[Emerging Infectious Diseases * Volume 3 * Number 3 * July-September 1997]

[Dispatches]

Deer Ticks (Ixodes scapularis) and the Agents of Lyme Disease and Human
Granulocytic Ehrlichiosis in a New York City Park

Thomas J. Daniels,*† Richard C. Falco,*† Ira Schwartz,† Shobha Varde,† and
Richard G. Robbins‡
*Fordham University, Armonk, New York, USA; †New York Medical College,
Valhalla, New York, USA; ‡Walter Reed Army Medical Center, Washington,
D.C., USA
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      Rodent trapping and drag sampling in Van Cortlandt Park, New
      York City, yielded all stages of Ixodes scapularis, the deer
      tick vector of Lyme disease and human granulocytic ehrlichiosis
      (HGE). Polymerase chain reaction analyses of the ticks showed
      Borrelia burgdorferi and the Ehrlichia sp. that causes HGE.

Lyme disease, a tick-borne spirochetosis transmitted by the deer tick
(Ixodes scapularis Say), was reported from 46 states in the United States
in 1996; for the past 6 years, an average of 20% of those cases have been
from Westchester and Suffolk Counties, New York (1). While spread of the
deer tick population in New York State has been documented north and west
of Westchester County (2), movement of ticks southward toward New York City
has been largely ignored, despite rising Lyme disease case numbers in
southern Westchester and a relatively high incidence of human parasitism by
vector ticks. The discovery in Westchester County of human granulocytic
ehrlichiosis (HGE), a second, potentially fatal, tick-borne disease (3),
and of the causative Ehrlichia equi-like rickettsial agent in I. scapularis
(4) highlights the significance of defining the geographic range of the
deer tick. This is particularly important in urban areas, where residents
may not be familiar with tick-borne diseases common in nearby suburban and
rural areas. Foci of Lyme disease can occur in forested urban areas, as
well as in rural sites, if ticks and their hosts are present (5).

Because of the proximity of Van Cortlandt Park to areas of southern
Westchester where I. scapularis have been collected (Falco, unpub. data),
the park's relatively large wooded area (approximately 60% of 468 ha), and
the wide range of vertebrate hosts on which this tick feeds, we examined
rodents live-trapped in the park to determine if deer ticks were present.

For one night in August 1995, during the period of larval I. scapularis
activity, trapping was conducted on five study grids, each 50 m by 50 m.
Fifty Sherman mouse traps (H.B. Sherman, Tallahassee, FL) and nine Tomahawk
traps (Tomahawk Live Traps, Tomahawk, WI) for larger mammals were baited
and placed on each grid. Mean distance between neighboring grids was 400 m,
and all were located in the northern half of the park, where woodland is
concentrated. Captured animals were lightly anesthetized with
methoxyflurane (Metofane, Pitman-Moore, Mundelein, IN); they were examined,
and their age, sex, and weight were determined. All ectoparasites were
collected, identified, and counted. Animals were released at the capture
site after recovery from anesthesia.

The presence of this tick species in the park might lead to a Lyme disease
or HGE focus and, therefore, the need for additional surveillance efforts.
To further evaluate the risk for park visitors from infected ticks,
host-seeking ticks were sampled in the summer (July 1996), when nymphal I.
scapularis were active. Drag sampling, in which a 1 m(2) panel of white
corduroy cloth is pulled along the ground and over vegetation to collect
host-seeking ticks, was conducted. Any ticks found on the drag cloth or on
researchers were removed with forceps, placed in a glass vial, and held
live until identification. Specimens were stored in 70% ethanol until
testing.

Polymerase chain reaction (PCR) analysis was conducted on all ticks
collected in 1995 and 1996 (6). For nymphal and adult ticks, each specimen
was dissected with sterile needles, and DNA was extracted by the Isoquick
DNA extraction kit (ORCA Research, Bothell, WA), according to
manufacturer's directions. Final DNA pellets were suspended in 50 µl of
sterile water. Each tick extract was tested for B. burgdorferi and the HGE
agent by PCR amplification of a 10 µl aliquot.

Even though neither B. burgdorferi nor other ehrlichiae are efficiently
transovarially transmitted (7,8), white-footed mice are competent
reservoirs of both agents (9). Given the likelihood that transovarial
transmission of the Ehrlichia sp. causing HGE is extremely low, larval I.
scapularis collected from mice might have acquired either agent while
feeding. Seven of the nine larvae removed from hosts were tested in pools
of two (n = 2) or three (n = 1) specimens; the remaining two larvae were
tested individually. Larvae were pooled only with ticks that had been
removed from the same host animal. Larval specimens were likewise dissected
in a tube, and DNA was extracted as described above.

B. burgdorferi-specific PCR targeted the spacer region between duplicated
23S rRNA genes with primer IS1 and IS2 (10). Amplified products were
electrophoresed on a 1.5% agarose gel, and DNA was transferred to nylon
membranes hybridized with a B. burgdorferi-specific probe (P19) (10). The
HGE agent was detected by amplifying a 151 bp fragment of 16S rDNA with
primers GER3 and GER4 (11). PCR products were resolved by electrophoresis
on 2% agarose gels and visualized by staining with ethidium bromide.

Of 33 captured mammals examined in the summer of 1995, 19 were white-footed
mice (Peromyscus leucopus), the primary reservoir of B. burgdorferi. Four
(21%) mice hosted I. scapularis; two mice each hosted a single larva, one
hosted two larvae, and one mouse hosted five larvae. Mice that hosted ticks
were captured on three of the five trapping grids. Examination of the nine
chipmunks (Tamias striatus), four gray squirrels (Sciurus carolinensis),
and one flying squirrel (Glaucomys volans) that also were captured did not
show any I. scapularis or other tick species.

To evaluate the relative density of host-seeking I. scapularis, i.e.,
unattached ticks available to parasitize a passing host, 5,840 m(2) of
woodland habitat was drag sampled on or adjacent to the five trapping
grids. One nymphal and two adult male I. scapularis were collected, along
with a single I. dentatus nymph.

Results of PCR analyses indicated that one pool of two larvae, removed from
a white-footed mouse that hosted five I. scapularis, was positive for the
Ehrlichia agent of HGE. Of the four host-seeking ticks examined, two male
I. scapularis were infected with B. burgdorferi; the single I. dentatus
nymph was not infected with either agent. No specimens were infected with
both agents. The primers used to amplify the HGE agent DNA would also yield
PCR product with the closely related E. platys (an agent of canine
ehrlichiosis) and a recently described Ehrlichia species from white-tailed
deer (12). However, neither of these bacteria has been reported in hosts in
the northeastern United States, nor are the invertebrate vectors known
(although Amblyomma americanum is a suspected vector of the deer Ehrlichia)
(12,13). Since the prevalence rate of the HGE agent in I. scapularis
collected in Westchester County, New York, is approximately 20% (14), it is
reasonable to conclude that in the current study, positive PCR results
reflect the presence of the HGE agent.

Although anecdotal reports of Lyme disease by New York City residents who
have not traveled to disease-endemic sites have previously suggested the
presence of I. scapularis within city limits, to our knowledge, this is the
first instance in which the deer tick has been confirmed on wildlife hosts
resident in the city. Examinations of tick collections at both the American
Museum of Natural History, New York (L.N. Sorkin, pers. comm.), and the
U.S. National Tick Collection at the Institute of Arthropodology and
Parasitology, Georgia Southern University (L.A. Durden, pers. comm.), also
indicate that no specimens of I. scapularis previously collected from
wildlife in New York City have been deposited.

These findings have several implications. First, the distribution of
infested hosts suggests at least three potential tick population foci
within Van Cortlandt Park. From these, a growing tick population may
develop. Second, the larvae collected in this study were likely derived
from eggs laid by replete females in the park. Thus, it is probable that
host-seeking adults had successfully found medium- to large-sized mammals
on which to feed during the previous adult season. The collection of nymphs
and adult ticks further supports our conclusion that a population of I.
scapularis is established in Van Cortlandt Park, though at a low level. By
comparison, average drag densities at a woodland site in central
Westchester County typically are one nymph per approximately 16 m2 during a
comparable period in the nymphal activity cycle (Daniels and Falco, unpub.
data). Third, the potential exists for increased exposure to the agents of
Lyme disease and HGE by park visitors. Rather than creating the
peridomestic exposure that marks suburban habitats, tick populations in
urban areas will likely result in more focal exposure, restricted to
woodland habitat "islands," which exist primarily as parkland. The presence
of white-tailed deer (Odocoileus virginianus) in such parks, even if it
occurs on an intermittent, seasonal basis (as appears to be the case in Van
Cortlandt Park), may serve to introduce new ticks into the park from
adjoining disease-endemic areas. In this case, Westchester County is the
apparent source of the sporadic deer migration. In addition, the presence
of deer in the park can feed host-seeking ticks active at that time and
thereby help increase the tick population. Even in the absence of
white-tailed deer, the preferred host of adult I. scapularis, small
populations of deer ticks may be maintained by medium-sized mammals such as
raccoons (Procyon lotor). Therefore, these ticks may be overlooked by
physicians unaware of the potential risk to their patients, resulting in
undiagnosed cases of Lyme disease and HGE.

The I. scapularis population in Van Cortlandt Park may have been present
for many years, though at such low densities as to be unnoticed. Moreover,
other wooded parks in the city, which can provide a refuge for urban
wildlife and ticks, may pose a risk of encountering ticks infected with
either or both of these tick-borne disease agents. Further surveillance
that measures the extant tick population is needed to assess the risk for
Lyme disease and ehrlichiosis in this urban area.

References

  1. Centers for Disease Control and Prevention. Lyme disease surveillance
     summary 1997;8:2.
  2. White DJ, Chang HG, Benach JL, Bosler EM, Meldrum SC, Means RG, et al.
     The geographic spread and temporal increase of the Lyme disease
     epidemic. JAMA 1991;266:1230-6.
  3. Centers for Disease Control. Human granulocytic ehrlichiosis - New York,
     1995. MMWR Morb Mortal Wkly Rep 1995;44:593-5.
  4. Bakken JS, Dumler JS, Chen SM, Eckman MR, Van Etta LL, Walker DH.
     Human granulocytic ehrlichiosis in the upper midwest United States.
     JAMA 1994;272:212-8.
  5. Magnarelli LA, Denicola A, Stafford KC, Anderson JF. Borrelia
     burgdorferi in an urban environment: white-tailed deer with infected
     ticks and antibodies. J Clin Microbiol 1995;33:541-4.
  6. Schwartz I, Varde S, Nadelman RB, Wormser GP, Fish D. Inhibition of
     efficient polymerase chain reaction amplification of Borrelia
     burgdorferi DNA in blood-fed ticks. Am J Trop Med Hyg 1997; 56:339-42.
  7. Magnarelli LA, Anderson JF, Fish D. Transovarial transmission of
     Borrelia burgdorferi in Ixodes dammini (Acari: Ixodidae). J Infect Dis
     1987;156:234-6.
  8. Dumler JS, Bakken JS. Ehrlichial diseases of humans: emerging
     tick-borne infections. Clin Infect Dis 1995; 20:1102-10.
  9. Telford III SR, Dawson JE, Katavolos P, Warner CK, Kolbert CP, Persing
     DH. Perpetuation of the agent of human granulocytic ehrlichiosis in a
     deer tick-rodent cycle. Proc Natl Acad Sci U S A 1996; 93:6209-14.
 10. Schwartz I, Wormser GP, Schwartz JJ, Cooper D, Weissensee P, Gazumyan
     A, et al. Diagnosis of early Lyme disease by polymerase chain reaction
     amplification and culture of skin biopsies from erythema migrans
     lesions. J Clin Microbiol 1992;30:3082-8.
 11. Munderloh UG, Madigan JE, Dumler JS, Goodman JL, Hayes SF, Barlough
     JE, et al. Isolation of the equine granulocytic ehrlichiosis agent,
     Ehrlichia equi, in tick cell culture. J Clin Microbiol 1996;34:664-70.
 12. Dawson JE, Warner CK, Baker V, Ewing SA, Stallknecht DE, Davidson WR,
     et al. Ehrlichia-like 16S rDNA sequence from wild white-tailed deer
     (Odocoileus virginianus). J Parasitol 1996;82:52-8.
 13. Rikihisa Y. The tribe Ehrlichiae and ehrlichial diseases. Clin
     Microbiol Rev 1991;4:286-308.
 14. Schwartz I, Fish D, Daniels TJ. Prevalence of the rickettsial agent of
     human granulocytic ehrlichiosis in ticks from a hyperendemic focus of
     Lyme disease. N Engl J Med 1997;337:49-50.

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Emerging Infectious Diseases
National Center for Infectious Diseases
Centers for Disease Control and Prevention
Atlanta, GA


URL: ftp://ftp.cdc.gov/pub/EID/vol3no3/ascii/daniels.txt