Withering Syndrome of Abalone
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Category
Category 3 (Host Not in Canada)
Common, generally accepted names of the organism or disease agent
Withering syndrome (WS), Withering disease, Foot withering syndrome, Abalone wasting disease, Withering syndrome - an intracellular Rickettsiales like prokaryote (WS-RLP), Withering syndrome caused by an infection with the Rickettsia like organism (WS-RLO).
Scientific name or taxonomic affiliation
Candidatus Xenohaliotis californiensis (CXc), is an intracellular prokaryote, with morphological characteristics of the class Proteobacteria, order Rickettsiales (Gardner et al. 1995; Friedman et al. 2000b to d) and family Anaplasmataceae (OIE 2012, Cicala et al. 2017), in the epithelium of the intestinal tract of abalone (Cruz-Flores et al. 2020). Note that the prefix Candidatus is reserved for prokaryotes which cannot be cultured in vitro and thus not conveniently characterized from a biochemical and serological point of view and indicate a provisionary status (Moore et al. 2002, Balseiro et al. 2006). The disease caused by C. X. californiensis is often called withering syndrome (WS, a term coined by Haaker et al. (1992)) because of the atrophy of the body mass in comparison to the shell size. Thus, the rickettsia-like disease agent (C. X. californiensis) is often referred to as WS-RLO, WS-RLP or more recently CXc. Alfjorden et al. (2017) indicated that the disease may be more appropriately termed abalone rickettsiosis. Nishioka et al. (2016) described a genetic variant of CXc and indicated that the original genotype and the variant had different host specificity based on cohabitation studies.
Initially, heavy infections of coccidia in the kidney were thought to cause the disease but, a correlation between coccidial infection and withering syndrome was not found (Steinbeck et al. 1992, VanBlaricom et al. 1993, Kuris et al. 1994, Friedman et al. 1997, Moore et al. 2002). Also, the muscle atrophy in the mantle and foot characteristic of the abalone disease called amyotrophia associated with a viral infection is different from withering syndrome of abalone (Otsu and Sasaki 1997, Momoyama et al. 1999, Nakatsugawa et al. 1999). A morphological variant of CXc is now known as being infected with a phage hyperparasite (Friedman and Crosson 2012) tentatively identified as a species in the Family Siphoviridae from the order Caudovirales (Cruz-Flores and Cáceres-Martínez 2016, Cruz-Flores et al. 2016). Cruz-Flores et al. (2018) provided the complete genome sequence of this novel phage. In addition to CXc , other unidentified rickettsia-like organisms of unknown pathogenicity are likely to occur in the digestive tract epithelial cells of abalone (Moore et al. 2002, Crosson et al. 2014, Horwitz et al. 2015 (2016), Cicala et al. 2017, Cáceres-Martínez et al. 2021). Also, abalone (i.e., Haliotis diversicolor supertexta) with gross signs of WS were found to be infected with Vibrio parahaemolyticus (Liu et al. 2000, Huang et al. 2001) and a rickettsia-like procaryote detected in basophilic inclusion bodies within intestinal epithelial cells was different in size and shape to CXc and did not react to the molecular assay developed for CXc (Chang et al. 2008).
Geographic distribution
Coast of California, USA, south of Point Conception and on the west coast of Baja California, Mexico (Cáceres-Martínez et al. 2011). In Diablo Cove, California (70 km north of Point Conception), disease and mortalities of abalone were limited to the immediate vicinity of a warm-water discharge. In 1996, there was evidence that this disease was progressing northward from Point Conception (Altstatt et al. 1996) and possibly as far north as San Francisco, California (Finley and Friedman 2000). In addition, CXc (but not the withering syndrome disease) was detected at two locations in northern California (Crescent City and Van Damme) (Friedman and Finley 2003). In surveys of abalone from Baja California, Mexico, this pathogen was detected in high prevalence in the digestive tract of symptomatic and non-symptomatic cultured and natural populations of Haliotis rufescens, Haliotis fulgens and Haliotis corrugata (Cáceres-Martínez and Tinoco-Orta 2000, 2001; Cáceres-Martínez et al. 2000; Álvarez-Tinajero et al. 2002; Cáceres-Martínez et al. 2011; Cicala et al. 2017). Candidatus Xenohaliotis californiensis was detected in H. rufescens cultured in Iceland (unofficial report from Gisli Jonsson in an e-mail dated November 8, 2004) and cultured in Chile (Campalans and Lohrmann 2009), and in Haliotis uberculate cultured in Ireland in 2006 and France (Balserio et al. 2006) with no associated mortalities in these 4 cases. In Galicia (NW Spain), experimentally grown stocks of H. tuberculate, originating in Ireland, experienced high mortality (45% to 100%) within 14 months of importation (most mortalities occurring during the spring and summer months) and were infected with CXc. However, in this case, the associated mortalities were attributed to a co-infection with a protistan pathogen (Balserio et al. 2006).
During a pilot survey, CXc was detected in commercially farmed Haliotis diversicolor supertexta from Thailand, Taiwan and the People's Republic of China. Infected abalone had no gross signs of clinical disease, normal looking histological structure of muscle fibers in the foot and no unusual losses in the culture facilities (Wetchateng et al. 2010). This pathogen was also reported from Japan in farmed Haliotis discus discus in association with 33% mortalities but again with little degeneration of the digestive gland and shrinkage of the foot muscle (Kiryu et al. 2013). In addition to H. discus discus, CXc infections were also detected in suspect Haliotis discus hannai, Haliotis gigantean, Haliotis diversicolor aquatilis and Haliotis diversicolor diversicolor by 17 fish diagnostic laboratories in Japan (Nishioka et al. 2016).
A similar looking disease of unknown etiology has been reported from farmed Haliotis discus hannai on the northern coast of China (Guo et al. 1999). Rickettsia-like organisms (RLOs) have also been reported in the digestive tract of abalone (Haliotis midae) from culture facilities in South Africa with no associated pathology (Mouton 2000). Azevedo et al. (2006) also observed RLOs in the epithelial cells of the digestive diverticula of commercially farmed abalone H. tuberculata in the northwestern region of the Atlantic Coast of Spain. Although infected abalone had symptoms corresponding to those caused by 'withering syndrome', Azevedo et al. (2006) could not establish a definitive connection between the presence of the RLOs and the disease, because of co-infections with the haplosporidian pathogen, Haplosporidium montforti.
Host species
Disease was first described and most evident in Haliotis cracherodii. However, the pathogen and sometimes the disease also occurs in Haliotis rufescens, Haliotis corrugata, Haliotis fulgens, Haliotis sorenseni, Haliotis kamtschatkana, Haliotis tuberculata, Haliotis diversicolor supertexta, Haliotis diversicolor aquatilis, Haliotis diversicolor diversicolor, Haliotis discus discus, Haliotis discus hannai, Haliotis gigantea and possibly in Haliotis midae and Haliotis walallensis. The CXc obtained from H. rufescens in Chile were not infectious to H. discus hannai (González et al. 2014). However, González et al. (2014) determined that the hybrid cross of the two abalone species did not inherited non-susceptibility or resistance characteristics of the parental H. discus hannai. Nishioka et al. (2016) described a genetic variant of CXc in H. diversicolor diversicolor and H. diversicolor aquatilis. In cohabitation studies, this genetic variant donated by H. diversicolor diversicolor was infective to H. diversicolor diversicolor but not to H. discus discus and H. gigantea. Conversely, CXc genetically similar to isolates from abalone in California and donated by H. discus discus in cohabitation studies was infective to H. discus discus and H. gigantea but not to H. diversicolor diversicolor (Nishioka et al. 2016). The phage hyperparasite of CXc has been reported in H. rufescens, H. cracherodii, H. corrugata and H. fulgens from California, US and/or Baja California, Mexico (Cruz-Flores et al. 2016).
Impact on the host
Withering syndrome (WS) is a direct transmitted, lethal disease that affects all sizes of abalone (e.g., H. rufescens 3 mm in shell length were experimentally infected with CXc Moore et al. 2002) and causes lethargy, retracted visceral tissues, and atrophy of the foot muscle (thereby adversely affecting the ability of the abalone to adhere to the substrate). Withering syndrome first appeared in the mid-1980s at the Channel Islands in high-density populations of H. cracherodii ( Moore et al. 2002). Significant mortalities induced by WS were noted in 1992 and by 2001 caused a 99.2% reduction of H. cracherodii on San Nicolas Island, California, USA (Vanblaricom et al. 2012). Infections with CXc begin in the posterior esophagus epithelium and cause morphological changes (metaplasia) in the digestive gland of the abalone host. The metaplasia enable the bacterium to infect the digestive gland (a secondary target tissue for CXc) and disrupt its function leading to catabolism of the foot muscle and eventually death of the host (Friedman et al. 2000b, 2014a; Braid et al. 2005). Abalone with WS, including lower values in the condition index, had 'normal' gut content apparently indicating that the disease reflected a digestive inability and not a feeding problem (Siqueiros-Beltrones et al. 2015). Di et al. (2016) assessed the immune enzyme activity of haemolymph and mucus, and protein changes in muscle and mucus of diseased Haliotis diversicolor using two-dimensional gel electrophoresis (2-DE) and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and detected physiological alterations attributed to WS-RLO. Unfortunately, Di et al. (2016) did not confirm the etiological agent in the diseased abalone and included references to amyotrophia associated with a viral infection, which also occurs in the region, indicating that the pathology cannot be confidentially attributed to either disease.
Elevated temperatures increased the onset of the disease, accelerated disease progression and decreased survival especially in H. rufescens, H. cracherodii and H. kamtschatkana (Moore et al. 2000b, 2002; Vilchis et al. 2005; Crosson and Friedman 2018). At 18 to 20°C, death of H. rufescens usually occurred within one month of the appearance of the clinical signs (Moore et al. 2000b, 2011). Rogers-Bennett et al. (2010) indicated that infected H. rufescens did not develop foot withering syndrome and had normal sperm and egg production at about 12°C. However, H. rufescens infected with CXc and exposed to warm water (about 18°C) develop the disease and did not produce mature gametes (Rogers-Bennett et al. 2010). Also, H. fulgens infected with CXc did not express disease signs under an experimental temperature regime (18°C) permissive for disease development in H. rufescens (Moore et al. 2009). In another study, García-Esquivel et al. (2007) indicated that H. fulgens maintained at 25°C displayed the signs of WS, whereas temperatures greater than 25°C could cause thermal stress, thereby contributing to physiological deterioration of the abalone and therefore vulnerability to CXc. Moore et al. (2009, 2011) proposed that the temperature at which clinical signs of WS are expressed is more closely related to the preferred temperature of each abalone species. In agreement with this perspective, González et al. (2012) suggested that the difference in temperature preference between H. discus hannai and H. rufescens could explain disease development in H. rufescens at the experimental temperature of 18°C and lack of infection in exposed H. discus hannai that has optimal growth at 20°C. Similar results were obtained by Crosson and Friedman (2018) who concluded that species with cool water evolutionary histories are most susceptible to WS and the most susceptible species appear to be closely related.
Ben-Horin et al. (2013) determined that in H. cracherodii, temperature variation of an intertidal habitat increased susceptibility to infection, but infected individuals remained asymptomatic until high mean water temperatures exceed thresholds modulating WS resulting in increased mortality rates of infected individuals. Thus, mass mortalities can occur before pathogen transmission is limited by density-dependent factors (Ben-Horin et al. 2013). Burge et al. (2014) claimed that climate change has been clearly linked to epizootics of withering syndrome.
Diseased H. cracherodii consumed 4.4 times less kelp, 1.2 times less oxygen and excreted 3.8 times more ammonia per gram wet weight than did healthy abalone (Kismohandaka et al. 1993). Also, haemocyanin concentration in the blood decreased, glycogen in the foot muscle was depleted, haemocyte abundance was reduced and haemocytes with abnormal morphology increased in wasted H. cracherodii (Friedman 1996, Shields et al. 1996). In addition, haemocytes were more chemotactically active but the capability of the stimulated cells to engulf and destroy foreign particles appeared to be compromised and may contribute to mortality associated with the disease (Friedman et al. 1999, 2000a). Mass specific ammonia excretion was observed in affected abalone indicating protein from the foot muscle was being used as an energy source. This conclusion was also suggested by Kismohandaka et al. (1995) who observed severe foot muscle fibre depletion in samples examined using histology. However, no pathogens were found in the muscle or blood tissues. Severe metabolic alterations and reduced physiological performance were detected in H. rufescens before visible atrophy of the foot occurred (González et al. 2012). Using high-throughput sequencing of the V4 region of the 16S rRNA gene in samples from the digestive gland of H. rufescens, Villasante et al. (2020) detected a differences in microbiota between uninfected and WS disease affected groups.
This disease was associated with mass mortalities of H. cracherodii. Withering syndrome progressively spread throughout the California Channel Islands causing population crashes on six of the eight Channel Islands by 1992 (95 to 100 percent of the H. cracherodii were lost) and closure of the California black abalone fishery in 1993. A dramatic increase in the number of cultured H. rufescens with foot withering syndrome was noticed in conjunction with El Niño - Southern Oscillation (ENSO) elevated seawater temperatures (Moore et al. 1999, Cone and Bishop 2015, Guo and Ford 2016). However, differences in susceptibility and tissue changes were noted between species with H. cracherodii being more susceptible than H. rufescens and survivors appear to be relatively resistant to the disease (Friedman et al. 2003b). Also, the most significant threat to population recovery that H. cracherodii faces is that imposed by the spread of withering syndrome (Neuman et al. 2010). Friedman et al. (2014a) indicated that the development of resistance and CXc relationship with H. cracherodii was evolving through dual host mechanisms of resistance to CXc infection in the digestive gland and via tolerance to infection in the primary target tissue (the post-esophagus) and possibly coupled with reduced pathogenicity of CXc by phage infection, which effectively reduced the infection load in the primary target tissue by half.
Diagnostic techniques
Crosson et al. (2014) indicated that the diagnosis of WS requires the identification of infection with the pathogen (CXc) detected via in situ hybridization or histology coupled with PCR and sequence analysis accompanied by morphological changes that characterize this disease (e.g. pedal and digestive gland atrophy, and digestive gland metaplasia). Further information on these techniques is presented below and provided by the OIE (2012).
Gross observations
Body mass relative to shell size is smaller than normal (Fig. 1) (Crosson et al. 2014). Affected abalone were discoloured and weakened, and the soft tissues were atrophied and not responsive to stimuli.
In the field, affected abalone can be detached from the substrate by hand and do not attempt to right themselves when turned upside down. In addition to the muscle and visceral mass atrophy (withered condition of the abalone foot), Valles-Ríos (2000) noted the loss of pigmentation in the oral and cephalic tentacles of H. cracherodii. However, other pathogens of abalone can cause similar looking disease. For example, Liu et al. (2000) and Chang et al. (2008) described "withering syndrome" in Haliotis diversicolor supertexta which was associated with Vibrio parahaemolyticus and a rickettsia-like procaryote unrelated to CXc, respectively. Also, the gross signs of disease in H. diversicolor depicted by Di et al. (2016) may have been caused by amyotrophia associated with a viral infection and not WS caused by CXc as claimed because identification and/or detection of the etiological agent was not indicated in the publication.
Squash preparations
Minced pieces (about 2 mm square) of gastrointestinal tract from the posterior portion of the esophagus to the posterior end of the crop were places on a microscope slide, gently pressed into the slide with a second slide and dried with low heat from a blow dryer for 20 min. Dried samples can be prepared for examination immediately or held indefinitely at 4°C with desiccant. To prepare for examination, the tissue was flooded with a 10 µg per ml solution of Hoechst 33258 (bisBenzimide, Sigma, St. Louis, MO, USA) in distilled water, covered with a coverslip, incubated in the dark for several minutes and viewed at 100 to 400X magnification with a epifluorescent ultraviolet light and filters appropriate for the spectra of 356 nm excitation and 465 nm emission. This staining technique caused the large inclusions of CXc, which are usually difficult to detect in unstained tissue, to fluoresce a bright blue against a black to dull red background. Although the abalone cell nuclei were also fluorescent, they were small (about 5 µm in length) in comparison to the inclusions (about 50 µm in length). An alternate nucleic acid-specific fluorochrome, propidium iodide (10 µg per ml in distilled water, Sigma), viewed with ultraviolet light and 530 nm excitation and 615 nm emission filters gave similar results (for further details see Moore et al. 2001a).
Cruz-Flores et al. (2015) described a procedure for the separation of intact CXc inclusions from host cells via a process of macerating (with a small mortar and pestle) heavily infected posterior esophagus from a diseased abalone followed by successive passage through filters from 100 to 10 µm pore size. The intact inclusions were visualized on the filters by staining them with a nucleic acid fluorochrome DAPI (Sigma-Aldrich®) solution in distilled water (20 μg/ml) and viewing them at 10 to 20 X magnification with epifluorescent ultraviolet light and appropriate filters (340 nm excitation, 488 nm emission). The 28 and 10 μm pore size filters retained inclusions that were completely separated from the host tissue but a few large host cell nuclei along with other cellular debris occurred on the 10 μm filter (Cruz-Flores et al. 2015).
Histology
Severe foot muscle fiber depletion (Fig. 2) plus occurrence of extensive infections of Gram-negative intracellular prokaryotes in the epithelium of the intestinal tract, especially in the post-esophagus (Fig. 3) observed via microscopy in routine histological sections are indicative of infection with CXc (Crosson et al. 2014).
The prokaryotes had morphological characteristics of the order Rickettsiales. They were accumulated into intracellular colonies (inclusions, sometimes called membrane bound vacuoles (MBVs), mostly spherical or oval in shape, and measured from 5 to 56 μm in size) within epithelial cells apical to the host cell nucleus (Moore et al. 2009, Wetchateng et al. 2010, Cáceres-Martínez et al. 2011, González et al. 2012, Kiryu et al. 2013). Occasionally, inclusions of intracellular colonies were observed in the lumen of the intestine (Wetchateng et al. 2010). The inclusions usually appear pink to purple with haematoxylin and eosin staining but the individual small rod-shaped bacteria within the inclusions usually cannot be discerned by light microscopy unless they are infected by a phage hyperparasite which makes them appear as large (mean of 3.2 to 3.4 μm long and 1.5 to 2.6 μm wide depending on the tissue fixative), pleomorphic bacteria that stain dark navy blue (Friedman and Crosson 2013, Crosson et al. 2014, Cruz-Flores and Cáceres-Martínez 2016, Cruz-Flores et al. 2016). The phage hyperparasites were observed being expelled into the lumen of the posterior esophagus when the infected inclusion of CXc and the host cell ruptured (Cruz-Flores and Cáceres-Martínez 2016, Cruz-Flores et al. 2016).
Infection of the digestive diverticula can be accompanied by a loss of digestive enzyme granules from epithelial cells and by a metaplasia of enzyme secretory cells into cells morphologically similar to epithelial cells lining the gut (Fig. 4) (Gardner et al. 1995, Crosson et al. 2014). This pathology in heavily infected abalone is speculated to be the cause of muscle tissue catabolism resulting in the withering disease.
Electron microscopy
Observation of rod-shaped prokaryotes (mean of 0.5 to 1.7 μm long and 0.1 to 0.8 μm wide depending on the tissue fixative) with electron dense, ribosome-rich area near the trilaminar cell walls accumulated into intracellular colonies within membrane-bound inclusions in the cytoplasm of gastrointestinal epithelial cells (Cáceres-Martínez et al. 2011, Friedman and Crosson 2012, Cruz-Flores and Cáceres-Martínez 2016). Candidatus Xenohaliotis californiensis infected by a phage hyperparasite were larger and more pleomorphic (mean of 2.3 to 3.1 μm long and 1.0 to 1.4 μm wide depending on the tissue fixative) than uninfected bacteria and containing spherical to icosahedral-shaped phage particles including capsids with electron dense granules (about 35 to 60 nm in diameter depending on the tissue fixative) (Friedman and Crosson 2012, Cruz-Flores and Cáceres-Martínez 2016). Some of the phages with electron dense capsids displayed a long uniform and flexible tail attached to the vertex of the capsid. The tail measured 35–75 nm (from vertex to end of tail) and had a width of 10–12.5 nm (Cruz-Flores and Cáceres-Martínez 2016, Cruz-Flores et al. 2016). Colonies containing infected CXc also had normal-looking, rod-shaped CXc along the periphery of the inclusions (Friedman and Crosson 2012, Crosson et al. 2014).
Di et al. (2016) described ultrastructural changes to the foot muscle and intestinal tract of diseased Haliotis diversicolor that they attributed to CXc. Unfortunately, Di et al. (2016) did not confirm the etiological agent in the diseased abalone and included references to amyotrophia associated with a viral infection, which also occurs in the region, indicating that the pathology cannot be confidentially ascribed to either disease.
DNA probes
The 16S rDNA was amplified, cloned and sequenced. A polymerase chain reaction (PCR) test was developed that specifically amplifies a 160 base-pair segment of CXc but not four other microbial species isolated from the gut of abalone. This PCR test greatly increases the ability to detect the pathogen (Andree et al. 2000). For example, Lafferty and Ben-Horin (2013) used this PCR test to detect CXc DNA in effluent discharged from shore-based abalone farms into coastal waters of California. Also, an in situ hybridization test was developed (Antonio et al. 2000). Application of these molecular assays indicated that the WS-RLO in Haliotis diversicolor from aquaculture facilities in People's Republic of China (PRC) and Thailand had extremely high molecular identity with CXc from California (100 and 99%, respectively). These data combined with the history of abalone movements for aquaculture purposes indicated that WS-RLOs observed in Thailand and Taiwan by PRC probably originated from California (Wetchateng et al. 2010). Similar results and conclusions were reported by Kiryu et al. (2013) for farmed Haliotis discus discus in Japan. Cicala et al. (2017) obtained inconsistent results using the standard OIE protocol (OIE 2012) and thus designed a new set of diagnostic primers that also target the 16S rDNA.
Friedman et al. (2014b) created a real-time quantitative PCR (qPCR) assay to specifically identify and enumerate bacterial loads of CXc in abalone tissue, fecal, and seawater samples based on 16S rDNA gene copy numbers. This qPCR assay designed to detect DNA of CXc was validated according to standards set by the World Organisation for Animal Health (Friedman et al. 2014b). Confirmation of infection cannot be done by PCR analysis alone but can be used as a proxy for infection in areas where the agent is established and is recommended for inclusion in abalone health examinations (Crosson et al. 2014).
A genetic variant of CXc with one base pair substitution at the 148ᵗʰ nucleotide position in the 16S rRNA partial sequence (113 base pairs long) was described by Nishioka et al. (2016). This variant was infective to H. diversicolor diversicolor but not to H. discus discus and H. gigantea in cohabitation studies (Nishioka et al. 2016). Cicala et al. (2017) amplified and sequenced five genes (16S rRNA, 23S rRNA, ftsZ, virD4, and virB11) of CXc from infected abalone. Analysis placed CXc as the most basal lineage in the family Anaplasmataceae ancestral to both fresh water and terrestrial species, thus supporting the hypothesis of a marine origin for this bacterial family.
Methods of control
Experiments indicate that the pathogen can be transmitted via the water column (including in effluent discharged from shore-based abalone farms) and did not require direct contact between infected and uninfected abalone (Moore et al. 2000a, 2001b; Friedman et al. 2002; Lafferty and Ben-Horin 2013). Crosson et al. (2020) determined that CXc DNA was unstable in seawater for longer than 2 days and a pathogen dose of 2.3 × 103 DNA copies/mL was required to generate a 50% infection prevalence in H. rufescens tissue. Moore et al. (2002) proposed 3 restoration activities for the recovery of California abalone populations: (1) establishing protected areas where populations could recover on their own; (2) aggregation of abalone to create densities necessary for successful fertilization; (3) out-planting of hatchery-reared larvae, juveniles, or adults. Caveats were associated with each of these proposals (Moore et al. 2002).
Above normal temperatures seem to have a synergistic effect on the disease (Cáceres-Martínez et al. 2000, Moore et al. 2000a, Raimondi et al. 2002). Results of experiments by Friedman et al. (1997) and Moore et al. (2000a, b) indicated that H. cracherodii and H. rufescens, respectively, held at elevated temperatures (20°C and 18.5°C, respectively) had higher mortality, more severe signs of WS and more severe infections with CXc than those held in cooler waters (13°C and 14°C, respectively). Also, the recovery of H. cracherodii populations affected by mass mortalities from foot withering syndrome seemed to be closely linked with temperature. In affected culture facilities, the severity of the disease may be curtailed if water temperatures could be reduced to about 15°C or less (Moore et al. 1999, Alfjorden et al. 2017). Results of subsequent long-term (447 days) experimentation employing fed and starved abalone indicated that the high morbidity and mortality exhibited by infected abalone is a consequence of disease and not direct thermal stress (Braid et al. 2005). However, Rogers-Bennett et al. (2010) suggest that temperature needs to be explicitly incorporated into at least H. rufescens recovery and management planning.
Oceanographic factors that result in elevated seawater temperatures (i.e., ENSO) had a strong negative impact on the recovery of H. cracherodii populations in southern California (Tissot 1995). These elevated temperatures were also associated with a dramatic increase in the number of H. rufescens with foot withering syndrome in culture facilities in California (Moore et al. 1999). Despite the devastation caused to H. cracherodii populations, a few large, old individuals can still be found and some small juveniles have been seen (Haaker 1997). Also, the research of Tissot (1995) suggests that H. cracherodii populations in southern California may recover with the subsidence of ENSO oceanographic conditions. Genetic structure of H. cracherodii populations in the California islands and central California coast was assessed in order to identify patterns of recruitment in surviving populations (Chambers et al. 2006). Some populations that have suffered catastrophic losses due to WS have developed resistance to the disease (Moore et al. 2002, Crosson et al. 2014, Friedman et al. 2014a). However, Miner et al. (2006) indicated that the significant decline in H. cracherodii populations in some areas resulted in a shift in the composition of the intertidal species assemblage from one dominated by bare rock and crustose coralline algae (good quality abalone habitat) to one with increased cover of sessile invertebrates and sea urchins. Thus, recruitment failure in these areas of dramatic shifts in habitat quality may indicate a poor outlook for the recovery of some wild H. cracherodii stocks (Miner et al. 2006).
Evidence indicated that the occurrence of CXc in H. rufescens at two new locations in northern California were associated with out-plants of hatchery-reared abalone, suggesting a link between restoration efforts and the present distribution of this pathogen (Friedman and Finley 2003, Guo and Ford 2016). The detection of the pathogen outside the previous known distribution (for example, in abalone farms in Thailand, Taiwan and the People's Republic of China) highlights the need for careful assessment of animal health before restocking depleted populations or transplanting animals for aquaculture (Wetchateng et al. 2010). Also, some species of abalone seem to be more resistant to infection and the disease than other species (Crosson et al. 2014, Cruz-Flores et al. 2016, Takase et al. 2016). For example, differences in susceptibility to infection with CXc at a given temperature (18°C) was also noted between H. rufescens and H. discus hannai, with H. rufescens being more vulnerable (González et al. 2012). In accordance, Vilchis et al. (2005) and Moore et al. (2009) suggested that future restoration efforts in southern California are more likely to succeed with H. fulgens than H. rufescens, given the changing temperature regime and the presence of CXc in the region.
Intramuscular injection and oral administration of the antibiotic oxytetracycline (OTC) was effective in reducing the losses of infected abalone (Friedman et al. 2003a, Alfjorden et al. 2017) and tissue retention of OTC in the digestive gland remained high for a prolonged time and was still detectable at least 160 days post treatment (Braid et al. 2005, Friedman et al. 2007, Rosenblum et al. 2008). However, other antimicrobials had no measurable effect on the disease (Friedman et al. 2000b). Rosenblum et al. (2006) used histology and nuclear magnetic resonance spectroscopy based metabolomics to determine that OTC administered via medicated feed eradicates CXc which in turn reduces the metabolic decay associated with WS at elevated seawater temperatures of about 17°C. However, metabolomics revealed, that the most significant metabolic changes in foot muscle depended upon post-treatment duration, irrespective of treatment and temperature (Rosenblum et al. 2006). García-Esquivel et al. (2011) demonstrated that an OTC water bath treatment induced the recovery of severely diseased juvenile H. fulgens. Howere, after prolonged (11 months) exposure to OTC in water baths, Winkler et al. (2018) concluded that for H. rufescens, the prophylactic use of OTC in abalone, to avoid the negative effects of WS on abalone farms, could have an undesired negative effect on abalone growth and the biological control exerted by the phage hyperparasite on CXc after OTC treatment. Nevertheless, Moore et al. (2019) published an OTC bath protocol to eliminate CXc in captive abalone populations.
Exposure of seawater containing CXc to >10 milligrams per litre [ppm] calcium hypochlorite and disinfection of equipment in a bath of 1% tamed iodine (various commercial iodophor formulations) in freshwater for 1 hour were effective disinfectants based on the use of these disinfection methods at a marine laboratory with flow-through seawater and a lack of detection of this pathogen in adjacent abalone populations (OIE 2012). Avoidance of WS is best accomplished by the establishment of a health history and multiple health examinations prior to movement of animals (Crosson et al. 2014).
References
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Citation Information
Bower, S.M. (2023): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Withering Syndrome of Abalone.
Date last revised: January 2023
Comments to Susan Bower
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