ARTHROPODBORNE ZOONOSES

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ARTHROPOD-BORNE ZOONOSES

• Rocky Mountain Spotted Fever
• Typhus
• Lyme disease
• Ehrlichiosis

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TICK-BORNE ZOONOSES

• Arthropods and Public Health
• Interaction of host and parasite
• Diseases associated with direct effect
• entomophobia - fear of insects revulsion to
  spiders, roaches, earwigs can cause enough
  anxiety to seek medical attention
• infestation - presence of living organisms on
  host pediculosis (louse), scabies (mite),
  internal (myiasis)
• bites and stings (venomous insect bites) -
  spider, scorpion
• contact poison - blister beetle, certain
  caterpillars

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TICK-BORNE ZOONOSES

• Arthropods and Public Health
• Interaction of host and parasite
• Diseases associated with effects of host,
  parasite, vector
• man as primary host
• dengue, typhus, malaria
• man as incidental host
• zoonoses plague, leishmania, tularemia,
  hemorrhagic fever
• once establihsed, may be transmitted from man to
  man by same or different vectors

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TICK-BORNE ZOONOSES

• Arthropods and Public Health
• Interaction of host and parasite
• Diseases associated with effects of host,
  parasite, vector
• mechanical transmission - insect picks up agent
  on body surfaces, transmits to humans (flies -
  bacillary dysentery)
• biological transmission - insect vector not only
  transmits, but is essential in life cycle of
  disease agent

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TICK-BORNE ZOONOSES

• Arthropods and Public Health
• Biological transmission
• propagative - disease agent grows or multiplies
  in vector without going through cycle
• cyclo-developmental - disease agent goes through
  essential part of cycle inside arthropod with no
  increase in numbers (ex filiariasis)
• cyclo-propagative - cycle change and increase in
  numbers (amplification) (ex malaria)

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TICK-BORNE ZOONOSES

• Arthropods - Ticks

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TICK-BORNE ZOONOSES

• Arthropods - Ticks

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TICK-BORNE ZOONOSES

• Arthropods - Ticks

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TICK-BORNE ZOONOSES
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ROCKY MOUNTAIN SPOTTED FEVER

• Other names tickborne typhus, pinta fever
  (Mexico)
• Agent Rickettsia rickettsii, a rickettsial
  infection
• a tick-borne zoonosis affecting animals and man

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RMSF

• First recognized in 1896 in the Bitter Root
  Valley (Montana), hence the name
• Major endemic regions
• South Atlantic states (DE MD to FL) - 50
• West Central states (AR, OK, LA, TX) - 20
• Rocky Mountain region accounts for only 2

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RMSF

• Microbiological features
• Rickettsia are small gram negative bacilli
• Obligate intracellular parasites
• Two primary groups defined by surface
  antigenicity
• Spotted-fever group (RMSF, rickettsialpox, etc.)
• Typhus group (Epidemic, murine, scrub)
• Scrub typhus now classified under genus Orientia
• Transmitted by bite of infected ticks or mites

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RMSF

• Microbiological features
• Biochemistry
• predominately grow within cells
• many require increased CO2 levels
• soluble and cell-bound antigens used for
  serological differentiation
• Virulence factors
• no enterotoxins formed
• a lethal toxin has been described for mouse
• not hemolytic

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RMSF

• Microbiological features
• Rickettsia rickettsii
• prototype of spotted fever group
• replicates in nucleus and cytoplasm of infected
  tick and mammalian cells
• labile, does not survive long under normal
  environmental conditions
• readily inactivated by heat and chemical
  disinfectants

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RMSF
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RMSF

• Clinical features
• humans
• sudden onset of moderate-high fever
• severe malaise, myalgia and headache
• conjunctival injection
• characteristic rash in 50 or cases
• maculopapular rash on extremities (especially
  soles, palms) on about the 3rd day, spreading
  centripitally within a few days

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RMSF

• Clinical features maculopapular rash

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RMSF

• Clinical features petechial rash

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RMSF

• Clinical features
• ddx (early RMSF)
• ehrlichiosis
• meningococcemia (meningitis)
• enteroviral infection
• case fatality rate up to 25 if untreated
• rarely fatal with treatment, although recently,
  up to 5 of case fatality with proper treatment
• risk factors delayed Ab therapy and 40 yrs of
  age

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RMSF

• Clinical features
• animals
• normally subclinical, but can be manifested in
  dogs
• fever, lethargy, neurological signs,
  lymphadenopathy, splenomegaly
• petechia observed in 20 of cases

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RMSF

• Diagnosis
• based on clinical signs supported by serology
• IFA of skin biopsy to detect organism
• ELISA
• CF (later)

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RMSF

• Epidemiology
• occurrence
• normally seen in late spring through the summer
  (April to September)
• occurs throughout the US, endemic foci southern
  Atlantic and south central
• more common in males in the West, and children in
  the southeast
• also documented in Canada, Mexico, Central and
  South America

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RMSF
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RMSF

• Epidemiology
• Reservoir
• certain species of Ixodid ticks through
  transovarial and transstadial passage, therefore
  considered principal reservoir
• broad host range - raccoons, voles, dogs can be
  infected
• voles play most prominent role as reservoirs for
  horizontal amplification of agent

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RMSF

• Epidemiology

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RMSF

• Epidemiology
• mode of transmission
• bite of tick
• at least 4-6 hours attachment for rickettsiae to
  become reactivated and infectious
• contamination of broken skin by crushed tissues
  also possible

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RMSF

• Epidemiology

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RMSF

• Epidemiology
• vector
• Dermacentor variablis (American dog tick) -
  eastern and southern US

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RMSF

• Epidemiology
• vector
• D. andersonii (Rocky Mountain wood tick) -
  northwest US

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RMSF

• Epidemiology
• vector
• Amblyomma americanum (Lone Star tick) -
  occassionally in southwest US

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RMSF

• Epidemiology
• vector
• Rhipicephalus sanguineus (Brown dog tick), A.
  cajennensus - Mexico, Latin America

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RMSF

• Exposure
• peridomestic-dogs bring infected ticks into
  environment
• recreational
• occupational

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RMSF

• Prevention
• avoid tick-infested habitats
• personal protection
• periodic total body search for presence of ticks
• early removal of tick (

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RMSF

• Prevention
• Vaccination
• killed or attenuated live vaccines available, but
  limited efficacy
• have been recommended for high risk individuals
• recombinant DNA methodology now being investigated

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RMSF

• Control
• interruption of peridomestic cycle
• tick control
• active surveillance of ticks and wildlife
• to monitor changes in the distribution
• to provide early detection
• to determine risk indices
• to provide prevalence data to evaluate
  effectiveness of prevention programs