playing 'possum, for the better

playing 'possum, for the better

The rabies virus is particularly insidious.  Many potentially lethal viruses appear to become less virulent, less rapidly lethal, as they spread through a population of victims.  Or perhaps it is more correct to say that variants that do not immediately kill victims become more prevalent.  Many deadly viruses require close, social contact for transmission from the infected host to another victim.  If the original host dies too quickly, before interacting closely with others, the virus dies with it.  No transmission and no survival of the viral species.  Rabies has not had to weaken itself at all because it forces its victims to actively seek out and actively infect additional hosts, actively turns new victims.  Therefore the former host can die relatively quickly and still complete its deadly mission.  The rabies virus uses the propensity of all mammals to bite to secure its own survival! 

But, biting comes in several varieties, with differing intents.  Biting can be aggressive and predatory used to kill a victim for food.  It can also rend foodstuffs in order to make them small enough to swallow.  And then there’s defensive biting used to damage and drive away foes and predators.  Finally there’s biting, nipping, that is at the height of emotional pleasure.  Our search involves the latter two forms.

The behaviors expressed as furious rabies make it clear that the rabies receptor is in a position within neuronal circuits to control rage and other emotional outburst behaviors.  The level of expression of this receptor in various people and various mammalian species may help explain their personalities.  And with tools to modulate its activity we can help those who find it nearly impossible to avoid the negative consequences of rage.  In this regard, I find it interesting that the opossum is known to be much less susceptible to rabies infection than other mammals.  Opossums do exhibit defensive rage, hissing and baring their teeth, but this is relatively short-lived, and when push comes to shove they quickly “play possum”.  That is, they play dead rather than attacking and biting their foe.  The opossum’s behavior is particularly amazing because the opossum is an omnivore, that is, it kills and eats other animals (although it tends to prefer carrion) as a routine part of its diet.  Clearly, aggressive, predatory behavior is not lacking in opossums, it’s only defensive rage that appears cut short. 

Is it possible that opossums express less of the receptor that rabies needs, that our brains need, to express rage behavior?   It will be very interesting to determine whether the rabies receptor protein is expressed at lower levels in opossums.  More speculation, but another testable hypothesis, at least once we identify the rabies receptor.