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

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

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

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

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

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Forest cover (and biodiversity) is the strongest predictor of malaria Risk in The Brazilian Amazon

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

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

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

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