Lyme disease in Wisconsin: epidemiologic, clinical, serologic, and entomologic findings

In 1980-82, 80 individuals (71 Wisconsin residents) had confirmed Lyme disease (LD-c) reported; 39 additional patients had probable or possible LD. All cases of LD-c occurred during May-November; 73 percent occurred during June-July; 54 (68 percent) occurred in males. The mean age was 38.7 years (range, 7-77 years). Among LD-c patients, likely exposure to the presumed vector Ixodes dammini (ID) occurred in 22 different Wisconsin counties. Antibodies to the ID spirochete that causes LD occurred in 33 of 49 LD-c cases versus 0 of 18 in ill controls (p less than .001) and in 13 of 26 LD-c cases treated with penicillin or tetracycline versus 16 of 19 LD-c cases not treated. Early antibiotic therapy appears to blunt the antibody response to the ID spirochete. Regional tick surveys conducted in Wisconsin during each November in 1979-82 have demonstrated regions of greater density of ID. Utilizing comparable tick collection in these surveys, increases were noted in the percentage of deer with ID from 24 percent (31/128) in 1979 to 38 percent (58/152) in 1981, in the standardized mean value of ID/deer from 1.0 in 1979 to 2.2 in 1981, in the percentage of ID of the total ticks collected from 13 percent in 1979 to 71 percent in 1981, or in the ratio of ID to Dermacentor albipictus ticks from 0.14 in 1979 to 2.44 in 1981. However, a reduction in the density of ID/deer was noted generally throughout Wisconsin in 1982 when compared to 1981. LD is widespread in Wisconsin, with ecologic and clinical features similar to those occurring along the eastern seaboard.     

Epidemiologic features of Lyme disease in New York

During 1982, surveillance identified 207 cases of Lyme disease in New York State. Cases were clustered in two geographic areas, eastern Long Island and northern Westchester counties. Symptoms and signs of Lyme disease in cases were consistent with previous reports, with erythema chronicum migrans (ECM) being the most frequently (77 percent) reported sign of disease. Facial palsy was reported in a surprisingly high 18 percent of cases. Of 160 cases whose sera were submitted for Lyme spirochete specific IgG antibody testing, 112 (70 percent) had titers greater than or equal to 64, while 88 (55 percent) had titers greater than or equal to 128. Positive titers were not associated with any single sign or symptom of disease, but were significantly associated with symptom onset or tick bite occurring during the three-month period of June, July, and August. We conclude that the incidence of Lyme disease in New York is much higher than previously recognized. In addition, our data suggest that a serologic test for Lyme-spirochete IgG antibody lacks sensitivity, but can be useful in confirming the diagnosis of Lyme disease when antibody titers are high.     

The antibody response in Lyme disease.

We determined the antibody response against the Ixodes dammini spirochete in Lyme disease patients by indirect immunofluorescence and an enzyme-linked immunosorbent assay (ELISA). The specific IgM response became maximal three to six weeks after disease onset, and then declined, although titers sometimes remained elevated during later disease. Specific IgM levels correlated directly with total serum IgM. The specific IgG response, often delayed initially, was nearly always present during neuritis and arthritis, and frequently remained elevated after months of remission. Although results obtained by indirect immunofluorescence and the ELISA were similar, the ELISA was more sensitive and specific. Cross-reactive antibodies from patients with other spirochetal infections were blocked by absorption of sera with Borrelia hermsii, but titers of Lyme disease sera were also decreased. To further characterize the specificity of the humoral immune response against the I. dammini spirochete, 35S-methionine-labeled spirochetal antigens were identified by immunoprecipitation with sera from Lyme arthritis patients. These polypeptides had molecular weights of 62, 60, 47, 37, 22, 18, and 15 kDa, and were not recognized by control sera. We conclude that the ELISA, without absorption, is the best method to assay the humoral immune response in Lyme disease, and we have identified methionine-containing spirochetal polypeptides that may be important in Lyme arthritis.     

Ixodes dammini: occurrence and prevalence of infection with Borrelia spp. in Minnesota

The distribution of Ixodes dammini in Minnesota was studied by collecting adult ticks from hunting dogs during the grouse seasons in September and October of 1985 and 1986. The tick was most frequently found in the east-central part of the state. Borrelia spp. were observed by immunofluorescence in 10% of the ticks. The locations where ticks were found coincide with the primary endemic areas for Lyme disease in the state.     

Seroprevalence of Lyme disease in gray wolves from Minnesota and Wisconsin.

To determine the seroprevalence of Lyme disease in gray wolves (Canis lupus) from various counties of Minnesota and Wisconsin (USA), 589 serum samples were collected from 528 wolves from 1972 to 1989. An indirect fluorescent antibody (IFA) test was used to detect the presence of antibodies against Borrelia burgdorferi. Titers of greater than or equal to 1:100 were considered positive. Results were confirmed by testing a few selected sera by Western blotting. Of the 589 sera tested, 15 (3%) had IFA titers of greater than or equal to 1:100. Three of the positive samples were collected from Douglas County in Wisconsin and twelve were from Minnesota counties. This study indicates that wolves are exposed to B. burgdorferi and are susceptible to Lyme disease.     

Avian and mammalian hosts for spirochete-infected ticks and insects in a Lyme disease focus in Connecticut.

Spirochetes and their vectors and reservoirs were studied in a Lyme disease focus in East Haddam, Connecticut, from mid-May through September 1983. Ixodes dammini subadults were comparable in number on white-footed mice (Peromyscus leucopus) (means = 2.9 +/- 3.6 SD) to those on 27 different species of birds (means = 2.3 +/- 4.2 SD) representing 11 families within the order Passeriformes. Less commonly found ticks on birds (means less than or equal to 0.1) were immature Ixodes dentatus and Haemaphysalis leporispalustris. Although spirochete-infected I. dammini larvae and nymphs were taken off eight and nine different species of birds, respectively, significantly fewer positive larvae were removed from birds than from white-footed mice. Spirochetes were detected in the midguts of I. dammini, Dermacentor variabilis, and H. leporispalustris and two species of insects (Cuterebra fontinella and Orchopeas leucopus). Possibly, arthropods other than I. dammini vector these spirochetes in northeastern United States. Spirochetes grew in a cell-free medium inoculated with bloods from four white-footed mice, one woodland jumping mouse (Napaeozapus insignis), one northern mockingbird (Mimus polyglottos), one gray catbird (Dumetella carolinensis), two prairie warblers (Dendroica discolor), one orchard oriole (Icterus spurius), one common yellowthroat (Geothlypis trichas), and one American robin (Turdus migratorius). We suggest that avian hosts, like mammals, develop spirochetemias of the causative agent of Lyme disease. Erythematous tissues from a white-footed mouse were infected with spirochetes.     

Spirochetes in ticks and antibodies to Borrelia burgdorferi in white-tailed deer from Connecticut, New York State, and North Carolina

Ticks were screened for spirochetes and serum samples from white-tailed deer (Odocoileus virginianus) were assayed for antibodies to Borrelia burgdorferi during 1983-1984. Using fluorescein isothiocyanate-labeled rabbit antibodies produced to B. burgdorferi, the etiologic agent of Lyme disease, spirochetes were detected in Ixodes dammini (10.5% of 1,193) and Dermacentor albipictus (0.6% of 157) adults from Connecticut, I. dammini nymphs (49.1% of 108) and adults (64.7% of 99) from Armonk, New York, and in I. scapularis (0.4% of 531) and Amblyomma americanum (3.5% of 173) adults from North Carolina. Infected ticks were either seeking hosts or feeding on deer during the summer and fall. Direct fluorescent antibody staining also revealed spirochetes in two larvae of I. scapularis that emerged from eggs deposited by separate females in the laboratory. Using indirect immunofluorescence tests, antibodies to B. burgdorferi were identified in white-tailed deer living in tick-infested areas of all three states. Aside from minor cross-reactivity, there was no serologic evidence of Treponema or Leptospira infections. Ixodes dammini is a primary vector of B. burgdorferi in northeastern United States, but in North Carolina, other ixodid ticks may transmit this spirochete to humans and wildlife.     

The New Zealand white rabbit: an experimental host for infecting ticks with Lyme disease spirochetes

Efficiency of the New Zealand white rabbit as a host for infecting larval Ixodes dammini, I. pacificus, and I. ricinus with Lyme disease spirochetes was evaluated. Rabbits inoculated with infected midgut suspensions of I. dammini from Shelter Island, New York, or fed upon by infected ticks from the same area, responded with spirochetemias of sufficient concentrations to infect as many as 30 percent of the ticks. When infected ticks were used as indicators, it appeared that spirochetemias persisting for up to ten days occurred as early as the tenth day after inoculation or feeding of ticks.     

Ixodes ricinus spirochete and European erythema chronicum migrans disease.

From three endemic locations of erythema chronicum migrans disease in North Rhine-Westphalia, Germany, we recovered 19 isolates of a spirochete from Ixodes ricinus ticks. The infection rate in adult ticks was 16 percent. The isolated spirochete is immunologically related to the Ixodes dammini spirochete, Borrelia duttoni, and Treponema pallidum. Using indirect immunofluorescence, the sera of 90 patients with erythema chronicum migrans disease showed antibody titers against the isolated spirochete, which correlated with the clinical course. Similarly, antibodies were demonstrated in the sera of 21 patients with acrodermatitis chronica atrophicans. These results suggest an etiologic role for the Ixodes ricinus spriochete in European erythema chronicum migrans disease.     

Geographical distribution and density of Ixodes dammini (Acari: Ixodidae) and relationship to Lyme disease transmission in New Jersey

As part of continuing studies of Lyme disease, deer were surveyed during three hunting seasons in 1981 to obtain information on geographic distribution and density of I. dammini in New Jersey. I. dammini occurred throughout central and southern New Jersey. Four deer management zones (DMZs) were shown to have high tick densities. Geographical distribution and density data were independently regressed against 25 environmental and physical factors. Elevation was shown to be the most important factor in explaining the variability in both I. dammini distribution and density. Lyme disease cases were closely associated with the distribution of I. dammini and 57.3 percent of 117 Lyme disease cases occurred in the four DMZs previously identified as having the highest tick density.     

Prevalence of the Lyme disease spirochete in populations of white-tailed deer and white-footed mice

The prevalence of the Ixodes dammini spirochete (IDS) in white-tailed deer (Odocoileus virginianus) and white-footed mice (Peromyscus leucopus) was studied on the eastern end of Long Island, New York. Both species commonly occur in a variety of habitats, are preferred hosts of Ixodes dammini, and can harbor the spirochetes in the blood. Each animal was examined for spirochetemia, tick infestation, and IDS infection rates in the ticks that were removed from it. The results obtained suggest that in winter deer can be infected by questing adult I. dammini. Adult ticks apparently are infected through transtadial transmission of spirochetes from subadult ticks which had fed earlier in their life history on infected animals. Deer are important hosts of adult ticks and the IDS in winter and probably are a reservoir host in other seasons. The patterns of spirochete prevalence suggest that deer and mice are reservoirs of the organism and thus are fundamental to the ecology of Lyme disease on Long Island.     

Epidemiological and clinical features of 1,149 persons with Lyme disease identified by laboratory-based surveillance in Connecticut

Laboratory-based surveillance of Lyme disease in Connecticut during 1984 and 1985 identified 3,098 persons with suspected Lyme disease; 1,149 were defined as cases. Lyme disease incidence in Connecticut towns ranged from none to 1,407 cases per 100,000 population in 1985. A comparison of 1985 data with data from 1977 epidemiologic studies indicated that incidence increased by 129 percent to 453 percent in towns previously known to be endemic for Lyme disease and that Lyme disease had spread northward into towns thought to be free of Lyme disease in 1977. Children aged five to 14 years had the highest incidence. Of persons with Lyme disease, 83 percent had erythema migrans, 24 percent had arthritis, 8 percent had neurologic sequelae, and 2 percent had cardiac sequelae. The distribution of symptoms was age-dependent: case-persons less than 20 years old were almost twice as likely to have arthritis than older case-persons (35 percent versus 18 percent). Of persons with arthritis, 92 percent of those less than 20 years of age, compared to 68 percent of older persons, did not have antecedent erythema migrans. We conclude that Lyme disease is increasing in incidence and geographic distribution in Connecticut. Of those with Lyme disease, children may be more likely than adults to develop arthritis and have it as their first major disease manifestation.     

Borreliosis in free-ranging black bears from Wisconsin

Blood, kidney and tick samples were obtained from 18 hunter-killed black bears (Ursus americanus) from three sites in northern Wisconsin. A Borrelia sp., morphologically and antigenically similar to Borrelia burgdorferi, was isolated from the blood of two of the animals, and from the kidney of a third. Ixodes dammini and Dermacentor variabilis were found on the bears. This is the first report of borreliosis in the Ursidae, and of the primary vector of Lyme disease, I. dammini, from this host.     

Lyme disease and migrating birds in the Saint Croix River Valley.

During a study of migrating land birds in 1987, we examined over 9,200 individual birds representing 99 species from the Saint Croix River Valley, a Lyme disease-endemic area of east central Minnesota and northwestern Wisconsin. We found that 250 deer tick (Ixodes dammini) larvae and nymphs infested 58 birds from 15 migrant species; 56 ticks (22.4%) were positive for the Lyme disease spirochete Borrelia burgdorferi. Five ground-foraging migrant bird species favoring mesic habitats, veery (Catharus fuscescens), ovenbird (Seiurus aurocapillus), northern waterthrush (S. novaboracensis), common yellowthroat (Geothlypis trichas), and swamp sparrow (Melospiza georgiana), accounted for nearly three-quarters of parasitized individuals. Nearly half of the spirochete-positive ticks were removed from migrating birds taken in a riparian floodplain forest. Recaptured migrants with infected ticks indicate that they transmit B. burgdorferi to hexapod larvae. We suggest that birds may be both an important local reservoir in the upper Mississippi Valley and long-distance dispersal agents for B. burgdorferi-infected ticks to other regions of the continent.     

Lyme disease and migrating birds in the Saint Croix River Valley

During a study of migrating land birds in 1987, we examined over 9,200 individual birds representing 99 species from the Saint Croix River Valley, a Lyme disease-endemic area of east central Minnesota and northwestern Wisconsin. We found that 250 deer tick (Ixodes dammini) larvae and nymphs infested 58 birds from 15 migrant species; 56 ticks (22.4%) were positive for the Lyme disease spirochete Borrelia burgdorferi. Five ground-foraging migrant bird species favoring mesic habitats, veery (Catharus fuscescens), ovenbird (Seiurus aurocapillus), northern waterthrush (S. novaboracensis), common yellowthroat (Geothlypis trichas), and swamp sparrow (Melospiza georgiana), accounted for nearly three-quarters of parasitized individuals. Nearly half of the spirochete-positive ticks were removed from migrating birds taken in a riparian floodplain forest. Recaptured migrants with infected ticks indicate that they transmit B. burgdorferi to hexapod larvae. We suggest that birds may be both an important local reservoir in the upper Mississippi Valley and long-distance dispersal agents for B. burgdorferi-infected ticks to other regions of the continent.     

Vectorial capacity of North American Ixodes ticks.

Ixodes dammini, the vector of Lyme disease and babesiosis, is distributed in various locations in the northeastern quadrant of the United States and nearby Canada. The life cycle of this tick, which includes larval, nymphal, and adult stages, spans at least two years. The tick over-winters between larval and nymphal feeding. Horizontal transmission of pathogens is facilitated by a feeding pattern in which both the larval and nymphal stages feed on the white-footed mouse, Peromyscus leucopus, and by a seasonal pattern of activity in which nymphs precede larvae. The species range appears to have expanded from a single island location, and has invaded new sites since the 1940s, some as recently as 1980. This increased abundance appears to be related to the increased abundance of deer, the preferred host of the adult stage. I. muris predominated in coastal Massachusetts before I. dammini became abundant, but is probably now extinct. I. scapularis, which is present in the southern U.S., is a poor vector of mouse parasites because about 90 percent of these immature ticks feed on lizards. To the extent that horizontal transmission occurs, we suggest that mice serve as the principal reservoir for the Lyme spirochete as well as Babesia microti.     

Bacteriophage in the Ixodes dammini spirochete, etiological agent of Lyme disease

A bacteriophage with a B-3 morphology was detected by electron microscopy in a spirochete isolated from the tick Ixodes dammini. It has a 40- to 50-nm elongated head and a tail 50 to 70 nm in length. It appears devoid of collars or kite-tail structure. The spirochete has been identified as the causative agent of Lyme disease.     

Discovery of the Lyme disease spirochete and its relation to tick vectors.

The various hypotheses concerning the etiologic agent of erythema chronicum migrans of Europe and of Lyme disease in the United States are reviewed, and an account of events that led to the discovery of the causative spirochetal agent in Ixodes dammini is presented. Spirochetes morphologically and antigenically similar, if not identical to, the organism detected in I. dammini were also found for the first time in Ixodes pacificus and Ixodes ricinus, the vectors hitherto incriminated, respectively, in western United States and Europe. In most infected ticks, spirochetal development was found to be limited to the midgut. Ticks with generalized infections were shown to transmit spirochetes via eggs, but infections decreased in intensity and became restricted to the central ganglion as filial ticks developed to adults. Although the mechanisms of transmission to a host are still under investigation, the spirochetes may be transmitted by saliva of ticks with generalized infectious and possibly also by regurgitation of infected gut contents, or even by means of infected fecal material.     

Geographic distribution of humans,raccoons, and white-footed mice with antibodies to Lyme disease spirochetes in Connecticut.

An indirect immunofluorescence test was used during 1982-1983 to identify antibodies to Lyme disease spirochetes in humans, white-footed mice, and raccoons. Serologic tests detected IgM or total Ig antibodies in serum samples from 67 persons. Onset of illness, as marked by erythema chronicum migrans (ECM), occurred mainly during July and August. The majority of the persons with Lyme disease lived in south central and southeastern Connecticut. Analyses also verified prior spirochetal infections in 29 of 323 (9 percent) white-footed mice and in three of 34 (9 percent) raccoons captured at sites with or without evidence of human infections. Results indicate potential for Lyme disease at numerous localities in Connecticut.     

Incompetence of catbirds as reservoirs for the Lyme disease spirochete (Borrelia burgdorferi)

We compared the relative infectivity to vector ticks of gray catbirds (Dumetella carolinensis) and white-footed mice (Peromyscus leucopus) for the Lyme disease spirochete (Borrelia burgdorferi). Of 28 catbirds captured in a site enzootic for this agent, 18 were infested by immature Ixodes dammini, the tick vector. By comparison, each of 32 mice sampled concurrently from the same site was infested, and by about 10 times as many ticks as were found infesting the 3 most commonly netted bird species. Although 76% of noninfected larval ticks placed on these mice in a xenodiagnosis became infected, none of the ticks similarly placed on 12 catbirds did so. Spirochetes were detected in ticks derived from 2 Carolina wrens (Thryothorus ludovicianus) and a common yellowthroat (Geothlypis trichas), but these species' potential contribution to infecting ticks does not compare with that of mice. Thus, although birds may help establish new foci of ticks, catbirds, at least, do not appear to contribute as reservoirs of infection.