A recent article in the Economist has brought us up to date on the progress to eliminate the guinea worm – a helminth parasite that has historically blighted millions of lives but now which faces extinction due to some major flaws in its life-cycle.
Most parasites that affect humans are hidden from view. They, like the guinea worm, reside within the host – in the gut, blood or wider vasculature, where they either replicate (eg. malaria) or reproduce (e.g. worms). The newly formed transmission stages are then released from the body of the host in various ways depending on the parasite species.
The aim of this activity is straightforward in principle – the parasites need to locate a new host for the species to survive and each progeny carries the genetic material of the parents. The dissemination of these stages is their only strategy for ensuring the genome continues to exist.
Guinea worm, like many other infectious organisms and parasites, succeeds in transmitting its genome over time by forcing a behaviour change in the host. Female worms carrying the immature larvae emerge from the skin of an infected human (or other mammal such as a dog) and generate a skin reaction that forces the host to seek water to ease the irritation. Contact with water causes a release of the larvae held by the adult female. Once released, the larvae seek their own host – small copepods called Cyclops. If an infected Cyclops is ingested through someone drinking contaminated water, the larvae enter the human host and the life cycle continues.
This strategy has worked for guinea worm since it adapted its current lifecycle – an unknown period but likely to be many, many millennia. So what went wrong (for the parasite) but went right for the millions of people previously exposed? And perhaps more importantly, why is guinea worm heading for extinction whilst other infections persist and even spread?
Putting the efforts and influence of a former US president (Jimmy Carter) to one side for a minute, the fact that guinea worm is even eradicable whilst other parasites persist is largely down to the fact that the worm is always highly visible at the point where it about to release its progeny. You might say it lacks discretion.
Add to this the fact that the copepods infected by the larvae are big enough to be filtered out by a muslin cloth and you now have 2 points in the life cycle where one can interject and prevent the life-cycle from being completed.
The life-cycle of guinea worm was described in 1905 but the parasite was visible to humans long before that. So there is no doubt that the personal interest of Jimmy Carter brought about the fundamental change in political will, human and fiscal resources needed.
But what of the rest (parasite species, not former US presidents)? There are many species to choose from. Some of them are less adaptable to environmental change than others, but none of them have that unique combination of flaws present in the guinea worm life-cycle. The low-hanging fruit has been sighted, picked and pulped. What remains is a a panoply of parasitic fauna requiring the will and resources of nation states and the collective efforts of researchers, perhaps another former US president (Bill Clinton has been active), charities and philanthropic organisations, foundations etc, the wider business sector, the building sector, the transport sector, the civil planning sector the pharmaceutical sector, individual citizens, and serving politicians to eradicate.
I am an epidemiologist based at a UK Higher Education establishment (Durham University, if you are interested). My research interests are primarily within the domain of Neglected Tropical Diseases (NTDs). I believe that the only way we can effectively tackle complex problems affecting populations living in tropics and sub-tropics is through trans-disciplinary collaboration. My working definition of transdisciplinary is undertaking research alongside so-called 'stakeholders' - groups and individuals who do not call themselves 'researchers' but whose experiences and knowledge can be used to great effect when combined with the experiences and knowledge of the research community. You can read my online CV at the link below.