Helminths

Why are helminths important?

Helminths are worm-like organisms which live inside their hosts; receiving nourishment and protection while disrupting their hosts’ nutrient absorption, causing weakness and disease. Intestinal worms are one of the most common parasites of humanity yet remain neglected in terms of the programmatic funding they receive and their position on national health agendas. Ascaris lumbricoides (roundworm), for example, affects over 1000 million people annually and for at least 20,000 of these, the infection results in death. Similarly the two types of hookworm, Ancylostoma duodenale and Necator americanus affect over 900 million people and the associated anaemia which they cause leads to at least 50,000 deaths annually. Trichuris trichiura, is also estimated to affect some 500 million people, commonly causing anaemia and protracted diarrhoea. While the mortality from helminth infections is generally low they cause significant pain and suffering among the populations they affect. In particular, they cause stunting in the growth of children and depress their cognitive development.

Intestinal worm infections occur as a result of poor sanitation, rather than water supply, although it seems that handwashing with soap helps to prevent them (Fung IC-H, Cairncross S. 2009). Dracunculiasis (Guinea Worm disease) is waterborne, however. The global efforts to eradicate it are testament to what can be achieved when sufficient scientific evidence, global pressure, coordination and funding are applied to improve the environmental and household conditions where infection occurs. In 1991 there were 400,000 cases worldwide and in 2013 there were just 143, with hopes that it could soon become the first parasitic disease to be eradicated and the first disease to be eradicated without the use of vaccines or medical treatment.

Professor Cairncross was instrumental in leading the WHO/UNICEF technical team for Dracunculiasis Eradication in Africa. Watch the presentation below where he describes his work with Guinea Worm disease in West Africa.


Our key contributions and research in this area:

Impact of drainage and sewerage on intestinal nematode infections in Brazil brazil

This study explored helminth infection in shanty towns in Salvador, Brazil which had installed public sewers. The study and showed that improved public sanitation reduced the number of people with worms overall. However the study also identified an additional interesting pattern among the remaining incident cases of worm infection. In communities where the sanitation was better the remaining cases were less randomly distributed throughout the community. Instead the authors noticed that cases tended to be clustered and that there was a tendency for the same children and individuals to get re-infected with worms. Essentially this pattern indicated that improvements to sanitation had removed some of the public risk factors but had not dealt with the household risk factors which continued to give rise to cases.

Promotion of cloth filters for the reduction of Dracunculiasis in Ghanaguineaworm3

This study looked at whether health promotion of cloth filters could reduce the prevalence of Guinea Worm Disease in Ghana. The findings demonstrate that the intervention had a measurable but limited impact on dracunculiasis prevalence. Face-to-face health education was successful in persuading 56% of households to buy filters. Ownership of at least one filter for every l0 people in the household was associated with a reduction of at least 20% in the risk of dracunculiasis. In particular the study noted a similar, but opposite, pattern to the Brazilian research whereby the household transmission of the intestinal worms had been significantly reduced yet cases remained due to environmental factors and poor public sanitation.

Development of a theory of public and domestic domains for disease transmission

The research conducted by the group in Ghana and  Brazil helped to inform the the ‘Domain Theory’ described by Cairncross et al. in 1996. This theory outlines a division between disease transmission occurring within the domestic domain – the area normally occupied by and under the control of a household-and that in the public domain, which includes public places of work, education, commerce and recreation as well as the streets and fields. Disease transmission in the public domain can allow a single case to cause a large epidemic, transmission in the domestic domain is less dramatic and often ignored, although it may account for a substantial number of cases. To control transmission in the public domain, intervention by public authorities is likely to be required. Disease control programs have traditionally focused on transmission in one domain only, whereas to fully interrupt cycles of disease transmission interventions in both domains are needed.

Our current projects in this area:

Helminth transmission in simple pit latrines in Tanzaniaascaris

This study sought to provide greater evidence about which forms of sanitation technology meet the minimum requirements to protect health by effectively separating faecal material from human contact and thus reducing helminth transmission. The study analysed soil from 72 simple pit latrines in rural Tanzania. Simple pit latrines are one of the cheapest forms of sanitation and consist of a dug-out pit covered with wooden branches and soil, and a squathole allowing for the disposal of faeces. Presently the WHO/UNICEF Joint Monitoring Programme (JMP) for Water Supply and Sanitation classifies simple pit latrines as an ‘unimproved’ form of sanitation and findings from this study support this classification with the majority of latrines testing positive for helminth eggs.

Full list of publications related to helminths:

 

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