A novel bacterial disease of the European shore crab, Carcinus maenas – molecular pathology and epidemiology

Abstract

A novel bacterial disease of the European shore crab, Carcinus maenas -molecular pathology and epidemiology Several rickettsia-like diseases have been reported in arthropods (insects and crustaceans), some of which result in significant losses of economically important species such as shrimp and crabs. This study reports on the molecular pathology of a recently emerged disease of the European shore crab, Carcinus maenas, termed milky disease -named as a result of the unusual milky appearance of the haemolymph (blood). This disease was more prevalent (.26 %) during summer months when the water temperature in a pilot crab farm was approximately 19 6C. The putative causative agent of the disease was a Gram-negative bacterium that could not be cultured on a range of agar-based growth media. Diseased crabs showed significant reductions in free blood cell numbers and total serum protein. Such animals also displayed raised levels of glucose and ammonium in blood. Ultrastructural and in situ hybridization studies revealed that the causative agent associated with milky disease multiplied in the fixed phagocytes of the hepatopancreas (digestive gland), ultimately to be released into the haemolymph, where the circulating blood cells showed little response to the presence of these agents. Attempts to induce the infection by short-term temperature stress failed, as did transmission experiments where healthy crabs were fed infected tissues from milky disease affected individuals. Sequence analysis of the 16S rRNA gene from the milky disease bacteria indicated that they are a previously undescribed species of a-proteobacteria with little phylogenetic similarity to members of the order Rickettsiales. INTRODUCTIONThere is increasing interest in the likely effect of global climate change on diseases in both wild and cultured organisms (Harvell et al., 1999(Harvell et al., , 2002Lafferty et al., 2004). In particular, aquatic animals are highly sensitive to temperature change and it is widely accepted that elevated temperatures can lead to reduced oxygen tension in the water, higher microbial growth and immunosuppression, resulting in higher prevalence of disease (Le Moullac & Haffner, 2000). For example, brown trout in alpine rivers and streams have been found to show increasing prevalence of proliferative kidney disease caused by the myxozoan parasite Tetracapsuloides bryosalmonae over the last 20 years (Hari et al., 2006). These increased temperatures drive the proliferation of T. bryosalmonae in its intermediate bryozoan host (Tops et al., 2006). Equally at very low water temperatures, some aquatic animals may become immunocompromised as a result of a failure of the immune system to mount an effective immune response to bacterial challenge (Chisholm & Smith, 1994).One potentially important result of climate change will be alterations in the effectiveness of aquaculture as a method of supplementing fish and shellfish for human and animal consumption taken from the wild (Alborali, 2006). Currently, it is thought that at least 15 ...

Metabolomic analysis of Atlantic blue crab, Callinectes sapidus, hemolymph following oxidative stress

“…6d). Environmental stress and infection have been shown to cause elevation of glucose levels (Eddy et al 2007;Hall and van Ham 1998). Lorenzon et al (1997) reported an increase in hemolymph glucose in several crustacean taxa following injection of lipopolysaccharide (LPS).…”

Tissue changes in the shore crab Carcinus maenas as a result of infection by the parasitic barnacle Sacculina carcini

“…Assays were performed as described in detail previously (Eddy et al 2007, Powell & Rowley 2007. Histopathology.…”

“…5 ml of Bouin's seawater fixative through unsclerotised membranes. Tissues were processed, stained and examined as described previously (Eddy et al 2007). …”

Disease will limit future food supply from the global crustacean fishery and aquaculture sectors

“…(Tubiash et al, 1975;Wang, 2011). Intracellular bacterial infections occur within specific types of host cell (see Vincent et al, 2004;Eddy et al, 2007). Fungal pathogens (Phycomycetes, Ascomycetes and Fungi Imperfecti) have been implicated in catastrophic epidemics and mortality events in decapod crustaceans (Unestam, 1973).…”