Helminths, commonly known as parasitic worms, infect one third of the world’s population, resulting in typically chronic and frequently deadly diseases. However, a clever parasite doesn’t want to kill its host, at least not straight away, and the loss of approximately 4 million disability-adjusted life years can be attributed to the protracted suffering that helminths inflict. 8 of the 17 neglected tropical diseases listed by the United Nations World Health Organisation are caused by these worrying worms, which are now becoming less exotic than we would like to think.
The spread of diseases once thought of as tropical to colder climes is a story we all too familiar with. Climate change is welcoming diseases, like malaria and dengue fever, into Europe with open arms. Unsurprisingly, this also means that conditions suitable for the transmission of pathogenic flatworms are expanding into areas somewhat closer to home. If we don’t step up the pace of vaccine development, we will be forced to continue the use of single-drug therapies leading to potentially catastrophic consequences.
Unfortunately for research purposes, working with these complex organisms in the laboratory is a tricky business. It is relatively simple to grow up a culture of your bacteria in a petri dish. What is not so easy is trying to replicate a life cycle that can be incredibly elaborate, fascinating, disturbing and often completely bizarre. With 300 million people infected by helminths each year, there is urgent need for vaccine development.
However, this is not as easy to do as you might think. Despite appearing so alien to us, we are quite closely related to pathogenic worms. This means that the cellular differences between them and us are more difficult to exploit and drug targets are more difficult to find. In the face of these bottlenecks, progress is being made in adapting technologies and we are nearing a transformation in our ability to study and manipulate helminths. Steadily improving methods of the genetic analysis are exciting developments in the face of helminths’ recalcitrance to genetic and cellular manipulation. In vitro cultivation systems are paving the way to understanding the stem cells that account for flatworms’ amazing regenerative capability and developmental plasticity. This, combined with targeted manipulation of helminth genes, is addressing several fundamental questions regarding the intricacies of host-parasite development. In addition to widening our methodological repertoire and comparative reference base, research into parasitic worms branches into some of the most exciting scientific fields.
Research into helminths is not only important for drug and vaccine development to treat the infections themselves, but also for the understanding it gives us in other areas of the field. The study of parasitic flatworms provides a source of totipotent somatic stem cells that are “immortal”. How do they retain this vitality? Parasitic worms also do a pretty great job of going unrecognised by the host immune system. This is rubbish for you but it’s exactly what you would want if you ever needed a new kidney from someone else. In this way, helminths serve as models for perfect organ transplantation and further study may help to elucidate mechanisms of preventing organ rejection.
Fighting parasitic worms is a major challenge. There are effective single-drug therapies and there has been some significant progress with disease eradication. However, an over-reliance on these treatments is unsustainable. The practicalities of drug distribution are difficult, and drug resistance and regular administration add to the list of problems. Moreover, drug treatment isn’t a complete solution. Infection from parasitic worms is preventable. And this is a crucial point: the burden of helminth infections is huge and unnecessary; this is a social development issue as much as it is a drug and vaccine development issue. Helminths infect the world’s poorest people. The provision of clean water, education and means for good sanitation is the answer to this global problem, with the added side note of the absolutely critical scientific research that accompanies it.