Needles and mosquitoes have more in common than just poking people; they can both transmit infectious diseases, serving as a reservoir external to human hosts.
That similarity is at the core of a new mathematical model developed by Brown University researchers that considers the spread of hepatitis C (HCV) through an indirect means, the needle/syringe, instead of a direct one, like person-to-person contact. For the scientists, this analysis highlights the importance of implementing existing harm reduction policies, like syringe exchanges and safe consumption spaces—but also of innovating new tools that for now are only being imagined.
By rendering “a picture of the different knobs and levers that determine” HCV transmission amongst people who inject drugs (PWID), Brandon Ogbunu, a Brown professor and the study’s senior author, believes that it will “give us a different lens on interventions and prevention measures.”
Specifically, the disease-prevention measures with the most “potential utility,” as the study authors wrote, are not those that “indiscriminately [remove] injection equipment from a system” (like the prosecutors who still throw the book at syringe exchange participants), but instead those that “[steer] the population of needles towards being more uninfected.”
Ogbunu and his colleagues see syringe service programs and safe consumption spaces as “ideal intervention efforts” to make any scarcity of sterile injection equipment obsolete. Tracing the flow of equipment in drug-user communities, the researchers find these interventions particularly useful since “they do not change the number of infected needles in the system directly, but can alter the sharing rate, and consequently, the probability of sharing an infected needle.”
By thinking about needles as mosquitoes, Ogbunu believes that the very viability of a syringe or needle as a means for the transmission of HCV must not be taken for granted. In the case of the blood-sucking pests, scientists have been able to genetically engineer mosquitoes so that they can’t spread malaria.
Could technology apply that principle to syringes?
As yet, the idea of an HCV-resistant needle or syringe has not been turned into reality. One speculated way to reduce HCV retention in the rig is to limit “dead space”—the space in a syringe in which infected liquid may remain after it has been used for an injection.
This idea came from the need to address the risks posed by a particular arrangement of injection equipment. People who inject drugs often prefer syringes with detachable needles, so they can filter drug mixtures into the syringe and replace a needle that is dulled or clogged. But these systems have been shown to retain more HCV than fixed syringe-needles, like those used for insulin injections. Unfortunately, syringes with detachable needles that reduced dead space were shown in a 2015 study to have insignificant benefits.
Ogbunu is hopeful, however, that his needles-as-mosquitoes model, in pointing toward mitigation rather than eradication, can help “spark creative ideas” to address the spread of a harmful virus.