The aim of this paper is to discuss the evidence for intestinal parasites in past human populations of Chinese ethnicity in order to better understand which species were most common and how infection might have varied throughout history. This is an important area of investigation, as such an approach could potentially identify changes in parasitism between hunter-gatherers, farmers cultivating rice or sorghum, the inhabitants of early small towns, and later large cities [1]. There may have been differences in species infecting those people living in the lush, well-watered regions of eastern and southern China compared with the more arid regions of central, northern, and western China. We could even identify the spread of parasites along the Silk Road and other trade routes [2].

Some of the publications describing ancient parasites are not widely known outside China as they have been published in regional Chinese journals that may not be easily read or accessed by the international community. Paleoparasitology is a relatively recent field of research in ethnically Chinese regions, compared to the century long tradition in Western countries [3]. In the past, parasite evidence from China has often been obtained from naturally preserved mummies that were analyzed by anatomists or physicians (Table 1). Other methods for sourcing ancient fecal samples, such as the pelvic soil from burials, latrine sediments, and coprolites from rubbish tips have not been widely used. In this paper, we will examine the evidence for parasites dating from the Neolithic period to the end of the Qing Dynasty (7,000 BCE to CE 1911/1912) (Table 2). This will start to shed light on when, how, and where the ancient communities of the area became infected by the range of parasite species now known in the region [4].

Having brought together all the available evidence, we can start to investigate which parasites may have been more common than others, if geographical location affected likelihood of infection, and if there seem to be changes in infection over time. However, we do need to be cautious and realistic in how we use this data. A total of 33 individuals and 1 latrine from the whole of ancient China have been analyzed for the eggs of intestinal parasites. These 33 individuals are represented by 13 mummies and 20 skeletonized burials. The time period over which these individuals lived and died is very large, over 3,000 years. Therefore, we cannot determine past prevalence of diseases in the way we might with much larger samples. Furthermore, many of the samples came from mummies in sophisticated tombs that would suggest they were the burials of wealthy people. This means the findings from the mummy evidence may not necessary apply to those of poor members of the population.

The most common parasites found were those of whipworm, roundworm, and Chinese liver fluke. Whipworm was found in 77% of the mummies (n=10/13) as well as on the personal hygiene sticks excavated from the latrine at Xuanquanzhi in Gansu Province (111 BCE-CE 109). Roundworm was found in the pelvic soil of 25% of burials (n=5/20) dating from the Spring and Autumn period from Zhengzhou in Henan Province. It was also identified on the Xuanquanzhi latrine sticks, and in 62% (n=8/13) mummies from across all times periods. Chinese liver fluke eggs were recovered from 46% of the mummies (n=6/13) and the Xuanquanzhi latrine. As whipworm and roundworm are spread by fecal contamination of food, possible explanations for their widespread presence are that in ancient China hands were not washed regularly, that drinking water was contaminated by human feces, or that human feces were being used a crop fertilizer [17,18].

Other species of intestinal parasites seem to have been much less common. Both the flukes F. buski and S. japonicum were found in just 15% of mummies (n=2/13), while pinworm (E. vermicularis) and Taenia sp. tapeworm were found in just 8% of mummies (n=1/13). Taenia sp. was also found on the personal hygiene sticks from the latrine at Xuanquanzhi. If the limited sample we have in this study is in any way representative of the wider population, this would suggest that far fewer people in ancient China might have suffered with these helminths than was the case for whipworm, roundworm, and Chinese liver fluke.

Geographical variation is more of a challenge to assess, as the locations where parasites have been studied are not evenly spread across ancient China. As we can see from our map (Fig. 4), the vast majority of samples came from eastern and southern China. Only 1 sample, the Xuanquanzhi latrine, was in northwest China. This leaves the northeast, north, center, west, and southwest of this huge region devoid of evidence.

It is interesting that 46% of the 13 mummies were infected with Chinese liver fluke. All the mummies were recovered from regions of China that are lush and well-watered by the Yellow, Yangtze, and Pearl River networks. Chinese liver fluke is found today just in eastern and southern China and Korea, where the life cycle of the parasite can be completed in the local water snails and freshwater fish. It is contracted if a person eats raw infected freshwater fish [19,20]. The mummies were almost all from the areas of eastern and southern China where we would expect to find the Chinese liver fluke.

In the 20th century, it was found that the region of China with the highest prevalence of Chinese liver fluke was Guangdong Province, with a prevalence of just 1.82% between 1988–1992, and 0.365% for the whole country [21]. Since 46% of the ancient mummies were infected, this would suggest either that these mummies were not representative of the population in which they lived, or that there has been a dramatic fall in the prevalence of Chinese liver fluke over this time. If there has been a genuine drop in liver fluke infection, we should ask ourselves if this might be due to advances in medical treatments, hygiene, toilets, and health education over this time. However, in the same 20th century survey, the prevalence of roundworm was 47% in China [21]. This is not that dissimilar to the 62% of ancient mummies infected by roundworm. This data suggests that while roundworm remained common in China for many centuries up to and including the late 20th century, Chinese liver fluke may have been much more common over the last 2,000 years than it was in the late 20th century. It seems unlikely that this change in Chinese liver fluke infection was due to advances in medicine and sanitation, as we would expect roundworm to have become rarer as well if that was the case. More likely explanations for this apparent change in prevalence for the liver fluke, but not roundworm, could be that this indicates either a change in the way freshwater fish was processed or eaten by Chinese people in the late 20th century compared with the previous 2,000 years, or that modern pollution in Chinese rivers has affected the intermediate hosts, such as water snails that are required for the transmission of this flatworm to humans.

The DNA of the Chinese liver fluke from the Phoenix Hill mummy (167 BCE) has been the focus of research. Samples from the gall bladder underwent genomic analysis, and the internal transcribed spacers 1 and 2 (ITS1 and ITS2) in ribosomal genes were sequenced. It was found that while ITS2 sequences were identical to modern strains of Chinese liver fluke, the ITS2 sequence differed by 15 nucleotides. It was proposed that this indicates the parasite has evolved over the last 2,000 years [22].

Taenia sp. tapeworm eggs of different species appear very similar on microscopy, so without DNA analysis, it is not possible to distinguish Taenia saginata contracted from eating beef, from Taenia solium and Taenia asiatica contracted from eating pork. However, written records from ancient China show that pork was widely eaten, and that beef was rare in the diet as cattle were used for their strength pulling farm machinery [23,24]. This might suggest that the infections noted were likely to have been due to either T. asiatica or T. solium, and not T. saginata. Texts written on Han Dynasty bamboo slips have described how it was common for pigs to be reared in captive environments where they would not be able to violate laws by disrupting crops [25]. Pig-shaped burial goods from a tomb dating from the Han Dynasty serves as an indication of the extent to which the pig was an important resource as a food product and as part of daily life in the period [26].

Chinese communities started to consume animal viscera in the period from the 11th century BCE to 221 BCE, in the Zhou Dynasty. The Book of Rites, a compilation of written accounts relating to aspects of conduct in society and to the ceremonial rights of the Zhou Dynasty, recorded that the roasted liver of a dog was considered to be a delicacy [27]. A noteworthy discovery was made the excavation of Mawangdui in central China. This excavation explored the burial places of elites dating from the Han Dynasty, and it gained widespread fame as a result of the recovery of an excellently preserved mummified female body. Numerous burial items of considerable value included models of animal viscera, including liver, stomach, lungs, and spleen [28,29]. The Book of Han (dating from CE 32–92) also referred to the consumption of sliced liver, bacon, incompletely cooked and roasted animal products, and dog and pig viscera [23,30]. These references are an indication of the widespread nature of these dietary habits over this period. In light of this, the identification of Taenia sp. tapeworm eggs in the Xuanquanzhi latrine and a Han dynasty mummy potentially reflect the well documented dietary practices of consuming raw pig viscera.

The Silk Road was a well-known long distance transport route that came to prominence during the Han dynasty (206/202 BCE-CE 220). It connected eastern China with central Asia, the Middle East, and Europe, and in its entirety was about 7,000 km in length [2,31]. It has been proposed to have acted as a route via which diseases, such as bubonic plague, anthrax, and leprosy might have spread between Asia and Europe [32–34]. However, the evidence supporting this hypothesis is based upon genetic similarity between bacterial strains in East Asia and Europe [35,36]. It remained unknown whether transmission was along the Silk Road itself, or to the north via Mongolia and Russia, or to the south via India. Past research using parasites as markers of migration to and from Asia include movement between Europe and the Middle East in the 15th century AD, and between China and America in the 19th century [37,38]. A study of the latrine at Xuanquanzhi relay station has for the first time allowed an investigation of an archaeological site on the Silk Road that was built for travellers. The presence of Chinese liver fluke on the personal hygiene sticks in the latrine is an important finding. This relay station at Dunhuang is located in an arid region of northwest China, at the eastern end of the Tamrin Basin. This basin contains the Taklamakan Desert, and is far too dry a region for the Chinese liver fluke to be able to complete its life cycle. Indeed, Dunhuang is 1,500 km away from any region where the Chinese liver fluke was endemic in the 20th century [21]. This suggests that a traveller from the well-watered areas of eastern or southern China contracted the parasite there, and travelled a huge distance along the Silk Road before using the latrine at Xuanquanzhi relay station. This provides the first archaeological evidence from along the Silk Road to show that ancient travellers were moving with their infectious diseases [13].

Here we have brought together the available evidence for intestinal parasites in ancient China and used this to better understand the consequences of infection for the people living in the region. We have been cautious in our interpretation due to the limited sample size and the long period over which the archaeological evidence originates. However, we have been able to draw some fascinating conclusions. Seven species of intestinal parasites have been identified in ancient China, but it was found that whipworm, roundworm, and Chinese liver fluke seem to have been by far the most common. Indeed, around a half to 3/4 of Chinese mummies so far studied have been infected by these parasites. While whipworm and roundworm remained common in Chinese people in the late 20th century, Chinese liver fluke had become much less common by then. This might suggest a reduction in the amount of raw freshwater fish eaten over time, or pollution in modern Chinese rivers. We have also seen evidence for the migration of people along the Silk Road with their parasites 2,000 years ago, with the discovery of Chinese liver fluke in a latrine in northwest China 1,500 km outside its endemic area. It is hoped that in the future Chinese archaeologists will start to sample the contents of latrines at the time of their excavation, so that we can increase our evidence base and enable us to create a much more reliable interpretation of intestinal parasite infection in past Chinese populations.