Tick Bites Tick: A Rare Case of Hard-Tick Hyperparasitism
Sometimes, parasites get a little taste of their own medicine.
Last August, a tick specimen submitted to the Alaska Department of Fish and Game offered a surprising look at hyperparasitic behavior among the species Ixodes angustus. After examination under a scanning electron microscope (SEM), researchers shared their findings in a new report in the Journal of Medical Entomology.
The image above shows the hyperparasitism, caught in the act: A large, engorged female I. angustus tick, which had been removed from a squirrel, shown with its own hitchhiker, a male I. angustus attached to its underside in typical feeding mode—with his palps splayed outside of her exoskeleton and his feeding apparatus (hypostome and chelicerae) inserted.
Lance A. Durden, Ph.D., professor at Georgia Southern University and lead author on the report, says he had never seen such a case of hyperparasitism in hard ticks (family Ixodidae), though it is more common in soft ticks (family Argasidae). “Engorged soft ticks can be besieged by unfed individuals who opportunistically drive their mouthparts into the fed individual to steal part of the bloodmeal,” he says.
But that’s not all that is notable about the specimen. Also visible in the image is another scar (lower, left of center) that Durden and colleagues say was likely caused by another male tick feeding on the female in the same way. And—yes, there’s more—when the specimen was originally submitted, there was another male attached, mating with the female. (It fell off in the course of preparing the specimen for SEM imaging.)
Ixodes angustus is a nidicolous, or nest-dwelling, species, meaning it can progress through its entire life cycle within the nest or burrow of its host (e.g., mouse, vole, etc.), and males are rarely found on hosts. It has been presumed that mating typically occurs in the nest, but nine males of I. angustus have been collected on hosts in the course of the Alaska Department of Fish and Game’s tick survey since 2010, and nearly all had been found mating with females. Their findings suggest mating outside the nest and hyperparasitism in I. angustus may both be more common than previously thought.
“Male ticks that were infected with a pathogen or parasite—(such as Lyme disease spirochetes or Babesia protozoans—previously during their life cycle, by feeding on an infected host, could transmit these pathogens to female ticks during hyperparasitism. Female ticks could then transfer these pathogens or parasites to their progeny by transovarial transmission,” Durden says. “Although we don’t know yet if pathogen or parasite transmission occurs between I. angustus ticks by these mechanisms, if it does occur, this could have epidemiological significance by amplifying the number of infected ticks.”
Journal of Medical Entomology