Objectives

    Infectious disease hasbecome a significant global environmental problem. This studyinvestigates the emergence and spread of Koi HerpesVirus (KHV) in Lake Biwa, Japan. KHV is apathogen responsible for episodic mass mortality of commoncarp (Cyprinus carpio carpio)  since the late1990s. The common carp is the original domesticated aquaculturespecies, and an important source of protein today .

    This study has three mainobjectives: (1) To describe Koi Herpes Virus diseaseecology, including: the specific links betweenanthropogenic changes to freshwater ecosystems and the emergence andspread of KHV disease; the impacts of KHV diseaseon local ecosystem services; the social and culturalattempts to address KHV disease; and the environmentalchanges associated with human adaptation; (2) Todescribe a general model of linkage betweenenvironments, pathogens and humans ; (3) To suggesthow interactions between pathogen and humans may be modifiedin order to mitigate the human andenvironmental damages associated with infectious diseases.

 

ResearchMethods and Organization

    Fields surveys areconducted at Lake Biwa, Japan, and Lake Erhai, China.Laboratory work is undertaken at RIHN.

Our project isorganized into five research groups, plus executive andadvisory groups, as follows:

   The Human AlterationsGroup investigates the effects of anthropogenicenvironmental alteration on the emergence

and spread of KHV and thebehavior of its host Cyprinuscarpio carpio.

   The Pathogen and HostEcology Group defines the biology and ecology of KHVand carp, and so describes

the environmental factorsinvolved in KHV infection and transmission.

   The Ecosystem ImpactsGroup examines the process of infection and theeffects of KHV disease on ecosystem

functions such as materialcycling.

   The Economics and CultureGroup investigates the losses associated with KHVdisease, including of ecosystem

services or other economicand cultural phenomena, and describes the socialattempts to redress those losses.

   The Feedback Groupexamines the human response to losses caused by KHVdisease, and the environmental

change associated withthis response.

   The Executive Group coordinates theactivities of each group and develops the model ofpathogen-human 

interactions.

   Finally, an Advisory Group composed ofrecognized experts in relevant fields makes suggestionsin order to

improve the research.

 

Perception andcontribution to global environmental problems 

     Field surveys are being conducted primarilyat Lake Biwa, Japan, where researchers from various disciplines and fishermen have accumulated much data, and at Lake Erhai, China. China is responsible for almost theentire global carp production. Lake Erhai is an inland lake in China that has never experienced anoutbreak of KHV. We will create a model to predict the outbreak and spread ofKHV in Lake Biwa by accumulating and synthesizing both new and existing data from Lake Biwa.  The model will be applied to Lake Erhai to provide suggestions for how to manage the lake to lessen the probability ofan outbreak of KHV disease. The practical application of this model to such animportant region is critical to attenuating the global problem of KHV disease.  The Lake Biwa model will bemodified to apply to other infectious diseases in other areas, to suggestenvironments that might prevent the outbreak and spread of infectious disease, and todemonstrate how to facilitate the safe coexistenceof humans and pathogens.

1) We found that water temperature on gentlegradient lakeshores is more spatially and temporallyvariable than on steep banks constructed by humans.This result suggests that gentle shores canprovide a wider range of thermal conditions that allows fishto finetune their (everyday) thermoregulatory behavior,acclimate efficiently to (longer-term) changes in watertemperature, and generally alleviate stresses associated with unfavorable water temperatures and soreduce susceptibility to KHV (Yamanaka et al. 2010).

2) We established a method to measure KHVpresence in natural water (Minamoto et al., 2009a;Honjo et al., 2010) and found that in the five years sinceits presence was first documented, KHV has spreadthroughout Lake Biwa (Fig. 4) (Minamoto et al., 2009b).

3) Telemetry tracking of carp behaviorrevealed that carp favor warmer water temperatures. This findingwas incorporated into our mathematical modelpredicting KHV disease outbreaks.

4) We found no evidence of KHV antibodies incarp smaller than 30cm, while 54% of carp largerthan 30cm were KHV positive. Of antibody-positiveindividuals, 44% contracted KHV by polymerase chainreaction (PCR), strongly suggesting that thosesurviving carp become KHV carriers. A few individuals werepositive by PCR but negative for antibodies,indicating recent infection. These results suggest thattransmission of KHV is still occurring within the nativecommon carp population in Lake Biwa (Uchii, et al.,2009).

5) We developed a non-invasive method (i.e. amethod that does not require handling fish) to quantifyhow water conditions stress carp. This method indicatesthat changes in water temperature do stress carp.

6) In Lake Erhai we found a pattern ofgradient and water temperature conditions similar to those ofLake Biwa. The similarity indicates Lake Biwa can serveas a model for other lakes.

7) At national and international conferences,we have presented our findings on the linkages betweenenvironment, pathogen and humans, and emphasized theirimportance to the prevention and control of infectiousdisease.

1) Develop a method to quantitatively detectKHV in sediment, organisms and other elements in aquaticecosystems.

2) Clarify the distribution of infectious KHVin Lake Biwa.

3) Develop a micro-device to measure thequantity and infectivity of KHV in situ.

4) Determine the environmental factorsinvolved in KHV dynamics and infectivity.

5) Use outdoor experimental tanks to defineoptimum water temperature for carp.

6) Describe the environmental characteristicsof the places where KHV and carp interact, and clarify thebehavior of the KHV-infected carp in order to revealthe locations where infection likely occurs .

7) Conduct controlled experiments to revealthe relationship water temperature and carp stress andsusceptibility to KHV.

8) Demonstrate the ecological effects of carpon species composition in experimental ponds.

9) Evaluate the cultural and nutritionalvalue of carp as a human food.

10) Assess the economic and cultural impactsof carp die-offs.

11) Create a preliminary model of theinteractions between environmental change, KHV and humans.

12) Survey the spatial and temporaldistribution of water temperature in Lake Erhai in order toestablish the applicability of Lake Biwa findings to LakeErhai.

13) Describe the common parameters of KHV andother infectious diseases.

14) Promote collaboration with the DIVERSITASprogram of international biodiversity science.

15) Develop a set of recommendations toprevent or minimize the emergence and spread of infectiousdiseases.