Colin mentioned the pox virus in one of his latest lectures and I wanted to find out a little more. This is a recent paper, published in 2011 which followed two estuarine dolphin (Tursiops aduncus) populations between 2003 and 2006.
The occurrence of the pox virus in cetaceans has been linked with environmental stresses, things like hypoxia, loss of salinity or a change in pH. It causes pin - hole lesions that look like grey blemishes on the skin and these in time can turn yellow or stippled and are referred to as ‘tattoo skin disease’. No Australian cases up until this point have been recorded and so the aim of this review was to see if there was any pattern between the flooding of two estuaries and the occurrence of skin lesions on the dolphins that occupy them.
Clarence River (CR) and Richmond River (RR) are used in this study as they are prone to flooding and therefore experience an influx of freshwater, which changes the rivers characteristics and causes stress to the marine flora. Four floods were noted within the study period and these were characterized by high rainfall and a rise in the water level by 5 times the original river height. Photo identification was used to keep track of the dolphins spotted in the two areas, with CR sustaining a large resident population of dolphins and RR sustaining a smaller population. 46 individuals in the CR were identified and of these 6 (13%) were reported to have pox virus - like lesions on their skin. These appeared first in the winter (June – August) of 2004 with no pox virus recorded before this date. The first flood occurred in autumn 2004. In RR 23 dolphins were identified and of these 4 (17.4%) were observed to have pox like lesions. The first sighting of lesions occurred in the spring (September – October) of 2004; this is 6 months after the first major flood in autumn (March - May 2004). However after floods 3 and 4, in the summer and autumn of 2005 and 2006 respectively, there were no new sightings of lesions in the RR. In all cases it was a calf or juvenile which had contracted the disease and so age has been significantly associated with it, this has been noted in other studies and it would be interesting to see how often pox virus occurs in adult dolphins, if at all.
The percentage affected by the pox virus in this study is compared to others in the discussion. Overall similar numbers of the disease have been found in resident and free - ranging dolphin populations with differences being put down to different water qualities and again different stresses on individual populations. One paper is mentioned however, Maldini et al 2010, which shows 80% of the population of dolphins recorded, had pox like lesions on their skin. The population is found in the Monterey Bay in California and the water there is particularly polluted suggesting skin lesions could be a biomarker of poor environmental conditions, or in the CR/RR case, a change in environmental conditions. In the Monterey population most of the dolphins affected were adults which may suggest long term exposure to the contaminated water is the cause of lesions. As only calves were affected in the estuarine study, maybe the short term change in water quality has a larger effect on the young dolphins leaving the adults mostly unaffected. This is not discussed in the paper.
The flooding of the estuaries brings about a lowering of salinity which is concluded to be the cause of the skin lesions seen in the estuarine dolphins. Although they move out of the estuary towards the coast when salinity is low it means they are exposed to rapidly changing environmental conditions which is suggested to exacerbate pox virus expression as lesions.
The sample size used here is very small and a longer termed experiment would have to take place to verify that the flooding and consequent change in water conditions is a major factor leading to pox virus in these dolphins. So far the evidence suggests it does and it would be interesting to investigate how the pox virus effects dolphins of different ages in more detail.
Fury and Reif (2011) Incidence of poxvirus-like lesions in two estuarine dolphin populations in Australia: Links to flood events, Science of the Total Environment vol 416
(other reference used Maldini et al., 2010
D. Maldini, J. Riggin, A. Cecchetti, M.P. Cotter
Prevalence of epidermal conditions in California coastal bottlenose dolphins (Tursiops truncatus) in Monterey Bay Ambio, 39 pp. 455–462)
D. Maldini, J. Riggin, A. Cecchetti, M.P. Cotter
Prevalence of epidermal conditions in California coastal bottlenose dolphins (Tursiops truncatus) in Monterey Bay Ambio, 39 pp. 455–462)
2 comments:
Hey, I found your post really quite interesting and easy to read. The fact that in CR and RR the reports of the disease was only recognised in young dolphins does suggest that it is something changing in the environment which is affecting the young, However I would have assumed that if the adults are unaffected they would have immunity and that the same antibodies used to provide them protection would be transferred to their young in their milk when they 'breast feed'? Although the presence of the disease in adults in Monterey Bay shows that adults can contract the virus; I guess its possible the the outcome of infection from the virus is directly related to the acuteness of the stressor, however it is strange that in Monterey the calves were not affected. Its quite perplexing really! Did the authors talk about any studies trying to understand the mechanisms behind the onset of the disease?
No mechanisms were not discussed in the paper unfortunately I wondered if another paper would show its head after this post. It is difficult to describe patterns as some calves are effected in some areas and not in another and the same with adults. It definitely has something to do with water and environmental conditions though with the young most likely to get effected by short term changes.
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