Influence of mouse strain, infective dose and larval burden in the brain on activity in Toxocara-infected mice

Outbred LACA mice and inbred NIH mice were administered low (100 ova), medi um (1000 ova), high (3000 ova) and trickle (4 x 250 ova) doses of Toxocara canis ova and the effect of infection on activity was examined with respect to: (i) the dose of ova administered and (ii) the number of larvae recover ed from the brain. Larval recovery from the brain was significantly reduced in NIH mice compared to LACA mice for the 1000, 3000 and trickle doses. Mi ce from each strain were divided into larval intensity groupings based upon the number of larvae recovered from their brain. Activity for each mouse w as measured pre- and post-infection by observing its behaviour in the home cage. Activity was assessed by monitoring six different independent categor ies of murine behaviour - ambulation, grooming, rearing, digging, climbing and immobility. Within each behavioural category, the duration of time spen t at each behaviour per mouse within one thousandth of a second, the number of short bouts performed and the number of long bouts of behaviour perform ed were recorded over a 20 min period. Activity of LACA and NIH mice differ ed prior to infection. LACA mice spent more time immobile compared to NIH m ice, which ambulated and climbed more. Variations in activity were also obs erved between groups of mice prior to infection. The effect of infection di ffered by strain, by dose and by larval intensity. Post-infection LACA mice became more immobile and ambulated less. NIH mice showed reduced immobilit y, but while ambulation decreased digging and climbing increased post-infec tion. Short bouts of activity remained unchanged among LACA mice post-infec tion but showed an increase for some behaviours in NIH mice.