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Host animal biodiversity and Host animal biodiversity and Regulation of Human Regulation of Human
diseasesdiseases
BORDES FrédéricDVM, PhD
ISEM CNRS Université de Montpellier 2Montpellier, France
Phnom Pen 18-19 Novembre 2014
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WHY BIODIVERSITY MATTERS FOR HUMAN DISEASES
OR
What are the links between animal biodiversity and human diseases ?
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1) 61% of human infectious diseases ARE ZOONOTIC DISEASES implying many different animal hosts ( pathogens are often generalists)
MULTI-HOST DISEASES
2) HOST SPECIES ARE NOT HOMOGENEOUS in terms of parasites’
susceptibility and potential of transmission: « COMPETENT » OR « INCOMPETENT » HOSTS MAY PLAY DIFFERENT ROLES
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PATHOGEN TRANSMISSION/DISEASE RISK
ALTERATION OF INTERACTIONS, BIOLOGY, ABUNDANCE AND DIVERSITY OF HOSTS
(VECTORS/ INTERMEDIATE HOSTS/DEFINITIVE HOSTS)
Agricultural and land uses changes ( crops, cattle, pesticides)
Deforestation, roads building,alteration habitats Dams, irrigation
3) « Anthropocene »: biodiversity loss is increasing. Whether and how biodiversity can protect humans against infectious diseases became crucial
Urbanization
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How biodiversity can theoretically be linked to human
diseases?
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Global approach: dilution or amplification?
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Global drivers of human pathogen richness and prevalence, Dunn et al.2010Proceedings Royal Society London B
AMPLIFICATION AT WORK ?
Mammal species richness
Davies & Bucley, 2011, Phil. Trans.Roy. Soc Lond B
Mammal species richness
Davies & Bucley, 2011, Phil. Trans.Roy. Soc Lond B
Geographical variation in Human pathogen richness, Dunn et al.2009, Procs
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ss
…….OR DILUTION AT WORK?
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Hot spots for emerging diseases
(Jones et al.2008, Nature)
Hot spots for erosion in mammals’ diversity(Schipper et al.2009,Science)
Focus on Asia-Pacific area: similar pattern
Biodiversity loss seems linked to an increase in zoonotic outbreaks (Morand et al.2014, Plos One)
Focus on Asia-Pacific area: similar pattern
Biodiversity loss seems linked to an increase in zoonotic outbreaks (Morand et al.2014, Plos One)
?
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REGIONAL APPROACH
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“
Lyme disease in USA: dilution
Ostfeld & Keesing, Conservation Biology2000
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1°) Associations between non passerine species richness and mosquito infection rates
West Nile in USA (Lousiana): dilution at work
2°) Relationship between human WNV disease and non-passerine Species Richness
Ezenwa V O et al. 2006
Ezenwa et al.2008
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Hantavirus prevalence
Rodents’ richness
Panama (Suzan et al.2009) ; USA (Clay et al.2009; Dizney et Ruedas, 2009), Belgium (Tersago et al.2008)
Blasdell et al.2011 Ecohealth
Rodents Hantaviruses: dilution at work USA, Europe Panama, SE ASIA
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Xavier et al. (2012) Lower Richness of Small Wild Mammal Species and Chagas Disease Risk. PLoS Negl Trop Dis
Dogs as sentinels of epidemiological risk for Humans for Chagas disease in Brazil
Chagas disease risk is higher when mammalian diversity is low
Geospatial analysis :reduction of the small mammal fauna (richness and abundance) is linked to higher exposure of dogs to infection.
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« Borrelia burgdorferi nymphal infection prevalence (NIP) was similar between island …contrary to what is predicted by the dilution effect hypothese »
States et al.2014 Infection Genetics and Evolution
Mammalian community on Block Island : 5 rodent Species and white tailed deer
Mammalian community on mainland : 35 species
Density of nymphs
Density of infected nymphs
Prevalence d’infection of nymphs
But Lyme disease is not always amplified in species –poor community
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Spatial analysis of a large data set (Valle & Clark, 2013)
Malaria burden in the Brazilean Amazon: rather amplification at work
Almost half of the death attributed to malaria in Americas occured in Brazil
bb
Forest cover (and biodiversity) is the strongest predictor of malaria Risk in The Brazilian Amazon
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Pattern for tropical parasites : dilution is not expected at all
Focus on 69 tropical zoonotic protozoa and helminths ( including Leishmnia, Trypanosoma sp., Plasmodium sp.,Toxoplasma, Taenia sp., Trichuris, Schistosoma )
* Projected link between biodiversity and these parasites (Wood et al.Ecology 2014)
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Negative = dilution effectPositive= amplification effect
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Parasitoloy,2012:
DILUTION AND DISEASES: A HOT AND CONTROVERSIAL DEBATE…… DILUTION AND DISEASES: A HOT
AND CONTROVERSIAL DEBATE……
Trends in Ecology and Evolution, 2013:Trends in Ecology and Evolution, 2013:
2013:
Ecology, 2014:
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Hosts diversity and richness is only one parameter
1.Vectors’ ecology and landscapes matter
2.Vectors’ amplification matters
3. Abundance of susceptible hosts matters
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EASTERN PERU BRAZILEAN AMAZON
ShrubsSecondary vegetation
soya Cattle,Pasture
Deforestation Deforestation
Anopheles darlingi Anopheles darlingi
Landscapes and Vectors’ ecology matter
MALARIA RISK
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VECTORS AMPLIFICATION : LYME DISEASE IN MASSACHUSSETS Deers are not competent hosts for B. Burgorferi but important hosts for ticks adult and mymphs (blood meals) .Despite limiting pathogen transmission they amplify vectors populations…
This non competent host increases disease risk for humans
Kilpatrick et al.2014, J . Med Entomology
Hunting
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Abundance of susceptible hosts matters
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Sites investigated for Lyme disease differed in
-small mammal richness and
-relative abundance of deer mice Peromyscus maniculatus
Werden et al. (2014) PLoS ONE
At sites where the relative abundance of mice is higher , species richness had little apparent effect on nymph infection
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Conclusion:
No generality at allBiodiversity is only one parameter of
Human regulation diseases
Thank you 23
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PATHOGEN TRANSMISSION/DISEASE RISK
ALTERATION OF INTERACTIONS, BIOLOGY, ABUNDANCE AND DIVERSITY OF HOSTS
(VECTORS/ INTERMEDIATE HOSTS/DEFINITIVE HOSTS)
Agricultural and land uses changes ( crops, cattle, pesticides)
Deforestation, roads building,alteration habitats Dams, irrigation
3) « Anthropocene »: biodiversity loss is increasing. Whether and how biodiversity can protect humans against infectious diseases became crucial
Hunting
Urbanization
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How dilution works ?
Two primary mechanisms:
1. Transmission interference ( mainly for vector borne diseases)
2. Susceptible host regulation ( mainly for directly transmitted diseases)
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Transmission interference : some less competent hosts can decrease human disease risk by intercepting pathogen transmission stages
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High Biodiversi
tyWith
different competence among
hosts
Reduced infected larval and nymhs
Reduced human risk
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Susceptible host regulation: when the presence of non-competent competitors in high –biodiversity context
- REDUCED the competent hosts’ density that results in less intraspecific transmission of a pathogen and hence a lower risk for humans
and/or - REDUCED hosts’ encounter rates between susceptible hosts
and then pathogen transmission
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Rodent species diversity
-EX: Clay et al.2009 Ecohealth
Pathogen prevalence
contacts
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Chiclero's ulcer , caused by the sandfly-vectored protozoan parasite Leishmania mexicana an other example of a decline in disease risk with loss of biodiversity
This parasite primarily infect « chicleros », the men who spend months in the forest collecting chicle, the latex produced by sapodilla trees.
Chiclero's ulcer