Experimental Rat Models in Induced Parasitic Infection: Inoculation Routes, Immune System Responses, and Seasonal Influences: A Review

Abstract

Experimental parasitology in laboratory rats has a long tradition, owing to the physiological proximity of the rat to humans and to the ease with which infection can be established under laboratory conditions. This review draws on work carried out over the past several decades and brings together three themes that the literature usually treats in isolation, although in practice they are deeply intertwined: the routes by which a parasite is introduced into the animal host; the immune mechanisms, early and late, that follow, comprising the rapid innate responses and the slower but more specific adaptive responses they instruct; and the influence that ambient temperature and seasonal variation exert on the strength and the direction of those responses. The parasites considered include Toxoplasma gondii, Leishmania species, Cryptosporidium parvum, Schistosoma japonicum, Fasciola hepatica, Strongyloidesratti and Echinococcus granulosus. A theme common to these organisms is that the mode of delivery, and therefore the anatomical setting of the first immunological encounter, can alter the character of the reaction: from a predominantly cellular to a predominantly humoral response, and from an acutely inflammatory to a more regulatory profile. The evidence likewise indicates a substantial seasonal variation in immune parameters, demonstrated experimentally in the published literature yet seldom reported in primary studies. The review closes with a call for greater attention to standardization, and to the explicit documentation of environmental conditions, in parasitological research that uses the rat as a model.