The paper paints a vivid picture of the wildlife trade and the passion for wild meat in urban restaurants and markets. “In the early 2000s,” the authors write, “the Vietnamese field rat trade was estimated to process 3,300-3,600 tons of live rats annually for consumption.”
The rats are considered healthy and nutritious food. “Field to fork” consumption, as Dr. Olson described it, has increased greatly in recent years, both in Vietnam and neighboring countries.
The research effort in testing for coronavirus RNA had several prongs. One was the sampling of field rats, of six species common to Vietnam, at different points on the supply chain. Another was sampling wildlife farms, and a third, bat guano farms. Small farmers build artificial bat roosts so they can collect the guano for fertilizer to use themselves or sell. Other animals and children often go under the roosts.
The researchers were spurred to look at coronaviruses because of the SARS epidemic and how common the viruses are in bats and other wildlife. Most cause minor or no illness in humans, but SARS showed how dangerous they could be.
They sampled 28 farms that raised Malayan porcupines and bamboo rats, a different creature entirely from field rats, which are more closely related to the rats familiar to Westerners. The farms were not specialized, however, they also were homes to “dogs, cattle, pigs, chickens, ducks, pigeons, geese, common pheasant, monitor lizards, wild boar, fish, python, crocodiles, deer, civets” and other creatures, such as pet monkeys and free ranging rats.
The researchers used oral and anal swabs of carcasses along the field rat supply chain. But at the farms they tested fecal samples. They found coronaviruses in all of the field rats at wildlife farms, in six percent of Malayan porcupines and about six percent of bamboo rats.