Lyme Disease Ecology

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Lyme Disease Ecology

• Lyme disease spirochete transmission cycle
  extremely efficient in the Northeastern United
  States
• Differences from North to South
• B. lonestari status
• Future needs for research

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Lyme Disease

• Caused by the spirochete Borrelia burgdorferi
  sensu stricto
• Transmitted by Ixodes scapularis
• Reservoirs for the spirochete include
• Small mammals (mice, squirrels, chipmunks, etc.)
• Birds
• Hosts for the tick include
• Small mammals (larvae nymphs)
• Deer and other large mammals (adults)
• Deer required for tick population maintenance

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Photo by R Johnson
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Lyme Disease Transmission Cycle

• Larvae Aug-Sept (Year 1)
• Nymphs May-July (Year 2)
• Adults Oct-Dec Mar-Apr (Year 2)
• Egg production May-June (new cycle)

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Key Point 1 Proportion of I. scapularis
infected with Bb extremely high in NE

• Larvae Uninfected
• Nymphs 15-25
• Adult Females 40-50
• Why is cycle so efficient?
• Immature ticks focus on competent hosts

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Peromyscus
Tamias
Photos from varied internet sites field guides
Microtus
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Sciurus
Photo from internet site or field guide
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Didelphis
Syviligus
Photo from internet site or field guide
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Odocoileus virginianus
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Hanincova et al. 2006Lake Gaillard, CT

• White-footed mouse
• Gray Squirrel
• Pine vole
• Eastern chipmunk
• Virginia opossum
• Raccoon
• Questing nymphs

• 90
• 32
• 26
• 23
• 10
• 8
• 69/178 39

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Key Point 2

• Nymphs are small (lt2 mm) and can feed for the gt48
  hrs required for transmission and escape detection

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BITING NYMPH
FREQUENTLY ESCAPES NOTICE BECAUSE OF ITS SMALL
SIZE
Photo Provided by D Fish
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T (1 - exp-?? (t - G)? ) k
From DesVignes et al
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Key Point 3

• In hyperendemic regions of the NE, lots of
  questing infected nymphal I. scapularis bite
  people

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Nymphal I. scapularis bites from health
department records

• Westchester County, NY
• N444 from 1985-1989
• Falco et al. 1996 Am J Epidemiol
• Westchester County, NY
• Deterministic Model 1991-94
• Estimate of 178,889 bites per year
• Campbell et al. 1998 Am J Epidemiol
• CT Agric Exp Station accepts ticks statewide for
  testing
• Average nymphal I. scapularis approx 5,000 per
  year (K Stafford, personal communication)

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SO WHAT IS DIFFERENT IN THE LYME DISEASE CYCLE
FROM NORTH TO SOUTH?ONE MAJOR DIFFERENCE---
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Photo by R Eisen
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Immature I. scapularis focus on lizards rather
than small mammals in the southeastern US

• Durden et al. 2002 Exp Appl Acarol St
  Catherines Is., Liberty Co, GA 309 reptiles
  exm broad-headed skink, southeastern 5-lined
  skink, eastern glass lizard-heavily infested w I.
  scapularis (gt51 larvae gt7 nymphs per lizard)
• Levine et al. 1997 J Med Entomol museum
  specimens from 80 N Carolina counties 117
  lizards infested with I. scapularis immatures
  (max 179). Most () from coastal plains.

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Immature I. scapularis in the southeast are few
far between on rodents

• Clark et al. 2001 J Parasitol A total of 237
  rodents from South Carolina
• 24 I. scapularis on 97 cotton mice (0.2_at_)
• 5 I. scapularis on 49 eastern woodrats (0.1_at_)
• 2 I. scapularis on 60 hispid cotton rats (0.03_at_)
• Cryptic cycle involving I. minor, I. affinis,
  woodrats

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Key points derived from focus of immature I.
scapularis on lizards in the Southeast

• In general, lizard complement is lytic to B.
  burgdorferi sensu stricto so lizards are not
  reservoir competent for these spirochetes. Thus,
  spirochetal infection in southeastern I.
  scapularis is extremely rare.
• Nymphal I. scapularis do not quest above the leaf
  litter in the southeast so they dont get picked
  up on drag samples and they dont bite people
• Some conflicting evidence in scientific
  literature

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WORST JOB IN SCIENCE TICK COLLECTING
Popular Science November 2004
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Tick Dragger Worst Science Jobs

• Go to remote, densely overgrown forest. Take out
  giant white corduroy sheet. Drag it behind you as
  you sing loudly to ward off bears. After 20
  meters, stop. Do not tarry to smack mosquitoes,
  for you must immediately tweezer several hundred
  tiny potentially Lyme disease carrying ticks that
  have covered both you and your white cloth, and
  drop them into a jar. Repeat 50 times a day. No
  this is not the instruction set for hell week at
  Phi Delta Sade. Its the protocol for a study
  assessing Lyme disease risk across the eastern
  U.S., headed by Yale University epidemiologist
  Durland Fish.

From Popular Science Nov 2004
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Density of host-seeking Ixodes scapularis nymphs
(2004 2006) Data by M Diuk-Wasser, Yale Univ.
Risk Map Study Group
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From Hayes Piesman, NEJM 2003
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Lone star tick

• Most common person-biting tick in southeastern US
• All three stages bite people aggressively
• All three stages feed mainly on deer
• Will occasionally feed on birds but almost never
  on rodents
• Schulze et al. 1984 Science spirochetes present
  in A. americanum from NJ

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Barbour et al. 1996 J Infect Dis

• 2 of A. americanum from MO, TX, NJ, NY infected
  with spirochetes
• Spirochetes could not be cultured in BSK
• PCR analysis based on 16S rRNA gene flagellin
  gene showed that it was a unique spirochete (only
  96 identity with B. burgdorferi on 16S)
• Provisionally named B. lonestari

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Current state of Knowledge on B. lonestari
Biology Ecology

• There is a group of Hard tick relapsing fever
  spirochetes that include
• B. miyamotoi sensu lato from Ixodes persulcatus,
  I. scapularis, I. ricinus
• B. lonestari from Amblyomma americanum
• B. theileri from Rhipicephalus (Boophilus) from
  Africa and Latin America
• These spirochetes are distinct from but closely
  related to classical TBRF organisms

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Rapid Progress Made by S Little Lab (Univ GA
Okla St Univ)

• Successful culture of B. lonestari in association
  with tick cells
• Lizard and mouse sera lytic for B. lonestari
• Deer develop spirochetemia when inoculated w B.
  lonestari whereas mice, calves, and dogs do not
• B. burgdorferi produces EM in rabbit model but B.
  lonestari has not, to date

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Results of culture attempt

• spirochetes found 14 days after inoculation with
  PCR-positive tick tissues

LS-1
From S Little, Oklahoma St Univ
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Results Deer fawns (n2)

• Inoculated B. lonestari spirochetes into deer ?
  infected and spirochetemic
• PCR
• One or both deer PCR positive DPI
  4,6,8,12,15,19,22,28
• Blood smear
• Rare spirochetes on blood smears from one or both
  deer collected DPI 6,8,12,15
• Culture
• B. lonestari re-isolated in tick cell co-culture
  from deer DPI 6, 12

From S Little Oklahoma State Univ
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FUTURE

• Determine to what extent potential person-biting
  questing ticks are infected w B. burgdorferi
  sensu stricto in the southeast
• Elucidate the role of lizards as reservoirs of B.
  burgdorferi
• Determine whether B. lonestari plays any role in
  causing Lyme disease in the southeast
• Identify any unknown pathogens associated with
  ticks in the southeastern US