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PubMed2025

Establishment of reverse genetics systems for Colorado tick fever virus.

The Colorado tick fever virus (CTFV), which has 12-segmented double-stranded RNA genomes, is a pathogenic arbovirus that causes severe diseases in humans. However, little progress has been made in the analysis of replication mechanisms and pathogenicity. This virological constraint is due to the absence of a reverse genetics system for CTFV; therefore, we aimed to establish the system. Initially, the efficacy of CTFV replication was investigated in various cell lines. CTFV was found to grow in many cell types derived from different hosts and organs. Subsequently, BHK-T7 cells stably expressing T7 RNA polymerase were transfected with plasmids encoding each of the 12 CTFV gene segments, expression plasmids encoding all CTFV proteins, and a vaccinia virus RNA-capping enzyme. Following transfection, the cells were co-cultured with Vero or HeLa cells. Using this system, we rescued monoreassortants and recombinant viruses harboring peptide-tagged viral proteins. Furthermore, an improved system using Expi293F cells expressing T7 RNA polymerase was established, which enabled the generation of recombinant reporter CTFVs. In conclusion, these reverse genetics systems for CTFV will greatly contribute to the understanding of viral replication mechanisms, pathogenesis, and transmission, ultimately facilitating the development of rational treatments and candidate vaccines.

Animals↗

PubMedDate not supplied

The outer surface protein A (OspA) of Borrelia burgdorferi: a vaccine candidate and bioactive mediator.

In the search for a suitable vaccine candidate for Lyme borreliosis the principles of protective immunity were studied in a murine model of Borrelia burgdorferi infection. It was found that the spirochetal outer surface protein A (lipOspA) in its native and recombinant lipidated form induces monospecific immune sera, which in passive transfer experiments protect SCID mice against experimental and tick-borne infection and disease. These and similar findings of independent groups led to the development of a vaccine formulation containing lipOspA. When tested in clinical phase I/II safety trials the recombinant lipOspA vaccine was shown to be safe, immunogenic and able to elicit borreliacidal antibodies. At present, clinical phase III efficacy trials are being conducted. B. burgdorferi infection involves the dissemination of the spirochetes from the site of the tick bite, infection of distant organs, and induction of a chronic inflammatory process. Recent studies indicate that the spirochetes may utilize host-derived enzyme systems to increase their virulence/pathogenicity. It was found that lipOspA serves as a surface receptor for the host-derived proteolytic enzyme plasmin(ogen), the central component of the so-called plasminogen activator system. Moreover, it was found that spirochetes are able to activate endothelial cells and blood-derived leukocytes, such as monocytes/macrophages, B cells and T cells, to express functions and/or secrete molecules, which are known to promote inflammatory responses. Part of these activities were exerted by the isolated lipOspA. The studies indicate an important role of lipOspA, both for the induction of a protective immune response by the host, as well as for the pathogenic processes elicited during B. burgdorferi infection.

Adult↗

PubMed1995

Targeting ticks for control of selected hemoparasitic diseases of cattle.

Development in and transmission of hemoparasites by tick vectors are phenomena closely synchronized with the tick feeding cycle. In all known life cycles, initial infection of tick tissues occurs in midgut epithelial cells and transmission is effected as ticks feed after parasites have developed and multiplied in salivary glands. Many factors reviewed affect development and transmission of hemoparasites by ticks including age of ticks, artificial temperature, climate and/or season, tick stage or sex, hemoparasite variation, concurrent infection of ticks with other pathogens, host cell susceptibility, transovarial transmission, effect of hemoparasites on tick biology, and the effect of infecting parasitemia level in cattle on infection rates in ticks. Four hemoparasites of cattle, Anaplasma marginale, Cowdria ruminantium, Theileria parva, and Babesia spp., are all dependent on ticks for biological transmission. Babesia is transmitted transovarially whereas the other three are transmitted transstadially. Mechanical transfer of infective blood via fomites and mouthparts of biting arthropods is also a major means of transmission for Anaplasma marginale but not of the others. Potential control methods for hemoparasites that target parasites as they are developing in their respective tick hosts include tick control, vaccines (against ticks and parasites), and drugs (against ticks and parasites). Successful application of control strategies will be dependent upon thorough understanding of parasite developmental cycles, biology of the tick vectors and the immune response of cattle to ticks and to hemoparasites. The most effective control measures will be those that are targeted against both ticks and the hemoparasites they vector.

Animals↗

PubMed1993

Progress in research on tick-borne diseases: theileriosis and heartwater.

The rapid population growth in subsaharan Africa necessitates a great increase in animal production in the more humid zones. Vector-borne diseases occurring in these zones will assume more importance, but are difficult to control. They include theileriosis and heartwater. Recent developments in research on these diseases are presented. Indigenous animal populations in endemic areas, subjected to natural selection, are far less susceptible than exotic stock. Heartwater, caused by the rickettsia Cowdria ruminantium, transmitted by Amblyomma ticks, causes high mortality in exotic ruminants. It has received much attention in recent years, partly because the disease has been introduced from Africa into the Caribbean and threatens the American mainland. Since the recent success of in vitro culture, much progress in research has been made, but so far prevention still relies mainly on acaricidal tick control; an infection and treatment method is used on a limited scale. Antigenic diversity is a complication for immunization procedures. Theileria parva (East Coast fever, Corridor disease and January disease) and T.annulata (Mediterranean or tropical theileriosis) are the most pathogenic of the 6 species of this protozoan genus that infect cattle. Great progress has been made in recent years in knowledge on the immunology, the epidemiology, the taxonomy and the chemotherapy of theileriosis. Intensive acaricidal tick control can now be supplemented by an attenuated schizont vaccine against T.annulata, while immunization against East Coast fever is carried out on a limited scale using virulent sporozoite infection and treatment. Research on recombinant vaccines is promising. Antigenic diversity in T.parva is a serious complication.

Africa↗

PubMed1994

First isolation of a rickettsia closely related to Japanese spotted fever pathogen from a tick in Japan.

In May 1993, we collected unfed ticks in Anan, Tokushima Prefecture, Shikoku District, Japan, a highly endemic area of Japanese spotted fever (JSF). We isolated JSF rickettsiae from these ticks by inoculating tick-emulsions into L-929 cells. Of the four genera and seven species of ticks examined, only one larva of Dermacentor taiwanensis Sugimoto yielded a rickettsial isolate. The isolate (DT-1 strain) was found to belong to the serotype common to the causative agent of JSF. This was based on its specific reactivity to mouse antisera and to a monoclonal antibody to JSF rickettsiae from the Shikoku District. This is the first tick-borne spotted fever group of rickettsia isolated in Japan. However, all stages of D. taiwanensis infrequently parasitize humans. Some ticks in the genus Haemaphysalis commonly infest humans and are frequently found to be rickettsia-positive in the hemolymph test when using the monoclonal antibody mentioned above. Therefore, the vectors of JSF rickettsiae to humans may be a complex of tick species.

Animals↗

PubMed1996

Establishment of the tick (Acari:Ixodidae)-borne cattle pathogen Anaplasma marginale (Rickettsiales:Anaplasmataceae) in tick cell culture.

Anaplasma marginale is a tick-borne rickettsia that causes bovine anaplasmosis worldwide. Despite its importance, A. marginale has thus far not been established in a continuous culture system. We have propagated A. marginale continuously for the 1st time in a tick cell line derived from the black-legged tick, Ixodes scapularis Say, using infected bovine blood as the inoculum. Erythrocytic stages invaded the tick cells and multiplied in membrane-lined vacuoles to form colonies typical of those observed in naturally infected ticks as demonstrated by light and electron microscopy. The rickettsiae have been passaged serially for 3 yr and have been cryopreserved in liquid nitrogen. Antigens present in A. marginale from tick cell culture were recognized by bovine immune serum against the blood stages of A. marginale. A. marginale grown in this tick cell line was infective for calves, and male ticks fed on the calves transmitted A. marginale to a susceptible calf. The ability to culture A. marginale removes a major impediment to the study of Anaplasma biology in vitro, and will enhance development of vaccines and diagnostic tests.

Anaplasma↗

PubMed1994

Use of partially engorged female ticks as laboratory animals in microbiological research.

Partially engorged female ticks were used as laboratory animals in microbiological research. The ticks, which were inoculated intracoelomally, became a convenient substrate for the detection of viruses, rickettsiae and protozoal parasites. This research concerned the isolation of newly recovered micro-organisms, the study of development, structure and distribution of microbial agents in ticks, and the study of their interaction with other pathogens or symbionts during mixed infection in a tick body. The isolation and maintenance of Rickettsiella phytoseiuli, the organism not of tick-borne origin, was achieved. For use in Central Europe the tick Dermacentor reticulatus is recommended for the above investigations.

Animals↗

PubMed1975

Plaque production by arboviruses in Singh's Aedes albopictus cells.

We report plaquing tests of 124 virus strains, mostly arboviruses of 21 serological groups, in Singh's line of Aedes albopictus cells. Thirty of these plaqued: all were arboviruses of six groups and were known or presumed to be mosquito borne. Failing to plaque were 86 strains of arboviruses, mostly tick borne, two strains of insect pathogens, and six animal viruses not classified as arboviruses. Among mosquito-borne agents, plaquing ability appeared related to serological classification. California group and most A-group viruses failed to plaque, but nearly all members of B and Bunyamwera groups readily plaqued. Within serological group B, 14 of 16 mosquito-borne agents plaqued, but none of 13 tick-borne or vector-unassociated viruses did so. Some implications of these results for recognition and classification of arboviruses are discussed.

Aedes↗

PubMed1984

DNA characterization of the spirochete that causes Lyme disease.

Lyme disease, a tick-borne disease long recognized in Europe but only recently recognized in the United States, was shown in 1982-1983 to be caused by a spirochete, the Lyme disease spirochete. Whether one or more species of the spirochete exists is unknown, as is its taxonomic status. To answer these questions, we determined (i) the DNA base (guanidine-plus-cytosine) content for five strains; (ii) the DNA relatedness of 10 strains from Europe or the United States (isolated from ticks, humans, and a mouse) by DNA hybridization (hydroxyapatite assay at 50 and 65 degrees C); and (iii) the DNA relatedness to other pathogenic spirochetes. The guanine-plus-cytosine content of the Lyme disease spirochete strains was 27.5 to 29.0 mol%, most similar to those of Borrelia hermsii (30.6 mol%) and Treponema hyodysenteriae (25.6 mol%) among the other spirochetes tested. DNA hybridization studies with 32P-labeled DNA from Lyme disease spirochete strain TLO-005, a human blood isolate, revealed divergence (unpaired bases) within related nucleotide sequences of only 0.0 to 1.0% for all nine Lyme disease spirochete strains tested for relatedness to TLO-005. Relatedness values of seven strains to TLO-005 were 58 to 98% (mean, 71%) in 50 degrees C reactions and 50 to 93% (mean, 69%) in 65 degrees C reactions. Two other strains, from which very low yields of DNA were obtained, showed less relatedness (36 to 50 degrees C, 38 to 47% at 65 degrees C). These were nonetheless considered to belong to the same species because of the low amount of divergence in the sequences related to TLO-005 and the absence of decreased relatedness in reactions done at 65 degrees Celsius compared with those done at 50 degrees Celsius. DNA from strain TLO-005 showed relatedness of 1% to DNAs of two leptospires and 16% relatedness to DNA from T. hyodysenteriae. B. hermsii DNA was 30 to 40% related to three Lyme disease spirochete strains in 50 degrees Celsius reactions. Divergence in these reactions was 16.5 to 18.5%, and relatedness in 65 degree Celsius reactions was 8 to 10%. On the bases of phenotypic similarity, guanine-plus-cytosine content, and DNA relatedness to B. hermsii, we conclude the Lyme disease spirochete is single previously undescribed species which belongs in the genus Borrelia.

Animals↗

PubMed1992

Identification of the tick-borne relapsing fever spirochete Borrelia hermsii by using a species-specific monoclonal antibody.

Borrelia hermsii causes a relapsing fever in humans and is one of several species of tick-borne spirochetes known to occur in the western United States. Spirochetes observed in the peripheral blood of patients acutely ill have been presumptively identified in the past by the geographic location of exposure and the probable species of tick vector. We describe a monoclonal antibody (H9826) that bound to the flagellar protein of B. hermsii but not to those of any of the other species tested, which included B. parkeri, B. turicatae, B. coriaceae, B. anserina, B. burgdorferi, and Leptospira interrogans serovar ballum. This antibody bound efficiently to B. hermsii in an indirect immunofluorescence assay and was used to rapidly detect and identify this spirochete in the peripheral blood of experimentally infected mice and in the central ganglia of Ornithodoros hermsi ticks. H9826 can rapidly confirm the identification of B. hermsii to increase our understanding concerning the geographic distribution, vector specificity, and epidemiological significance of this zoonotic human pathogen.

Antibodies, Bacterial↗

PubMed1981

Serotypes of tick-borne spotted fever group rickettsiae from western California.

A rickettsial survey of ixodid ticks known to bite man was conducted in 1979 in four coastal counties of California to obtain isolates from tick species that might be involved in the transmission of spotted fever-like illnesses, and to examine serologic characteristics of the rickettsiae relative to defined members of the spotted fever group (SFG). One hundred and seventy (19.4%) of 877 ticks comprising three species were shown by hemolymph test to harbor rickettsia-like organisms. A total of 85 SFG rickettsia isolates was obtained by Vero-cell culture; 82 were from Dermacentor occidentalis, two were from D. variabilis, and one was from Ixodes pacificus. As determined by microimmunofluorescence, the isolates comprised four distinct serotypes. Two serotypes were obtained only from D. occidentalis, and one each only from D. variabilis and I. pacificus, respectively. Most D. occidentalis isolates possessed the serologic characteristics of Rickettsia rhipicephali, but there were similar to yet distinguishable from, R. rickettsii and are members of an unclassified serotype referred to as 364D. The two isolates from D. variabilis resembled the unclassified 369C serotype previously shown to be associated with this species and D. andersoni elsewhere in the United States. The I. pacificus isolate was similar to strains of the unclassified Tillamook serotype isolated from this tick in several localities in western Oregon. Representative strains of the four serotypes could also be distinguished on the basis of pathogenicity for Vero cells, chick embryos, guinea pigs, and/or meadow voles. The significance of these findings relative to occurrence of tick-associated illnesses in western California is briefly discussed.

California↗

PubMed1985

Variability of Powassan virus cultured in tissue explants and organism of Hyalomma anatolicum ticks.

The variability of Powassan virus was studied during successive passages in Hyalomma anatolicum ticks or prolonged reproduction in their tissue explants. It had been shown that in the course of tick passages and during reproduction in the explants, pathogenicity of the virus in respect to causing acute disease in mice after peripheral inoculation was decreased, while virus ability to cause death after intracerebral (i.c.) inoculation remained unchanged. In mice infected with the original strain P-40 of Powassan virus damaging effect of the immune response prevailed, while in mice infected with the strains passaged for a long time in ticks (strain P-40Hat) or in tick tissue explants (strain P-40Haex), the protective effect of the immune response was prominent.

Animals↗

PubMedDate not supplied

[Tick-borne viruses in tropical area (author's transl)].

Arboviruses, transmitted by ticks and pathogenic to man in tropical areas, are discussed. They are considered according to, first the faunal region in which they can be found, then the type of syndrome they cause. The greater part is of little medical importance, some are noxious but of a rare occurrence (Thogoto, Wanowrie, Langat) or geographically restrained (Kyasanur forest disease), so the Crimean-Congo hemorrhagic fever is the only infection to show a notorius importance. As severe in the tropics of the oriental faunal region (Pakistan, India) as it is Europe, it seems to be of little importance in the afrotropical faunal region. Nevertheless, its severity remains to be ascertained by the means of extensive serological surveys and by taking in account this virus in presence of every hemorrhagic syndrome.

Animals↗

PubMedDate not supplied

[Tick-borne arboviruses associated with marine birds; a general review (author's transl)].

About forty different arboviruses have been isolated from ticks associated with marine birds along all the coast of the world. The majority of these viruses belongs to 8 serogroups: Hughes, B, Kemerovo, Quaranfil, Nyamanini, Sakhalin, Unkuniemi and Upolu, while some others are non-grouped arboviruses. Two kinds of specialized ticks chiefly harbour these arboviruses: 1. The ticks of Ornitbodoros capensis complex from tropical, subtropical and temperate zones - 2. The ticks Ixodes uriae (= I. putus) and Ixodes signatus from subpolar, arctic and antarcitc zones and the surrounding temperate areas. All these ticks may attack humans, and severe pruritus and/or undifferenciated febrile illness may result. From a pathological point of view, some of these arboviruses, i.e. Soldado, Aride, Saumarez Reef, act as pathogens for marine birds inducing nest desertion and death or abnormal development of newly batched chicks. On the other hand, antibodies against other viruses, with well known or suspected epidemic potency, such as West Nile, Tyuleniy, Okhotskiy viruses, are currently found in human beings in certain coastal areas. These epidemiological data deserve further attention from concerned Health autorities.

Animals↗

PubMed1995

[Rickettsia slovaca: an agent of the group of exanthematous fevers, in Portugal].

BACKGROUND: Identification of Rickettsia isolated from Dermacentor marginatus ticks from Portugal. METHODS: Using recently developed techniques (shell-vial isolation, PCR/RFLP genetical methods, SDS-PAGE), serological studies and animal induced pathology to isolate and characterize tick-borne rickettsiae. RESULTS: A total of 632 adults D. marginatus ticks were captured. From the collected ticks, we isolated 18 Rickettsia strains and the results confirm that the isolates from the haemolymph were identical to R. slovaca reference strain. CONCLUSIONS: Dermacentor marginatus ticks infected with Rickettsia slovaca were found in Portugal. This occurrence extended the known, geographical area for this microorganism. It is also a factor that could alter the seroprevalence rates of butonneuse fever. The pathogenicity of this Rickettsia should be evaluated to determine its responsibility for diseases other than butonneuse fever.

Animals↗

PubMedDate not supplied

[The frequency of generalized infection in adult fasting ticks of the genus Ixodes in foci of borreliosis in Russia and the USA].

A total of 740 adult Ixodes persulcatus ticks were collected from the vegetation by flagging in Russian foci where Borrelia afzelii and B. garinii circulate, and 156 I. dammini ticks were collected in northwestern USA regions in foci with B. burgdorferi s.str. circulation. Smears prepared from the internal organs of ticks were stained according to Romanovsky-Giemsa and analyzed under a microscope at a x 1125 magnification. All borreliae in 250 microscopic fields were counted, and concentration of microbial bodies per 100 microscopic fields was determined. The general level of infection by Borrelia in both vectors was similar: 26.2 x 3.2 in I. persulcatus and 26.3 +/- 7 in I. dammini. However, the proportions of ticks with generalized infections differ considerably (12.9 +/- 4.8 in I. persulcatus compared with 2.4 +/- 4.8 in I. dammini; significance of difference t = 3.1). We did not reveal any definite increase in the proportion of ticks with borreliae in the salivary glands among ticks with high concentrations of microbial bodies in the gut. In 25 I. persulcatus ticks with generalized infections, series of actual numbers of borreliae (per 100 microscopic fields) found in the gut and salivary glands did not correlate with one another (r = -0.23). These results confirm our previous conclusion (Korenberg, 1994) that frequencies of generalized infection in main vectors of different ixodid tick-borne borrelioses are also different, which is probably due to peculiarities of relationships between spirochetes of each species and corresponding tick vectors. These factors can be responsible for differences in the ways of horizontal and vertical transmission of pathogens belonging to the group under study.

Animals↗

PubMed1995

[Tick-transmitted arbovirus in Maghreb].

The problem of arbovirus infections in Maghreb has been relatively neglected in the pst in spite of a rich diversity of biotopes, the presence of potential reservoirs and vectors, and their position on the flight path of the Palearctic-african bird migration systems, western branch. Moreover, West Nile virus has been isolated from southern Algeria since 1968. From 1979 to 1989, ticks were collected from wild birds, pigeons, bats, rodents, poultry, camels, wild boars, domestic mammals and man, and assayed for viruses. On the whole, 424 ticks were virologically studied from Morocco, 582 from Algeria and 601 from Tunisia. Four tick-borne arboviruses have been isolated so far: three from Morocco, Soldado (Nairovirus), Essaouria (Orbivirus) and Kala Iris (Orbivirus) from Ornithodoros (A.) maritimus ticks parasitizing marine birds, and one from Tunisia, Tunis (Phlebovirus), from Argas reflexus hermanni infesting domestic pigeons. Soldado virus may infect man working into colonies of gulls for ornithological or entomological purposes and this infection is associated with a self-limited febrile illness and pruritus. In addition, antibody to Essaouira virus was detected in a wild rodent in Morocco. On the contrary it is unlike that Tunis virus may infect man because A. r. hermanni is a strickly ornithophilic tick. However, Uukuniemi group antibody has been previously evidenced in wild rodents in Tunisia. Finally, it is not excluded that other, more pathogenic, arboviruses such as Congo-Crimean haemorrhagic fever might be accidentally introduced in this sensitive geographical area.

Africa, Northern↗

PubMedDate not supplied

[Antibacterial therapy as a means of preventing ixodid tick-borne borreliosis].

A special epidemiological experiment to prevent borreliosis in persons bitten by infected ticks was performed in 1992-1994 in the Russia's Perm region where Borrelia garinii and B.afzelii circulate, and Ixodes persulcatus tick is the sole vector transmitting these pathogens to human beings. Adult ticks were removed from the bodies of persons who had referred to health facilities for first aid. Vital preparations were made from the material obtained from the gut of each tick and examined microscopically (up to 250 microscopic fields per preparation). The patients bitten by infected ticks were divided into experimental and control groups and kept under special medical and serological control for 4-5 months. The patients of the experimental group received doxycycline (100 mg twice daily) for 3-5 days after ticks had bitten. Borreliosis was diagnosed by a combination of clinical and serological data. The control group consisted of 97 patients who took no antibiotics after ticks biting and 12 of them contracted borreliosis. In 823 cases Borrelia were not revealed while microscopically analyzing the ticks removed from the patients' bodies; in this group six patients contracted borreliosis. The morbidity rate (per 100 patients) in the experimental group was 1.1, i.e. 11 times lower than that in control group. Among the patients bitten by infected ticks and untreated with antibiotics, this index was 17.6 times higher than in the group bitten by ticks in which Borrelia were not found. There is no absolute probability of detecting the pathogen during a direct microscopic analysis of the preparation made from the tick removed from the body of a bitten patient. However, this rapid identification of Borrelia, followed by short-term antibiotic treatment for microbiological evidence is an effective tool for preventing patients from contracting borrelioses.

Animals↗