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At least 217 records · Page 12Linked to original sources
PubMed1997

Cold hardiness, supercooling ability and causes of low-temperature mortality in the soft tick, Argas reflexus, and the hard tick, Ixodes ricinus (Acari: Ixodoidea) from Central Europe.

Seasonal supercooling points (SCPs=temperature of crystallization) and cold hardiness were investigated in the indigenous hard tick, I. ricinus, and in A. reflexus, a soft tick introduced to Central Europe from the South. Both species proved to be freeze-susceptible as well as highly susceptible to inoculative freezing. None of the postembryonic developmental stages of either species showed any distinct seasonal pattern of SCP. Unexpectedly, the introduced A. reflexus exhibited a distinctly higher degree of cold hardiness in terms of lower lethal temperature (LT(50): 24h exposure) as well as lethal time (T(50): time of survival at -10.1 degrees C) than I. ricinus. Engorged I. ricinus larvae as well as engorged summer acclimatized A. reflexus larvae showed some mortality at temperatures well above the SCP. This mortality was generally expressed as a failure of the following stage to eclose properly. A 10-day cold acclimation at +3 degrees C eliminated that kind of mortality in summer acclimatized A. reflexus larvae, but not in I. ricinus larvae. It was frequently observed that freezing of ticks resulted-possibly via leakage from the midgut-in a subsequent reddish brown discoloration of the ticks after thawing. Taking into account that discoloration was an indication of previous freezing, it was concluded, that after long-term exposure (for >/=30 days) at -10.1 degrees C, a temperature well above the SCP, some tick mortality could be observed that was not caused by previous freezing. Weighing experiments clearly demonstrated, that the level of dehydration was not critical for survival of A. reflexus during long-term cold exposure, even at low RH. This indicates, that cold-related factors other than freezing and dehydration were detrimental to this species.

Journal Article↗
PubMedDate not supplied

Detection of the tick-borne encephalitis virus (TBEV) in ticks in several federal "Länder" of Germany by means of the polymerase chain reaction (PCR)--characterization of the virus.

The aim of the present study was to analyse the current epidemiological situation with respect to TBE in the new federal "Länder" of Germany and in Saarland through detection of the TBEV genome in unengorged ticks using an RT-PCR technique. 22,273 ticks (Ixodes ricinus) were collected in the five new "Länder" (and some in Bavaria and Baden-Württemberg) and divided into 294 pools. It was possible to detect TBEV RNA in six pools of ticks from Mecklenburg Western-Pomerania [4], Brandenburg [1], Thuringia [1] (and in three pools from Bavaria and Baden-Württemberg). The nucleotide sequence data of the PCR products were analysed and compared. In Saarland 8,780 ticks were collected in 70 habitats from all the geographic regions and analysed using the PCR in 21 pools; two pools produced positive PCR signals (Saarlouis, Perl). We cannot as a result make a general recommendation that TBE-immunization be introduced in Saarland and in the new federal Länder of Germany. In Germany, however, TBE immunoprophylaxis in Bavaria and Baden-Württemberg is very important.

Animals↗
PubMed1999

Protective immune mechanisms to ticks and tick-borne diseases of ruminants.

A workshop of the European Union (EU) Concerted Action Project on the Integrated Control of Ticks and Tick-borne diseases (CA-ICTTD) recently assessed protective immune mechanisms to ticks and tick-borne diseases. The consensus achieved there is summarized here by Patricia Preston and Frans Jongejan. The current understanding of this field is expanded upon by the accompanying articles, and Poster, in this special issue of Parasitology Today.

Animals↗
PubMed2001

Forecasting habitat suitability for ticks and prevention of tick-borne diseases.

Climate and vegetation are the major factors affecting the distribution of ticks. Consequently, spatial distributions can be analysed by statistical methods that look for correlations between abiotic factors and known data about tick presence/absence. Remote sensing features can be obtained from a wide database of sensors with different characteristics, then applied to the problem of mapping prediction of tick distribution. Some studies had demonstrated that the use of these abiotic variables from satellite imagery has biological significance, therefore statistical accuracy of these distribution models can be interpreted under an ecological framework. Furthermore, models can be linked to these predictive maps, enabling the forecast of spatial and temporal dynamics of ticks, looking for seasonal patterns of activity and accurate use of acaricide treatments.

Animals↗
PubMed1994

Geographic correlation of schizophrenia to ticks and tick-borne encephalitis.

Schizophrenia prevalence in the United States is highest in urbanized Northeastern, Northwestern, and Great Lakes States. The viral theory of schizophrenia attributes this distribution to enhanced susceptibility to viral infections in crowded, urban areas. Such infections during fetal or perinatal development are hypothesized to result in the eventual onset of schizophrenia. This study attempts to identify which viral infections have a similar geographical distribution to schizophrenia. Examination of the geographical distribution of infectious diseases in the United States reveals that the spreading foci of Lyme disease and its primary vectors, Ixodid ticks, correlate significantly with high schizophrenia rate areas. Ixodid ticks are vectors in North America and throughout the world of tick-borne encephalitis (TBE). The international distribution of TBE is shown to be concentrated in countries where the highest rates of schizophrenia are found: Croatia, Norway, Finland, Germany, Ireland, and others. The geographical specificity of this correlation and the plausibility of a tick-associated or TBE theory of schizophrenia are discussed.

Animals↗
PubMed2001

Tick-borne Langat/mosquito-borne dengue flavivirus chimera, a candidate live attenuated vaccine for protection against disease caused by members of the tick-borne encephalitis virus complex: evaluation in rhesus monkeys and in mosquitoes.

Langat virus (LGT), strain TP21, a naturally avirulent tick-borne flavivirus, was used to construct a chimeric candidate virus vaccine which contained LGT genes for premembrane (preM) and envelope (E) glycoprotein and all other sequences derived from dengue type 4 virus (DEN4). The live virus vaccine was developed to provide resistance to the highly virulent, closely related tick-borne flaviviruses that share protective E epitopes among themselves and with LGT. Toward that end the chimera, initially recovered in mosquito cells, was adapted to grow to high titer in qualified simian Vero cells. When inoculated intraperitoneally (i.p.), the Vero cell-adapted LGT TP21/DEN4 chimera remained completely attenuated for SCID mice. Significantly, the chimera protected immunocompetent mice against the most virulent tick-borne encephalitis virus (TBEV). Subsequently, rhesus monkeys were immunized in groups of 4 with 10(5) or 10(7) PFU of LGT strain TP21, with 10(5) PFU of DEN4, or with 10(3), 10(5), or 10(7) PFU of the chimera. Each of the monkeys inoculated with DEN4 or LGT TP21 became viremic, and the duration of viremia ranged from 1 to 5 days. In contrast, viremia was detected in only 1 of 12 monkeys inoculated with the LGT TP21/DEN4 chimera; in this instance the level of viremia was at the limit of detection. All monkeys immunized with the chimera or LGT TP21 virus developed a moderate to high level of neutralizing antibodies against LGT TP21 as well as TBEV and were completely protected against subsequent LGT TP21 challenge, whereas monkeys previously immunized with DEN4 virus became viremic when challenged with LGT TP21. These observations suggest that the chimera is attenuated, immunogenic, and able to induce a protective immune response. Furthermore, passive transfer of serum from monkeys immunized with chimera conferred significant protection to mice subsequently challenged with 100 i.p. 50% lethal doses of the highly virulent TBEV. The issue of transmissibility of the chimera by mosquitoes was addressed by inoculating a nonhematophagous mosquito, Toxorhynchites splendens, intrathoracically with the chimera or its DEN4 or LGT parent. Neither the LGT TP21/DEN4 vaccine candidate nor the wild-type LGT TP21 virus was able to infect this mosquito species, which is highly permissive for dengue viruses. Certain properties of the chimera, notably its attenuation for monkeys, its immunogenicity, and its failure to infect a highly permissive mosquito host, make it a promising vaccine candidate for use in immunization against severe disease caused by many tick-borne flaviviruses.

Animals↗
PubMed1999

Molecular characterization of ticks and tick-borne pathogens.

Ticks and their vertebrate hosts often carry several pathogens simultaneously, which either belong to different or to the same genera. Conventional methods (such as blood smear examination or tick salivary gland staining) are often unable to discriminate between pathogens. Therefore, molecular methods for the detection and differentiation of tick-borne pathogens are increasingly used. Technical problems still remain to identify pathogens within tick tissues, or within host animals when infection rates are very low. Recently we developed an integrated approach to identify several pathogens with only one molecular test. This approach, the reverse line blot hybridization (RLB) reduces costs of analysis, gives quicker results. and allows standardized inter-laboratory comparisons. Finally, this paper also focuses on the molecular diagnostic techniques currently used in the laboratories of the Mediterranean countries.

Animals↗
PubMed2002

Biology of Ixodes species ticks in relation to tick-borne zoonoses.

At least six tick-borne zoonoses are transmitted by members of the Ixodes ricinus species complex in northern hemisphere temperate regions, and include the relatively recently emerged diseases, Lyme borreliosis and ehrlichiosis. An understanding of the biology of these ticks is essential for the prevention and control of the zoonoses they transmit and this review summarises established knowledge in addition to addressing recent work on host specificity of ticks, inter- and intra-specific biological variation and factors affecting tick distribution and abundance.

Animals↗
PubMed1977

Tick-borne diseases in the United States: Rocky Mountain spotted fever and Colorado tick fever. A review.

The historical, clinical, ecological, and epidemiological features of Rocky Mountain spotted fever and Colorado tick fever, the two important tick-borne diseases in the United States, are reviewed. Rocky Mountain spotted fever, once considered a disease of the past, has again become a measurable public health problem. Its nationwide incidence has steadily increased since 1960 and has reached record proportions in 1976. The various factors responsible for this trend as well as for the mortality rates, which in spite of availability of effective antibiotics ranges from 5 to 10%, are discussed. Education of the public about ticks and their potential role as vectors of Rickettsia rickettsii and/or Colorado tick fever virus, and about the clinical manifestations of Rocky Mountain spotted fever, is considered the best means for preventing high incidence and mortality from these diseases.

Antibodies, Viral↗
PubMed1990

Immunization of guinea-pigs against Rhipicephalus appendiculatus adult ticks using homogenates from unfed immature ticks.

Guinea-pigs immunized with homogenates of unfed larvae and nymphs of the tick Rhipicephalus appendiculatus developed significant levels of protective immunity to infestation with adults of this species. The mean engorged weight of female ticks feeding on immunized animals (181.96 +/- 05.63 mg and 170.11 +/- 11.54 mg) was reduced by an average of 46% and 51%, respectively, compared to that of female ticks feeding on control guinea-pigs, although in some individual animals the reduction was as high as 86%; the mean egg mass weight was also significantly reduced. Electrophoretic separation of the homogenates followed by immunostaining with post-infestation sera revealed several antigen bands common to all stages. Two bands of 36,500 and 23,000 molecular weight (MW) were recognized in all homogenates by post-adult infestation serum, but not by post-larval or post-nymphal infestation sera, suggesting that these may be antigens specifically involved in feeding by adult ticks, and are either not presented to the host's immune system or presented only in minimal amounts during feeding by immature stages. Sera from animals immunized with the homogenates did not recognize either of these antigens. Post-immunization sera did, however, stain two bands of 84,000 and 60,000 MW in the homogenates which were not recognized by post-infestation sera.

Animals↗
PubMed1986

Peculiarities of tick-borne encephalitis virus reproduction in Haemaphysalis inermis ticks and their explants.

Virological, electron microscopic and immunomorphological investigation on the reproduction of tick-borne encephalitis (TBE) virus in Haemaphysalis inermis ticks and in tissue explants from nymphs during their metamorphosis revealed that the virus reproduced in the cells of different tissues and organs of ticks which were in different phases and stages of life cycle. During the eclipse phase of TBE virus persistence in ticks, when no virus could be demonstrated by infectivity assay, viral particles were detected by electron microscopy.

Animals↗
PubMed1985

Replication of tick-borne encephalitis (TBE) virus in ticks Dermacentor marginatus.

In the laboratory experiments, the virophoric period in D. marginatus ticks lasted 61 to 81 d, the premoulting period (nymphs - adults) amounted to 17 to 18 d. The titres of individually examined females and males for the presence of TBE virus ranged from 10(1) to 10(5.5) ic mouse LD50/0.03 ml between the 14th and 29th day after hatching. In the laboratory experiments 77% of ticks were positive. In the field experiments, the virophoric period in D. marginatus ticks lasted 79 to 114 d, the premoulting period amounted to 34 to 38 d. The titres of individually examined adults for the presence of virus ranged from 10(1) to 10(5.5) ic mouse LD50/0.03 ml between the 13th and 80th day after hatching. In the field experiments 96.5% of ticks were positive.

Animals↗
PubMedDate not supplied

[Changes in the synthesis of the virion antigen of the tick-borne encephalitis virus after passage through ixodid ticks and small mammals].

Large-plaque strains of tick-borne encephalitis (TBE) virus possess a high peripheral activity, and in acute infection in continuous pig embryo kidney cells (PEK) synthesize a virion antigen (VA) whose subpopulations differ in their mobility in agarose gel electrophoresis: the bulk portion of VA moves towards the cathode and a small one towards the anode. After long-term passages of these strains in Ixodid ticks they lose their peripheral activity and produce only small plaques. In reproduction in PEK cells the amount of the infectious virus remains the same but VA synthesis changes significantly. There is almost no synthesis of VA moving towards the cathode and that of VA moving towards the anode remains unchanged or decreases insignificantly. The decrease in the synthesis of the major portion of VA is accompanied by the reduction of the hemagglutinating properties of the strains and retention of the nonvirion antigen production. Reversion to the initial properties of the strains passaged in ticks occurs after their inoculation into natural hosts of tick-borne encephalitis virus: small mammals (bank vole and common vole).

Animals↗
PubMedDate not supplied

[Effect of the diapause in the Ixodes ricinus (Ixodidae) tick on the multiplication of the tick-borne encephalitis virus in its body].

The tick encephalitis virus was found to multiply more intensively in ticks developing without diapause. Thus, in larvae developing with diapause, in 4 and 8 weeks after they feed on infected animals, the virus titers were 3.0 and 3.5 lg LD50 respectively. At the development without diapause the titers were 4.3 and 5.3, respectively (P less than 0.05). The virus titers in infected nymphs developing without diapause were 2.5 to 3.9 lg LD50 higher than those of the diapausing individuals. In diapausing larvae and nymphs the tick encephalitis virus remained for a long time (8 to 10 weeks) without fall of titers. The fall of virus titers was not recorded either during the moulting of larvae for nymphs and nymphs for imago but in hungry ticks, which were maintained for a long time at 18 to 23 C, the amount of virus gradually diminished.

Animals↗
PubMed1979

Tick infestations and tick-borne diseases in Zimbabwe Rhodesia.

The distribution of tick species in Zimbabwe Rhodesia is significantly influenced by land utilization practices. The most commonly occurring species in the over-grazed tribal areas is Boophilus decoloratus. By contrast, well-managed commercial farms and ranches support a wide range of tick species, the most important of which is Rhipicephalus appendiculatus. Until recently tick-borne diseases of cattle were efficiently controlled through dipping. The low incidence of disease was an important factor contributing to over-grazing in tribal areas. Between 1973 and 1978 political unrest resulted in a collapse of the dipping service in tribal areas. Populations of B. decoloratus built up and outbreaks of babesiosis and anaplasmosis occurred, normally between one and three years after the cessation of dipping. Reduced grazing pressure after the initial disease waves resulted in increased grass cover, allowing species such as R. appendiculatus and Amblyomma hebraeum to become re-established. Outbreaks of theileriosis and heartwater usually followed, decimating the already depleted herds. The heavy cattle mortality resulted from lack of immunity to tick-borne diseases, as a result of efficient disease control through dipping in previous years.

Animals↗
PubMed1984

Occurrence of ixodid ticks--the main vectors of tick-borne encephalitis virus in urbanized territory.

The influence of urbanization on ticks I. ricinus and I. persulcatus--the main vectors of tick-borne encephalitis virus is discussed on the basis of concrete examples. It has been revealed that under favourable conditions the populations of these tick species can exist for a long time not only in towns and new housing estates, but in the old residential districts as well. The necessity of studying the ecology of urban populations of ixodid ticks is pointed out.

Animals↗
PubMed1978

Studies on the experimental infection of Hyalomma dromedarii (Koch) ticks with tick-born encephalitis virus.

The replication dynamics of 4 strains of tick-borne encephalitis virus, differing in neurovirulence towards white mice, and their penetration to the salivary glands and ovaries of H. dromedarii were examined. The ticks were infected by being artificially fed a large dose of the virus and were observed for 44 days. The virus actively multiplied in whole ticks and examined organs. A relation between the neurovirulence of the strains towards white mice and persistence of infection in the ticks and their organs was observed.

Animals↗
PubMed1999

Incidence from coincidence: patterns of tick infestations on rodents facilitate transmission of tick-borne encephalitis virus.

Tick-borne encephalitis (TBE) virus has a highly focal distribution through Eurasia. Endemic cycles appear to depend on the transmission of non-systemic infections between ticks co-feeding on the same rodent hosts. The particular features of seasonal dynamics and infestation patterns of larval and nymphal Ixodes ricinus, but not Dermacentor reticulatus, from 4 regions within TBE foci in Slovakia, are such as to promote TBE virus transmission. The distributions of larvae and nymphs on their principal rodent hosts are highly aggregated and, rather than being independent, the distributions of each stage are coincident so that the same ca. 20% of hosts feed about three-quarters of both larvae and nymphs. This results in twice the number of infectible larvae feeding alongside potentially infected nymphs compared with the null hypothesis of independent distributions. Overall, co-feeding transmission under these circumstances brings the reproductive number (R0) for TBE virus to a level that accounts quantitatively for maintained endemic cycles. Essential for coincident aggregated distributions of larvae and nymphs is their synchronous seasonal activity. Preliminary comparisons support the prediction of a greater degree of coincident seasonality within recorded TBE foci than outside. This identifies the particular climatic factors that permit such patterns of tick seasonal dynamics as the primary predictors for the focal distribution of TBE.

Animals↗