The idea that mental disorders could be due to infection is not new, but remains surprisingly difficult to accept. Just as what was once called “general paresis” ultimately was shown to be caused by syphilis and curable with antibiotics, some cases of sudden onset pediatric obsessive compulsive disorder are traceable to strep and respond to immune-based treatments. A proposed broader syndrome would include those with similar symptom but no clear link to strep.

Autism is always surprising. What was once considered a rare disorder is now reported as affecting 1 in 88 children, 1 in 54 boys. Do these new numbers, up 78 percent from 2002 and 23 percent from 2006, reflect a growing problem—an epidemic—or an improvement in our ability to diagnose and serve those affected?

Autism-like behaviors in mice have been reduced, using an experimental agent being tested in patients for a related disorder.