De?nition ofemerging diseasean infectiousdisease that has newly appeared in a population or that has been known for sometime but is rapidly increasing in incidence or geographic rangeMultiple environmental stressors infreshwater ecosystemsFreshwaterecosystems are the most severely tainted and distorted ecosystems on the earth becausehumans have always need water for the survival that’s why the live nearfreshwater bodies for millennia.
Their comparatively small volumes and the factthat fresh waters receive terrestrial run-off have contributed to theirdegradation whilst dam construction, canalisation and water abstraction haveextensively altered freshwater habitats (for review see Davis, Sim& Chambers,2010; Tockner et al., 2010. In marine ecosystemsintroductions for sports ?sheries are unfeasible because of the huge and open environmentof the marine habitation although introductions via aquaculture may haveimplicated for emerging disease.certainly, thenumber of deaths rate in freshwater environment are greater than in most earthlyenvironments (Dudgeon et al., 2006), and also freshwater ecosystem have morerisks of endangered and endangered species than in marine or terrestrialsystems (Ricciardi& Rasmussen, 1999).
Emerging diseases have interrelatewith these high environmental losses in fresh waters in various ways.Finally,fresh waters are challenged by outstanding habitation loss via water build ascompeting human stakeholders effect an increasing shortage of clean freshwateras a result of climate change (Johnson et al., 2009; Grantham,Merelender, 2010).Unique environmental attributes offresh waters may contribute to DiseaseParasitescaused many diseases which have complicated life cycles that include both marineand terrestrial stages (e.g. Lv et al.
, 2011), and freshwater systems presentdifferentiate and inherent facial appearance agreeable to such life histories. experience possibility between transferableagents and vulnerable hosts is increased by the small volumes and the linearnature of rivers Freshwaterecosystems also linked with the other ecosystems like terrestrial and marineecosystems. This has inference for disease emergence if anadromous species actas vectors to move pathogens between marine, estuarine and freshwaterenvironments. For example, the fungal-like parasite of marine ?sh,IchthyophonushoferiPlehn, can rapidly establish in freshwateraquaculture situations following feeding with infected material. Thus, at leastsome marine pathogens are capable of invading freshwater systems if theopportunity arises (Ono et al., 1966Baseline data and understandinglong-term trendsFirst and leadingis the common lack of baseline data need to assess whether the rate of diseasesare increasing in frequently or strictlyThe data isvery useful for the establishment of international guidence of aquatic ?shdiseases due to the increasing occurrence arising from pollutant contactTrophic loss and ecosystem functionThe relatedstructural and functional transformations of ecosystems caused by over?shingraise the thorny question of whether longterm overexploitation of resources mayact as an underlying driver of subsequent change and argue for caution whenidentifying causes of disease emergence and disease management strategies.
Alternatively,disease outbreaks may occur if trophic changes result in habitat degradationthat in turn cause stress and greater susceptibility to disease. For instance,loss of higher trophic levels via over?shing may precondition for speciesintroductions or eutrophication (e.g.
via the harvesting of suspension-feedingoysters in Chesapeake Bay; Jackson, 20 An unresolved issue is whether thelonger period of over?shing and ecosystem transformation in freshwater systemsis signi?cant for disease emergence. Did the effects of over?shing infreshwater systems occur so long ago that the loss of trophic structure may nolonger underlie and contribute to disease emergence01) both of which in turn havebeen linked with disease emergence.. At present, it is not clear whetherdisease emergence might facilitate such shifts, although links witheutrophication suggest that diseases may play a role in driving communitiesfrom one state to another. There is evidence that marine diseases maycontribute to ecosystem change, with diseases of corals facilitating phaseshifts from a coraldominated state to an algal-dominated state.
Some environments are improvingAlthough theemerging diseases are always depend on the environment, the change in theenvironment is causing disease emergence in a number of situations, it is alsothe case that some freshwater bodies are improving in quality. For example, theenvironmental recovery of the River Thames demonstrates the dramatic turnaroundpossible in environmental quality and ?sh biodiversity following remediationactions such as improved sewage ef?uent treatment and reductions in industrialwaste inputs.