Dalhousie Biologist Shelley Adamo and her team have discovered that one of the most unique sexually transmitted diseases nature has to offer is more disturbing than previously thought.
The virus, IIV-6/CRIV, infects and transmits through cold-blooded organisms and was first identified in crickets over a decade ago. It’s been well established that the disease castrated crickets. But Dr. Adamo and her team have identified a new, unexpected behavioural element to the virus: it makes them want to have more sex, despite being sterile.
Her findings, published in the Journal of Experimental Biology, generated international headlines this month, mentioned in publications ranging from National Geographic to The Week.
“I was working on stress responses in crickets when I found the virus,” explains Dr. Adamo, professor in both the Department of Psychology and Neuroscience and the Department of Biology. She had brought in reptiles — bearded dragons, in particular — to serve as predators for the study, and it soon turned out they were carriers of IIV-6/CRIV.
“At first I didn’t notice anything different because [the crickets’] behaviour was absolutely normal. Usually you notice quickly if the crickets are infected: infected crickets don’t move around very much; they certainly don’t mate, and they don’t eat. However, these crickets looked and acted perfectly normal. The only reason I found out was because the females stopped laying eggs. By the time I noticed, the virus had infected the entire population.”
After examining infected crickets housed in her laboratory, Dr. Adamo and her team noticed the virus not only rendered the crickets sterile but also changed their behaviour: they continued to mate with each other when infected, and infected males courted females more quickly.
While the team is not yet certain exactly how the virus works, it appears to affect communication between the immune and nervous systems. By preventing typical illness responses (loss of appetite, decline in desire to mate), the virus makes the cricket more likely to mate, and therefore to spread the virus. In some cases, the virus did not require the crickets to have sex and was transferred during courtship rituals.
“What is happening is not unusual for many parasitic organisms,” explains Dr. Adamo. “A parasite wants to hijack the host and get as much energy as it can without killing the host. If the host dies, the parasite dies and cannot reproduce. For many of them, including this virus, the organ system that can be removed without killing the host is the reproductive system.
“Now all that energy that is usually used by the host for reproduction can be used by the parasite to help make more viruses. How the virus causes the shift in behaviour is interesting in a sick, fascinating way.”
The team believes the virus, a parasitic manipulator, may yield interesting applications through further research.
“If I were to follow up with this I would look into how sickness behaviour is shut off,” says Dr. Adamo. “That is an issue that goes much deeper than crickets and could have broader impact. Sexually transmitted infections run the gamut of pathogens, from viruses to bacteria, and if studied further this issue we might find common pathways they use to suppress sickness behaviour.”
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