Epidemiologists have long known that socially connected individuals like friends,family,and co-workers, are more likely to transmit pathogens to each other.

But when an individual becomes obviously ill,their social connections become temporarily reduced:when we feel sick we tend to stay away from others.

And when we appear sick,others tend to stay away from us.

That distancing usually helps to slow down the spread of a pathogen.

But not all social relationships work the same way.

Parents of sick children will continue to care for those children at the risk of their own health.

And that devotion is true beyond humans.

Consider vampire bats.

They usually groom their own offspring as well as other bats.

And they share food.