Fresh water skin disease in dolphins: a case definition based on pathology and environmental factors in Australia

Abstract

A distinct ulcerative dermatitis known as “freshwater skin disease” is an emerging clinical and pathological presentation in coastal cetaceans worldwide. In Australia, two remarkably similar mortality events enabled the creation of a case definition based on pathology and environmental factors. The first affected a community of endemic Tursiops australis in the Gippsland Lakes, Victoria, while the second occurred among T. aduncus resident in the Swan-Canning River system, Western Australia. The common features of both events were (1) an abrupt and marked decrease in salinity (from > 30ppt to < 5ppt) due to rainfall in the catchments, with hypo-salinity persisting weeks to months, and (2) dermatitis characterized grossly by patchy skin pallor that progressed to variable circular or targetoid, often raised, and centrally ulcerated lesions covering up to 70% of the body surface. The affected skin was often colonized by a variety of fungal, bacterial and algal species that imparted variable yellow, green or orange discoloration. Histologic lesions consisted of epidermal hydropic change leading to vesiculation and erosion; alternately, or in addition, the formation of intra-epithelial pustules resulting in ulceration and hypodermal necrosis. Thus, the environmental factors and characteristic pathologic lesions, are necessary components of the case definition for freshwater skin disease.

High site-fidelity in common bottlenose dolphins despite low salinity exposure and associated indicators of compromised health

“…For each dolphin in June and September 2017, veterinarians conducted a skin assessment using a standardized form to document the location and description of each lesion type (Supplemental Materials). Visual assessment of freshwater-like lesions was typically characterized by hypopigmented, circular and/or irregular, multifocal to coalescing lesions and may or may not have had associated ulcerations and were consistent with freshwater lesions described in other studies [ 13 , 14 ]. Two experienced researchers (LS and CS) reviewed photographs of each dolphin to confirm the presence or absence of freshwater-like lesions.…”

“…Our results have applicability to Southeastern U.S. bottlenose dolphin stocks, as well as marine mammal populations/species worldwide that have long-term site fidelity and limited ranging patterns to a given habitat. For example, dolphins in Australia ( Tursiops aduncus and Tursiops australis ) exhibited similar skin lesions after sudden and weeks/months-long exposure to hypo-saline conditions due to intense rainfall [ 13 ]. Indo-Pacific humpback dolphins ( Sousa chinensis ) in China and Taiwan [ 81 – 83 ] and the Chilean and Guinean dolphins ( Cephalorhynchus eutropia and Sotalia guianensis , respectively) in South America [ 84 , 85 ] are also species/populations that are impacted by many of the same environmental stressors as Barataria dolphins.…”

“…In addition, skin may become overgrown with external mats consisting of fungi, algae, and/or bacteria that can penetrate the skin as the impacts of lower saline waters become more severe. Once the skin is compromised, the individual may develop secondary infections and/or net gain of low saline water into the body [ 13 ]. Similarly, gastrointestinal integrity may also be compromised, depending on how much water an individual consumes [ 15 ], leading to intracellular and extracellular absorption and potential for infections after incidental ingestion of low saline water.…”

Natural Entrapments of Killer Whales (Orcinus orca): A Review of Cases and Assessment of Intervention Techniques

“…As in other cetaceans exposed to fresh water for an extended period (e.g., Priddel and Wheeler, 1997), killer whales in Nushagak River (and Barnes Lake) had a skin condition characterized by severe degenerative changes caused by fungal and bacterial overgrowth (Bain, 1995;Raverty et al, 2020). Such compromised condition, known to have lethal consequences in cetaceans (Duignan et al, 2020), was confirmed to have contributed to mortality in this specific case (Raverty et al, 2020).…”

Salinity and Water Temperature as Predictors of Bottlenose Dolphin (Tursiops truncatus) Encounter Rates in Upper Galveston Bay, Texas

“…Dolphins are physiologically adapted to inhabit brackish to oceanic coastal waters with salinities that typically range from 15 to 35 ppt (Ewing et al, 2017;McClain et al, 2020;Booth and Thomas, 2021). Those that remain in an area subject to a low salinity event may suffer from freshwater intoxication due to oral ingestion and/or skin absorption, leading to serious negative health consequences (Ewing et al, 2017;Deming et al, 2020;Duignan et al, 2020;Fazioli and Mintzer, 2020;McClain et al, 2020;McBride-Kebert and Toms, 2021). Effects of freshwater exposure on dolphins can include development of hydropic degeneration and ulcerative or erosive skin lesions (e.g., Wilson et al, 1999;Mullin et al, 2015;Duignan et al, 2020;Fazioli and Mintzer, 2020;McClain et al, 2020;Toms et al, 2020;Townsend, 2020;Takeshita et al, 2021), corneal edema (Deming et al, 2020), and changes in blood chemistry and electrolytes (Ewing et al, 2017;Deming et al, 2020;McClain et al, 2020).…”