Eating Soft-Shelled Turtles Spreads Cholera

Soft-shelled turtles, eaten as a delicacy in China, have been implicated in the spread of cholera.

AsianScientist (Jun. 15, 2017) – Eating soft-shelled turtles has been linked to the spread of cholera, according to a study published in Applied and Environmental Microbiology.

A team of researchers in China has found that the bacteria which causes cholera, Vibrio cholerae, can colonize the surface and the intestines of soft shelled turtles.

To track the growth of V. cholerae, the researchers inserted genes for bioluminescent proteins into the serogroup 0139 strain of the bacteria. They then dipped turtles into a solution containing the bioluminescent bacteria and monitored bacterial growth over the next four days.

By the first day, bacteria could be detected on the surface of the turtles. At 96 hours, the entire dorsal side of the turtles’ shells were emitting bioluminescence. Importantly, bacteria were also found on the turtles’ limbs and necks as well as the calipash, a gelatinous tissue found directly below the carapace and locally regarded as a delicacy.

Bioluminescent bacteria could be detected on the intestines 72 hours after they were introduced to the guts of the turtles. Furthermore, the researchers also showed that the bacteria required a surface protein called mannose-sensitive hemagglutinin to stick to the turtles’ dorsal surfaces and intestines.

The study was driven by the hypothesis that consumption of cholera-carrying soft-shelled turtles had caused outbreaks of the disease, said corresponding author Dr. Kan Biao.

“Cholera is a life-threatening diarrheal disease,” said Kan, who is professor of pathogenic biology and infectious disease control at the Chinese Center for Disease Control and Prevention, Beijing.

Of the 39 diseases surveilled under China’s Law of Infectious Disease Control and Prevention, cholera is in the most dangerous category, along with plague, Kan added. He also noted that the O139 serogroup, the major strain spread by the turtles, is an emerging disease in China.

Elsewhere in the world, the Haitian outbreak which began in 2010 has infected nearly 800,000 people and has caused more than 9,000 deaths. In 2014, a total of 190,549 cases worldwide were reported to the World Health Organization, including 2,231 deaths. But the number of reported cases has varied widely year to year, with a post-millennium high of over 600,000 in 2011. But other sources have reported as many as three million cases annually this decade.

A side benefit of the study is that the soft-shelled turtle could serve as a new animal model for studying how V. cholerae interacts with aquatic hosts. Unlike other aquatic models such as zebrafish, soft-shelled turtles can be anesthetized and their surfaces sampled out of water for relatively long periods without killing them. Using aquatic models is particularly beneficial since cholera is a mostly waterborne disease.

Besides soft-shelled turtles, aquatic hosts of V. cholerae include zooplankton, fish, shellfish, egg masses of midges, waterfowl, and crustaceans. Fish and shellfish are proven to spread this disease.

The article can be found at: Wang et al. (2017) Colonization of Vibrio cholerae on the Soft-shelled Turtle.


Source: American Society for Microbiology; Photo: Billy/Flickr/CC.
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