Fresh water Skin Disease in Dolphins - New Scientific paper

Mar 12

Written By Dr Kate Robb, Director and Head of Research

Check out our latest scientific paper published in Nature Scientific Reports “Fresh water skin disease in dolphins: a case definition based on pathology and environmental factors in Australia documents”.

This important collaborative study documents an emerging disease in dolphins associated with environmental change. Dr Kate (Marine Mammal Foundation), along with co-authors Dr Padraig Duignan (Marine Mammal Centre) and Dr Nahiid Stephens (Murdoch University) assesses case studies in both the Gippsland Lakes, Victoria and Swan-Canning, WA.

Importantly, with another event unfolding in the Gippsland Lakes and precited La Nina impacts to come, we are working hard to understand the complex nature of this disease.

Duignan, P.J., Stephens, N.S. & Robb, K. 2020. Fresh water skin disease in dolphins: a case definition based on pathology and environmental factors in Australia. Sci Rep 10, 21979.

To read the paper in full please use this link.

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.

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FRESHWATER SKIN DISEASE – DR NAHIID STEPHENS

Freshwater Skin Disease (FWSD) is due to the detrimental effects of freshwater exposure in coastal bottlenose dolphins, and is an emerging cause of morbidity and mortality in many regions. We provide a case definition based on two Australian mortality events. The 1st affected Burrunan dolphins (Tursiops australis) in Victoria’s Gippsland Lakes in 2007. The 2nd event occurred in 2009 and affected the resident Indo-Pacific bottlenose dolphins (T. aduncus) in WA’s Swan-Canning Riverpark. Simultaneously with the Gippsland Lakes event, the first outbreak of FWSD in US waters was recorded for common bottlenose dolphins (T. truncatus) entrapped in Lake Pontchartrain, Louisiana, USA, following Hurricane Katrina in 2007. However, the dermatopathology was not described for the US event, as post-mortem examinations were not conducted. By contrast, the Australian events occurred where the resident populations were well documented by long-term and ongoing field ecology, population, and behaviour studies; the waters inhabited by the dolphins were intensively monitored for physical and chemical parameters before, during and after the events; and when mortalities occurred, thorough and systematic post-mortem examinations were carried out.

Based on these data, FWSD occurs when there is a sudden (over days) and precipitous (>25ppt to <5ppt) decrease in salinity, persisting for weeks to months. The skin lesions initially appear as patchy pale areas that progress to raised targetoid areas of ulceration and opportunistic colonisation by algae, diatoms, fungi and bacteria. In our paper, we detail the gross and histological appearance of the characteristic skin lesions of FWSD. Death may ensue from fluid loss and electrolyte imbalance – because the ulcerative skin lesions are akin to severe third-degree burns and often affect a large % of the body surface.

In Australia, the outbreaks followed the resumption of seasonal rainfall following a prolonged drought that flooded the Gippsland Lakes (normally brackish to marine saline) with fresh water. In WA, unusually high winter-spring rainfall in the river catchments similarly turned a normally marine/brackish habitat to freshwater. In the Gulf of Mexico, USA, events have followed the heavy rainfall and storm surges in the aftermaths of Hurricanes Katrina and Harvey. Common to all events is a preceding extreme weather event – which are predicted to increase in frequency and severity with Climate Change. Therefore, FWSD is an emerging disease of cetaceans which we are likely to see increasing in frequency in vulnerable estuarine and coastal habitats

WAYS TO HELP US

Unfortunately, we are seeing another dolphin mortality event in the Gippsland Lakes, Victoria. The Burrunan dolphins are again impacted by freshwater skin disease, which has resulted in six deaths and a number of the resident population in a compromised health condition.

Dr Kate and the Marine Mammal Foundation research team are increasing survey effort to track the prevalence and severity of the lesions and the health condition. We are working with key government organisations in gaining a greater understanding of the causes related to this mortality event.

If you are on or around the Gippsland Lakes and you see a dead dolphin, or one that looks sick and has ulcer-like lesions on its skin, please report it immediately to the Whale and Dolphin Emergency Hotline 1300 136 017, with the location, date, time and number of animals

To offer your support and assist our researchers further investigate this disease please head to our donate page to make a tax-deductible donation.