Flu season is almost upon us, so millions of us are already rolling up our sleeves to get the annual shot. This jab is formulated to introduce our immune system to this year's circulating strains of the virus so that it will remember how to make the specialized antibodies to fend it off the viral particles it might encounter later. Octopuses, as far as we know, don't get the flu. But if they did, they would be out of luck. Because vaccinations are useless for cephalopods; they lack the acquired immunity we depend on for many of our preventive medical treatments.

And it's not like they're living in a germ-free world. "Wild and reared cephalopods are affected by a wide variety of pathogens," wrote the researchers of a paper in the special "Cephalopod Biology" issue of the Journal of Experimental Marine Biology and Ecology this month. Bacterial infections, skin ulcers, protozoa and parasites are all known to cause harm to cephalopods. Even small crustaceans are known to become macro-parasites, inhabiting these animals' mantel, skin and gills.

This presents a challenge—and not only in the wild. With octopus aquaculture just getting off the ground and a directive in the European Union that scientists reduce the use of wild-caught animals in research, we will likely need a way to protect against damaging infections among their stock, in much the way that we vaccinate cows, pigs and other animals raised in large operations. In close confines, an affliction could spread rapidly through an octopus population—even if all they share is a water supply—with no way of vaccinating against it. "One of the disadvantages of acquaculture is the increase in the incidence of pathologies produced by bacteria and/or transmissible parasites that could be a serious risk for the production," the authors of the paper noted. Other factors in artificial environments, such as low salinity, seem to further reduce octopuses' immune response to pathogens.

Researchers still know relatively little about these ailments, and much of the study of octopus infections (including papers upon papers dedicated to parasites that live specifically in octopus kidneys) has been with an eye toward taxonomy rather than pathology. Additionally, "current diagnostic techniques are rather limited," the researchers noted. So we're largely still in the dark about these short-lived animals' common afflictions.

The octopus's immune system—what it has of one—relies on innate capabilities alone, limiting its attacks to things that product the signatures of infection. But scientists are still searching for details about how it works: what genes it engages and how it battles recurrent invaders it cannot build lasting immunity against. To that end, the researchers call for an effort to sequence the genomes of these animals to better understand how the immune system responds to various attacks.

In the meantime, better hope those octos stay healthy. Because even our cleverest vaccines wouldn't be able to help these cephalopods.

Illustration courtesy of Ivan Phillipsen