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Dogs can be trained to detect more than 90 percent of Covid-19 infections even when patients are asymptomatic, according to research published Monday, which authors hope could help replace the need to quarantine new arrivals.
Using their remarkable sense of smell -- which can pick up the equivalent of half a teaspoon of sugar in an olympic-sized swimming pool -- dogs have already shown that they can sniff out maladies such as cancer, malaria and epilepsy.
Several previous studies have shown proof-of-concept that dogs can detect SARS-CoV-2. Researchers from the London School of Tropical Medicine wanted to see if dogs could detect a distinctive odour given off from chemical compounds associated with someone who is Covid positive but doesn't show symptoms.
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They gathered samples of clothing and face masks from people who had tested positive for mild or symptomatic SARS-CoV-2.
Samples of the socks of 200 Covid-19 cases were collected and arranged in lab tests for six dogs that had been trained to indicate either a presence or absence of the chemical compound.
The dogs needed to be trained not to identify "false positives" in a bid to hack their reward system and obtain treats even if there were no Covid-19 samples in a given test.
"This means that the dog fully understands and gets a reward for a correct negative as well as a correct positive," said Claire Guest, from the school's Faculty of Infectious and Tropical Diseases.
Overall, the dogs were successfully able to identify between 94 and 82 percent of SARS-CoV-2 samples.
The researchers then modelled how effectively these success rates, combined with traditional PCR tests, could help detect mild or asymptomatic Covid-19 cases.
They found that using dogs to screen arrivals at terminuses such as airports could detect 91 percent of cases, resulting in a 2.24 times lower rate of transmission than with PCR tests alone.
Authors of the research, which has yet to be peer-reviewed, said they hoped it could eventually replace the need for travellers to quarantine -- which necessarily disrupts every arrival even though the vast majority are not Covid positive.
"The key thing is that dogs are significantly quicker than other tests," said co-author James Logan.
"What we're suggesting is that dogs would give the first initial screening, and then those (arrivals) that were indicated as positive would then receive a complimentary PCR test."
The team said that out of a plane full of arrivals -- around 300 people -- less than one percent were statistically likely to be carrying SARS-CoV-2.
Under current quarantine regulations employed by some countries, all 300 would need to isolate, causing significant inconvenience.
But given the sensitivity of trained dogs, a maximum of 35 people on board would be indicated as positive, the paper said.
Of these, only around 3 would be expected to return a positive PCR test. "This is a really important start and could lead to a useful, usable system," said Mick Bailey, professor of Comparative Immunology at the University of Bristol, who was not involved in the research.
"But there's a lot more validation needs to be done before we could be confident that the dogs can reliably and specifically detect asymptomatic SARS-CoV-2 infection in people in airports and train stations."