Field studies on Lyme disease in North...

CONSENSUS CONFERENCE ON LYME DISEASE

Field studies on Lyme disease in North America

JOSEPH PIESMAN, SeD

J PIESMAN. Field studies on Lyme disease in North America. Can J Infect Dis 1991;2(2):55-57. The primaJy tick vector of Borrelia burgdorjeri in eastern a nd central North America is Ixodes dammini: in wes tern North America, Ixodes pacificus. Searching for th e appropriate vector is the first step in determining whether a region is endemic and enzootic for the s pirochete B burgdorjeri. the e tiological agent of Lyme disease , followed by examination of the ticks (questing or already a ttach ed to hosts) aJ1d wildlife for the spiroch ete. Questing ticks can be collected through a variety of methods . The two major animal hosts for I dammini are the white-footed mouse Peromyscus Leucopus and the while- tailed deer Odocoileus virginianus. Sampling strategies should consider habitat and season. All three life stages of the vector tick s hould be loca ted , indicating a self-sustaining popula tion. Although B burgdorjeri can be detected in many ways, there is no substitute for isolating the spiroch ete in Barbour-Stoenner-Kelly II medium for definitive proof of the presence of the Lyme disease spiroch ete.

Key Words: Detection, Lyme disease. Vectors

Etudes sur place de Ia maladie de Lyme en Amerique du Nord RESUME: Bon·eLia burgdorjeri est principalement transmis par Ixodes dammini dans !'Est de !'Amerique et en Amerique centra le, et par Ixodes pacificus dans !'Ouest de !'Ameriqu e du Nord. La premiere etape consiste a rech ercher le vecteur approprie afin de determiner s i une region donnee est endemique et enzootique pour le spirochete B burgdorjeri, !'agent etiologique de Ia maladie de Lyme: il fa ul ensuite examiner les liques (attaches a leurs h6tes ou non) et les animaux sauvages a Ia recherch e du spirochete. Les tiques peuvent etre recu eillis par diverses methodes . I dammini est principalement heberge par Ia souris a pattes blanches Peromyscus Leucopus et le cerf de Virginie Odocoileus virginianus. Les strategies doiveni tenir compte de !'hab itat et de Ia saison . Le tique devrait etre repere a ses trois stades de vie, lesquels indiquent une population auto-entretenue. Bien que B burgdorjeri puisse e tre detecte de nombreuses far;ons. rien ne surpasse le milieu de culture 8-S-K II pour obtenir Ia preuve definitive du spirochete responsable de Ia maladie de Lyme.

Division ofVecior·Bome Injeclious Diseases. Ceniersfor Disease Conirol. Pori Collins . Colorado. USA CorTespondence and reprinis: Dr J Pies man. Division of Vecior·Bome Injeclious D iseases, Ceniers for Disease Conirol. Box

2087. Pori Collins. CO 80522. USA. Telephone (303) 221·6408

CAN J INFECT DIS VOL 2 No 2 SUMMER 1991 55

PIESMAN

KNOWLEDGE OF' THE ECOLOGY OF' LYME DISEASE IN

North America is rapidly e:>.rpanding. In eastern and central North America the primary tick vector of BorreLia burgdmjeri has been identified as Ixodes dammini. whereas in western North America the primary vector appears to be Ixodes pacifi.cus. A primary step in determining whether a region is endemic and enzootic for B burgdo1jeri should be the search for the appropriate t ick vector, I dammini or I pacifi.cus. Subsequently, ticks and wildlife should be examined for infection with the Lyme disease spirochete, B burgdoTjeri. In the investigation of the risk of acquiring Lyme disease in a new region, it is essential to isolate the etiological agent. The present. article reviews the methods currently available to survey for B burgdoTjeri and its tick vectors.

DETECTION OF TICK VECTORS The proper method for detecting the presence of

ticks in the Ixodes ricinus 'complex· depends on the type of habitat under investigation. The two major categories of ticks available for detection are questing ticks and ticks a lready attached to hosts. Questing ticks can be collected through a variety of methods, such as flagging, dragging. walking or using carbon dioxide-baited traps.

Comparative studies of these different methods have revealed that carbon dioxide-baited traps are not very efficient tools for the collection of I dammini. since these ticks move relatively short distances compared to other tick species ( 1 ,2). Walking samples are effective in collecting adult licks that quest off the forest floor. but flagging or dragging where possible is preferable for the collection of immature I dammini. Dragging is adequate for the collection of I dammini in heavily forested areas with high canopy and sparse undergrowth, generally in inland regions (eg. Westchester County, New York) (1). In contrast, regions of coastal Massachusetts have luxurious undergrowth: in coastal regions, fl agging appears to be the preferred collection method (3).

The three stages of I dammini are active at different Limes of year. The peak of larval activity occurs in August-September: nymphs are active in May-June; and adults feed during the cooler months. October-April (4-6) . Sampling strategies for determining the presence and quantity of questing I dammini must take into account the habitat type and season of the survey.

The key animal hosts for I dammini appear to be the white-footed mouse Peromyscus leucopus for immature ticks and the white-tailed deer OdocoiLeus virginianus for adult ticks. Intensive examination of these two hosts for ticks shou ld be an important component of any Lyme disease field

56

survey. Examining deer for I dammini during hunting season may be the most sensitive tool for determining whether these ticks are present in an area. Individual ticks, however, may appear adventitiously on isolated deer in the absence of a self-sustaining lick population. Such may be the case in certain regions (eg, Indiana) (7). where hundreds of deer have been examined for ticks, with less than 12 adult 1 dammini collected. Thus, deer surveys should be combined with whitefooted mouse surveys t.o confirm that an active, thriving population of I dammini is present. Surveys of other species of wildlife and domestic animals, especially domestic dogs, may serve as adjuncts to surveys of deer and white-footed mice. Moreover, the host spectrum surveyed in western North America may differ, clue to the alternative feeding strategy of I pacifi.cus (8).

DETECTION OF B BURGDORFERI Although there are many ways to detect the

presence of B burgdmjeri in ticks, wildlife and humans, there is no substitute for isolation of the spirochete in Barbour-Stoenner-Kelly (BSK) II medium. Ticks can be examined for spirochetes by clarkfield. direct fluorescent. and indirect OuOl·escent microscopy. In areas where B burgdmferi has been isolated repeatedly from I dammini, such microscopic methods may suffice . False positives may occur, however, due to the presence of other microorganisms, artefact. or nonspecific fluOl·escence. The polymerase chain reaction was first adapted for detection of the DNA of B burgdmjeTi by Rosa and Schwan (9). and has been used to detect B bLLrgdmjeri DNA in ticks (10). Thus. the polymerase chain reaction holds great promise for the detection of B burgdmjeri in lick populations. Individual ticks or pools of ticks can be homogenized or dissected and placed in BSK II medium. These cu ltures can be routinely checked for spirochetal growth; if spirochetes are detected, they can be reacted with monoclonal antibodies or DNA probes, thus establishing definitively the presence of B burgdoTjeri in an area. The major handicap to culturing B burgdmjeri from licks is contamination of licks with other microorganisms. Careful technique and repeated sampling should decrease contamination problems.

Detection of B bwgdmjeri in vertebrates shou ld concentrate on the principal reservoir host, P leucopus, in areas where I dammini is known to exist. Nondestructive sampling of mice can be accomplished through ear punch biopsy for culture in BSK II (11). Destructive sampling of rodents may include cultures of urinary b ladder (12) or a variety of other internal organs (13). Attempts to cuilure spirochetes from other species of wildlife and

CAN J INFECT DIS VOL 2 No 2 SUMMER 1991

domestic animals should be secondary to surveys of white-footed mice, except in western North America, wh ere other reservoirs may be more important than peromyscus. Extreme caution must be used in interpretation of serological surveys for B burgdorjeri in wildlife and domestic animals . Without doubt, cross reaction between B burgdorferi and other bacterial compounds the difficulties associated with human serology, and the impact of cross reactivity on wildlife and domestic animal serology have not been well evaluated. At present, serology should be used as a relative rather than an absolute tool to determine the presence or absence of B burgdorjeri in a study area.

CONCLUSION A comprehensive approach is best when evalu

ating the risk of Lyme disease acquisition. Tick surveys should include a variety of methods to detect questing and host-attached ticks. All three life stages of the vector tick should be located , to confirm that a permanent population has been established. There is no substitute for culturing B burgdorjeri in BSK II medium when one is attempting to establish definitive proof that the Lyme disease spirochete is extant in a study area.

REFERENC ES l. Falco RC, Fish D. Prevalence of Ixodes dammini

near the homes of Lyme disease patients in Westchester County, New York. Am J Epidemiol 1988; 127:826-30.

2. Ginsberg HS, Ewing CP. Comparison of flagging , walking, trapping, and collecting from hosts as sampling methods for northern deer ticks , Ixodes dammini, and Lone-Star ticks , AmbLyomma americanum (Acari : lxodidae). Exp Appl Acarol 1989;7:313-22.

CAN J INFECT DIS VOL 2 No 2 SUMMER 1991

Field studies on Lyme disease

3. Piesman J, Math er TN, Dammin GJ, Telford SR III, Lastavica CC, Spielman A. Seasonal variation of transmission risk of Lyme disease and human babesiosis. Am J Epidemiol 1987; 126:1187-9.

4. Piesman J , Spielman A. Host-associations and seasonal abund ance of immature Ixodes dammini in southeastern Massachu setts. Ann Entomol Soc Am 1979;72:829-32.

5. Main AJ, Carey AB, Carey MG, Goodwin RH. Immature Ixodes dammini (Acari: Ixodidae) and small animals in Conn ecticu t, USA. J Med Entomol 1982; 19:655-64.

6. Daniels TJ, Fish D, Falco RC. Seasonal activity and survival of adult Ixodes dammini (Acari: lxodidae) in southern New York State. J Med Entomol 1989;26:610-4.

7. Pinger RR, Glancy T. Ixodes dammini (Acari: lxodidae) in Indiana. J Med Entomol 1989;26:130-~ .

8. Lane RS, Loye JE. Lyme disease in California: Interrelationship of Ixodes pacificus (Acari: lxodidae), the western fence lizard (SceLopurus occidentaLis), and BorreLia burgdorjeri. J Med Entomol 1989;26:272-8.

9 . Rosa PA, Schwan TG. A specific and sensitive assay for the Lyme disease spirochete BorreLia burgdorjeri using the polymerase chain reaction . J Infect Dis 1989;160:1018-29.

10. Persing DH, Telford SR III , Spielman A, Barthold SW. Detection of BorreLia burgdorjeri infection in Ixodes dammini ticks with the polymerase chain reaction. J Clin Microbial 1990;28:566-72.

11 . Sinsky RJ, Piesman J. Ear punch biopsy method for detection and isolq.tion of BorreLia burgdorjeri from rodents. J Clin Microbial 1989;27: 1723-7.

12. Schwan TG, Burgdorfer W, Schrumpf ME, Karstens RH. The urinary b ladder, a consistent source of BorreLia burgdorjeri in experimentally infected white-footed mice (Peromyscus Leucopus) . J Clin Microbiol 1988;26:893-5.

13. Johnson RC, Marek N, Kodner C. Infection of Syrian hamsters with Lyme disease spirochetes . J Clin Microbial 1984;20: 1099-10 l.

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