Viruses occasionally contend with parasites resembling sponges. These so-called cheats could be more prevalent and significant than previously recognized by biologists. In influenza cases, such viruses can outnumber typical ones in almost a third of instances, potentially lessening the infection’s severity.

The virus compels infected cells to reproduce copies of itself. While they leverage the cell’s existing machinery, several proteins specified by the viral genome are crucial for this process.

However, mutations may eliminate the viral genes responsible for these critical proteins, leading to defective viruses that can invade cells but fail to replicate. A different virus might also infect the same cell, supplying the missing protein or proteins.

The cells combine both viral copies. In fact, they may produce more defective or incomplete viruses since these have a reduced genome size. Consequently, these less complete viruses equate to a virus that avoids paying its share at a pub, thereby slowing the infection process.

The existence of these deceptive interfering viruses, often referred to as defective interfering viruses, was confirmed back in 1970 by Usher Leak at the University of British Columbia, Canada. “But this raises an important question: Are they fundamentally significant?”

His team is striving to answer this query. Previous studies have shown that these fraudulent viruses exist in nature, but their prevalence remains uncertain, as establishing this requires sequencing numerous viruses from infected individuals. Given the risks associated with H5N1 avian influenza, the USDA is currently sequencing for different purposes, and the raw data has become publicly accessible.

The dataset comprises various influenza species, states Leeks. “We’ve got ostriches, cattle, cows, poultry, waterfowl, and raptors.”

Based on preliminary estimates from USDA sequencing, which are not yet published, his team’s findings indicate a notable prevalence of these con artist viruses. “Roughly one in three infected individuals carries at least one viral cheat sequence. This implies that during influenza infections, about one-third of the time, these non-functional viruses dominate the population.”

“Their presence is not unexpected,” he states. “It’s remarkable how abundant they are, and intriguing that they are found across various host species and influenza subtypes.”

Evidence suggests that high levels of con artist viruses diminish infection severity, so their presence could serve as a predictor for disease severity.

Other researchers are exploring whether these fraudulent viruses could potentially be utilized to treat infectious diseases. In fact, human trials are set to begin soon for HIV, following successful outcomes in monkeys.

“I don’t design therapeutics, but our findings aim to provide insights regarding their safety and efficacy,” remarks Leeks.

Raphael Saint-Juan from the University of Valencia in Spain notes that specific findings cannot be discussed until complete results are available. However, there is generally a possibility of application to influenza, as opposed to other viruses.

“Some viruses tend to generate more ‘con artists’ than others,” states Sanjuan. “Influenza viruses, in particular, are known to be extremely prolific in this regard.”