Dogs Could Be Crucial to Saving U.S. Citrus Trees from Incurable Bacteria
Disease-sniffing canines are proving to be faster and more accurate than lab-testing methods.
Several years ago, a group of researchers started to consider the possibility that the fate of Florida's orange groves could rest on the small, furry shoulders of an almost-three-year-old dog named Mira. Well, that's not entirely accurate: the fate of all of those oranges was actually resting on her little wet nose.
Mira, a German Shepherd-Belgian Malinois mix, had been trained to sniff out Candidatus Liberibacter asiaticus, a bacteria that is deadly to citrus trees. Her nose proved to be more accurate than DNA-based testing—and she delivered her results by "alerting" at the base of the tree, which is a faster turnaround than what a human-staffed lab can deliver.
The USDA's Agricultural Research Service (ARS) department has continued to train dogs to detect the bacteria that causes huanglongbing, also known as citrus greening, in the hopes that early detection could help contain its spread. There is no cure for citrus greening, so identifying and removing infected trees is currently the only way to slow it down.
ARS recently published some of its findings in the Proceedings of National Academies of Science (PNAS). "This technology is thousands of years old—the dog’s nose," USDA researcher and study co-author Timothy Gottwald told the Associated Press. "We've just trained dogs to hunt new prey: the bacteria that causes a very damaging crop disease."
The 19 dogs that were chosen for the ARS study were given a brief acclimation period before receiving eight to 10 weeks of obedience and sensitization training, in which they learned how to recognize a specific odor and to alert their handlers when they detected it. (Yes, this is very similar to what bomb-sniffing dogs do.)
During practical tests with real trees, their results were surprisingly good: according to the USDA, the dogs had over 99-percent accuracy at detecting infected trees—and on the rare cases they gave a false positive result, the healthy tree was located where a diseased one had been placed during a previous test.
"We found that, once trained, these dogs were able to identify infected trees within two weeks of the trees being inoculated," Gottwald said. "The dogs also were able to distinguish the citrus greening pathogen from a variety of other citrus bacterial, viral, fungal, and spiroplasma pathogens, including closely related Liberibacter species." (That early detection part is crucial, because a tree can appear to be asymptomatic for months after being infected by the bacteria).
Citrus greening has been called "the world's most insidious citrus disease," and over the course of the past decade, it has caused Florida's orange production to decline by an astounding 70 percent. If a tree has been infected by the bacteria, it will bear small, bitter-tasting fruit—and the tree will ultimately die. The first U.S. cases of the disease were identified in Florida in 2005, and it has since spread to California, Georgia, Louisiana, and Texas.