Puffy Skin Disease Is an Emerging Transmissible Condition in Rainbow Trout Oncorhynchus mykiss Walbaum

Abstract

The transmission of puffy skin disease (PSD) to rainbow trout Oncorhynchus mykiss Walbaum was tested in the laboratory by conducting co-habitation challenges with puffy skin (PS)-affected fish (Trojans) collected from the field. Two separate challenges were conducted using Trojans sourced from two different sites and diploid (first trial) or triploid (second trial) naïve fish. PSD-specific clinical signs were observed in both groups of naïve fish, with 66% of the fish sampled during the challenges showing signs of varying severity. The first clinical features of PSD were presented as white oval skin patches on one or both flanks 15–21 days post-challenge (dpc). The extent of the lesions ranged from 10 to 90% of the body surface, depending on the severity of the lesion. Both the severity and number of affected fish increased during the challenge. Macroscopically, oedema of the skin and multifocal petechial haemorrhaging were observed towards the end of the trials. Abnormal fish behaviour consisting of “flashing” and excessive mucous production was noted from 15 dpc onwards. Fish with severe PSD lesions also displayed inappetence and associated emaciation. Rodlet cells were observed in 41% of the fresh skin scrapes analysed from the second trial. Histologically epidermal oedema was observed in 31% of the naive fish showing gross pathology, with additional 12% displaying epidermal hyperplasia, mostly observed at the end of the challenge. Other concomitant features of the PSD lesions in challenged fish were epithelial erosion and sloughing, and occasionally mild or focal inflammation. No consistent pathology of internal organs was observed. The parasites Ichthyophthirius multifiliis and Ichthyobodo necator were observed in skin samples of a proportion of naïve challenged fish and in Trojans but not in control fish. The presence of these and other known fish pathogens in the skin of PSD-fish was confirmed by high-throughput sequencing analysis. In summary, we have demonstrated that PSD is a transmissible condition. However, even though a number of known fish pathogens were identified in the skin tissues of PSD-fish, the actual causative infectious agent(s) remain(s) unknown.

Epitheliocystis in fish: An emerging aquaculture disease with a global impact

“…Given that it is also a disease that is often overlooked compared to other emerging diseases of aquaculture systems (Murray et al., ), it is perhaps unsurprising that thorough systematic studies of epitheliocystis in specific fish species are currently lacking and that there are extensive gaps in our basic knowledge of the pathogenesis of this disease and the factors that may influence it. Epitheliocystis is not alone in this respect, with a number of similar emerging bacterial diseases of complex or unknown aetiology such as “strawberry” disease (Lloyd et al., ), acute dermatitis (Peeler et al., ) and puffy skin disease (Cano et al., ) causing serious economic losses in established aquaculture species with little basic information available on the epidemiology and pathogenesis of these agents either.…”

Case of highly prevalent papilloma‐like skin lesions in whitespotted char (Salvelinusleucomaenis) in Kamchatka (Russia)

“…The histopathological alterations in the whitespotted char had some similarities with puffy skin disease (PSD). Progressive epithelial hyperplasia, accompanied by proliferative epidermal necrosis and occasionally diffuse haemorrhages, and vascular dilation are some of the characteristics of PSD reported in rainbow trout in the United Kingdom (Cano et al., 2016; Peller et al., 2014) all of which were also noted in the affected whitespotted char.…”

“…We were unable to determine the aetiology of the skin lesions in the whitespotted char as is the case with other skin diseases such as RMS, SD and PSD. The consensus is that they are of an infectious nature (Cano et al., 2016; Peller et al., 2014; Verner‐Jeffreys et al., 2008). Flavobacterium psychrophilum (Ferguson et al., 2006) and rickettsia‐like organisms (Galeotti et al., 2017; Lloyd et al., 2008; Metselaar et al., 2010; Oh et al., 2019) have been suggested as aetiological agents.…”

“…Among these would be included pathologies such as red mark syndrome (RMS), also known as cold water strawberry disease (Verner‐Jeffreys et al., 2008), strawberry disease ( SD ) (Lloyd, 2009) and puffy skin disease (PSD) (Peller et al., 2014). Although these diseases have a low mortality rate, they cause significant economic damage due to a decrease in product marketability (Cano et al., 2016; Ferguson et al., 2006; Oidtmann et al., 2013). Since their causes are not fully determined, they are difficult to diagnose, treat and prevent.…”

Cranial Mandibular Fibrosis Syndrome in Adult Farmed Rainbow Trout Oncorhynchus mykiss

“…PSD is characterised by epidermal hyperplasia and emaciation of fish, resulting in a downgrading of carcasses at slaughter [ 10 , 11 ]. Although a plethora of parasites has been associated with PSD-impacted fish, among them Ichthyophthirious multifiliis (Fouquet 1876) and Ichthyobodo necator (Henneguy 1883), the actual causative agent(s) of PSD remain unclear [ 12 ]. Another infectious skin disease affecting rainbow trout is red mark syndrome (RMS), also known as cold water strawberry disease (CWSD).…”