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.