Helminth transmission and morbidity are dependent on the number of mature parasites within a host, however, observing adult worms is impossible for many natural infections. An outstanding challenge is therefore relating routine diagnostics, such as faecal egg counts, to the underlying worm burden. This relationship is complicated by density-dependent fecundity (egg output per-worm reduces due to crowding at high burdens) and the skewed distribution of parasites (majority of helminths aggregated in a small fraction of hosts). We address these questions for the carcinogenic liver fluke Opisthorchis viverrini, which infects approximately ten million people across Southeast Asia, by analysing five epidemiological surveys (n = 641) where adult flukes were recovered. Using a mechanistic model, we show that parasite fecundity varies between populations, with surveys from Thailand and Laos demonstrating distinct patterns of egg output and density-dependence. As the probability of observing faecal eggs increases with the number of mature parasites within a host, we quantify diagnostic sensitivity as a function of the worm burden and find that > 50% of cases are misdiagnosed as false negative in communities close to elimination. Finally, we demonstrate that the relationship between observed prevalence from routine diagnostics and true prevalence is non–linear and strongly influenced by parasite aggregation.

This dataset brings together individual-level worm and egg data on human infections with the liver fluke Opisthorchis viverrini from five previously published epidemiological surveys. Further details are provided in the published article (Crellen T. et al. Diagnosis of helminths depends on worm fecundity and the distribution of parasites within hosts. 2023 Proc. Roy. Soc. B)

Original data sources:

• Sithithaworn, P., Tesana, S., Pipitgool, V., Kaewkes, S., Pairojkul, C., Sripa, B., Paupairoj, A. and Thaiklar, K. 1991. Relationship between faecal egg count and worm burden of Opisthorchis viverrini in human autopsy cases. Parasitology, 102(2), pp.277-281
• Ramsay, R.J., Sithithaworn, P., Prociv, P., Moorhouse, D.E. and Methaphat, C. 1989. Density-dependent fecundity of Opisthorchis viverrini in humans, based on faecal recovery of flukes. Transactions of the Royal Society of Tropical Medicine and Hygiene, 83(2), pp.241-242.
• Elkins, D.B., Sithithaworn, P., Haswell-Elkins, M., Kaewkes, S., Awacharagan, P. and Wongratanacheewin, S. 1991. Opisthorchis viverrini: relationships between egg counts, worms recovered and antibody levels within an endemic community in northeast Thailand. Parasitology, 102(2), pp.283-288.
• Haswell-Elkins, M.R., Satarug, S., Tsuda, M., Mairiang, E., Esumi, H., Sithithaworn, P., Mairiang, P., Saitoh, M., Yongvanit, P. and Elkins, D.B. 1994. Liver fluke infection and cholangiocarcinoma: model of endogenous nitric oxide and extragastric nitrosation in human carcinogenesis. Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis, 305(2), pp.241-252.
• Sayasone, S., Vonghajack, Y., Vanmany, M., Rasphone, O., Tesana, S., Utzinger, J., Akkhavong, K. and Odermatt, P. 2009. Diversity of human intestinal helminthiasis in Lao PDR. Transactions of the Royal Society of Tropical Medicine and Hygiene, 103(3), pp.247-254. 

The file is a comma-separated plain text file (.csv) with a header and six columns. The file can be viewed using a plain text viewer (e.g. Notepad in Windows or TextEdit in MacOS). To analyse the data, it is advisable to import it into statistical software such as R. 

Code to run models which analyse the data can be found at the GitHub repository - https://github.com/tc13/worm-inference