Virus may trigger some mood disorders.

A virus known to cause behavior disruptions and neurological disease in several animal species may also infect humans, scientists now report. In people, the virus may help elicit some cases of major depression and other severe mood disorders.

The alleged culprit, Borna disease virus (BDV), was first reported more than 100 years ago to cause a neurological disease of horses in Borna, Germany. Since then, outbreaks of the same viral disease have been documented in sheep, cattle, and cats.

"The presence of [BDV] markers seems to coincide with acute episodes of mood disorders," write Liv Bode, a virologist at the Robert Koch Institute in Berlin, and her colleagues in the March Nature Medicine. "The markers disappear during recovery or at least during a significant decrease of symptoms, thus pointing to a new human virus infection possibly threatening mental health."

Rats injected with BDV suffer damage to brain cells in the limbic system, a set of structures that in humans is implicated in mood disorders. In previous work inspired by these findings, the German team found a higher concentration of antibodies specific to BDV in blood samples from patients hospitalized for major depression or related disorders than in blood from healthy people.

In addition, Bode's group reported, antigens that spark the release of BDV antibodies appear more often in the blood cells of people with mood disorders.

In their new report, the German investigators cite evidence of BDV genetic material in the blood cells of four patients hospitalized for major depression, organic mood disorder, or obsessive-compulsive disorder. BDV antigens had already been identified in these individuals during 6 weeks of hospitalization.

About 5 percent of the BDV genome isolated from each participant's blood was compared to the corresponding chemical sequences of BDV genetic material taken originally from infected horses and maintained in human cells. The analysis yielded nearly perfect genetic matches.

In the two patients with chronic disorders, BDV-specific antigens and genetic material appeared both in an initial test and at a follow-up 7 1/2 months later. The other two patients, hospitalized shortly after becoming ill, were tested on several occasions and displayed both of these molecular markers only when their psychiatric symptoms flared up.

Neither of these molecular markers for the virus appeared in two additional patients, one diagnosed with depression and the other with panic disorder, who had been hospitalized for only 1 to 2 weeks. Several weeks later, however, BDV antigens showed up in both individuals, the researchers point out.

More work is needed to isolate the offending virus itself in people with depression and other psychiatric disorders, Bode's group adds.