Tailed biosensors
Ferrets sniffed bird flu in duck droppings
Sergey Kolenov, N+1
As noted in the article for the journal PLoS One, the use of trained ferrets will allow controlling the spread of non-pathogenic variants of the virus, which do not cause clinical symptoms in carriers and escape the attention of specialists, but can mutate into more dangerous forms at any moment.
Outbreaks of avian influenza cause serious damage to agriculture, leading to the death of millions of poultry in factories and farms around the world. The damage from them is estimated at billions of US dollars. Moreover, some strains of this disease are transmitted to humans and can potentially cause new pandemics. It is not surprising that scientists are looking for a way to identify infected individuals as early as possible. However, it is sometimes not easy to do this. The fact is that sometimes domestic birds are infected from wild relatives or from each other with low-pathogenic variants of the virus that do not cause clinical symptoms in them and therefore are not diagnosed by specialists. Only after some time the causative agent of the infection mutates into a highly pathogenic form that kills its carriers.
A team of researchers led by Glen J. Golden from The University of Colorado proposed to identify birds infected with low-pathogenic strains of influenza by smell. As experts have long known, infections and parasites change the smell of the host, affecting the composition of volatile substances released by it – and the noses of some mammals are sensitive enough to notice this. For example, mandrills (Mandrillus sphinx), large primates from the forests of Central Africa, use the sense of smell to identify relatives who suffer from intestinal parasites. And dogs can be trained to sniff out malaria, covid and other diseases in humans.
Since the training and maintenance of dogs capable of diagnosing diseases by smell is quite expensive, to test their idea, Golden and his co–authors focused on another species - the domestic ferret (Mustela putorius furo). Previously, these small predators have already demonstrated that they have an excellent sense of smell and are able to inform a person about the presence of the desired smell by scratching the surface near its source with their claws.
At the first stage, the researchers divided sixty healthy ducks of different sexes into four groups and injected three of them with different concentrations of H6 influenza viruses (these individuals made up the first cohort). The droppings of all birds were collected every few days for two weeks and stored in the freezer before the tests began. In addition, the blood of experimental ducks was analyzed for the presence of viral RNA to make sure that individuals from the experimental groups really got sick. Birds from three other small groups (the second cohort) were infected with influenza type H5, as well as two other viral diseases: Newcastle disease and infectious laryngotracheitis.
Then Golden and his co-authors selected six sterilized male ferrets over fifteen weeks old and taught them to find the litter of infected ducks from the first cohort, which included sixty individuals. To do this, each animal was placed in front of the installation with five boxes, each of which contained a glass container containing duck droppings. In order for the ferrets to smell the bird secretions, the lids of the containers were made of filter paper. In one of the five containers (the instructor who worked with the animals did not know which one) there was a litter of a duck infected with a low-pathogenic strain of avian influenza, and the rest were filled with the excrement of healthy individuals. If a ferret showed interest in a box with the droppings of an infected bird and scratched its surface, he was rewarded with a treat.
After a few days, the ferrets learned to sniff out bird flu with high accuracy, the researchers moved on to the next stage. At first, the specialists reproduced the same tests as during training. Ferrets coped with this task with an average accuracy of seventy-three (in experiments without remuneration) to ninety-nine percent (in experiments with remuneration). Similar results were obtained when repeating the experiment using droppings collected on different days. When experimental animals were provided with five containers, two of which contained the droppings of two different infected ducks, they also almost always made the right choice (its accuracy ranged from ninety-six to one hundred percent). Ferrets continued to find almost unmistakably the secretions of flu-infected birds even after adding to the sample a litter of ducks from the second cohort, with the smell of which they were not yet familiar, as well as ducks infected with Newcastle disease and infectious laryngotracheitis.
According to Golden and his colleagues, in general, the accuracy of the diagnosis of low-pathogenic avian influenza with the help of ferrets exceeded ninety percent. The animals not only detected the droppings of ducks infected with this virus, but also distinguished it from the secretions of birds suffering from other viral diseases. Apparently, this is due to the fact that each disease corresponds to specific volatile substances released by its carrier, which ferrets smell. For comparison, mice whose abilities were tested in previous studies coped with a similar task a little worse: the accuracy of their choice was eighty to ninety percent.
The results of the work clearly demonstrate that mammals are perfectly suited for the role of avian influenza biodetectors. For example, ferrets living in the laboratory can be used to test for the presence of this virus samples of the droppings of domestic and wild birds. And if dogs are trained in a similar way, then the spread of influenza will be able to be tracked directly in the wild – by the secretions of wild near-water birds, which serve as its natural reservoir.
New Zealand scientists used the keen nose of ferrets and cats against them. A month before the breeding of three rare species of waders, bird-scented tags were placed in their nesting sites on the Southern Island of the archipelago. The smell attracted the interest of imported ferrets and stray cats – however, not finding the desired eggs and chicks, they associated it with the lack of food and gradually stopped visiting the treated areas. As a result, the survival rate of waders' clutches increased by 1.7 times.
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