Vector competence of Ixodes muris (Acari: Ixodidae) for Borrelia burgdorferi.

The vector competence of Ixodes muris (Bishopp & Smith) was determined for Borrelia burgdorferi, the etiologic agent of Lyme disease. Larval I. muris were fed on ICR outbred mice infected with the B-31 laboratory strain of B. burgdorferi. Replete larvae, at 5 d after feeding, were assayed for infection by culture in Barbour-Stoner-Kelly (BSK-H) media. Infection frequency in I. muris replete larvae was 66%. Resultant nymphs were fed on naive ICR outbred mice to determine the ability of I. muris to transmit infection. Infection frequency in fed nymphs declined to 38% and only 1/5 mice was positive for B. burgdorferi on ear biopsy culture. We demonstrated that I. muris is capable of acquiring and transmitting B. burgdorferi but is a relatively poor vector compared with I. scapularis (Say).

Attempt to control ticks (Acari: Ixodidae) on deer on an isolated island using ivermectin-treated corn.

We report an attempt by an offshore island community to control the vector tick of Lyme disease by providing ivermectin-treated corn to an isolated herd of free-ranging white-tailed deer, Odocoileus virginianus Zimmerman. Medicated corn was supplied in troughs within the island village and from automatic feeders at remote sites during 5 consecutive fall and spring adult tick questing seasons. Acaricide consumption was monitored by assaying its presence in fresh deer pellets and its concentration in deer sera. Its effectiveness was evaluated by recording the number of adult ticks collected from the hides of deer, the number of females becoming sufficiently engorged to oviposit, and the success of subsequent oviposition and eclosion. Entomologic risk was monitored by collecting immature ticks from hosts and adult ticks from vegetation. Estimates based on a subsequent deer reduction program indicated that up to twice as many deer had been present during the project as originally presumed. For this and other reasons related to deer behavior, target levels of serum ivermectin were achieved in a minority of deer. Nevertheless, > 90% control of female tick infestation, subsequent oviposition, and larval eclosion was obtained in those 8 of 16 sampled deer with serum ivermectin levels of > or = 15 ng/ml. In addition, the ratio of females to males, the numbers of females engorging > 10 mg body weight, and the numbers of those eventually hatching, were all significantly less among ticks from island deer in comparison with ticks from untreated deer. No consistent changes in the numbers of ticks found on immature-stage hosts or removed from vegetation were noted within 3 yr of the cessation of treatment.

Severe reaction in domestic animals following the bite of Ixodes muris (Acari: Ixodidae).

Free tick identification has been offered by our laboratory since 1989, during which time > 8,000 specimens have been submitted. We have noted that the bite of 1 of the less frequently identified ticks, Ixodes muris Bishopp & Smith, may be associated with a severe reaction in domestic animals characterized by extreme pain and swelling at the site and, with more complete engorgement, lethargy, anorexia, and high fever. These symptoms may be confused with other serious illness if the tick is not found. This reaction has not been seen following the bite of other species of ixodid ticks in Maine. Here we report 43 such cases, most involving dogs and cats from which ticks were removed by veterinarians and submitted to our laboratory for identification. Although I. muris was initially widespread in the United States and eastern Canada, its current range is unclear. In view of the potential for severe reaction to the bite of I. muris, the current distribution of the tick needs better definition, as does the mechanism of this response in animals that are unnatural hosts.

Participation of birds (Aves) in the emergence of Lyme disease in southern Maine.

The contribution of migratory and resident birds to the introduction of Lyme disease will vary with the degree to which various species expose themselves to, and are infested by, juvenile vector ticks, and their ability to support and transmit the infectious agent. To examine the relative contribution of various passerine species during the emergence of this disease, we compared the abundance and infection rates of the blacklegged tick, Ixodes scapularis Say, removed from mist-netted birds with those from live-trapped mice at a coastal study site in southern Maine, collected during an 8-yr period in which the range of this tick and the incidence of Lyme disease increased in the state. Weekly bird-banding sessions using six 12-m Japanese mist nets were carried out from May through August 1989-1996. In 1989, 1991 and 1993, mice were live-trapped in a Sherman trap grid (7 by 7 m) during five 3-night sessions, June through August; in 1994-1996, 2 such grids were similarly trapped. Annual adult tick abundance was estimated by flagging vegetation. We removed 2,633 juvenile deer ticks from 1,713 of 1,972 birds examined. Twenty-five of 64 bird species were infested. The percentages of birds infested and the rate of infection among removed larvae and nymphs increased over the years, but species varied markedly in their ability to infect ticks. No infected larvae were removed from catbirds or towhees. The larval to nymphal ratio was higher in mice than in birds. Infection rates among bird-derived larvae were less than among mice-derived larvae, but increased with time. Because of the different ways in which individual species of passerine birds contribute to the availability of vector ticks and respond to the agent of Lyme disease in emerging areas, further research into host competency and borreliacidal mechanisms is needed.

First records of Amblyomma americanum, Ixodes (Ixodes) dentatus, and Ixodes (Ceratixodes) uriae (Acari: Ixodidae) from Maine.

The first records of 3 ixodid tick species collected in the state of Maine are reported. A total of 23 records of the lone star tick, Amblyomma americanum (L., 1758), in 11 counties from hosts with no history of travel outside the state demonstrates that this tick is now a resident of Maine. Ixodes dentatus Marx, 1899 is recorded from Waldo and Lincoln counties, and Ixodes uriae White, 1852 is recorded from Matinicus Rock in Knox County. This is the first report of I. uriae from the eastern United States. Disease agents such as those causing human monocytic ehrlichiosis, Lyme disease, Rocky Mountain spotted fever, and several arboviruses have been recorded from 1 or more of these tick species.

Low seroprevalence of human Lyme disease near a focus of high entomologic risk.

To investigate a low rate of reported human Lyme disease adjacent to an area where the vector tick had become well established, we performed human and canine serosurveys and gathered data on environmental factors related to the risk of transmission. In March 1993, we obtained serum samples and conducted questionnaires that included information on outdoor activities, lot size, and frequency of deer sightings from 272 individuals living within a 5-km strip extending 12 km inland from a study site in south coastal Maine where collections revealed an abundant population of deer ticks. Serologic analysis was done using a flagellin-based enzyme-linked immunosorbent assay (ELISA) followed by Western immunoblot of positive and equivocal samples. Sera from 71 unvaccinated dogs within the study area were also analyzed for anti-Borrelia antibodies by ELISA. Human seropositivity was limited to two individuals living within 1.2 km of the coast. The frequency of daily deer sightings decreased sharply outside this area. Canine seropositivity, 100% within the first 0.8 km, decreased to 2% beyond 1.5 km. Canine serology appears to correlate with the entomologic indicators of the risk of Lyme disease transmission. Possible explanations for the low human seroprevalence are offered.

Role of bird migration in the long-distance dispersal of Ixodes dammini, the vector of Lyme disease.

To evaluate the role of migratory birds in the long-distance dispersal of Ixodes dammini ticks and in the spread of Lyme disease, a 6-year study of migrating birds to an offshore New England island was conducted during 1989-1994. I. dammini are not endemic on this island, therefore allowing assessment of long-distance tick dispersal rather than local infestation. Of 11,324 spring migrants examined, 1.2% were infested with I. dammini. Of 8607 fall migrants examined, 0.2% were infested. Of nymphal ticks examined, 20% were infected with Borrelia burgdorferi. OspB DNA sequencing of 6 B. burgdorferi isolates was identical to sequences of 2 strains common in coastal Maine. It is evident that bird migration allows for long-distance dispersal of I. dammini from areas where they are endemic to areas where they are not and that a few bird species account for the majority of tick dispersal. The likelihood of establishment of enzootic Lyme disease by this mechanism is discussed.

Norway rats as reservoir hosts for Lyme disease spirochetes on Monhegan Island, Maine.

To determine whether the agent of Lyme disease, Borrelia burgdorferi, may be maintained in the absence of its usual white-footed mouse reservoir host, Ixodes dammini ticks from an island where mice are absent were examined. Prevalence of spirochetal infection was described for ticks removed from mammals, birds, and vegetation on Monhegan Island, Maine. Forty percent of adult I. dammini removed from vegetation were infected. Norway rats were heavily infested with ticks, and > 60% of such ticks contained spirochetes. Other hosts were less frequently infested by ticks, and few such ticks were infected by spirochetes. The prevalence of antibody to B. burgdorferi was 23% in dogs and cats; 4% of island residents had Lyme disease. Thus, rats maintain Lyme disease spirochetes on Monhegan Island, and there may be transmission of this agent by I. dammini to island residents and their pets.

Competence of Peromyscus maniculatus (Rodentia: Cricetidae) as a reservoir host for Borrelia burgdorferi (Spirochaetares: Spirochaetaceae) in the wild.

Although capable of maintaining and transmitting Borrelia burgdorferi Johnson, Schmidt, Hyde, Steigerwalt & Brenner, the causative spirochete of Lyme disease, in the laboratory, the specific ability of deer mice, Peromyscus maniculatus Le Conte, to support this zoonosis has not been established. Demonstration that P. maniculatus is a competent reservoir host in the wild would indicate that the spread of Lyme disease is not limited to the range of the primary reservoir host, P. leucopus Rafinesque. Isle au Haut, an offshore Maine island upon which the vector tick Ixodes dammini Spielman, Clifford, Piesman & Corwin has become established, supports an isolated population of mice that are exclusively P. maniculatus. We examined the reservoir competence of this species by comparing infection rates of B. burgdorferi among juvenile ticks removed from livetrapped mice on this island with those removed from P. leucopus obtained at a mainland site endemic for Lyme disease. Equivalent rates of infection among engorged larval ticks, survival of infection through the larval-nymphal molt, and the isolation of B. burgdorferi from mice at both sites attest to the reservoir competence of P. maniculatus.

Diversity of tick species biting humans in an emerging area for Lyme disease.

BACKGROUND: Although most tick bites in humans in areas of the northeastern United States in which Lyme disease is highly endemic are due to Ixodes dammini, no study documents the frequency of I. dammini bites in low-prevalence or emerging areas for Lyme disease. Data on the proportion of tick bites in humans that are due to I. dammini in a region may have implications for public health policy and clinical management. METHODS: A statewide survey of the tick species that parasitized humans in Maine was conducted during 1989 and 1990. Tick submissions from throughout the state were elicited through media announcements. All ticks that had been removed from humans were identified, and data were collected that included bite seasonality and geography and demographics of tick bite victims. RESULTS: Of 709 ticks submitted, only 17% were I. dammini. Ixodes cookei, a vector for Powassan encephalitis, accounted for 34% of bites, and Dermacentor variabilis accounted for 45%. Other tick species were occasionally implicated. CONCLUSIONS: The likelihood that a tick bite was due to I. dammini was lower in Maine than in areas in the northeastern United States in which Lyme disease is highly endemic. Other tick vectors, associated with diseases other than Lyme disease, were more frequently implicated. Regional tick bite surveys may prove useful in assessing the risk of Lyme disease following a tick bite.

Canine seroprevalence and the distribution of Ixodes dammini in an area of emerging Lyme disease.

This study evaluates the relative usefulness of canine serosurveys to predict risk of exposure in an area of emerging Lyme disease by comparing the distribution of canine seroprevalence with that of vector ticks. From 16 veterinary clinics throughout the State of Maine, 828 canine sera were obtained during the heartworm-testing months of April and May 1989 and measured for anti-Borrelia antibodies by enzyme-linked immunosorbent assay. In the same year, 1605 ticks, including 585 Ixodes dammini, were collected from pets, humans, small mammals, and deer. Thirty-six dogs were seropositive, 28 of which had not traveled to endemic areas. Eighty-nine percent of all seropositive dogs were from towns within 20 miles (32 km) of the coast; the great majority lived within 5 miles (8 km) of tidewater (odds ratio =4.45, P = .002). Positivity varied from 17% in a southern coastal clinic to 0% in four northern clinics. Of 585 I. dammini identified, all but 5 (99.1%) were also from towns within 20 miles of the coast. Comparison of I. dammini submissions with those of another commonly found tick, Ixodes cookei, corroborated this predominantly coastal distribution. Canine seropositivity generally coincided with this coastal range. These data predicted areas of risk for human Lyme disease, although the prevalence of reported cases remained low.

Potential for Lyme disease in Maine: deer survey of distribution of Ixodes dammini, the tick vector.

A survey of deer brought to tagging stations at 24 sites in Main revealed the presence of the deer tick, Ixodes dammini, on 5.1 percent of deer. Ticks were found almost exclusively on deer from southwest coastal sites in the state. The potential for endemic Lyme disease in coastal Maine merits further study.

Application of an isolated heart model to investigate blood-oxygen delivery.

To avoid the compensatory hemodynamic responses, which have limited interpretation of hemoglobin-oxygen affinity modifications in animal experimentation, an isolated blood-perfused rabbit heart model providing metabolic, functional, and vectorcardiographic measurements has been developed. Fixed-flow perfusions of unchanged or affinity-modified red blood cell suspensions were carried out to assess the benefits of high affinity during hypoxic hypoxia and of low affinity during posthypoxic recovery. Using fully saturated suspensions, the influence of affinity level during restricted flow and reperfusion was also studied. Higher myocardial oxygen consumption (MVO2) was associated with high-affinity blood during mild hypoxia and low-affinity blood during posthypoxic recovery. At low flows, heart rate and MVO2 tended to be lower in high-affinity perfusions, and to recover more completely during low-affinity reperfusions. Ventricular function, vectorcardiographic patterns, and lactate levels were affected by hypoxia and ischemia, but not by level of affinity. The relevance of these observations to the therapeutic potential of hemoglobin-oxygen affinity modification is discussed.