The impact of biodiversity changes The impact of biodiversity changes

on human healthon human health

Oliviero Spinelli

Objective of the literature study

To provide an overview of existing information on therelationships between changes in biodiversity and two ecosystem

services related to human health:

ü Regulation of infectious diseases

ü Provision of medicines

Infectious diseases selectedDISEASE

BIODIVERSITY/ ECOSYSTEM

CHANGE PATHOGEN VECTORS No ESTIMATED

CASES/YEAR

ORIGINAL ENDEMIC AREAS

Malaria Deforestation, water changes

Plasmodium spp.

Mosquitoes (Anopheles spp) 350-500 millions

All continents with the exception of

Europe

Yellow fever Deforestation,

invasion of alien species

Alphaviruses Flavivirus

Mosquitoes Aedes spp.

(Stegomya subg.) 200,000 South-East Asia,

and West Africa

Dengue and Dengue

hemorrhagic Fever

Urbanisation, deforestation,

invasion of alien species

Flavivirus Mosquitoes Aedes

spp. (Stegomya subg.)

50 millions Central-South America, Asia,

Africa

Chikungunya fever

Water changes, invasion of alien

species Alphavirus

Mosquitoes Aedes spp.

(Stegomya subg.) Very variable

Continental areas and Islands of the

Indian Ocean

West Nile Fever

Pathogens, vectors and hosts changes Flavivirus Mosquitoes

(Culex spp.) Very variable Africa and South America

Leishmaniasis Deforestation,

agricultural development

Leishmania spp

Sand flies (Phlebotominae) 600.000

South Europe, Africa, Asia

Middle East South America Indian

subcontinent Tick borne

encephalitis Sylviculture, water

management Flavivirus Ticks Ixodes spp. 10-12,000 European

countries

Lyme disease Depletion of predators,

deforestation Borrelia spp. Ticks

Ixodes spp. Undetermined North hemisphere countries

Avian flu

Disappearance of wetland, Pathogens,

vectors and hosts diversity

Influenza A viruses Poultry Undetermined Asia

Schematic overview

Human behaviour

Drivers of biodiversity

changes

Host/ reservoir population

Vector/ Host habitat

Pathogen transmission

Vector population

Infectious disease incidence

Socio-economic burden

The inter-linked relationships between human behaviour, ecological modifications and changes in infectious disease incidence

Biodiversity changes relevant to the infectious disease incidence

Changes in species diversityü Pathogensü Vectorsü Hostsü Preysü Predators

Changes in habitats structural diversityü Deforestationü Modifications of aquatic

ecosystemsü Changes in agro-ecosystemsü Urbanisationü Soil alteration

Changes in species diversity: Hosts

This “dilution effect” reduces disease incidence through:

ü transmission reduction, a reduction in the probability of transmission of the disease from infected hosts to vectors,

ü encounter reduction, a reduction in the rate of encounters between hosts and infected vectors,

ü susceptible host regulation, a reduction in the number of susceptible hosts,

ü vector regulation, a reduction in infected vector density.

Infection rates among vectors, and ultimately humans, will be lower in highly diverse host communities, where incompetent hosts dilute rates of disease transmission between vectors and highly competent hosts.

Changes in hosts diversity: the West Nile Virus (1)

Changes in hosts diversity: the West Nile Virus (2)

Ostfeld (2008) raises a hypothesis on the dilution effect in the WNV:

Ø Mosquitoes occurring in areas of low avian diversity have a high probability of encountering a competent reservoir for WNV and therefore a high probability of acquiring infection during blood meals.

Ø Mosquitoes occurring in areas of high avian diversity have a higher probability of taking a blood meal from one of the many species that are less competent or incompetent as reservoirs forWNV.

Changes in hosts diversity: the West Nile Virus Conclusions

Counties in the USA with high avian diversity should have a low human incidence of WNV disease, whereas those with low avian diversity should have a high WNV incidence.

Ezenwa et al. 2007 found that in the Gulf Coast of Louisiana infection rates in Culex mosquitoes were negatively correlated with wetland area and that wetland area was positively correlated with non-amplifying bird hosts. This suggests that preserving large wetland areas, and by extension, intact wetland bird communities, may represent a valuable ecosystem-based approach for controlling WNV outbreaks.

Changes in hosts diversity: open questions

According to Ostfeld et al. (2008), the following questions on the interaction between host diversity and infectious disease remain:

üHow does host diversity interact with diversity in other components of the broader disease system?

üWhich are the effects of hosts diversity per se (e.g. species richness or evenness) and which effects depend on the species composition in the host community?

üWhat is the shape of the relationship between host diversity and disease risk?

Changes in habitats structural diversity: Deforestation

Clearing forests alters the main elements of local ecosystems, such as:

ü microclimate (such as temperature and humidity)ü soil (pH and microorganisms)ü aquatic conditions (i.e. disappearance of the small ponds inside the forest)ü ecology of local flora and fauna, including human disease vectors

Deforestation destroys natural boundaries that protect humans from exposure to new diseases

Deforestation: Tick borne encephalitis (1)

The border of known TBE endemicity is defined by the red dotted line

Deforestation: Tick borne encephalitis (2)

Changes in forest cover are likely to affect the occurrence of tick vectors (Ixodes ricinus and I. Persulcatus) and competent vertebrate hosts (Apodemus spp.).

Ungulates are dilution or non-competent hosts (i.e. they act as tick hosts, but are not responsible for virus transmission between ticks).

The presence of wild ungulate species, such as red deer (Cervus elaphus) and roe deer (Capreolus capreolus), has been shown to be essential in maintaining and amplifying tick populations and, consequently, the TBE virus.

Deforestation: Tick borne encephalitis Results

Substantial changes in vegetation structure that improve habitatsuitability for the main TBE reservoir hosts (small mammals), as

well as an increase in roe deer abundance due to changes in landand wildlife management practices, are likely to be among the

most crucial factors affecting the circulation potential of Western TBE virus and, consequently, the risk of TBE emergence in

humans in western Europe.

Rizzoli et al. (2009) analysed the effect of a larger-scale increase in deer abundance in combination with changes

in forest structure on TBE incidence in humans in northern Italy.

The estimated cost of the Louisiana 2002 WNF epidemic (329 cases) was US$ 20.1 million

from June 2002 to February 2003,

including:

• a US$ 10.9 million cost of illness (US$ 4.4 million medical and US$ 6.5 million non-medical costs)

•a US$ 9.2 million cost of public health response.

Malaria costs Africa more than USD 12 billion a year,

which is about 3% of the total GDP of the Region (WHO-

AFRO, 2004).

“In some countries with a heavy malaria burden, the

disease may account for as much as 40% of public health

expenditure, 30-50% of inpatient admissions, and up to 50% of outpatient visits”

(WHO, 2009).

Estimates carried out in the United States show that about $ 75 billion of pharmaceuticals of natural origin are sold each year (Kaimowitz, 2005).

…not just ecological values

Conclusions (1)

Infectious disease and maintaining biodiversity have rarely been considered together, despite the recognition of the great importance of biodiversity for human health.

A health care strategy for an infectious disease must take into account its biology and ecology, the possible range

of adverse effects, costs and benefits of protective actions and risks in decision making.

Conclusions (2)

Ø the role of biodiversity in the emergence, spread and transmission of infectious diseases;Ø the relations between man-made changes in ecosystems, biodiversity and transmission of infectious diseases to humans, including their economic impact;Ø the value of biodiversity in protecting against infectious diseases.

Further interdisciplinary research (combining ecology, biology, epidemiology, pharmacology, medicine, social sciences and economics) is needed in order to better understand:

Thank you for your attention!!!

Oliviero Spinelli