Transcript and biodiversity

Host animal biodiversity and
Regulation of Human diseases
BORDES Frédéric
DVM, PhD
ISEM CNRS Université de Montpellier 2
Montpellier, France
Phnom Pen 18-19 Novembre 2014
WHY BIODIVERSITY MATTERS FOR
HUMAN DISEASES
OR
What are the links between animal
biodiversity and human diseases ?
2
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
3
3) « Anthropocene »:
biodiversity loss is increasing. Whether and how
biodiversity can protect humans against infectious diseases became crucial
Deforestation, roads building,alteration habitats
•
Urbanization
Agricultural and land uses changes
( crops, cattle, pesticides)
Dams, irrigation
ALTERATION OF INTERACTIONS, BIOLOGY, ABUNDANCE
AND DIVERSITY OF HOSTS
(VECTORS/ INTERMEDIATE HOSTS/DEFINITIVE HOSTS)
PATHOGEN TRANSMISSION/DISEASE RISK
4
How biodiversity can
theoretically be linked to human
diseases?
5
HYPOTHESIS 1 : « AMPLIFICATION EFFECT »
Hosts serve as habitats and resources for parasites
Biodiversity is expected to be linked to a higher « parasites pool »
Biodiversity begets infectious disease
HYPOTHESIS 2 « DILUTION EFFECT »
Hosts are heterogeneous
Biodiversity is expected to be linked to reduced or « wasted » transmissions
Biodiversity buffers infectious diseases
6
Global approach:
dilution or amplification?
7
AMPLIFICATION AT WORK ?
Geographical variation in Human pathogen richness,
Dunn et al.2009, Procs
Global drivers of human pathogen richness and prevalence, Dunn et al.2010
Proceedings Royal Society London B
Mammal species richness
Davies & Bucley, 2011, Phil. Trans.Roy. Soc Lond B
8
s
…….OR DILUTION AT WORK?
?
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)
9
REGIONAL APPROACH
10
Lyme disease in USA: dilution
“
Ostfeld & Keesing, Conservation Biology
2000
West Nile in USA (Lousiana): dilution at work
Ezenwa et al.2008
1°) Associations between non passerine species richness and mosquito infection rates
2°)
Relationship between human WNV disease and non-passerine Species Richness
Ezenwa V O et al. 2006
Rodents Hantaviruses: dilution at work
USA, Europe Panama, SE ASIA
Hantavirus prevalence
Blasdell et al.2011 Ecohealth
Rodents’ richness
Panama (Suzan et al.2009) ; USA (Clay et al.2009; Dizney et Ruedas, 2009),
Belgium (Tersago et al.2008)
13
Chagas disease risk is higher when mammalian diversity is low
Dogs as sentinels of epidemiological risk for
Humans for Chagas disease in Brazil
Geospatial analysis :
reduction of the small mammal fauna
(richness and abundance) is linked to
higher exposure of dogs to infection.
Xavier et al. (2012) Lower Richness of Small Wild Mammal Species and Chagas Disease Risk. PLoS Negl Trop Dis
14
But Lyme disease is not always amplified in species –poor community
Density of nymphs
Mammalian community on Block Island :
5 rodent Species and white tailed deer
Density of infected nymphs
Prevalence d’infection of nymphs
Mammalian community on mainland :
35 species
« 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
15
Malaria burden in the Brazilean Amazon: rather amplification at work
Almost half of the death attributed
to malaria in Americas occured in Brazil
Spatial analysis of a
large data set (Valle & Clark, 2013)
Forest cover (and biodiversity)
is the strongest predictor
of malaria Risk in The
b
Brazilian Amazon
16
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)
Negative = dilution effect
Positive= amplification effect
17
Parasitoloy,2012:
Ecology, 2014:
2013:
DILUTION AND DISEASES: A HOT
AND CONTROVERSIAL DEBATE……
Trends in Ecology and Evolution, 2013:
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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
19
Landscapes and Vectors’
ecology matter
EASTERN PERU
BRAZILEAN AMAZON
Deforestation
Secondary
vegetation
Shrubs
Anopheles darlingi
Deforestation
soya
MALARIA
RISK
Cattle,Pasture
Anopheles darlingi
20
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
Hunting
Kilpatrick et al.2014, J . Med Entomology
21
Abundance of susceptible hosts matters
Sites investigated for Lyme disease differed in
-small mammal richness and
-relative abundance of deer mice Peromyscus maniculatus
At sites where the relative abundance
of mice is higher , species richness
had little apparent effect on nymph
infection
Werden et al. (2014) PLoS ONE
22
Conclusion:
No generality at all
Biodiversity is only one parameter of
Human regulation diseases
Thank you
23
3) « Anthropocene »:
biodiversity loss is increasing. Whether and how
biodiversity can protect humans against infectious diseases became crucial
Deforestation, roads building,alteration habitats
•
Urbanization
Hunting
Agricultural and land uses changes
( crops, cattle, pesticides)
Dams, irrigation
ALTERATION OF INTERACTIONS, BIOLOGY, ABUNDANCE
AND DIVERSITY OF HOSTS
(VECTORS/ INTERMEDIATE HOSTS/DEFINITIVE HOSTS)
PATHOGEN TRANSMISSION/DISEASE RISK
24
25
How dilution works ?
Two primary mechanisms:
1. Transmission interference ( mainly for vector borne
diseases)
2. Susceptible host regulation ( mainly for directly
transmitted diseases)
26
Transmission interference : some less competent hosts can decrease
human disease risk by intercepting pathogen transmission stages
High
Biodiversity
With
different
competence
among
hosts
Reduced infected
larval and nymhs
Reduced human risk
27
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
EX: Clay et al.2009 Ecohealth
Rodent species diversity
contacts
Pathogen prevalence
28
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
29