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Emerging Infectious Disease, Zoonoses and the Human-Livestock-Wildlife Health Interface. A Primer for Conservationists. College of African Wildlife Management Mweka, Tanzania July 2008. 19-year-old Egyptian Dies of Avian Flu (Bloomberg).

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Emerging Infectious Disease, Zoonoses and the Human-Livestock-Wildlife Health Interface

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emerging infectious disease zoonoses and the human livestock wildlife health interface

Emerging Infectious Disease, Zoonoses and the Human-Livestock-Wildlife Health Interface

A Primer for Conservationists

College of African Wildlife Management

Mweka, Tanzania

July 2008

anthrax claims 20 cows cattle market closed new indian express

19-year-old Egyptian Dies of Avian Flu (Bloomberg)

Anthrax Claims 20 Cows, Cattle Market Closed (New Indian Express)

Two Die in Spain from Human Form of Mad Cow Disease (Reuters)

emerging infectious disease
Emerging Infectious Disease
  • Emerging Infectious Disease
    • An infectious disease that has newly appeared in a population or is rapidly increasing in incidence or geographic range
  • On average, 1 newly identified infectious disease every year for each of the last 30 years (WHO)
  • Zoonotic Disease:
    • Disease entities readily transmissible between human and animal populations
  • Avian Influenza
  • Severe Acute Respiratory Syndrome (SARS)
  • Monkeypox virus
  • Rabies virus
  • Brucellosis
  • Ebola virus
  • West Nile virus
  • Nipah virus
  • Bovine tuberculosis (mycobacterium bovis)
emerging infectious disease5
Emerging Infectious Disease
  • Approximately 75% of recent emerging infectious diseases have been zoonoses

Avian Influenza Virus

Ebola Virus


nature study
Nature Study
  • 335 emerging infectious diseases identified between 1940 and 2004
    • Outbreaks were positively correlated with growing population densities
    • US/Europe had highest frequency of reported outbreaks… Why?
    • 60.3% were zoonoses
    • 71.8% of these originated in wildlife
  • Jones, Patel, Levy, et. al. Nature, 2008 Feb. 21; 451 (7181):990-3
nature study7
Nature Study
  • EID events: 1940 - 2004
nature study8
Nature Study
  • Regression analysis adjusted for:
    • Human population density and growth
    • Rainfall
    • Latitude
    • Wildlife host species richness

Global Distribution of Relative Risk of an EID Event

(a) zoonotic pathogens from wildlife, (b) zoonotic pathogens from non-wildlife, (c) drug-resistant pathogens, (d) vector borne pathogens

human livestock wildlife interface
Human-Livestock-Wildlife Interface
  • Food Security
  • Public Health
  • Conservation
human livestock wildlife interface10
Human-Livestock-Wildlife Interface
  • Global Commerce in Livestock Products
  • Increased Demand for Animal Protein
  • Loss of Wildlife Habitat
    • Ecosystem Degradation
    • Cleared Land for Agricultural Use
  • Increased Opportunity for Human-Animal Interaction
human livestock wildlife interface11
Human-Livestock-Wildlife Interface
  • Bush Meat Trade

N. Wolfe

human livestock wildlife interface12
Human-Livestock-Wildlife Interface
  • Logging, Agricultural Encroachment, and Wildlife Habitat Loss


public health challenges in africa
Public Health Challenges in Africa
  • Poverty/malnutrition
  • Lack of infrastructure
  • Inadequate water and sanitation
  • Difficulty accessing medical care
  • Weak public health services
  • +/- post-conflict
  • High degree of human/animal co-existence
zoonotic disease impacts in africa
Zoonotic DiseaseImpacts in Africa
  • 70% of continent’s rural poor are linked to livestock production (> 200 million people)
  • Population is exquisitely vulnerable:
    • Loss of livelihoods associated with livestock disease/disease control efforts (cull/quarantine)
    • Threats to human health
    • Contribute to entrenched cycles of illness, malnutrition and poverty
non zoonotic livestock disease impacts
Non-Zoonotic Livestock Disease Impacts
  • Foot and Mouth Disease
    • Endemic in Tanzania
    • Costs:
      • Loss of livelihoods/poor productivity
      • Loss of export markets; movement restrictions
      • Direct threats to wildlife health
  • Others: Rinderpest, African Swine Fever
  • Threats to Domestic and International:
    • Food Security
    • Biodiversity
    • Economic Development
threats to biodiversity conservation
Threats to Biodiversity Conservation
  • Why should conservationists be concerned about zoonoses and emerging infectious disease?
  • Direct threats to wildlife health
  • Direct threats to human health (loss of conservation capacity)
  • Threats to food security (increased use of bush meat)
  • Threats to livelihoods (contributing to unsustainable land use practices)
  • Threats to ecotourism initiatives
zoonoses case studies
ZoonosesCase Studies
  • Avian Influenza (H5N1)
  • West Nile Virus
  • Nipah Virus
  • Rift Valley Fever
avian influenza
Avian Influenza
  • 20th century pandemics:
    • 1918 (~50 million deaths globally)
    • 1957 (~1 million)
    • 1968 (~750,000)
  • 1997: currently circulating H5N1 strain
avian influenza20
Avian Influenza
  • Influenza A, H5N1
  • Extensive list of susceptible hosts
  • Currently Bird  Bird and Bird  human transmission
  • No demonstrated, sustained human to human transmission to date
avian influenza21
Avian Influenza
  • Pandemic potential:
    • Rapid viral mutation rates
    • Recombination event between HPAI and seasonal flu
  • Pandemic influenza poses significant public health risk
    • No pre-existing immunity to H5N1 in human population
    • Isolates have demonstrated some anti-viral resistance
    • Vaccine has been developed, but may not cover pandemic strain
    • Difficulty of containment
  • Projected Pandemic Costs:
    • 10-180 million deaths worldwide
    • Economic Impact: 2-3.1 % of global GDP (>2 trillion USD) (World Bank)
west nile
West Nile
  • August 1999, New York City
  • Case clusters of human meningoencephalitis
  • 59 patients presented with clinical signs of muscle weakness, encephalitis, paralysis
  • Case fatality rate of 12%
west nile24
West Nile
  • June, unusual crow die-off observed at Bronx Zoo
  • July, veterinarians examined birds with neurologic signs
  • September, tissue samples positive for WN-like virus
  • Subsequent months: bird die-offs in adjacent states (CT, NJ, NY)
  • Both human cases and bird-die offs were linked to West Nile via identical WN viral genomic sequences isolated from bird and human cases
west nile25
West Nile
  • Flavivirus
  • Initially identified West Nile district of Uganda 1937
  • Transmission via infected mosquito
  • Primary reservoir in birds
  • Dead end hosts: humans, horses
west nile26
West Nile


west nile27
West Nile
  • First documented incidence of West Nile virus in the Western Hemisphere
  • Within 3 years, had become endemic throughout all 48 contiguous states, Canada and Mexico
  • Role of migrating birds
west nile28
West Nile
  • National Cumulative 2007 Human Disease Cases: 3623


the nipah story
The Nipah Story
  • Nipah virus
    • Malaysia 1999
    • Paramyxovirus
    • 265 people exposed on pig farms and at slaughterhouses
    • Case fatality rate of 40%
the nipah story30
The Nipah Story
  • Pigs showed mild clinical signs of neurologic and respiratory disease
  • Human cases presented with fever, headache, signs consistent with encephalitis
  • 93% of human cases had occupational exposure to infected pigs suggesting transmission was via direct contact with pigs
the nipah story31
The Nipah Story
  • Pork production recently had expanded in Malaysia
  • Land had been cleared and farms established in close proximity to rainforest
  • Prime bat habitat
  • Farm on which Nipah outbreak occurred had fruit orchards adjacent to the pens
  • Increased transmission opportunities between bats and pigs
the nipah story32
The Nipah Story
  • Suspected that excreta (saliva/feces/urine) of bats overhanging pens exposed pigs
  • Pigs were present at such high stocking densities on the farm that they served as amplifiers of the virus
  • Humans infected from close contact with pigs
  • Social, environmental factors framed the outbreak
  • Outbreak cost the Malaysian government > 450 million USD
the nipah story33
The Nipah Story
  • Fruit bats subsequently identified as the reservoir of Nipah in Malaysia
  • Bats are silent carriers of the virus
  • Bats --> Pigs --> Humans


wildlife reservoirs
Wildlife Reservoirs
  • Bats potential or proven reservoirs for:
    • Rabies virus - Nipah virus
    • Ebola virus - Rift Valley fever
    • Lassavirus - West Nile virus
  • Rodents (hantaviruses, coronaviruses)
  • Japanese wild boars (hepatitis E virus)
  • Non-human primates (SFV, SIV)
rift valley fever
Rift Valley Fever
  • Virus (Phlebovirus)
  • First identified in Kenya, 1930
  • Domestic livestock (cattle, small ruminants, camels) and humans susceptible
  • Transmitted by:
    • Mosquitoes
    • Direct exposure to infected tissues
  • Outbreaks typically follow heavy rainfall
rift valley fever37
Rift Valley Fever


Countries with endemic disease and substantial outbreaks of RVF

Countries known to have some cases, periodic isolation of virus, or serologic evidence of RVF

rift valley fever38
Rift Valley Fever
  • Livestock Clinical Signs:
    • Fever
    • Abortion
    • Death (lambs/kids/calves)
  • Human Clinical Signs:
    • Fever
    • Headache
    • Bleeding
    • Malaise



rift valley fever39
Rift Valley Fever
  • Prior outbreak: Kenya 1997-1998
    • Associated with heavy rains/flooding
    • ~89,000 people infected (seroprevalence survey)
    • 478 deaths
  • Kenya outbreak: November 2006-January 2007
    • Followed unusually heavy rains (3x national average)
    • Human cases: 404
    • Deaths: 118
    • Case fatality rate: 29%
  • Greatest risk factor for human infection was interaction with livestock
rift valley fever42
Rift Valley Fever
  • Control Measures:
    • Movement restrictions/quarantine
    • Slaughter ban/meat inspection
    • Livestock vaccination
    • Public outreach/education/radio
  • Impacts:
    • Loss of livelihoods/income (markets closed)
    • Nutritional/dietary (slaughter ban/ meat price leading to  bush meat consumption)
    • Broader Economy (trade restrictions/control costs)
    • Wildlife health (impacts on wild ruminants unknown)


rift valley fever43
Rift Valley Fever
  • Proactive Solutions:
    • Climate forecasting to predict where heavy rains may predispose to RVF outbreak
    • Rainfall predictions coupled with livestock disease surveillance may provide a functional early warning system
    • Education of high risk populations
      • Use of mosquito nets/repellent
      • Avoiding contact with suspect animals/animal tissues
      • Thorough cooking of meat/dairy products
rift valley fever44
Rift Valley Fever
  • Interdisciplinary coordination for surveillance and response



tools community based surveillance
Tools:Community Based Surveillance
  • Train community members to detect and report cases using standard diagnostic criteria
  • Strengths:
    • Improves diagnostic sensitivity
    • Allows real-time ongoing monitoring with minimal resources at minimal cost
    • Fosters community education and awareness
  • Weaknesses:
    • First stage in outbreak detection: laboratory or health worker confirmation needed
    • Requires good communication/chain-of-command
tools outbreak control and response
Tools:Outbreak Control and Response
  • Confirmatory Diagnosis
  • Case Identification
  • Quarantine and perimeter control
  • Livestock culls and destruction of contaminated livestock products
  • Compensation
  • Disinfection of premises
  • Vaccination Decisions
the way forward
The Way Forward
  • Understanding the complex factors that lead to disease emergence
    • Social (poverty & instability)
    • Economic (livestock & wildlife trade)
    • Environmental (ecosystem degradation & climate change)
  • Improve data collection/analysis/sharing
  • Empower communities to proactively monitor and rapidly respond
  • Multi-disciplinary approach
additional resources
Additional Resources
  • ProMED Mail www.promedmail.org
  • World Organization for Animal Health (OIE) www.oie.int
  • Centers for Disease Control and Prevention www.cdc.gov
  • Google: Predict and Prevent Initiative www.google.org
  • HealthMap www.healthmap.org/en
  • Consortium for Conservation Medicine www.conservationmedicine.org