Parasitic infection impairs spatial learning in mice

Abstract

Although parasite modification of host behaviour is well established, little is known about the effects of parasites on the spatial learning abilities of the host. The effects of an acute, sub-clinical infection with the naturally occurring, single host, enteric, protozoan parasite, Eimeria vermiformis, on spatial water-maze learning by male laboratory mice, Mus musculus, were examined. Individual mice had to learn the spatial location of a submerged hidden platform using extra-maze visual cues. Determinations of spatial acquisition were made with different groups of mice on days 4 (pre-nfective), 7 (onset of infectivity or patency) and 10 (infective) post-infection. Task retention was examined in a probe trial 1 day later. The infected mice displayed significantly poorer acquisition and retention of the water-maze task over 1 day of testing (six blocks of four trials) than either sham-infected or control mice, with mice at days 4 and 7 post-infection displaying significantly poorer spatial performance than mice on day 10 post-infection. This attenuation of spatial learning occurred in the absence of either any symptoms of malaise or illness, or any evident motor, visual and motivational impairments. These parasitic-infection-induced decreases in spatial learning are likely to arise as side-effects of the immunological and neuromodulatory responses of the host and may be considered as a fitness cost associated with response to infection.