Elevated water temperature increases the levels of reo-like virus and selected innate immunity genes in hemocytes and hepatopancreas of adult female blue crab, Callinectes sapidus

Abstract

Seasonal changes in water temperature directly affect the aquatic ecosystem. The blue crab, Callinectes sapidus, inhabiting the Chesapeake Bay has been adapted to seasonal changes of the environmental conditions. In this, the animals halt their physiological process of the growth and reproduction during colder months while they resume these processes as water temperatures increase. We aimed to understand the effect of the elevated temperatures on a disease progression of reo-like virus (CsRLV) and innate immunity of adult female C. sapidus. Following a rise in water temperature from 10 to 23 °C, CsRLV levels in infected crabs rose significantly in hemocytes and multiple organs. However, in hemocytes, the elevated temperature had no effect on the levels of three innate immune genes: Cas-ecCuZnSOD-2, CasPPO and CasLpR three carbohydrate metabolic genes: CasTPS, CasGlyP; and CasTreh and the total hemocyte counts (THC). Interestingly, the hemocytes of CsRLV infected animals exposed to 23 °C for 10 days had significantly elevated levels of Cas-ecCuZnSOD-2 and CasTPS, compared to those of the uninfected ones also exposed to the same condition and compared to hatchery-raised females kept at 23 °C. Despite the lack of changes in THC, the types of hemocytes from the animals with high CsRLV levels differed from those of uninfected ones and from hatchery animals kept at 23 °C: CsRLV-infected crabs had hemocytes of smaller size with less cytosolic complexity than uninfected crabs. It therefore appears that the change in temperature influences rapid replication of CsRLV in all internal tissues examined. This implies that CsRLV may have broad tissue tropism. Interestingly, the digestive tract (mid- and hindgut) contains significantly higher levels of CsRLV than hemocytes while hepatopancreas and ovary have lower levels than hemocytes. Innate immune responses differ by tissue: midgut and hepatopancreas with upregulated Cas-ecCuZnSOD-2 similar to that found in hemocytes. By contrast, hepatopancreas showed a down-regulated CasTPS, suggesting carbohydrate stress during infection.

Systems and techniques used in the culture of soft‐shell swimming crabs

“…) and that the pathogenicity of this virus is related to high temperatures (Chung et al . ). These findings would reinforce an additional advantage of closed production systems over open systems, due to greater possibility of control of environmental variables, including temperature, in this kind of system.…”

“…In addition to the operational advantages of the closed system, recent studies have reported the occurrence of acute mortality in companies producing soft crab caused by a crab-specific reovirus (CsRV1) (Bowers et al 2010;Flowers et al 2016) and that the pathogenicity of this virus is related to high temperatures (Chung et al 2015). These findings would reinforce an additional advantage of closed production systems over open systems, due to greater possibility of control of environmental variables, including temperature, in this kind of system.…”

Parasites affect hemocyte functionality in the hemolymph of the invasive Atlantic blue crab Callinectes sapidus from a coastal habitat of the Salento Peninsula (SE Italy)

“…Generally the PO activity increases after the crabs' treatment with β-1,3-glucan, LPS or inactivated V. harvey and V. anguillarum (Sritunyalucksana & Sӧderhӓll, 2000). While, in the case of animals carrying reo-like virus infection (Chung et al, 2015), slightly higher levels of PO gene transcripts have been evidenced in comparison to those that are uninfected. However, considering that also in the Chinese white shrimp Fenneropenaeus chinensis the levels of PO expression are down regulated (Li et al, 2014) and that upon acute WSSV infection, these shrimps up regulate immune responsive genes, we can suppose a different response of hemocytes to the different extraneous organisms present in the hemolymph.…”

Climate and season are associated with prevalence and distribution of trans-hemispheric blue crab reovirus (Callinectes sapidus reovirus 1)

“…It has been reported that Pacific white shrimp Penaeus vannamei are able to clear white spot syndrome virus (WSSV) and have reduced WSSV-related mortality at high temperatures (Rahman et al 2006, You et al 2010) through expression of immune-related genes (Lin et al 2011, Shields 2019. Similarly, in C. sapidus, CsRV1-infected crabs cultured in elevated water temperature have increased immune and metabolism-related gene expression in hemocytes and an elevated proportion of small and non-granulated hemocytes (Chung et al 2015). Thus, the lower CsRV1 prevalence in higher temperature zones might be a result of an upregulated immune response of the host to combat the virus infection.…”

“…Temperature is particularly im portant for the distribution of most viral pathogens (Ford & Chintala 2006, Hawley & Garver 2008, Goodwin & Merry 2011, Samuel et al 2016, and susceptibility to infections is expected to vary with temperature due to alterations of the host's metabolic rate, immune response, and behavioral adaptations (Brady et al 2014, Hoberg & Brooks 2015, Franke et al 2017, Labaude et al 2017, Behringer et al 2018. For example, CsRV1-infected blue crabs have upregulated immune gene expression in water temperatures exceeding 23°C (Chung et al 2015). Behavioral adaptations of the blue crab include overwintering dormancy, peaks in mating and reproduction, and associated migrations.…”