How Well Do Surrogate Hosts Serve as Model Systems for Understanding Pathogenicity

Abstract

Experimental infection studies are of crucial importance to find and characterize virulence factors of pathogens or to identify novel compounds that can be used to treat the corresponding infections. The use of mammalian infection models including mice, rats, and guinea pigs is restricted due to several reasons including high costs, low statistical power, and ethical reservations. Simple, invertebrate models have been introduced as surrogate hosts as they are inexpensive, they can be used in great numbers, and doing experiments with them is not accompanied by ethical reservations. The soil nematode Caenorhabditis elegans and the fruit fly Drosophila melanogaster have served as the most important surrogate hosts. Both organisms have served as workhorses in various biomedical disciplines. They combine simple and cheap handling and housing with an enormous armamentarium of genetic tools available to the scientific community. As their innate immune systems share substantial similarities with our own one, human bacterial and fungal pathogens often also infect these surrogate hosts. Nevertheless, it has to be kept in mind that both hosts share some drawbacks such as the apparent lack of adaptive immunity or the inability to survive at 37 °C. The latter point is relevant for especially those pathogens that require higher temperatures to become pathogenically triggered, and thus it would be helpful to seek the introduction of alternative models that can be used under these conditions. The greater wax moth Galleria mellonella exactly fits into this gap although it lacks most of the benefits supplied by the “classical” model organisms.