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Zoonoses

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ringworm in humans and animals. Glanders and tetanus in horses and humans ... ringworm first described in 1840s; cat as reservoir of human M. canis in 1902 ... – PowerPoint PPT presentation

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Title: Zoonoses


1
Zoonoses
  • Diseases and infections which are naturally
    transmitted between vertebrate animals and man
    (WHO)

2
Zoonoses Historical aspects
  • Conditions dating back for centuries
  • encephalitis in dog with Rabies
  • ringworm in humans and animals
  • Glanders and tetanus in horses and humans
  • Epidemic of urban plague
  • Late 1600s Leeuwenhoek invented the microscope,
    investigation of etiological agents soon followed

3
Zoonoses Historical aspects
  • Mycotic diseases
  • ringworm first described in 1840s cat as
    reservoir of human M. canis in 1902

4
Zoonoses Historical aspects
  • Bacterial diseases
  • tick-borne relapsing fever (spirochete)- 1873
  • B. anthracis (Koch) 1877
  • by 1890, most bacterial zoonoses known to occur
    at that time had been described

5
Zoonoses Historical aspects
  • Rickettsial diseases
  • Rocky Mountain spotted fever (R. rickettsii)
    1909
  • most rickettsial agents described by 1930s

6
Zoonoses Historical aspects
  • Viral diseases
  • 1798 Jenner reported protection from human
    smallpox conferred by innoculation of cowpox
  • first confirmed viral zoonosis (rabies) 1903
  • most initial reports in 1930s after advent of EM

7
Zoonoses Historical aspects
  • Parasitic diseases
  • most cestodes described by 1800
  • most trematodes by the 1870s
  • most nematodes by late 1800s, filarids by 1930s
  • most zoonotic protozoa1885 to 1915
  • plasmodia of primates 1930 to 1960s
  • clarification of coccidia and their role more
    recent to present

8
Definitions
  • communicable disease - illness that results from
    transmission of agent from infected host to
    susceptible host
  • host - animal (vertebrate/invertebrate) that
    harbors agent (primary, secondary, incidental)

9
Definitions
  • reservoir - host in which agent normally lives
    and multiplies and depends on for survival and
    transmission

10
Definitions
  • infection - entry and development of agent
  • infectious disease - clinically apparent disease
    that results from infection
  • infected individual - harbors infectious agent
    and either has either apparent or inapparent
    disease (carrier)

11
Definitions
  • carrier - harbors infectious agent in absence of
    clinically apparent disease
  • healthy or asymptomatic carrier
  • convalescent carrier
  • can either be transient or chronic
  • communicable period - period during which an
    infectious agent can be transmitted (direct or
    indirect) to a susceptible host

12
Definitions
  • incubation period - period between initial
    contact with infectious agent and onset of
    symptoms
  • contamination - presence of an agent on the
    surface of the body or on the surface of
    inanimate objects such as clothing, bedding,
    food, water

13
Definitions
  • Index case first individual recognized as being
    affected with disease
  • Proband (propositus) first (primary) case
    having disease
  • Efficient disease control when the index case
    primary case with increased frequency

14
Natural history of disease
Preclinical
Clinical
Outcomes Cure Control Disability Death
Healthy
Symptoms (clinical onset)
Biological onset
Diagnosis
Tertiary prevention
Primary prevention
Secondary prevention
15
Classification of zoonoses
  • Direct zoonoses
  • transmitted from infected host to a susceptible
    host by direct contact, inanimate object, or a
    mechanical vector
  • no developmental change or propagation of the
    organism occurs during the transmission
  • Example rabies, trichinosis, brucellosis

16
Classification of zoonoses
  • Metazoonoses
  • agent multiplies, develops, or both in an
    invertebrate host before transmission to a
    vertebrate host is possible
  • a definite prepatent or incubation period must be
    completed before transmission
  • Examples arboviruses, Lyme disease

17
Classification of zoonoses
  • Cyclozoonoses
  • Requires more than one vertebrate host, but no
    invertebrate host
  • Example human taeniasis, echinococcosis

18
Classification of zoonoses
  • Saprozoonoses
  • Transmission requires a non-animal development
    site or reservoir, such as food plants, soil, or
    other organic material
  • Example larva migrans, mycotic diseases

19
Emerging zoonoses
  • zoonotic diseases caused either by apparently new
    agents, or by previously known microorganisms
  • appearing in places or in species in which the
    disease was previously unknown

20
Emerging zoonoses
  • most involve transmission to humans from an
    ongoing reservoir
  • some are derived from a newly established life
    cycle in humans that no longer depends on the
    animal reservoir

21
Emerging zoonoses
  • Factors explaining emergence
  • modification at the individual host level
  • changes in immunological status
  • physiological changes
  • behavioral changes

22
Emerging zoonoses
  • Factors explaining emergence
  • modification at the host population level
  • immunological changes
  • behavioral changes
  • societal changes
  • movement

23
Emerging zoonoses
  • Factors explaining emergence
  • length of time the animal is infective
  • length of the incubation period in animals
  • the stability of the agent
  • population density

24
Emerging zoonoses
  • Factors explaining emergence
  • husbandry practices
  • maintenance procedures and control of wild
    rodents and insects
  • virulence of the agent
  • route of transmission

25
Emerging zoonoses
  • Factors explaining emergence
  • modifications at the environmental level
  • ecological changes
  • changing climate
  • encroachment--urban sprawl
  • bioterrorism

26
Emerging zoonoses
  • Factors explaining the emergence of a zoonotic or
    potentially zoonotic disease
  • mechanisms at the molecular level (agent and
    host)
  • mutation
  • natural selection
  • evolution

27
Emerging zoonoses
  • Since 1973, majority of newly recognized
    pathogens/infectious diseases are zoonoses
  • Lyme disease
  • Ebola viral hemorrhagic fever
  • Human ehrlichiosis
  • Hantaan viral disease
  • E. coli O157H7
  • Cyclosporiasis

28
Emerging zoonoses
  • In past decade
  • Hendra virus
  • Nipah virus
  • Australian bat Lyssa fever
  • Bartonella henselae
  • new variant Creutzfeldt-Jakob disease

29
Zoonoses
  • Central precept of public health regarding threat
    of disease
  • there is always a risk, and quantification of
    that risk is imperative in order to ensure
    appropriate prevention and control of disease

30
Principals of zoonotic diseases
  • Disease surveillance
  • detection of disease
  • measure extent of occurrence
  • identify needed interventions
  • evaluate impact of interventions
  • Disease monitoring
  • all of the above except evaluation of
    intervention aspect

31
Principals of zoonotic diseases
  • Detection (surveillance) dependent on knowledge
    of life cycle
  • reservoir host
  • definitive (primary)
  • intermediate (secondary)
  • carrier
  • asymptomatic (healthy or subclinical)
  • convalescednt (incubationary)

32
Principals of zoonotic diseases
  • Detection (surveillance) dependent on knowledge
    of life cycle
  • habitat of host(s)
  • sylvatic - wildlife
  • domiciliated - rats, mice
  • area of infected maintenance hosts called natural
    focus (nidus, niche)

33
Principals of zoonotic diseases
  • Epidemic unusual occurrence of disease
    exceeding the expected number (endemic)
  • Outbreak a cluster of cases that may or may not
    be an epidemic
  • Pandemic widespread occurrence of disease
    globally

34
Principals of zoonotic diseases
  • Outbreak or epidemic can be due to
  • Common source indirect transmission due to
    exposure to a common vehicle (food, air, water,
    mechanical)
  • Point source brief period of exposure
  • Propagative secondary cases resulting from
    exposure to primary case which serve to extend
    period of infectivity

35
Principals of zoonotic diseases
  • Prevention
  • inhibiting the introduction of a disease causing
    agent into a specific area, population, or
    individual
  • Control
  • steps taken to reduce and maintain at a tolerable
    level

36
Principals of zoonotic diseases
  • Eradication
  • elimination of a disease causing agent from a
    specific area or population
  • total versus practical eradication
  • Smallpox only disease totally eradicated
    worldwide
  • not practical due to economic and other
    constraints (geopolitical)

37
Principals of zoonotic diseases
  • Prevention and control involve
  • reservoir neutralization
  • removal
  • test and slaughter
  • mass therapy
  • manipulation of environment or vehicle
  • pasteurization
  • disinfection
  • sterilization

38
Principals of zoonotic diseases
  • Prevention and control involve
  • reduction of contact potential
  • isolation - keep the agent in
  • quarantine - keep the agent out
  • population control - benign such as leash laws or
    restriction of movement of livestock more
    drastic - reduction
  • herd immunity

39
Principals of zoonotic diseases
  • Prevention and control involve
  • increasing host resistance either to prevent or
    lessen severity
  • genetic selection (manipulated or natural)
  • chemoprophylaxis
  • immunization

40
Mechanisms of transmission
  • direct - immediate transfer
  • touch
  • bite
  • sexual transmission
  • droplet projection

41
Mechanisms of transmission
  • indirect - transmission by intervening factor
  • vector-borne (mechanical or biological)
  • arthropod-borne
  • tick-, flea-, mosquito-borne
  • vehicle-borne
  • food-, water-, soil-borne

42
Mechanisms of transmission
  • airborne - dissemination of infectious aerosols
    to a suitable port of entry
  • suspension of agents may remain for long periods
    of time
  • small particles (usually lt 5 ?) are easily drawn
    into alveoli
  • droplet nuclei - result from evaporation of
    fluids or atomization
  • dust - particles which arise from soil

43
Mechanisms of transmission
  • horizontal - direct or indirect transmission from
    infected individual to susceptible individual
  • various modes of interspecies spread of zoonoses
  • vertical transmission from one generation to
    another
  • dam to offspring in utero or via colostrum
  • important feature in many vector-borne zoonoses

44
Epidemiology - who, when, where
  • risk factors characteristics that increase or
    decrease likelihood of exposure, subsequent
    infection, and prognosis
  • predicting risk comes from knowing
  • Host age, sex, breed/race, etc.
  • Place geographic features of occurrence
  • Time time of day, seasonal
  • Environment factors (time place)

45
Emerging zoonoses
Zoonotic disease reports 1/2001 6/2001 (Promed)
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