DISEASE TRANSMISSION AT THE WILDLIFE-HUMAN INTERFACE

STAN FENWICK

REGIONAL TECHNICAL ADVISOR USAID-ONE HEALTH WORKFORCE

TUFTS UNIVERSITY-UNIVERSITY OF MINNESOTA

Course Outline

Ecosystems and human health

Ecosystem change and increasing human wildlife contact

Wildlife and disease emergence

Ecosystems, Ecosystem Health and Conservation

Medicine – General Concepts

Definitions

An Ecosystem is a biological community of interacting organisms and their physical environment

Ecology is the biological discipline that deals with the interaction of organisms with the environment, and impacts on all aspects of human and animal health

Biodiversity is the variability among living organisms from all sources, including terrestrial, marine and other ecosystems and ecological complexes of which they are a part

Ecosystem health is a trans-disciplinary concept that bridges the natural, social and health sciences. It can incorporate human values and perceptions that are important in the

management of disease

A healthy ecosystem is defined as a socio-ecological unit that is stable and sustainable, maintaining its character in

composition, organization and function over time while remaining economically viable and sustaining human

communities

Definitions

vet.tufts.edu

Conservation medicine strives to understand health in an

ecological context (identifying the environmental determinants

of health) and uses that understanding to develop preventive or corrective

approaches and to maintain the health of all species in a

sustainable fashion

Central Hypothesis

Climate change and vulnerable ecosystems are leading to an increase in emerging and re-emerging diseases

Economic, social, political and behavioral factors can influence the environment and affect health

SIGNS OF ECOSYSTEM STRESS

• Appearance of emerging infectious diseases

• Loss of habitat and biodiversity

• Increase in “generalist” opportunist species over “specialists”

e.g. seagulls, sparrows, pigeons, rats and mice versus more

specialized animal species

• Decline in species necessary for plant pollination

• Decline in natural predators of pest organisms

• Proliferation of algal blooms along coastlines and waterways

Vietnam News, July 2015

• Biodiversity inhibits population explosions of pest species

• Reduction in biodiversity can lead to closer contact between animal diseases and people – an example is Lyme Disease and white-footed mice, increasing due to a decrease in predators and habitat restructuring, efficient maintenance host for ticks

IMPACT OF BIODIVERSITY ON HEALTH

http://www.alleghenyfront.org/sites/default/files/styles/slideshow_medium_626/public/MouseWithTicks.jpg?itok=F-9pktIb

Human-Livestock-Wildlife Interface

Land Use Change & Human Population

Growth

Increased Contact Between Humans,

Livestock, & Wildlife

Enhanced Flow of Pathogens

Health Risks to Humans, Livestock, & Wildlife

Livelihood Impacts & Economic

Pressures

ENVIRONMENTAL CHANGES INFLUENCING HUMAN AND WILDLIFE CONTACT

Deforestation: removes habitats, predisposes to floods and landslides, habitat fragmentation, changes in vector and reservoir habitats

Changes in surface water availability: increased animal and vector ranges

Bangkok Post July 2015

Overpopulation: expansion into previously uninhabited areas, increased synanthropic animal species (those species ecologically associated with humans)

ENVIRONMENTAL CHANGES INFLUENCING HUMAN AND WILDLIFE CONTACT

Road building: allows access to wildlife and wilderness areas

Climate change

Affects food production and

population nutrition

Can lead to an increase in range

of pathogen reservoirs and

vectors

Contributes to a loss of biodiversity

ENVIRONMENTAL CHANGES INFLUENCING HUMAN AND WILDLIFE CONTACT

Example of Hantavirus transmission in the US

Local enzootic transmission; Sin

Nombre reservoir is deer mice; many

hantaviruses each has a single rodent host

Mild winters and summer rain lead to large increases in rodent numbers;

crowding leads to many infections; mice may enter homes; humans inhale virus or come into contact with urine, faeces or nests; cats, dogs, coyotes can be infected

but do not transmit CDC

Intensive farming practices: result in monocultures, e.g. palm oil plantations impinging on orangutan habitats; impact on vector and reservoir species, e.g. bats and fruit trees

ENVIRONMENTAL CHANGES INFLUENCING HUMAN AND WILDLIFE CONTACT

Increased temperatures

Increase in natural disasters

e.g. floods, rats and leptospirosis

Flooding in Hanoi http://i.telegraph.co.uk

Flooding in Manila news.bbc.co.uk

ENVIRONMENTAL CHANGES INFLUENCING HUMAN AND WILDLIFE CONTACT

Anthropogenic change, wildlife trade, tourism bushmeat consumption etc. all result in closer

contact between humans and other animal species

OTHER EXAMPLES OF HUMAN AND WILDLIFE CONTACT

WILDLIFE AND DISEASE EMERGENCE

• Emerging diseases are those caused by ‘new’ agents or by previously known organisms appearing in places or in species in which the disease was previously unknown

• Includes new animal diseases with an unknown host spectrum, many are zoonotic

• Wildlife reservoirs represent a more frequent source of ‘new’ agents

WHO/FAO/OIE DEFINITION

“An emerging zoonosis is a zoonosis that is newly recognised or newly evolved, or that has occurred previously but shows an increase in

incidence or expansion in geographical, host or vector range”

So, emerging infectious diseases can be -

A known agent appearing in a new geographic area

(e.g. West Nile Virus)

A known agent or its close relative occurring in a hitherto unsusceptible species

(e.g. Avian influenza)

A previously unknown agent detected for the first time

(e.g. SARS coronavirus)

WHY IS THE RATE of ZOONOTIC DISEASE EMERGENCE INCREASING?

…..because the number of high-risk interfaces for disease transmission is increasing, especially

in developing countries

Emerging zoonoses

Approximately 60% of human EIDs are zoonoses (868/1415)

Approximately 72% originate in wildlife

54.3% caused by bacteria (includes rickettsiae) 25.4% by viruses or prions

10.7% by protozoa 6.3% by fungi

3.3% by helminths

IMPORTANCE OF ZOONOSES

Public health

Economic impact

Impact on vulnerable communities

Political impact

24

Principles: Disease Ecology

Pathogen flow and drivers at the

human-livestock-wildlife

interface

The arrows indicate direct,

indirect or vector-borne

pathogen flow. Each box

represents a driver

Jones et al, 2013

The “spillover theory” and drivers of spillover

• Spillover theory – humans constantly challenged with pathogens from animals, only a small proportion invade and fewer still succeed in causing disease

• Can also be used for spillover from wildlife to domestic animals, or

from humans and domestic animals to wildlife • Environmental and climate change • Socio-economic, demographic and political drivers

– Agricultural intensification – Livestock keeping – Bushmeat hunting

Spillover and Disease Emergence

Animal Amplification

C

A

S

E

S

TIME

Human Cases

Wild Animal

Domestic Animal

N.B. spillback to wildlife can also occur

Is relatedness more important than contact for spillover (or spillback)?

Phylogenetic distance from

humans

# o

f sh

ared

pat

hogen

s

Probability of contact with

humans

# o

f sh

ared

pat

hogen

s

Contact rate and spillover risk

Henipaviruses

Lyssaviruses

Flaviviruses

Bunyaviruses

Many ways (direct and indirect) to be exposed to wildlife diseases….

Handling contaminated materials Ingesting infected meat, water Bites or scratches from infected wildlife Inhaling contaminated air, materials Bites from infected insects which have

bitten wildlife

Viral diversity in the host and disease emergence

Hepatitis viruses

SIV/HIV

….a “pool of pathogens”

Known viruses, corrected for number of species & sampling effort per Order

0 5 10 15 20 25 30 35 40

ARTIODACTYLA

CARNIVORA

CHIROPTERA

LAGOMORPHA

NON-HUMAN PRIMATES

PERISSODACTYLA

RODENTIA

Viruses identified per species

Host diversity exposure and disease emergence

photo: C. Gomes Köndgen et. al. Current Biology 2008

Pandemic Human Viruses Cause Decline of

Endangered Great Apes (HMPV, RSV)

Human Metapneumovirus Respiratory syncitial virus

Date Community Symptoms Morbidity Mortality Causative pathogen

March 1999 North

Respiratory

32 (all)

8/32

Streptococcus pneumoniae (a), RSV B

March – December

2001

Middle

Chronic respiratory

1/12

1/12

Non detected

March 2004

South

Respiratory

41 (all)

9/41

S. pneumoniae (b), Pasteurella multocida, HMPV

Haemophilus influenzae

August 2005

South Respiratory 32 (all) 2/32 RSV B

February 2006

South Respiratory 34 (all) 1/34 S. pneumoniae (b) RSV B

February 2006

East Respiratory ? 3/? S. pneumoniae (a) RSV B

Chi et al. 2007, J. Bact.; Köndgen et al. 2008, Curr. Biol.

Pandemic Human Viruses Cause Decline of Endangered Great Apes (HMPV, RSV)

Zoonotic Agent Families in Wildlife

• Rhabdoviridae (Rabies, ABL) • Paramyxoviridae (Nipah, Hendra) • Retroviridae (SIV/HIV) • Flaviviridae (West Nile) • Togaviridae (WEV/EEV/VEV) • Herpesviridae (Herpes B) • Filoviridae (Ebola, Marburg) • Coronaviridae (SARS) • Bunyaviridae (Hantaviruses,

RVFV) • Orthomyxoviridae (H1N1, H5N1

influenza) • Others?????????????

J. Epstein copyright 2006

37

Kock 2014

Estimated global mortality from selected wildlife zoonoses

Log scale

Five stages have been proposed for the evolutionary transformation of an animal pathogen

Stage 1: Pathogen only in animals Stage 2: Pathogen moves occasionally from

animals to humans (‘primary infection’) Stages 3/4: ‘Secondary infections’ increasing

transmission from animal to humans and humans to humans

Stage 5: Pathogen exclusive to humans

EVOLUTION OF INFECTIOUS DISEASES

Action, events or circumstances which may trigger a wildlife disease event

Human-wildlife

interactions

Livestock-wildlife

interactions

Wildlife management

actions

Climatic events

Can result in the introduction of disease or alters the manner in which an existing disease occurs

Individual effect

Population effect

Ecosystem effect

Host-parasite ecological continuum and disease emergence

• Few diseases affect only one group • Complex relationships set scene for disease emergence

• Arrows show factors driving disease emergence

Daszak et al., 2000. Science; 287

Canine distemper

Lyme disease

Taeniasis

Rabies

Population growth and urbanisation

Technology and industry

Travel and trade

Wars and social disruption

Ecological changes due to economic development and

land use

Microbial adaptation

Emerging Infectious Diseases Some factors contributing to infectious disease emergence

Human vulnerability (drugs, alcohol, immunosuppression)

Climate and weather Changing ecosystems

Poverty and social inequality Breakdown of public health measures

Lack of political will Intent to harm

Increases in numbers of unregulated companion animals, synanthropic animals and birds and arthropod vectors

Concentrated populations of wild and domestic animals outside cities expose people to zoonotic agents by direct or indirect contact

Growing population of drug and alcohol impaired and immuno-suppressed people worldwide are at higher risk of zoonoses

SOME RECENTLY EMERGED ZOONOSES

Human immunodeficiency virus (HIV)

Haemorrhagic fevers (Ebola, Marburg)

Henipaviruses

Highly Pathogenic Avian Influenza (HPAI)

Severe Acute Respiratory Syndrome (SARS/MERS)

Bat Diseases

Bats have become one of the most significant reservoirs for emerging zoonotic diseases over the past 2 decades • Lyssavirus (Australia) • Rabies (world wide distribution) • Hendra (Australia) • Nipah (Malaysia, S. Asia) • Menangle (Australia) • SARS (Asia & world wide spread) • Ebola, Marburg (Africa) • Paramyxoviruses (possibly mumps) (worldwide)

Fruit bats a major reservoir

Family Filoviridae – Genus Filovirus EBOLA VIRUS

• First recognised in 1976 in Sudan and DRC (near Ebola river) • Average case fatality rate of ~50% • First outbreaks in remote villages of Central Africa near rainforests,

recent outbreak has spread to urban areas • 5 species – Zaire, Bundibugyo, Sudan, Tai Forest (all from Africa)

and Reston (non-pathogenic, from Philippines) • Pteropid bats thought to be the natural hosts although natural

reservoir not confirmed • Primates, antelope and porcupines can be infected and die

humans handle or eat carcass of dead primate or duiker human infection occurs

Suspected Ebola transmission in Africa

Bat Wild primate Duiker

In 2003, 114/128 people infected with Ebola in Congo/Gabon died – and an estimated 6-800

gorillas!

www.cdc..gov

Total cases in the 3 worst affected West African countries, 2014-15 (Sierra Leone, Liberia, Guinea)

In the recent Ebola outbreak, which started in 2014, there have been around 24,000 cases

with 14,000 deaths, over 58% mortality

Control of emerging diseases from wildlife or to wildlife – requires a One

Health approach

Animal

Amplification

C

A

S

E

S

TIME

Wildlife ecologists

Some of the ‘characters’ in One Health

Conservationists

Veterinarians

Behavioral Scientists Field Epidemiologists

Diagnosticians

Medical and Public Health Practitioners

Many difficulties in dealing with wildlife diseases…

Hard to sample wildlife; hard to detect diseased animals and carcasses rarely found

Few diagnostic tests for wild animals Knowledge of wildlife diseases, transmission and cycles

lacking People very protective of wildlife

Few interventions used for livestock can be used in wildlife,

e.g. culling

Although when such interventions are used a lack of ecological understanding can lead to unforeseen problems

..should have involved wildlife ecologists in the planning

SMART surveillance

Strategic selection of geographic locations for surveillance

Strategic selection of species for surveillance

Animal

Amplification

C

A

S

E

S

TIME

Human Cases

Wild Animals

Domestic Animals

Early Detection and Control

Opportunities

Wildlife Surveillance and Forecasting

This enables interventions or surveillance to be targeted

DAY

CA

SES

Current Outbreak Detection and Response

Adapted from J. Davis, Climate Adaptation Workshop, Nov. 2003

First Case

Detection & Reporting

Laboratory Confirmation

Response

Opportunity for control

DAY

CA

SES

First Case Detection & Reporting

Lab Confirmation

Response

However, if we have effective early warning systems in place

Surveillance, Observations

and Monitoring Information

Adapted from J. Davis, Climate Adaptation Workshop, Nov. 2003

Opportunity for control

What’s Next?

• Recently a number of new avian influenza virus strains have infected humans, the most serious being H7N9

• A new coronavirus, MERS, has been identified in the Middle East, closely related to SARS virus and reservoir probably bats; humans most likely infected via contact with camels

• Most recently an epidemic of Ebola virus has occurred in West Africa, probably linked to initial bush meat consumption (bats, primates)

http://virologydownunder.blogspot.com.au/

From March 2013 – May 2015 there have been 665 confirmed cases of human H7N9 infection, with 229 deaths = 34.4% mortality rate. Most cases in China, few in travellers (HK,

Taiwan, Malaysia)

Middle East Respiratory Syndrome (MERS) is a viral respiratory illness that is new to humans. It was first reported in Saudi Arabia in 2012 and has since spread to several other countries, including the United States. Most people infected with MERS-CoV developed severe acute respiratory illness, many of them have died. Camels and bats are believed to be linked to the epidemiology of the disease To June 2015 there have been 1329 cases, with 525 deaths (39% mortality)

MERS in South Korea

An outbreak of MERS was reported in South Korea in

May 2015, in a traveller returning from Saudi

Arabia. The outbreak was poorly contained by

hospitals

Since June 29th there have been 182 confirmed cases (1

in China) with 32 deaths, 17.6% mortality,

considerably lower than in Saudi Arabia (44%)

In Conclusion

•The occurrence of emerging zoonotic diseases is multifactorial, and is affected by many causal factors, including ecological conditions

•Overpopulation has stressed the environment and resulted in closer contact between people and wild animals

•Environmental stability and biodiversity are important for ecological, human and animal health

•Control of new emerging diseases needs to take into account related environmental factors

The Final Word From SEAOHUN (again)!!