Host–Symbiont Relationships: Understanding the Change from Guest to Pest

Abstract

The several meanings for the term "symbiosis" create confusion, which can be avoided when the author provides details of the interrelationships between the symbiotic organism and the "host" so that a reader can clearly understand what definition is implied in each case. For example, we, as opposed to many other mentioned readers, consider a symbiont as an organism living in an association with another regardless of whether it causes a pathologic response or not, but from our title, the reader may incorrectly infer that we consider a parasite to be different from a symbiont. A symbiont is an organism that uses another organism as a habitat. This chapter discusses the primary associations and associated conflicts involving the terminology. It also provides both differentiation between and conflicting views regarding the interpretation of the terms "infect" and "infest," "infection" and "disease," and other terms. Many seemingly harmless symbionts of a wide array of taxonomic groups are triggered to become pathogenic or virulent, and we provide several examples of the provoking (stimulating) triggers, with the understanding that in most cases, the conditions for the triggered activities are much more complex and complicated than presented. Examples of triggers follow: environmental ones like temperature, toxic chemicals (dose), chemotherapeutics, dietary changes, and geographic habits; internal ones like host site, host resistance or susceptibility, and host modifications; and combinations of these and other conditions. We provide examples involving multiple triggers for organisms associated with termites, for an endemic virus being affected by multiple factors and having multiple effects on its commercial penaeid shrimp hosts, and for contrasting variables associated with two exotic viruses in wild and cultured commercial penaeid shrimps with an emphasis on hypothesizing how the pathogenicity developed in these two viruses. The chapter ends by trying to answer the question of why would a symbiont become pathogenic in some hosts and not in others from an evolutionary perspective. It uses two hypotheses to explain the increased virulence.

Virulence of Melissococcus plutonius and secondary invaders associated with European foulbrood disease of the honey bee

“…faecalis treatment, no differences for larval mortality or weight were observed for the different infection treatments. Similar to virulence of M. plutonius there might also be strain specificity in the secondary invaders like P. alvei and E. faecalis and they may even originate from the larval gut microbiota (commensals) (Overstreet & Lotz, 2016). So far, we have no conclusive explanation for the different outcome of both infection studies (Giersch et al, 2010;present For artificial infections, the quality of the larval food (batch of royal jelly) seems to be of high importance for infection success (Giersch et al, 2010).…”

“…Although, during the current study there was an EFB‐typical foul smell perceptible in diseased larvae of the M. plutonius / P. alvei treatment as well as in M. plutonius / E. faecalis treatment, no differences for larval mortality or weight were observed for the different infection treatments. Similar to virulence of M. plutonius there might also be strain specificity in the secondary invaders like P. alvei and E. faecalis and they may even originate from the larval gut microbiota (commensals) (Overstreet & Lotz, ). So far, we have no conclusive explanation for the different outcome of both infection studies (Giersch et al., ; present study), except for the bacterial strains and host genetic background.…”

A community perspective on the concept of marine holobionts: state-of-the-art, challenges, and future directions

“…Dysbiotic individuals frequently display higher variability in their microbial community composition than healthy individuals, an observation in line with the "Anna Karenina principle" (Zaneveld et al 2017), although there are exceptions to this rule (e.g., Marzinelli et al 2015). A specific case of dysbiosis is the so-called "Rasputin effect" when benign endosymbionts opportunistically become detrimental to the host due to processes such as reduction in immune response under food deprivation, coinfections, or environmental pressure (Overstreet and Lotz 2016). Many diseases are now interpreted as the result of a microbial imbalance and the rise of opportunistic or polymicrobial infections upon host stress (Egan and Gardiner 2016).…”

Diseases and Mortalities of Fishes and Other Animals in The Gulf of Mexico

“…Because penaeids are cultured commercially worldwide, considerable data on shrimp health have been published (e.g., Overstreet 1973Overstreet , 1983cOverstreet , 1987Lightner 1996;Sindermann and Lightner 1988;Lotz and Overstreet 1990;Overstreet and Lotz 2016). For purposes of this chapter, we will discuss select ciliates, microsporidians, and viruses as examples of pathogenic organisms.…”

“…Lightner (2011) provided a mini-review of all the viruses in the Americas, and Lightner et al (2012) reviewed the history of all shrimp pathogens in the Americas (Figure 14.82). The first known virus, Baculovirus penaei, occurs in the natural environment (Overstreet 1994;Overstreet and Lotz 2016) and provides a good contrast to the introduced viruses. Overstreet and Lotz (2016) indicated how both B. penaei and the viruses introduced into the Gulf can revert from being relatively harmless to the shrimp population to becoming highly pathogenic.…”