TOXOPLASMA INFECTION AND BEHAVIOURAL CHANGES–ANIMAL MODEL
Toxoplasma infection is prevalent amongst rodents, but, as in humans, acute
postnatal infection seems to be an infrequent cause of morbidity or
mortality. However, long standing Toxoplasma infection has recently been
associated with significant alterations in rodent behaviour. In mice, long
standing Toxoplasma infection is associated with increased movement,
particularly short bout behavioural pattern. Movement is increased
with inhibition of the normal progression of exploratory behaviour.
Amongst rats, natural or laboratory induced Toxoplasma infection is associated
with a reduction in neophobic behaviour and enhanced susceptibility to
entrapment. Other parasitic infections of rats have no demonstrable effect
on behaviour.
Putative mechanisms by which Toxoplasma infection may lead to altered
behavioral patterns include release of metabolic products from intracerebral
cysts, direct effect of cysts on central nervous tissue and alteration in brain
concentrations of neurochemicals such as homovanillic acid and dopamine. It is
proposed that Toxoplasma infection leads to a reduction in the ability of the
infected mouse to learn with shortened attention span, resulting in increased
but ineffective movement when attempting familiarization with the
environment. Amongst the rat population, toxoplasma infection may cause
diminished fear of novel stimuli. In both species this altered behaviour
is associated with an increased propensity to feline predation, favoring the
secondary host to primary host transmission of Toxolasma gondii.
The established association between Toxoplasma infection and altered rodent
behaviour suggests that long standing infection in humans should be carefully
assessed for previously unrecognized sequelae.