Disease affecting wildlife is part of the ecosystem and its occurrence should be seen as one of the drivers of equilibrium within the system. Many diseases and parasitic conditions are endemic within populations of wildlife, and they often only manifest negatively if there is an imbalance within the system, or when human intervention causes a change in the system that has a roll-on effect on all its components. Disease ecology deals with the mechanisms that determine how parasites and other causes of disease spread through and influence populations and communities (Hudson et al., 2002 and Collinge & Ray, 2006). Disease ecology is closely related to the newly developing discipline of ecological immunology
Human intervention has resulted over time in the appearance of emerging infectious diseases that cross species barriers, that have had a major impact on humans, and on other animals within the system. Common examples of these diseases in humans include SARS, ebola, Marburg virus infection, HIV, and others that have over time constituted serious zoonotic threats to the human population.
Interference with ecosystems does not only involve infectious diseases in the system, but my also result in pollution and nutritional imbalances that may have a serious impact on the sustainability of an ecosystem. One such example is the mass mortality of Nile crocodiles and African sharptooth catfish due to pansteatitis in the lower reaches of the Olifants River in South Africa. This event appears to be the consequence of severe pollution of the river, eutrophication of a dam in the lower reaches of the river, and the introduction of a new prey species into the river and dam systems that created as situation in which some of the fish species and the Nile crocodile population were subjected to severe oxidative stress and the consequent development of pansteatitis that proved to be fatal to a large proportion of the respective fish and crocodile populations.
Since the mass mortality of large Nile crocodiles in the lower Letaba and Olifants rivers in 2008, fish health investigations in the Olifants River Gorge and other sites in and around the Kruger National Park have shed light on the cause of the crocodile mortality. The crocodile deaths were ascribed to pansteatitis, a nutritional disease rarely encountered in wild animals. At sites in the Kruger National Park where pansteatitis was diagnosed in crocodiles my team discovered the same disease in African sharptooth catfish, Clarias gariepinus (Burchell). In the Olifants River Gorge, the epicentre of the crocodile mortalities, a rising prevalence of the disease was observed in catfish sampled from 2009 to 2011.
- Hudson, P. J., Rizzoli, A. P., Grenfell, B. T., Heesterbeek, J. A. P., & Dobson, A. P. (2002). Ecology of wildlife diseases (pp. 1-5). Oxford University Press.
- Collinge, S. K., & Ray, C. (Eds.). (2006). Disease ecology: community structure and pathogen dynamics. Oxford University Press.
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