Vector Of Lyme Disease Research Articles

Vegetation structure influences the burden of immature Ixodes dammini on its main host, Peromyscus leucopus.

To determine whether the relative abundance of immature Ixodes dammini (the vector of Lyme disease and human babesiosis) is related to habitat structure, we examined tick burdens on their main host, the white-footed mouse (Peromyscus leucopus), in 4 structurally diverse sites on Great Island, Massachusetts, USA. Vegetation structure at each site was quantified with respect to 25 habitat variables. Principal components analysis was used to reduce this set of habitat variables to seven new and orthogonal variables. Immature tick abundance varied widely among grids. Regression analysis of tick burdens on the habitat principal components showed that larval burdens were related strongly to the density of woody vegetation and negatively to herbaceous vegetation. Nymphal burdens were related negatively to herbaceous vegetation, but the relationship was not as strong as in the case of larvae. An experimental reduction in the abundance of white-tailed deer (Odocoileus virginianus), the main host of adult ticks, substantially reduced tick burdens and altered their relationships to habitat structure. Nymphal burdens were unrelated to habitat structure following deer removal. Manipulating habitat structure may have utility as a control strategy against this important vector.

Genetic Markers for the Identification of Three Australian Tick Species at Various Stages in Their Life Cycles

An allozyme electrophoretic study was conducted on different life cycle stages of 3 Australian tick species, Amblyomma limbatum Neumann, 1899, Aponomma hydrosauri (Denny, 1843), and Ixodes holocyclus Neumann, 1899. Sixteen enzymes encoding a presumptive 19 loci were of sufficient staining intensity and resolution to identify accurately the 3 species at either the larval, nymphal, or adult stage of the life cycle. For each species, the larvae, nymphs, and adults all had alleles in common at all 19 loci. However, fixed genetic differences were detected among the 3 species at 15 or 16 of the 19 enzyme loci examined. The large number of genetic markers that have been established from a limited sample volume (e.g., individual unfed larvae) allows accurate identification of the species at each life cycle stage. Data presented show that the technique of allozyme electrophoresis can provide genetic evidence for the identification of species at any life cycle stage even where life cycle stages are morphologically quite different. A major problem facing researchers in parasitology and indeed pest control management is the inability to identify confidently, by morphological characters, life cycle stages of many parasite taxa. Different parasites often have evolved along lines that culminate in remarkable morphological similarity between disparate species. Inability to detect and use morphological characters to assign individuals to a species with confidence is compounded when within a species there are marked differences in the structure at various stages in the life cycle and where morphological changes occur during feeding on the host. Electrophoretic studies have revealed the existence of morphologically similar but genetically distinct (i.e., cryptic) parasite species (e.g., Bull et al., 1984; Baverstock et al., 1985; Andrews et al., 1989), demonstrating that conventional morphological classifications are not always adequate for species recognition. It is surprising that few investigators have applied the technique to assist in the identification of species at different life cycle stages. Insufficient numbers of enzyme loci have been established for species identification due to the small volume of sample available for electrophoresis. Species of ticks often are diagnosed on the basis of slight morphological differences, host specificity, and/or the geographical locality from which they were collected. However, morphological characters sometimes are insufficient to identify unequivocally the species to which specimens belong. For example, the tick known to transmit Lyme disease in America, Ixodes dammini Spielman, Clifford, Piesman, and Corwin, 1979, is difficult to distinguish morphologically from the closely related species Ixodes scapularis Say, 1821, in areas where they coexist (Oliver, 1988). Similarly, Ixodes holocyclus Neumann, 1899, has been implicated as the vector of Lyme disease in Australia (Munro and Dickeson, 1989), and yet morphological characters are insufficient to distinguish it from other closely related ixodid species (Arundel and Sutherland, 1988). Furthermore, ticks feeding on hosts undergo structural changes and are particularly difficult to identify using morphological characters. Moreover, the identification of larvae and nymphs of many species requires laboratory culture until they engorge to repletion and molt to the adult stage. In view of the significant morphological changes between different life cycle stages, the accurate identification of larvae, nymphs, and adults to a given species by the use of diagnostic genetic markers would be of taxonomic and systematic value. Allozyme electrophoresis has been used to distinguish several tick species worldwide (Bull et al., 1984; Hunt and Hilburn, 1985; Hilburn et al., 1989), but no comprehensive genetic study has been conducted to identify and characterize larvae and nymphs of any of these species. For the present study we selected 3 morphologically distinct species, 2 reptile ticks, Amblyomma limbatum Neumann, 1899, and Aponomma hydrosauri (Denny, 1843), and 1 mammal tick, I. holo-

Distribution, density, and Lyme disease spirochete infection in Ixodes dammini (Acari: Ixodidae) on white-tailed deer in Maryland.

A Statewide survey of ticks parasitizing white-tailed deer was carried out in Maryland during November 1989 to assess the status of the deer tick, Ixodes dammini Spielman, Clifford, Piesman & Corwin, the major vector of Lyme disease in the northeastern United States. Ticks were collected from deer carcasses brought in by hunters at 23 check stations (one per county). A total of 3,437 I. dammini were collected from 538 of 1,281 deer (42%), together with 2,013 Dermacentor albipictus (Packard) and 23 Amblyomma americanum (L.) from 34 and 0.5% of deer respectively. I. dammini prevalence ranged from 0 to 79% of deer and mean abundance from 0 to 7.3 ticks per deer at different check stations. Lyme spirochete, Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner, infection rates in ticks ranged from 0 to 21%, with a mean of 8%. Deer-tick density and spirochete infection rates varied with physiographic region and were low in the Appalachian, intermediate in the Piedmont, and high in the Western and Eastern Coastal Plains regions. County-based human case rates correlated positively with I. dammini abundance. We concluded that I. dammini was well established except in the mountainous western region of Maryland and was involved in Lyme disease transmission.

A MODEL OF THE ENZOOTIOLOGY OF LYME DISEASE IN THE ATLANTIC NORTHEAST OF THE UNITED STATES

A mathematical model is presented for the dynamics of the rate of infection of the Lyme disease vector tick Ixodes dammini (Acari: Ixodidae) by the spirochete Borrelia burgdorferi, in the Atlantic Northeast of the United States. According to this model, moderate reductions in the abundance of white‐tailed deer Odocoileus virginianus may either decrease or increase the spirochete infection rate in ticks, provided the deer are not reservoir hosts for Lyme disease. Expressions for the basic reproductive rate of the disease are computed analytically for special cases, and it is shown that as the basic reproductive rate increases, a proportional reduction in the tick population produces a smaller proportional reduction in the infection rate, so that vector control is less effective far above the threshold. The model also shows that control of the mouse reservoir hosts Peromyscus leucopus could reduce the infection rate if the survivorship of juvenile stages of ticks were reduced as a consequence. If the survivorship of juvenile stages does not decline as the rodent population is reduced, then rodent reduction can increase the spirochete infection rate in the ticks.

Lyme Borreliosis

The skin diseases Erythema (chronicum) migrans (ECM, EM), Lymphadenosis benigna cutis (LABC), and Acrodermatitis chronica atrophicans (ACA) have long been described in northern Europe, and dermatologists are very familiar with these manifestations, which have been successfully treated with penicillin for about 40 years without the causative agent being known. Certain neurologic symptoms could be linked to tickbites during the 1920's and later also to EM. In 1977, Steere et al. reported a new form of inflammatory arthritis, mainly in school children in the community of Lyme, Connecticut, U.S.A., which they could also associate with preceding erythema and tickbites. Five years later, Burgdorfer was able to isolate Borrelia spirochetes from Ixodes ticks, which are known to be vectors of Lyme disease as well as of EM and ACA. The following year, Borrelia spirochetes were also isolated from Ixodes ticks and from skin lesions of patients in Sweden and Germany. These findings resulted in a large number of reports of new discoveries related to this infection, which is now known under the names of tick-borne or Lyme borreliosis and, in the U.S., also as Lyme disease or Lyme arthritis. It has proven to be a great imitator disease, mainly through its involvement of the neurological system, and to be far more widespread than previously thought. The full course of the disease is not yet known, however it is clinically, like another spirochetosis, syphilis, divided into early and late stages. Manifestations involve mainly the skin, the joints, the nervous system (Neuroborreliosis), and the heart. Antibiotic treatment is effective, especially in the early stages. Like syphilis, the disease can be self-healing without treatment. People who are exposed to ticks should be aware of the risk of contracting this disease, also in Japan where Ixodes ticks have been shown to be carriers of Borrelia spirochetes. Cases, particularly of EM, but also with neurological symptoms, have already been diagnosed in Hokkaido, Honshu, Shikoku, and Kyushu. As Lyme borreliosis is now proven to exist in Japan, it is beneficial for dermatologists to know about the various presentations of this disease. This paper will briefly summarize the historical background, the clinical stages, the diagnosis, and the treatment of Lyme borreliosis, with a summary of the present situation in Japan.

Sperm precedence in the deer tick Ixodes dammini

ABSTRACT We determined whether female deer ticks Ixodes dammini Spielman, Clifford, Piesman & Corwin (Acari: Ixodidae) can be inseminated repeatedly and whether sperm from first or second matings take precedence in fertilizing eggs. Such information is essential to the design of attempts to reduce the fertility of these vectors of Lyme disease. Although spermatophores are present in about half of questing female ticks, they are present in virtually all those found on deer; the abundance of males on deer exceeds that of females and copulation is common. Females must be inseminated before commencing the rapid engorgement phase of feeding. Males need not be in attendance during feeding, provided that the female has been inseminated preprandially. Thus, preprandial insemination suffices to stimulate rapid engorgement, but less blood is taken than when the female is perprandially inseminated. Both types of insemination effectively fertilize eggs. Eggs from females sequentially inseminated by irradiated and non irradiated males, were fertilized mainly by sperm from the last male. Cobalt‐irradiated males mate effectively and their sperm compete with those of non‐irradiated males. Sperm from the second two sequential inseminations fertilize most of the eggs. By infesting deer with such irradiated male I.dammini, the abundance of these vector ticks may effectively be reduced.

Erythema Migrans: A Chronicle

Arvid Afzelius first described and named erythema migrans (EM), a clinical entity that he assumed to be caused by an agent transmitted by the bite of a tick (Ixodes reduvius). Certain neurologic, cutaneous, and other syndromes observed in Europe were recognized in the 1920s and 1930s to be disabling sequelae of EM. In the 1940s and 1950s the effectiveness of penicillin as therapy for EM was demonstrated. In 1968 the first patient with EM and neurologic sequelae in North America benefited from treatment with penicillin. In 1975, an epidemic arthropathy appeared in the area of Lyme, Connecticut. Despite resemblance to EM (the initial appearance of cutaneous lesions), the complex was called Lyme disease because of the occurrence of cardiac, neurologic, and arthritic sequelae. The vector of Lyme disease, Ixodes dammini--a tick that harbors agents that cause Lyme disease and babesiosis--was identified and characterized in 1979. The spirochete that causes Lyme disease was designated Borrelia burgdorferi. The North American and European species of spirochete and the clinical syndromes to which they are related are described.

Potential for exposure to tick bites in recreational parks in a Lyme disease endemic area.

Eight recreational parks located in a Lyme disease endemic area of southern New York State were surveyed for the presence of ticks during the summer of 1985 by drag sampling. Ixodes dammini, the primary vector of Lyme disease in the northeast, was found in all but one park and accounted for 580 (91.8 per cent) of the 632 ticks collected. Of these, 18 per cent were larvae, 80 per cent were nymphs, and 2 per cent were adults. An I. dammini encounter distance, defined as the mean number of meters traveled before encountering a nymphal or adult I. dammini on a drag cloth, ranged from 36 m in high-risk parks, to infinity (no tick encounters). Generally, areas of high use presented higher encounter distances (lower risk) than those of the entire park. Two of the three parks with the highest annual attendance also had the highest I. dammini population indices as projected from our sampling regimen. These results indicate that recreational parks in Lyme disease endemic areas represent a substantial human risk for tick bites and Lyme disease.

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.

EMERGING PATTERN OF LYME DISEASE IN THE UNITED KINGDOM AND IRISH REPUBLIC

In the past year there have been 68 cases of Lyme disease in the United Kingdom and Republic of Ireland. 41 patients had erythema chronicum migrans, and 8 of them had associated neurological disease. 13 further patients presented with neurological disease without a preceding skin lesion. Myocarditis was present in 1 patient. Ixodes ricinus was confirmed as the vector for Lyme disease. In two areas deer were found to be infected by Borrelia burgdorferi, the causative organism of Lyme disease. 86% of 45 deer sera tested had significant antibody titres against B burgdorferi.

Transfusion-Acquired Babesiosis and Failure of Antibiotic Treatment

HUMAN babesiosis is a zoonosis characterized by fever, malaise, and hemolytic anemia. In the United States, the disease is generally caused by the species Babesia microti , a protozoan parasite of rodents, and is transmitted by Ixodes dammini , the northern deer tick. 1 Most of the 200 known cases of human babesiosis in the United States followed exposure to I dammini on the coastal islands of the Northeast, particularly Nantucket Island, Massachusetts, and Shelter Island, New York. Asymptomatic infections occur frequently 2 and create potential for transmission of infection through blood donation. 3-6 Recently the range of I dammini , which is also the principal vector of Lyme disease, has increased dramatically, with a resulting increase in the incidence of human babesiosis and Lyme disease. 7 Herein we report the first case of babesiosis acquired in New Hampshire and cite evidence indicating that the infection was transfusion acquired. This case also documents

Ixodes dammini (Acari: Ixodidae) in Maryland, USA, and a preliminary survey for Babesia microti.

In 1980–1981, immature and adult ticks generally conforming to published descriptions of Ixodes dammini were found within the Maryland section of Assateague Island. Previously this tick, the principal vector of human babesiosis and Lyme disease, had not been identified south of New Jersey. Adult specimens also were collected at other localities in eastern Maryland. Peromyscus leucopus was host to immature I. dammini and Dermacentor variabilis. Adult D. variabilis and Amblyomma americanum were taken at CO2 trapping sites and by flagging on the island. No direct evidence of Babesia microti was detected in tick or mouse populations. However, indirect fluorescent antibody tests performed on P. leucopus sera indicated a possibility of previous natural mouse exposure to this hemoparasite.

Amblyomma americanum: a potential vector of Lyme disease in New Jersey.

Amblyomma americanum is a likely secondary vector of Lyme disease in New Jersey. Ticks of this species were removed from the site of the characteristic skin lesion known as erythema chronicum migrans on two patients with the disease, and the Lyme disease spirochete was isolated from nymphs and adults of this species. That A. americanum is a potential vector is supported by its similarities to Ixodes dammini, the known tick vector, in seasonal distribution and host utilization. The extensive range of A. americanum may have great implications for potential Lyme disease transmission outside known endemic areas.

Spirochete Isolated in Tick Vectors of Lyme Disease

Spirochete Isolated in Tick Vectors of Lyme Disease

Lyme disease-a tick-borne spirochetosis?

A treponema-like spirochete was detected in and isolated from adult Ixodes dammini, the incriminated tick vector of Lyme disease. Causally related to the spirochetes may be long-lasting cutaneous lesions that appeared on New Zealand White rabbits 10 to 12 weeks after infected ticks fed on them. Samples of serum from patients with Lyme disease were shown by indirect immunofluorescence to contain antibodies to this agent. It is suggested that the newly discovered spirochete is involved in the etiology of Lyme disease.