antibiotic resistant strains from developing and spreading.
Perhaps most importantly, this research also demonstrates a key role of genomic surveillance methods in unambiguously helping to determine the true prevalence of yaws within a community. Genomic surveillance provides a means to identify the presence of yaws in mild cases lacking any definite clinical or serological signs, and thus the spread of disease across populations can be tracked. This technology is hugely advantageous in being able to identify every case of the disease, which is an invaluable asset in order to effectively eradicate something as insidious as yaws for good.
Clifford Sia is a medical student at the University of Cambridge, and the BlueSci website editor.