The Infection Connection

Microbes that cause mental illness can also enter the body another way--on one's fork. In the mid-1990s, an outbreak of Creutzfeldt-Jakob disease struck fear into meat-eaters, especially in England, where 35 people died after eating infected beef. While alive, the victims of what was dubbed "mad cow disease" exhibited bizarre symptoms such as continual screaming, inappropriate laughter, failure to bathe and compulsive walking.

Scientists theorized that the "mad cows" became infected because they were fed on sheep afflicted with the disease known as scrapie, but a similar infection endemic to cows may be to blame. (Scrapie in sheep, bovine spongiform encephalitis in cows and Creutzfeldt-Jakob disease in humans are all believed to be caused by what's known as a prion, or infectious protein, which acts in a manner similar to a virus.) Contaminated human growth hormone, corneal transplants and surgical instruments have also been suspected of communicating the disease to humans. Earlier this year, the British medical journal The Lancet reported that multiple surgeries and living on a farm are risk factors for CJD. Though the disease is considered rare, Yale neuropathologist Laura Manueldis, M.D., who thinks that the causative agent is actually a small virus rather than a prion, suspects that CJD is more common than we believe, and is often misdiagnosed as Alzheimer's.

Why doesn't every child with a strep throat develop an anxiety disorder? Or dementia strike every adult with syphilis? Our bodies protect us from most invasions by unfriendly microbes, but the vulnerable-those with poor health, weakened immune systems or, perhaps, genetic susceptibility--are less equipped to fend off the viruses and bacteria that may eventually cause mental illness.

Continuing research is likely to bring more effective vaccines and antibiotics, but prevention and treatment will have to be every bit as shrewd as the infectious agents themselves, which spread and reproduce in seemingly countless ways. More worrisome is the fact that illness-causing organisms may be outwitting our antimicrobial strategies. With the development of antibiotics and antivirals, researchers had hoped to vanquish viruses and bacteria once and for all. But they underestimated the wily ingenuity of these microbes, which soon produced strains resistant to the new miracle medicines.

Likewise, scientists at one time believed that infectious agents evolved to become less potent, if only to ensure their own survival: the longer an infected host stays alive, after all, the greater the number of people who can be exposed to the pathogen, and the more likely the microbe is to reproduce itself. But recent research has turned up a less reassuring reality: under some conditions, microbes can flourish with increased virulence in crowded modern cities. These densely populated areas can maintain dangerous pathogens that otherwise might whip through a community and then have nowhere else to go.

To fight these pathogens successfully, doctors will have to tailor the treatments to the specific disease. Sometimes, for example, they may want to relieve an infected patient's fever and inflammation; at other times, fever must be left alone to kill off heat-sensitive viruses. Syphilis can be cured with penicillin, and doctors have had some success in prescribing antibiotics to people with anorexia. Other illnesses require more involved treatment, such as Swedo's plasma replacement for children with OCD, and some ailments cannot be helped much at all. The only way to treat HIV dementia, for example, is to try to slow the replication of the virus itself. No current therapy does this permanently, and many HIV-positive patients still suffer psychiatric symptoms. (In fact, suicide is a leading cause of death among the HIV-infected.) There's no treatment for Creutzfeldt-Jakob disease beyond palliative care, and by the time influenza-induced schizophrenia becomes apparent, the neurological damage is already done.