Epidemiology and Control of Zoonotic Infections

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Epidemiology and Control of Zoonotic Infections

• Emerging Infections
• Monkeypox, Nipah virus, Avian influenza
• Jason Stull, CDHS, Veterinary Public Health
• Jstull_at_dhs.ca.gov
• 916-552-9740

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Overview Emerging Zoonoses

• Background
• Examples
• Monkeypox
• Nipah virus
• Avian Influenza

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Monkeypox
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Monkeypox - Background

• Rare zoonosis found in Western and Central Africa
• 1st identified in1958 in primates
• Documented in numerous animal species
• 1st human infection 1970
• gt 400 documented human cases

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Monkeypox Virus

• Orthopoxvirus
• Double stranded DNA
• Similar but distinct from Smallpox and Vaccinia

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Clinical Features - Animals

• Fever
• Cough
• Ocular discharge
• Lymphadenopathy
• Dermal rash
• Decreased appetite
• Death possible

Gambian giant rat
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Clinical Features - Humans

• Transmission - bite or contact, respiratory
  droplets
• Incubation 10-14 days
• Clinical signs Fever, headache, muscle aches,
  swollen lymph nodes
• Papular rash, lesions in the same stage, milder
  than smallpox, illness lasts 2-4 weeks before
  lesions crusted
• Rarely fatal no specific treatment
• Smallpox vaccine is protective

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Monkeypox outbreak - 2003

• April 9, 2003 762 African rodents imported to
  Texas ? Midwest

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Monkeypox outbreak - 2003

• Redistribution leads to prairie dogs infected at
  pet stores

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Monkeypox outbreak - 2003

• Infected prairie dogs infect buyers

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Monkeypox outbreak - 2003

• 71 cases
• 35 lab-confirmed
• Several states
• Median age 28 y.o.
• 26 hospitalized, no deaths
• 30 get smallpox vaccination

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Californias Response

• Alerted animal-related professionals
• Conducted onsite inspections of the 13 facilities
  possessing prairie dogs
• CDFG permit required to possess most wildlife
• No cases identified, illegal importation?

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NIPAH VIRUS
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Nipah Virus - Background

• First identified in 1999 in Malaysia
• Paramyxoviridae
• Single stranded RNA virus
• Natural host Fruit Bats (Flying Fox)

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Nipah Virus Malaysia and Singapore Outbreak

• Sept 1998-April 1999
• 265 human cases
• 105 Deaths
• 93 Pig farm/abattoir workers
• gt900,000 pigs culled

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Nipah Virus Epidemic Curve
Update Outbreak of Nipah Virus -- Malaysia and
Singapore, 1999 MMWR, 199948
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Nipah Virus - Transmission

• Flying Foxes

Pigs
?
Humans
?
Close contact
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Nipah Virus - Animal Disease

• Natural Reservoir - Fruit bats
• Asymptomatic
• Virus in urine
• Pigs
• Other animals
• Cats
• Dogs
• Horses

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Nipah Virus - Human Disease

• Incubation 3 to 14 days
• Symptomatic cases
• Onset influenza-like illness
• Progresses to encephalitis
• 40 fatal if symptomatic
• Treatment
• Supportive care
• Ribavirin (efficacy?)

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Nipah Virus - Human Disease

• Live virus found in human respiratory secretions
  and urine
• No known human-to-human transmission during
  outbreak
• Relapse encephalitis (12 cases)
• Late-onset encephalitis (10 cases)
• Mean time for complications 8.4 months

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Nipah Virus - Diagnostic Tests

• Serology
• Immunohistochemistry
• MRI
• Histopathology
• Vasculitis
• Endothelial damage
• Characteristic viral inclusions

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Nipah Virus Control Prevention

• Swine control
• Slaughter
• Transportation bans
• Education
• Protective equipment
• Surveillance to detect swine and human cases

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Nipah Virus Continues

• Outbreaks in 2001 and 2003 in Bangladesh
• 25 cases
• No obvious zoonotic source
• Transmission
• Close contact with other patients?
• Exposure to common source?

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Avian Influenza
See presentation by Dr. Janice Louie, Key
Microbial Threats Seasonal and Pandemic
Influenza CIDER (Feb 1, 2005) Web-cast
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Influenza - Background

• Orthomyxoviridae family
• Gene segments can re-assort
• Infected species include birds, pigs, humans,
  horses and sea mammals.

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Influenza - Key Viral Features

• Surface proteins
• Hemagglutinin (HA)
• Site of attachment to host cells
• Antibody to HA is protective
• Neuraminadase (NA)
• Helps to release virions from cells
• Antibody to NA can help modify disease severity

NA
HA
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Genetic Changes

• Drift constant small genetic changes caused by
  natural selection when antibodies to virus are
  made
• Partial antibody protection
• May result in epidemic
• Shift- abrupt, major genetic change creating new
  hemagglutinin and/or neuraminidase proteins
• Little or no antibody protection
• May result in pandemic

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The Ultimate Mixing Vessel?
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Virus Classification - Birds

• Low Pathogenic (LPAI)
• Most AI virus strains
• Cause little or no clinical disease
• Can mutate to HPAI
• Highly Pathogenic (HPAI)
• Highly infectious to chickens
• Can inflect flocks without warning
• Spreads rapidly in flocks and flock to flock
• Morbidity and mortality can approach 100
• Death within 12 days of onset

Source USDA, APHIS
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Influenza - Birds

• Clinical signs
• Decline egg production
• Mild respiratory disorder
• Chronic respiratory infection
• Death
• Diagnosis serology, egg inoculation
• Control
• Management is best prevention (Biosecurity)
• De-population
• Vaccinate?

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Influenza A - Birds

• Outbreaks occur throughout the world
• Low pathogenic avian influenza
• Limited to poultry
• Sporadic
• Recently in U.S.
• Texas (2004) H5N2
• Maryland (2004) H7N2
• Pennsylvania (2004) H2N2
• Delaware New Jersey (2004) H7N2

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Influenza - Animal Transmission

• Migratory waterfowl natural reservoir
• Initial source of infection
• Poultry, migratory waterfowl, domestic pigs, pet
  birds
• Shed by feces, nasal secretions, saliva
• Aerosol
• Shared drinking water
• Fomites

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Influenza - Humans

• Transmission
• Droplets/aerosol, contact
• Incubation 1-4 days
• Shedding day before onset to 5 days after
• Acute febrile respiratory illness
• Symptoms may differ by age
• Types A and B viruses cause substantial illness
  and death among humans

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Impact of Influenza - Humans

• Seasonal epidemics in temperate regions
• U.S., Canada, Europe, Russia, China, Japan,
  Australia, Brazil, Argentina
• Year-round activity in tropical climates
• Equatorial Africa, Southeast Asia
• U.S. impact
• Average of gt200,000 influenza-related
  hospitalizations/year
• Average of gt36,000 influenza-related deaths/year
• 3 global pandemics in the 20th century

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H5N1 in Asia, 2003-05

• Unprecedented highly pathogenic avian influenza A
  (H5N1) outbreak among poultry
• Farms, backyard flocks affected
• Millions of chickens, ducks died gt100 million
  culled

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H5N1 in Asia, 2003-05
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H5N1 in Asia - Human cases

• Cumulative of confirmed cases (Jan. 2004 Feb.
  2, 2005)
• Cambodia 1 case (1 death)
• Thailand 17 cases (12 deaths)
• Vietnam 37 cases (29 deaths)
• Total 55 cases (42 deaths)
• Most cases had contact with sick or dead poultry
• Majority of cases children, young adults
• Viruses resistant to antiviral drugs amantadine,
  rimantadine (susceptible to oseltamivir)
• No evidence of sustained human-to-human
  transmission

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Additional H5N1 Issues

• Can infect cats
• domestic
• tigers, leopards (Thailand)
• Can infect pigs
• Ducks may be infected without illness

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U.S. Surveillance for H5N1

• Testing for avian influenza (H5N1) should be
  considered for hospitalized or ambulatory
  patients with
• a.   Documented temperature of gt38C (gt100.4F),
  AND
• b.   One or more of the following cough, sore
  throat, shortness of breath, AND
• c.   History of contact with poultry (e.g.,
  visited a poultry farm, a household raising
  poultry, or a bird market) or a known or
  suspected human case of influenza A (H5N1) in an
  H5N1-affected country within 10 days of symptom
  onset.

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Avian Influenza - Public Health

• Can spread from poultry to humans
• Genetic re-assortment ? virus more easily
  transmitted among people
• Infection is uncommon, but preventive measures
  are critical
• If sustained human-human transmission

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Prediction Prevention of Emerging Zoonoses

• Enhanced communications across disciplinary and
  agency boundaries
• Assessment/development of surveillance tools
• Examination of link between animal-human health
  outcomes
• Cross-disciplinary training and research

Perspectives on emerging zoonotic disease
research Can Vet J, 20054665-78
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