(CN) — In a discovery that may help scientists pinpoint treatments for coronavirus, researchers revealed Thursday that pangolins — the scaled anteater-like mammals pegged as a potential transmitter of Covid-19 — lack the virus-detecting genes that act as an alarm when an intruder enters their body.
In a study published Thursday in the journal Frontiers in Immunology, researchers analyzed the genome sequence of pangolins and compared with those of other mammals including humans, cats, dogs and cattle.
They found even though pangolins lack two virus-detecting genes — interferon-induced with helicase C domain 1 (IFIH1) and Z-DNA-binding protein (ZBP1) — they appear able to tolerate coronavirus through some other unknown evolutionary mechanism.
Scientists hypothesized the loss of IFIH1 and ZBP1 are evolutionary advantages that reduce inflammation-induced damage to host tissues and contributed to a switch from resistance to tolerance of viral infections in pangolins.
The study identified the genetic differences between pangolins and other mammals but did not probe how those differences affect antiviral response. Scientists don’t yet understand why pangolins survive coronavirus but believe the lack of the two signaling genes may have something to do with it.
Pangolins, along with bats, have been zeroed in on as the possible agents of infection that caused the interspecies jump responsible for the current Covid-19 pandemic.
Scientists have also pinpointed stray dogs roaming the wet markets of the Wuhan province of China, where Covid-19 is believed to have originated, as an intermediary host for the disease.
Mounting research warns human activity that causes environmental changes or ecological disturbances — including agriculture and human settlement — contribute to the increase in zoonotic diseases.
The United Nations Environmental Program estimates 75% of “emerging” diseases such as Ebola, HIV, avian flu, Zika and Sars – another type of coronavirus – originate from animals.
But while pangolins may also have spread Covid-19 to humans, they may also be the answer to learning how to treat the disease.
"Our work shows that pangolins have survived through millions of years of evolution without a type of antiviral defense that is used by all other mammals,” co-author Dr. Leopold Eckhart, of the Medical University of Vienna in Austria, said in a statement.
"Further studies of pangolins will uncover how they manage to survive viral infections, and this might help to devise new treatment strategies for people with viral infections."
Unlike the exotic animals unaffected by coronavirus, when humans are infected, they experience an inflammatory immune response called a cytokine storm that worsens outcomes.
The authors of the study found pharmaceutical suppression of gene signaling — the cellular response which involves a change in gene expression — could be a possible treatment for severe cases of Covid-19, but Eckhart said the strategy could cause secondary infections.
"The main challenge is to reduce the response to the pathogen while maintaining sufficient control of the virus," Eckhart said.
An overactivated immune system can be moderated "by reducing the intensity or by changing the timing of the defense reaction,” he added.
Eckhart said RIG-I, which also acts as a virus detector, should also be studied to determine if it can defend against coronaviruses.
Researchers last month hypothesized overactive white blood cells called neutrophils could be the culprit behind the most severe cases of Covid-19.
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