The case continues to build that the parasite Toxoplasma gondii is
linked with some cases of schizophrenia.
In 2005 Alan Brown, M.D., an associate professor of clinical psychiatry and
clinical epidemiology at the New York State Psychiatric Institute, and
colleagues reported that serum antibodies taken from pregnant women 40 years
earlier suggested a link between the parasite and the development of
schizophrenia in their offspring (Psychiatric News, May 6, 2005).
And now Australian scientists have not only found that some young people
acquiring schizophrenia possessed antibodies to T. gondii, but that
such possession could be linked with the severity of their psychosis symptoms.
The lead scientist was G. Paul Amminger, M.D., an associate professor of child
and adolescent psychiatry at the University of Melbourne. Results appeared in
the May 15 Biological Psychiatry.
"This is an interesting study," Brown told Psychiatric
News. "A strength of the study is the fact that prodromal subjects
are included, suggesting that lifestyle factors that co-exist with
schizophrenia or other psychotic disorders don't explain the
Amminger and his coworkers studied 105 young adults (average age 19) who
were at very high risk of acquiring schizophrenia because of genetic risk plus
a decrease in functioning, attenuated psychotic symptoms, or limited
intermittent psychotic symptoms.
Subjects were evaluated for psychotic symptoms and their severity. Blood
samples were also taken from each subject and sent to the Stanley Laboratory
of Developmental Neurobiology in Baltimore to determine whether they contained
antibodies to various infectious agents such as herpes simplex virus type 1,
herpes simplex virus type 2, cytomegalovirus, Epstein-Barr virus, or the
T. gondii parasite.
Seventy-two percent of subjects tested positive for Epstein-Barr virus; 48
percent for cytomegalovirus, 42 percent for herpes simplex virus Type 1, 31
percent for herpes simplex virus Type 2, and 17 percent for T.
Amminger and his coworkers then evaluated whether there was a connection
between the severity of subjects' psychotic symptoms and having antibodies to
any of these infectious agents. The answer was yes only for T. gondii
and Epstein-Barr virus. Having antibodies to the parasite was significantly
associated with more severe psychotic symptoms, while testing positive for
Epstein-Barr antibodies was significantly associated with less severe
The reason why Epstein-Barr-positive subjects had less severe symptoms than
the other subjects is not clear, the scientists said. But they believe that
their findings add to the argument that T. gondii is implicated in
certain cases of schizophrenia.
The question then is when the parasitic infection is acquired. The
researchers believe that it is probably a pre-existing infection, perhaps
going back to the prenatal state. One reason is because of the research by
Brown and colleagues cited above. Another is because they could find a
significant link only between IgG antibodies to T. gondii and
psychotic symptoms, not between IgM antibodies to T. gondii and such
symptoms. Whereas an IgG antibody response may reflect either an active or
reactivated infection, an IgM antibody only mirrors a recent one.
Amminger and his group are now attempting to see whether they can replicate
their results in another cohort of subjects. They are also following their
current cohort to determine whether T. gondii infection is truly
involved in the transition from a pre-schizophrenia state to a full-blown case
of the disorder in certain very-high-risk individuals. If a causal link is
established, Amminger told Psychiatric News, then it would provide a
rationale to determine whether antimicrobial drugs effective against T.
gondii, such as trimethoprim-sulfamethoxazole or azithromycin, might be
able to keep subthreshold psychotic symptoms from developing into full-blown
The investigation was funded by the Stanley Medical Research Institute;
National Health and Medical Research Council in Canberra, Australia;
Janssen-Cilag, Australia; and the Karl-Hermann Spitzy Award by Bayer,
An abstract of "Antibodies to Infectious Agents in Individuals
at Ultra-High Risk for Psychosis" is posted at<www.journals.elsevierhealth.com/periodicals/bps/article/PIIS000632230601273x/ab...>.▪