Sometimes you find a paper with a title so intriguing you just have to find out a little more about it. Recently, I came across a paper about ‘entombed pigs’, so how could I possibly ignore it? I learned a fair bit about animal-disease control methods in Asia and the use of quicklime to decompose corpses , a fairly standard weekend for me.
The work centres on foot-and-mouth disease (FMD), a viral infection of hoofed animals caused by Aphthovirus. It causes significant suffering in animals and has serious economic consequences: a 2001 outbreak is estimated to have cost the UK £8 billion.
Millions of infected animals were culled in South Korea in 2010/11, then buried (rather than burnt, as they are in the UK). The slaughtered animals were placed in five-metre-deep pits and covered with quicklime and copious amounts of soil to prevent the FMD spreading. Problem solved? Well, perhaps not.
A large number of the burials took place during the winter of 2010, when the ground was cold. As the weather changed and the ground warmed, many of the sites saw large amounts of liquid (called leachate) leak from the rotting corpses. Water contaminated by this leachate could prove a serious health risk to neighbouring communities, although no issues have been reported to date.
Researchers in Korea wanted to see how the microbial community in the leachate changed over time, so they put a dead pig in a scaled-down version of a burial pit and kept it in a constant temperature room. Obviously. Samples of leachate were collected weekly for a month, then monthly for five months, with DNA analysis allowing the team to monitor how the microbes changed as the pig decomposed. The bugs that were sequenced were split into three categories: those present in all samples, those only present in early samples and those only present in late samples.
Of the bacteria present in all samples, two strains were found to be closely related to Bacteroides coprosuis, a species known to grow in pig manure – no great surprise there. Another constant was a species similar to Sporanaerobacter acetigenes, an anaerobic bacterium also found in manure, which helps to produce the ‘malodorous substances’ associated with animal excreta.
Of the species that appeared in the early samples, the anaerobes Clostridium cochlearium, Fusobacterium ulcerans and Fusobacterium sp. have all been shown to be involved in skin necrosis and have been observed in septicaemia. Clostridium haemolyticum, which can cause bacillary haemoglobinuria in animals, was isolated from the late leachate samples (16–24 weeks into the experiment).
This research shows how dynamic the microbial communities are during decomposition. Some were only present for a very brief period of time, whereas others – particularly those associated with pig excrement – were ever present.
The study is interesting because it differs from previous experiments that have looked at the microbes collected from the soil around decomposing corpses. Many of these bugs are fairly immobile, so by looking at the leachate – which has the potential to move much further – the researchers revealed the impact it may have on water systems and human health. If another outbreak occurs, this work should help to inform health officials about where to position burial pits. Keeping them away from rivers seems a safe bet.
Yang, S. (2012). Characterization of Microbial Community in the Leachate Associated with the Decomposition of Entombed Pigs Journal of Microbiology and Biotechnology, 22 (10), 1330-1335 DOI: 10.4014/jmb.1205.05006