[Evolution of tick-borne encephalitis and a problem of evolution of its causative agent]

The evolution of tick-borne encephalitis (TBE) is marked by the expanded nosological area, the transformation of landscapes, the formation of anthropurgic foci, the change of environmental systems, the increase of mortality rate mainly among urban dwellers, as well as pathomorphism. The evolution of natural TBE virus (TBEV) populations was studied in Eastern and Western Siberia, Middle Urals, and the European part of the nosological area. The paper first describes the types of evolutionary transformations of viral populations under the conditions of a varying environmental and epidemiological situation. These include: 1) the change of TBEV subtypes over 50-60 years; substitution of the Far-Eastern subtype for its Siberian subtype (the Sverdlovsk and Kemerovo regions); 2) the steady-state circulation of one Siberian subtype with mutanttypes being accumulated (the Vologda region); 3) co-existence of the Far-Eastern and Siberian subtypes with the common vector Ixodes persulcatus (the Yaroslavl and Irkutsk regions, etc.); 4) original mixed TBEV strains including the gene sites of proteins E and NSI of two subtypes. There is new evidence that the Siberian subtype is able to induce focal TBE forms, leading to death.

[Organization of supervision of tick-borne encephalitis and ways of its prevention in the Russian Federation]

The paper presents the data characterizing the epidemiological situation associated with tick-borne virus encephalitis (TBVE) in the Russian Federation in 2006. There is a 22.7% reduction in morbidity as compared with 2005; however, the situation is considered to be of strain; a rise in the incidence of TBVE is recorded in a number of subjects of the Russian Federation. There is a high activity of natural and anthropurgic foci of TBVE; there are as many as 250 recourses to a doctor for tick bites. In some regions, tick virus carriage has been established at 13-29%. TBVE vaccination coverage is quite insufficient; in many cases emergency prophylaxis is not made due to the fact that specific immunoglobulin is in short supply whereas some areas continue to unwarrantedly inject a serum for lack of rapidly tick virus-determining laboratories. There are essential faults in the organization of acaricidal measures and in the propaganda of knowledge of personal TBVE prophylaxis in the population. Tasks for increasing the level of comprehensive prophylaxis are defined to substantially reduce TBVE morbidity in the Russian Federation.

[Molecular genetic characteristics of tick-borne encephalitis virus]

Flaviviruses from a tick-borne encephalitis virus (TBEV) complex circulate in about all the countries widely distributed in Northern Eurasia. Complete nucleotide sequences for genomes of different 15 tick-borne encephalitis viruses have been determined in the past years. Phylogenetic analyses of these sequences showed their significant genetic variability. Thus, the genetic differences in the genomes of TBEV strains are as high as 17.3%, but the differences in the amino acid sequences are 9%. These genetic differences permit determination of the time of divergence of the current TBEV genovariants from the common viral precursor in 1700 to 2100. Novel genetic variants of the Far-Eastern TBEV subtype, which are represented by Senzhang and Glubinnoe/2004 viruses, have been discovered in the pastyears. New variants of the same Far-Eastern subtype of TBEV, which are able to induce hemorrhagic tick-borne encephalitis, have been found in Western Siberia. The fact that there are considerable genetic differences in Turkish and Spanish sheep encephalitis viruses has been established within the European subtype of TBEV. The Siberian subtype of TBEV is genetically more uniform; however co-circulation of the Far-Eastern and Siberian subtypes of TBEV has been found in the natural TBEV foci of Siberia. This suggests that there may be at present a change in the genotypes of TBEV in different geographical regions.

Substitution of conserved cysteine residues in wheat streak mosaic virus HC-Pro abolishes virus transmission by the wheat curl mite

Substitutions in the amino-proximal region of wheat streak mosaic virus (WSMV) HC-Pro were evaluated for effects on transmission by the wheat curl mite (Aceria tosichella Keifer). Alanine substitution at cysteine residues 16, 46 and 49 abolished vector transmission. Although alanine substitution at Cys(20) had no effect, substitution with arginine reduced vector transmission efficiency. Random substitutions at other positions (Lys(7) to Asn, Asn(19) to Ile, and Arg(45) to Lys) did not affect vector transmission. These results suggest that a zinc-finger-like motif (His(13)-X2-Cys(16)-X29-Cys(46)-X2-Cys(49)) in WSMV HC-Pro is essential for vector transmission.

Brevipalpus mites Donnadieu (Prostigmata: Tenuipalpidae) associated with ornamental plants in Distrito Federal, Brazil

Brevipalpus mites colonize a great number of fruit and ornamental plants. Mite species belonging to this genus have been associated with many plant viruses. Citrus leprosis (CiLV) is the most economically important virus transmitted by B. phoenicis mites. It has recently been shown that ornamental plant species can be alternative hosts of this virus. The high volume of trade and frequent movement of live ornamental plants make them efficient pest disseminators. Because of this, it is desirable to expand knowledge of potential pests aiming to guide the adoption of quarantine measures. This work reports ornamental plant hosts of Brevipalpus mites in the Distrito Federal (DF), as well the occurrence of symptoms consistent with Brevipalpus-borne plant viruses in these same hosts. Between July and September of 2005, five surveys were carried out in 14 localities within DF. Leaves and branches of fifty-five ornamental plant species were sampled. The species Pithecellobium avaremotemo Mart. is for the first time reported as a host for B. phoenicis (Geijskes), B. californicus Banks and B. obovatus Donnadieu species. Additionally, seven new species are reported as hosts for Brevipalpus within South America. New hosts are also listed for individual mite species. Typical symptoms of Brevipalpus-borne viruses were observed in Ligustrum sinense Lour., Pelargonium hortorum L.H. Bailey, Hibiscus rosa-sinensis L. and orchids (Dendrobium and Oncidium). The results of this work emphasize the potential role of the ornamental plants as vehicles for dissemination of Brevipalpus mites.

Tick-borne flavivirus infection in Ixodes scapularis larvae: development of a novel method for synchronous viral infection of ticks

Following a bite from an infected tick, tick-borne flaviviruses cause encephalitis, meningitis and hemorrhagic fever in humans. Although these viruses spend most of their time in the tick, little is known regarding the virus-vector interactions. We developed a simple method for synchronously infecting Ixodes scapularis larvae with Langat virus (LGTV) by immersion in media containing the virus. This technique resulted in approximately 96% of ticks becoming infected. LGTV infection and replication were demonstrated by both viral antigen expression and the accumulation of viral RNA. Furthermore, ticks transmitted LGTV to 100% of the mice and maintained the virus through molting into the next life stage. This technique circumvents limitations present in the current methods by mimicking the natural route of infection and by using attenuated virus strains to infect ticks, thereby making this technique a powerful tool to study both virus and tick determinants of replication, pathogenesis and transmission.

Alkhurma hemorrhagic fever virus in Ornithodoros savignyi ticks

Evidence for the tickborne nature of Alkhurma hemorrhagic fever virus (AHFV) is indirect because AHFV has not been detected in arthropods. One Ornithodoros savignyi tick from Saudi Arabia contained AHFV RNA. This is the first direct evidence that AHFV is a tickborne flavivirus and confirms the association between human AHFV cases and tickbite history.

Genetic characterization of tick-borne flaviviruses: New insights into evolution, pathogenetic determinants and taxonomy

Here, we analyze the complete coding sequences of all recognized tick-borne flavivirus species, including Gadgets Gully, Royal Farm and Karshi virus, seabird-associated flaviviruses, Kadam virus and previously uncharacterized isolates of Kyasanur Forest disease virus and Omsk hemorrhagic fever virus. Significant taxonomic improvements are proposed, e.g. the identification of three major groups (mammalian, seabird and Kadam tick-borne flavivirus groups), the creation of a new species (Karshi virus) and the assignment of Tick-borne encephalitis and Louping ill viruses to a unique species (Tick-borne encephalitis virus) including four viral types (i.e. Western Tick-borne encephalitis virus, Eastern Tick-borne encephalitis virus, Turkish sheep Tick-borne encephalitis virus and Louping ill Tick-borne encephalitis virus). The analyses also suggest a complex relationship between viruses infecting birds and those infecting mammals. Ticks that feed on both categories of vertebrates may constitute the evolutionary bridge between the three distinct identified lineages.

Host range specificity of flaviviruses: correlation with in vitro replication

Vector-borne flaviviruses have been traditionally grouped into either mosquito-borne or tick-borne group. However, this vector range specificity has sometimes been questioned because of the puzzling records of occasional isolation of mosquito-borne viruses from ticks and of tick-borne viruses from mosquitoes. In this study, host range of the flaviviruses representing not only the two vector-borne groups but also insect flaviviruses and vertebrate viruses that are not arboviruses was comprehensively reexamined by a serial passage experiment in vitro by using cell cultures derived from mosquitoes, ticks, and vertebrates. The results showed that the host range specificity in the four groups of viruses, based on replication for five consecutive passages as a criterion to evaluate the ability of viruses to replicate in three different cell cultures, agreed with the conventional grouping as well as phylogenetic clustering. Thus, this assay provides useful, supplementary information regarding host range for those flaviviruses when their natural host range is unknown, ambiguous, or questionable.

[Characterization of the natural foci of Congo-Crimean hemorrhagic fever on the territory of Ukraine]

The natural foci of the Congo-Crimean hemorrhagic fever (CCHF) in Ukraine were characterized by their geographical factors. The circulation of CCHF virus was found to occur mainly in forest and forest-steppe zones irrespective of the location of administrative regions. The territories found to be most favorable for the prolonged existence of the focus of CCHF were those having high humidity. The possibility of using geoinformation technologies for the correction of the boundaries of natural foci, the evaluation of the influence of geographical factors on the circulation of the virus was shown.

Kinetics of African swine fever virus infection in Ornithodoros erraticus ticks

The kinetics of African swine fever virus (ASFV) infection in Ornithodoros erraticus ticks were investigated in specimens collected in the field at different times following an outbreak of the disease in Portugal in 1999 and in ticks infected experimentally with a virus isolated from a tick collected during this outbreak. In ticks collected from the field, initial screening for ASFV was carried out by PCR, followed by attempts to isolate the virus in macrophage cultures. Considering total numbers of ticks tested independently of developmental stages, ASFV DNA was detected in 42.3, 26.4 and 22.4% of specimens collected at weeks 0, 32 and 63 following the outbreak, respectively. Although virus was not isolated from most of these ticks, the proportion of isolations from large nymphs and adults increased between weeks 0 and 32 from 2 to 9 % and from 5 to 11.5%, respectively. These results, together with the higher virus titres at week 32, suggest that virus replication occurred. In contrast, virus isolations from small nymphs decreased over this period, from 5 to 1.3%. At week 63, infection rates decreased for all stages. Experimental infections showed the occurrence of virus replication within 4 weeks post-feeding and maintenance of high titres in almost 100% of ticks until 20 weeks post-infection. At weeks 41 and 61, a drop in virus titres and infection rates was observed. Relevant to the understanding of African swine fever epidemiology, our results show that ASFV replicates and persists in O. erraticus, but a viral clearance occurs at later times in both natural and experimental infections.

[Crimean-Congo Hemorrhagic Fever]

Crimean-Congo Hemorrhagic Fever (CCHF) virus is a tick-borne virus, which is a member of Bunyaviridae family, Nairovirus genus. CCHF virus has been isolated from 31 different tick species so far, and genus Hyalomma includes the basic vectors of which H. anatolicum, H. marginatum, H. detritum, H. dromedarii, H. excavatum and H. turanicum are frequently found in the geography in which Turkey takes place. The virus is transmitted via the bite of infected ticks or direct contact with CCHF infected patients and the products of infected animals. Following 2-9 days incubation period, the disease abruptly starts with fever, feeling cold, shivering, headache, muscle and joint aches. After a few days hemorrhage develops at various parts of the body. Since an effective vaccine and a specific antiviral therapy have not been found yet, the high mortality rate which may reach to 10-60%, and a wide geography affecting approximately 40 countries including Turkey, CCHF attracts the attention of both scientific and mediatic world, in recent years. In this article, the structure, vectors and reservoirs of CCHF virus, together with the epidemiology, clinical features, laboratory diagnosis and strategies of treatment and prevention, have been reviewed.

Inclusion body disease in snakes: a review and description of three cases in boa constrictors in Belgium

Inclusion body disease, a fatal disorder in Boidae, is reviewed, and three cases in boa constrictors, the first reported cases in Belgium, are described. The snakes showed nervous signs, and numerous eosinophilic intracytoplasmic inclusions, which are considered to be characteristic of the disease, were found in the liver and pancreas. The disease is suspected to be caused by a retrovirus, but transmission electron microscopic examinations of several tissues from one of the snakes did not reveal particles with a typical retroviral morphology.

TBE incidence versus virus prevalence and increased prevalence of the TBE virus in Ixodes ricinus removed from humans

Traditionally, the classification of risk areas of tick-borne encephalitis (TBE) is based on the recording of autochthonous cases of the disease. In Germany, an extension of these areas over the years and an increasing virus prevalence in ticks have been observed in recent years. Registration of foci with autochthonous TBE cases, recording of disease incidence and virus prevalence in ticks are all proven epidemiological methods to characterize TBE risk areas. These data are necessary for a scientifically proven recommendation of TBE vaccines, and they need to be updated regularly. These epidemiological methods have advantages and disadvantages with respect to the risk assessment of TBE areas. Despite the fact that these methods are suitable for risk assessment in practice, disease incidence (new cases per year/100,000 inhabitants) and virus prevalence in questing ticks did not correlate. Using nested RT-PCR we were able to demonstrate that the prevalence of TBE virus (TBEV) in ticks removed from humans was significantly higher than in unfed, free-living Ixodes ricinus of the same area. The 561 ticks collected from humans in doctors' surgeries in Bavaria in 2002 were examined by nRT-PCR. The estimated overall virus prevalence in tested ticks was 8.8% (95% CI: 6.45-11.57%). The removed ticks examined were classified according to the sites of exposure of the patients in the individual districts. Peak values were measured in the district of Regen with 20.6% and in the district of Freyung-Grafenau with 18.3%. In recent studies on unfed I. ricinus (nymphs, adults), the average TBEV prevalence in ticks in Bavarian risk areas was between 0.5% and 2%.

[Tick-borne encephalitis (TBE) with special emphasis on infection in horses]

The tick-borne encephalitis (TBE), also known as early summer meningo-encephalitis, is a geographically limited virus infection transmitted mainly by ticks. The importance of TBE is largely underestimated. The causative agent TBE-Virus (TBEV) is grouped into the genus Flavivirus of the virus family Flaviviridae. Clinical disease including fatal outcomes has been described for men and dogs. With regard to horses only a limited number of case reports is available. In a study performed at the Institute of Virology, Justus-Liebig-University Giessen serum samples from the German endemic region of Marburg-Biedenkopf were tested for antibodies against TBEV. From 240 sera tested 7 (2.9%) were regarded as positive in a serum neutralization test (SNT). In an ELISA, performed in parallel to confirm the SNT results, 5 out of 7 positive sera from the SNT were also positive. The remaining two samples with low SNT-titres and all sera from horses negative in the SNT were also negative in the ELISA. This article is focussed on TBE of horses. In this context different aspects of TBE are included such as properties of the causative agent, interactions between causative agent, host animals and environment, spread of TBEV, pathogenesis, clinical symptoms, diagnosis and control.

A new eriophyid mite-borne membrane-enveloped virus-like complex isolated from plants

A decade ago, a new mite-transmitted disease was described on wheat (Triticum aesativum) and maize (Zea mays) that due to its geographical location was referred to as High Plains Disease (HPD). To determine the etiology, we established colonies of HPD pathogen-transmitting eriophyid wheat curl mites (Aceria tosichella) on wheat plants for maintenance of a continuous source of infected material. Analyses of nucleic acid obtained from infected plants showed the presence of HPD-specific RNAs ranging from 1.5 to 8 kilobases, but comparisons between the sequence of cDNAs and the databases did not reveal any clear identity with known viruses. We demonstrate that a diagnostic HPD-specific 32-kDa protein that accumulates in plants is encoded by a small RNA species (RNA-s). Upon infestation of upper wheat parts with viruliferous mites, the RNA-s encoded protein becomes detectable within a few days in the roots, indicative of an effective virus-like mode of transport. Membranous particles, resembling those observed in thin sections of infected plants, were isolated and shown to envelope a thread-like ribonucleoprotein complex containing the RNA-s encoded 32-kDa protein. This complex was associated with single-stranded (-)-sense RNAs, whereas free (+)-sense RNA was only detected in total RNA of infected plants. Based on the collective properties, we conclude that HPD is caused by a newly emerged mite-borne virus, for which we propose the name Maize red stripe virus (MRStV).

Experimental infection of Hyalomma marginatum ticks with West Nile virus

To define the possible role of Hyalomma marginatum ticks in the transmission of West Nile virus (WNV) in Portugal an experimental infection was established. Ticks were fed on viremic rabbits previously infected with WNV. In different developmental stage of H. marginatum virus isolation and detection of viral antigen and viral RNA were attempted. The oral infection rates were 3%, 33% and 75% for engorged larvae, nymphs and females after oviposition, respectively. Transstadial transmission rates for nymphs exposed to virus as larvae, for adults exposed as larvae, and for adults exposed as nymphs were 33%, 11% and 46%, respectively. No evidence of transovarial transmission was obtained. Ticks in the stages of nymphs and adults were able to transmit the infection to uninfected hosts. This study demonstrated that H. marginatum could be involved in the natural circulation of WNV in Portugal.

Ein Fall einer autochthonen Frühsommermeningoenzephalitis (FSME) in Mecklenburg-Vorpommern

HISTORY

A 61-year-old man was bitten by a tick at Lake Woblitz, near the town of Neustrelitz in former East Germany. Nine days later he saw his general practitioner because of fever and headache. Three weeks after the tick bite he was hospitalized with fever (39.2 degrees C) and mental confusion. Because he had taken a Nile cruise six months earlier, malaria was considered and he was transferred to the department of tropical medicine and infectious diseases of the University of Rostock.

INVESTIGATIONS

The patient was somnolent, his speech was slurred, and he had amnesic aphasia, as well as impaired fine motor control, but no meningism, focal signs, pyramidal tract or sensory impairment. Cerebrospinal fluid (CSF) showed mild lymphocytosis (9,400 leukocytes per microL; 89% lymphocytes) and elevated protein concentration (1322 mg/L) with blood brain barrier impairment and intrathecal IgM synthesis. Anti-tick-bite encephalitis (TBE) antibodies (ELISA: IgG and IgM) were present in serum and CSF, and serum immunofluorescence showed an eight-fold titer increase within two weeks. These findings confirm the diagnosis of TBE. Other infections (including those with cross-reacting flaviviruses) were excluded by appropriate antibody testing.

THERAPY AND CLINICAL COURSE

There is no specific antiviral treatment for TBE, but on symptomatic therapy the patient recovered fully within four weeks.

CONCLUSION

The site of the patient's infection is located 10 km to the west of an old TBE focus, but no TBE virus had been detected there after 1975. The case demonstrates that TBE should be included in the differential diagnosis of meningoencephalitis, even if the patient has not been in an acknowledged TBE endemic area.

Tick-borne Great Island Virus: (I) Identification of seabird host and evidence for co-feeding and viraemic transmission

Great Island Virus (GIV) is an arbovirus present in the tick Ixodes uriae, a common ectoparasite of nesting seabirds. Common guillemot (Uria aalge) and black-legged kittiwake (Rissa tridactyla) are the preferred and most abundant hosts of I. uriae on the Isle of May, Scotland. As part of a study to understand the epidemiology of GIV, the ability of guillemot and kittiwake to support tick-borne transmission of GIV was examined. GIV was present in ticks feeding in isolated guillemot colonies and guillemots had virus-specific neutralizing antibodies demonstrating previous GIV infection. By contrast, only uninfected ticks were found in colonies inhabited solely by kittiwakes. GIV was isolated from kittiwake ticks in colonies which also contained breeding guillemots but no virus-specific neutralizing antibodies were present in blood samples of kittiwake on which infected ticks were feeding. Thus guillemots are the main vertebrate hosts of GIV on the Isle of May whereas kittiwakes do not appear to be susceptible to infection. Virus infection of adult ticks feeding on guillemots was highly efficient and may involve both viraemic transmission and transmission from infected to uninfected ticks feeding together on birds that do not develop a patent viraemia.

Tick-borne Great Island Virus: (II) Impact of age-related acquired immunity on transmission in a natural seabird host

Tick-borne pathogen transmission is dependent upon tick number per host and the physical and temporal distribution of each feeding stage. Age-related acquired immunity to tick and pathogen may also be important but has received less attention. In this study we evaluate which of these parameters has the greatest impact on Great Island Virus (GIV) transmission between Ixodes uriae ticks and common guillemots (Uria aalge). The study system is well suited to investigate age-related effects because the guillemot population is naturally divided into 2 groups, older breeding and younger pre-breeding adult birds. The physical distribution and timing of adult and nymphal tick feeding was similar for both guillemot age groups. However, breeding birds were parasitized by significantly more ticks (mainly nymphs). Calculations based on tick number predict virus prevalence should be higher in ticks that have fed on breeding rather than pre-breeding birds. However, empirical evidence indicates the reverse. Protective acquired immunity to GIV infection may be the reason why GIV prevalence is actually significantly lower in ticks that have fed on breeders. Far more breeding (74%) than pre-breeding (12%) guillemots had antibodies that neutralized 1 or more GIV strains. Estimates of the force of infection support the view that pre-breeding birds experience higher rates of virus infection than breeding birds. The results indicate age-related acquired immunity is a key factor in GIV transmission and highlight the need to consider age-related effects and host immunity when undertaking quantitative studies of tick-borne pathogen transmission.

Dengue y otras fiebres hemorrágicas virales

Few diseases generate such alarm among the general population and health professionals as viral hemorrhagic fevers (VHFs). VHFs are acute infections with high associated mortality that are difficult to clinically diagnose and differentiate. Reliable laboratory diagnosis is required for proper patient support and to limit the risk of transmission and the development of secondary cases. Even today many factors related to origin, pathogenesis, treatment and control of these diseases remain uncertain.

A multigene analysis of the phylogenetic relationships among the flaviviruses (Family: Flaviviridae) and the evolution of vector transmission

The genus Flavivirus (family Flaviviridae) presently comprises around 70 single-strand positive-sense RNA viruses. These replicate in a range of vertebrate and invertebrate cells and may be mosquito-borne, tick-borne or have no-known-vector. Since transmission mode correlates strongly with phylogeny, the flaviviruses constitute a valuable model for the evolution of vector-borne disease. Attempts to resolve the higher-level taxonomic relationships of the flaviviruses through molecular phylogenetics have thus far proved inconclusive because of conflicting positions for the three main transmission groups. We conducted the most comprehensive phylogenetic study to date, involving maximum likelihood analyses of the NS3 and NS5 genes and the entire genome sequences available at present. For the first time, we use and test a variety of more robust methods of sequence alignment and appropriate models of amino acid replacement to study these highly divergent sequences, and explicitly test specific hypotheses of tree topology. We show that (i) the NS5 gene contains insufficient phylogenetic signal to choose between competing topological hypotheses, (ii) the NS3 gene and whole genome data indicate that the mosquito-borne flaviviruses represent an outgroup to the remaining flaviviruses, and (iii) that tick-borne transmission is probably a derived trait within the genus.

Vectorial role of some dermanyssoid mites (Acari, Mesostigmata, Dermanyssoidea)

Among transmissible diseases, vectorial diseases represent a major problem for public health. In the group of acarina, while ticks are the most commonly implicated vectors, other arthropods and notably Dermanyssoidea are also involved in the transmission of pathogenic agents. Since the role of this superfamily is at present largely unknown, we have reviewed the vectorial role of these mites in the appearance, survival and propagation of pathogens. Various authors have shown that Dermanyssoidea are implicated in the transmission of both bacteria (Salmonella, Spirocheta, Rickettsia or Pasteurella) and viruses (equine encephalitis viruses, West Nile virus, Fowl pox virus, the virus causing Newcastle disease and tick borne encephalitis viruses or hantaviruses). Finally, some authors have also shown their role in the transmission of some protozoa and filaria. As the vectorial character of such mites has been more clearly demonstrated (Dermanyssus gallinae, Omithonyssus bacoti and Allodermanyssus sanguineus), it would be interesting to continue studies to better understand the role of this superfamily in the epidemiology of certain zoonoses.

Experimental Transmission of West Nile Virus (Flaviviridae: Flavivirus) byCarios capensisTicks from North America

Seabird soft ticks, Carios capensis (Ixodida: Argasidae), originally collected from coastal Georgia, USA, were allowed to ingest a blood meal from pekin ducklings (Anas domesticus) infected with WNV. After 35 days of extrinsic incubation, the ticks transmitted virus to naive ducklings. WNV was detected via plaque assay and RTPCR in ticks and in tissues and serum of ducklings 7 days post infestation.

Plant virus HC-Pro is a determinant of eriophyid mite transmission

The eriophyid mite transmitted Wheat streak mosaic virus (WSMV; genus Tritimovirus, family Potyviridae) shares a common genome organization with aphid transmitted species of the genus Potyvirus. Although both tritimoviruses and potyviruses encode helper component-proteinase (HC-Pro) homologues (required for nonpersistent aphid transmission of potyviruses), sequence conservation is low (amino acid identity, approximately 16%), and a role for HC-Pro in semipersistent transmission of WSMV by the wheat curl mite (Aceria tosichella [Keifer]) has not been investigated. Wheat curl mite transmissibility was abolished by replacement of WSMV HC-Pro with homologues of an aphid transmitted potyvirus (Turnip mosaic virus), a rymovirus (Agropyron mosaic virus) vectored by a different eriophyid mite, or a closely related tritimovirus (Oat necrotic mottle virus; ONMV) with no known vector. In contrast, both WSMV-Sidney 81 and a chimeric WSMV genome bearing HC-Pro of a divergent strain (WSMV-El Batán 3; 86% amino acid sequence identity) were efficiently transmitted by A. tosichella. Replacing portions of WSMV-Sidney 81 HC-Pro with the corresponding regions from ONMV showed that determinants of wheat curl mite transmission map to the 5'-proximal half of HC-Pro. WSMV genomes bearing HC-Pro of heterologous species retained the ability to form virions, indicating that loss of vector transmissibility was not a result of failure to encapsidate. Although titer in systemically infected leaves was reduced for all chimeric genomes relative to WSMV-Sidney 81, titer was not correlated with loss of vector transmissibility. Collectively, these results demonstrate for the first time that HC-Pro is required for virus transmission by a vector other than aphids.

[Increasing prevalence of early summer meningoencephalitis in Europe]

The importance of TBE has increased considerably since the mid 70 s in the whole of Europe and Far East. The number of registered clinical cases has risen and risk areas have expanded. For this development a number of factors are responsible ( i. e. global warming, ecological, political, social changes). Because of the high quality and immunogenicity of TBE vaccines available for children and adults TBE should not have to be considered any longer as a problem, subject to the fact that every person at risk has been vaccinated. An important prerequisite for a scientifically based vaccine application are the constant surveillance of TBE risk areas and an actual data base. Epidemiological data with respect to the expansion of risk areas and its level of risk are available covering most European countries with TBE risk and can be made available for medical purposes when travelling.

Argasid ticks as possible vectors of West Nile virus in Israel

Mites and soft ticks collected directly from wild and domestic birds and their nests were tested for the presence of West Nile virus (WNV). The cattle egret argas, Argas arboreus, was collected from the nests of seven cattle egret colonies. Out of 1,000 A. arboreus pools examined, 16 were positive for WNV based on RT-PCR technique. The positive pools were from four nesting colonies of birds. Out of 37 cattle egret squabs examined, 37.8% had serum-neutralizing antibodies to WNV. WNV RNA was also detected in one out of 15 pools of R. turanicus, in one out of 21 pools of O. sylviarum, and in one out of 18 pools of D. gallinae, while 63 pools of A. reflexus, 11 of R. sanguineus, and 30 of Hyalomma spec. were negative. The role of mites and ticks in maintaining the endemic state of WNV in Israel is discussed.

Attempt to detect evidence for tick-borne encephalitis virus in ticks and mammalian wildlife in The Netherlands

To investigate if tick-borne encephalitis virus (TBEV) is present in mammalian wildlife species or ticks in The Netherlands, serum samples and ticks were tested for TBEV antibodies and TBEV RNA, respectively. Serum samples were collected from wild boar (666), deer (13), fox (399), and rodents (90), and were tested for TBEV antibodies, using ELISA, and SN test or HI test. Over a period of 4 years, a total of 906 ticks was collected from seven regions in The Netherlands. In four different regions, this was done on a monthly basis and during four consecutive summers. All ticks were tested for TBEV RNA by RT-PCR. TBEV antibody was detected by ELISA in two (0.5%) sera of foxes and 49 (7%) sera of wild boar, but not confirmed by HI or SNT. TBEV RNA was not detected in any of 906 ticks. It was concluded that there is no real evidence for a TBEV reservoir in ticks or wildlife in The Netherlands.

The basic reproductive number of tick–borne encephalitis virus

Tick-borne encephalitis virus (TBEV) is reciprocally transmitted between Ixodes ricinus ticks and small mammals. Recently, transmission between co-feeding ticks has been postulated as an epidemiological by important mechanism of perpetuating the agent. To empirically examine the question whether the "traditional" mode of transmission is sufficient to maintain enzootic TBEV transmission, the basic reproductive number R(0) of TBEV could be estimated under this model for sites in which TBEV is enzootic. I propose an empirical estimator of R(0) for TBEV which is based on longitudinal stage-specific local tick infestation densities assessed by live trapping of small mammals. A Gibbs sampler-based 95%-credibility interval is presented. When applied to published field data from TBEV enzootic sites sub-critical R(0) estimates are obtained for both sites. I discuss potential shortcomings of this method and possible implications of these findings on the discussion of supplemental mechanisms of transmission.

[Ticks (Acarina: Ixodidae) as vectors and reservoirs of pathogen microorganisms in Spain]

Hard and soft-ticks are obligate haematophagous arachnids of medical and veterinary significance mainly because of the animal disease agents transmitted by them, which include an array of different pathogens (virus, bacteria, protozoa and nematodes). Ticks transmit microbes by several routes including salivary secretions, coxal fluids, regurgitation and faeces. Among the biological factors that contribute to the high vector potential of ticks are their living habits and characteristic properties of their saliva secretions and blood digestion. In the Iberian Peninsula, the prostriata tick Ixodes ricinus, and the metastriata Dermacentor marginatus, Rhipicephalus sanguineus and Hyalomma marginatum are the main species that could bite man, and are involved in the transmission of Borrelia burgdorferi sensu lato, several genoespecies of Rickettsia (R. conorii, R. slovaca, R. aeschlimannii) and Anaplasma phagocytophila.

[Gradual variability of the parasitic system of tick-borne encephalitis]

It has been shown that the temperature conditions of hibernation in the major vectors of tick-borne encephalitis viruses (TBEV) the ticks Ixodes ricinus and Ixodes persulcatus occupy a special place among a lot of factors that determine the spatial distribution and the specific features of functioning of the parasitic system of tick-borne encephalitis. These conditions determine the borders of distribution of the major vectors of TBEV, their sympatric zone, and the physiological features of individual races of the ticks. The conditions of hibernation in the vectors also affect the properties of circulating RBEV strains. The reasons for variability in TBEV virulence in different landscape and climatic zones are discussed.

[Monitoring of tick-borne encephalitis virus populations and etiological structure of morbidity over 60 years]

The Siberian subtype of the virus of tick-borne encephalitis (TBE), which is predominant in Russia, constantly circulated in its eastern European regions in 1943-2003 and in the Urals and West and East Siberia in 1960-2003. This subtype is transmitted by two types of ticks: Ixodes persulcatus and I. ricinis. Changes were not found in the structure of viral populations at the peak and drop of the incidence of TBE. There was new evidence on the genetic heterogenicity of the Siberian subtype: in addition to the strains containing histidine (H) or glutamine (Q) in the position of 234 of protein E gene, there were strains having tyrosine (V). There were differences in the eastern European and Asian populations of the Siberian subtype. The strains with labeled amino acids of H and Q amounted to 87.1 and 3.2% in the eastern European population and 60 and 40% in the Asian population, respectively. The eastern European strains with labeled amino acid of H differed from the same Asian strains in the level of nucleotide replacements in the studied E gene fragment. The strains containing tyrosine in position 234 were found only in the eastern European population. Sixty-two cases of TBE were analyzed, which showed a significantly established role of a certain subtype. The Siberian and Far Eastern subtypes in the area of joint circulation were found to cause the whole spectrum of infection manifestations from unapparent to severe focal forms with a fatal outcome. There were no differences in the location of the virus and the topography of CNS morphological changes in patients who had died after infection with the Siberian or Far Eastern subtypes of the virus of TBE. The chronic forms of TBE are mainly associated with the Siberian subtype. These three subtypes (European, Far Eastern, and Siberian) may cause the disease via unpasteurized milk.

Tick-borne viruses

At least 38 viral species are transmitted by ticks. Virus–tick–vertebrate host relationships are highly specific and less than 10% of all tick species (Argasidae and Ixodidae) are known to play a role as vectors of arboviruses. However, a few tick species transmit several (e.g.Ixodes ricinus,Amblyomma variegatum) or many (I. uriae) tick-borne viruses. Tick-borne viruses are found in six different virus families (Asfarviridae, Reoviridae, Rhabdoviridae, Orthomyxoviridae, Bunyaviridae, Flaviviridae) and at least 9 genera. Some as yet unassigned tick-borne viruses may belong to a seventh family, theArenaviridae. With only one exception (African swine fever virus, family Asfarviridae) all tick-borne viruses (as well as all other arboviruses) are RNA viruses. Tick-borne viruses are found in all the RNA virus families in which insect-borne members are found, with the exception of the family Togaviridae. Some tick-borne viruses pose a significant threat to the health of humans (Tick-borne encephalitis virus,Crimean-Congo haemorrhagic fever virus) or livestock (African swine fever virus,Nairobi sheep disease virus). Key challenges are to determine the molecular adaptations that allow tick-borne viruses to infect and replicate in both tick and vertebrate cells, and to identify the principal ecological determinants of tick-borne virus survival.

Crimean-Congo hemorrhagic fever

Crimean-Congo hemorrhagic fever (CCHF) is a tick-borne disease caused by the arbovirus Crimean-Congo hemorrhagic fever virus (CCHFV), which is a member of the Nairovirus genus (family Bunyaviridae). CCHF was first recognized during a large outbreak among agricultural workers in the mid-1940s in the Crimean peninsula. The disease now occurs sporadically throughout much of Africa, Asia, and Europe and results in an approximately 30% fatality rate. After a short incubation period, CCHF is characterized by a sudden onset of high fever, chills, severe headache, dizziness, back, and abdominal pains. Additional symptoms can include nausea, vomiting, diarrhea, neuropsychiatric, and cardiovascular changes. In severe cases, hemorrhagic manifestations, ranging from petechiae to large areas of ecchymosis, develop. Numerous genera of ixodid ticks serve both as vector and reservoir for CCHFV; however, ticks in the genus Hyalomma are particularly important to the ecology of this virus. In fact, occurrence of CCHF closely approximates the known world distribution of Hyalomma spp. ticks. Therefore, exposure to these ticks represents a major risk factor for contracting disease; however, other important risk factors are known and are discussed in this review. In recent years, major advances in the molecular detection of CCHFV, particularly the use of real-time reverse transcription-polymerase chain reaction (RT-PCR), in clinical and tick samples have allowed for both rapid diagnosis of disease and molecular epidemiology studies. Treatment options for CCHF are limited. Immunotherapy and ribavirin have been tried with varying degrees of success during sporadic outbreaks of disease, but no case-controlled trials have been conducted. Consequently, there is currently no antiviral treatment for CCHF approved by the U.S. Food and Drug Administration (FDA). However, renewed interested in CCHFV, as well as increased knowledge of its basic biology, may lead to improved therapies in the future. This article reviews the history, epidemiology, ecology, clinical features, pathogenesis, diagnosis, and treatment of CCHF. In addition, recent advances in the molecular biology of CCHFV are presented, and issues related to its possible use as a bioterrorism agent are discussed.

Characterization of tick-borne encephalitis virus from Estonia

Tick-borne encephalitis virus (TBEV) is a severe problem in Estonia. In the present article the first genetic analysis of Estonian TBEV strains is described. In total, seven TBEV strains were isolated from ticks (Ixodes ricinus and I. persulcaus), rodents (Apodemus agrarius and Cletrionomys glareolus), and serum from a tick-borne encephalitis (TBE) patient. The nucleic acid sequences of the viral genome encoding almost the complete E protein (nt 41-1250) and the 3'-NCR-termini of the Estonian TBEV strains were determined by direct sequencing of RT-PCR products. The results showed that all three known TBEV subtypes, Western TBEV (W-TBEV), Far-Eastern TBEV (FE-TBEV), and Siberian TBEV (S-TBEV), co-circulate in Estonia. The Estonian TBEV strains of the S-TBEV and W-TBEV subtypes clustered with the previously reported strains from Latvia and Lithuania. Within the FE-TBEV subtype, however, the Estonian strain Est2546 clustered together with the strain Sofjin, originating from the Far-East of Russia, but not with the strain RK1424, isolated in the neighboring Latvia. This suggests a different evolutionary history for the Estonian and the Latvian strains in the FE-TBEV subtype. The Estonian TBEV strain (Est3535), which belonged to the S-TBEV subtype, had an organization of the 3'-NCR similar to that of strains from the Far-East of Russia (Irkutsk). The 3'-NCRs of Estonian strains of the W-TBEV subtype (Est3051, Est3053, Est3476, and Est3509) were very similar to those of the strain Ljubljana I from the Balkans. In the 3'-NCR sequence of the Estonian strain Est2546, which belonged to the FE-TBEV subtype, a deletion from position 10461 to 10810 extending approximately 10 nucleotides into the core element, was detected.

[ELISA and RT-PCR-based research of viruses in the ticks collected in the foci of Crimean-Congo fever in Kazakhstan and Tajikistan in 2001-2002]

Different species of ticks were found, in the territories of Kazakhstan and Tajikistan, to be infected with the virus of Crimean-Congo hemorrhagic fever (CKHF). The virologic evaluation included determination of antigen and RNA of the CKHF virus by ELISA and RT-PCR, respectively. The below tick species were found to be involved in the epidemic process: Hyalomma asiaticum, Dermacentor niveus (Kazakhastan) and Hyalomma anatolicum (Tajikistan). The results testify to the fact that Hyalomma ticks are the main carrier of the above virus in the Middle Asia. At the same time, Dermacentor niveus ticks are infection carriers in Kazakhstan.

[Study of virus contamination of Ixodes ticks in the foci of Crimean-Congo hemorrhagic fever in Kazakhstan and Tajikistan]

The data on the contamination of different of ticks with Crimean-Congo hemorrhagic fever (CCHF) virus on the territory of Kazakhstan and Tajikistan were obtained. The methods of the evaluation of the virus contamination of ticks included the determination of the antigen and CCHF virus RNA by the methods of the enzyme immunoassay and the reverse transcription PCR respectively. Different tick species were found to be involved in the epidemic process: Hyalomma asiaticum, Dermatocentor niveus (Kazakhstan) and Hyalomma anatolicum (Tajikistan). The results obtained in this study confirmed that the main vector of CCHF virus in Central Asia were ticks of the genus Hyalomma, and in Kazakhstan the vectors of this virus also included ticks Dermatocentor niveus.

Tick-borne virus diseases of human interest in Europe

Several human diseases in Europe are caused by viruses transmitted by tick bite. These viruses belong to the genus Flavivirus, and include tick-borne encephalitis virus, Omsk haemorrhagic fever virus, louping ill virus, Powassan virus, Nairovirus (Crimean-Congo haemorrhagic fever virus) and Coltivirus (Eyach virus). All of these viruses cause more or less severe neurological diseases, and some are also responsible for haemorrhagic fever. The epidemiology, clinical picture and methods for diagnosis are detailed in this review. Most of these viral pathogens are classified as Biosafety Level 3 or 4 agents, and therefore some of them have been classified in Categories A-C of potential bioterrorism agents by the Centers for Disease Control and Prevention. Their ability to cause severe disease in man means that these viruses, as well as any clinical samples suspected of containing them, must be handled with specific and stringent precautions.

Short report: duration of tick attachment required for transmission of powassan virus by deer ticks

Infected deer ticks (Ixodes scapularis) were allowed to attach to naive mice for variable lengths of time to determine the duration of tick attachment required for Powassan (POW) virus transmission to occur. Viral load in engorged larvae detaching from viremic mice and in resulting nymphs was also monitored. Ninety percent of larval ticks acquired POW virus from mice that had been intraperitoneally inoculated with 10(5) plaque-forming units (PFU). Engorged larvae contained approximately 10 PFU. Transstadial transmission efficiency was 22%, resulting in approximately 20% infection in nymphs that had fed as larvae on viremic mice. Titer increased approximately 100-fold during molting. Nymphal deer ticks efficiently transmitted POW virus to naive mice after as few as 15 minutes of attachment, suggesting that unlike Borrelia burgdorferi, Babesia microti, and Anaplasma phagocytophilum, no grace period exists between tick attachment and POW virus transmission.

[Ixodes ricinus, transmitted diseases and reservoirs]

The tick Ixodes ricinus has been recorded in most Italian regions especially in thermo-mesophilous woods and shrubby habitats where the relative humidity allow the tick to complete its 3 year developmental cycle, as predicted for the European climatic ranges. This tick acts both as vector and reservoir for a series of wildlife zoonotic pathogens, especially the agents of Lyme diseases, Tick borne encephalitis and Human Granulocytic Ehrlichiosis, which are emerging in most of Europe. To assess the spatial distribution of these pathogens and the infection risk for humans and animals within the territory of the Province of Trento, we carried out a long term study using a combination of eco-epidemiological surveys and mathematical modelling. An extensive tick collection with a GIS based habitat suitability analysis allowed us to identify the areas where tick occurs at various density. To identify the areas with higher infection risk, we estimated the values of R0 for Borrelia burgdorferi s.l., TBE virus and Anaplasma phagocytophila under different ecological conditions. We assessed the infection prevalence in the vector and in the wildlife reservoir species that play a central role in the persistence of these infections, ie the small mammals A. flavicollis and C. glareolus. We also considered the double effect of roe deer (Capreolus capreolus) which act as reservoir for A. phagocytophila but is an incompetent host for B. burgdorferi and TBE virus, thus reducing the infection prevalence in ticks of these last two pathogens. Infection prevalence with B. burgdorferi and A. phagocytophila in the vector was assessed by PCR screening 1212 I. ricinus nymphs collected by dragging in six main study areas during 2002. The mean infection prevalence recorded was 1.32% for B. burgdorferi s.l. and 9.84% for A. phagocytophila. Infection prevalence in nymphs with TBE virus, as assessed in a previous study was 0.03%. Infection prevalence in rodents was assessed by screening (with ELISA and PCR) tissues and blood samples collected from 367 rodent individuals trapped extensively during 2002 within 6 main study areas. A. flavicollis (N=238) was found to be infected with all three pathogens investigated, with infection prevalence ranging from 3.3% for TBE virus to 11.7% for A. phagocytophila, and 16.6% with B. burgdorferi s.l. C. glareolus (N=108) showed an infection prevalence of 6.5% with A. phagocytophila and 12.7% with B. burgdorferi s.l., while no individuals were infected with TBE virus. We also screened 98 spleen samples collected from roe deer with PCR, resulting in a mean prevalence of infection with A. phagocytophila of 19.8%. Using a deterministic model we explored the condition for diseases persistence under different rodent and roe deer densities. R0 values resulted largely above 1 for B. burgdorferi s.l. in the vast majority of the areas classified as suitable for I. ricinus occurrence in Trentino, while the condition for TBE persistence appeared to be more restricted by a combination of climatic condition and host densities.

[Tick borne zoonosis: selected clinical and diagnostic aspects]

Tick-borne zoonotic infections are among the most diffuse vector borne diseases: these large group of infections is caused by different microorganisms: Babesia spp., Borrelia spp., Rickettsia spp., Ehrlichia spp., Francisella tularensis, Coxiella burnetii) and tick-borne encephalitis virus. Babesiosis is caused by the protozoa (sporozoa) Babesia microti and it is quite rare in humans in Europe. The ixodids ticks are the competent vectors. A few symptomatic cases have been reported, mainly in splenectomized patients. The laboratory diagnosis is made by the microscopic identification of the parasites within the red blood cells in blood smears. The serologic diagnosis, based mainly upon IFA and WB techniques has only an epidemiological interest. Lyme borreliosis (Lyme disease) has been recognized as the most frequent vector borne disease in mild climate areas. The etiologic agent is a spirochete, belonging to the Borrelia burgdorferi sensu lato complex: B. burgdorferi sensu stricto, B. garinii and B. afzelii. Several additional species of this geno-complex have been identified but their pathogenic capability for humans still needs to be elucidated. Lyme borreliosis is clinically divided into three different clinical stages: the early disease, the disseminated infection and the persistent infection. Individual stages are caused by the diffusion of the spirochetes to different anatomic districts of the body. The main clinical symptoms are, for each stage: the erythema chronicum migrans in the early infection, the peripheral nerves and joint involvement in disseminated diseases and the acrodermatitis chronica atrophica (ACA) with central nervous system involvement in the late disseminated infection. The microbiological diagnosis is achieved by serologic techniques (IFA, EIA, WB) and by isolation of the spirochetes (in vitro culture and DNA amplification methods). Tick-borne relapsing fever (TBRF) is occasionally transmitted to humans by the soft ticks Ornithodorus and is caused by Borrelia spp. Different borreliae are responsible for TBRF in various geographic areas. The laboratory diagnosis is based upon the identification of spirochetes in peripheral blood by microscopic observation of Giemsa stained smears. Rickettsiosis diseases are caused worldwide by the obligate intracellular bacteria belonging to the genus Rickettsia. In the Mediterranean area the most frequently identified rickettsia is R. conorii, that causes the so called Mediterranean spotted fever. The serologic detection of a specific antibody response by IFA techniques is the most prominent tool for the diagnosis. In addition, the PCR method can be applied. Bacteria of the genus Ehrlichia are well known pathogens in veterinary medicine. Since the last decade their zoonotic capability has emerged and E. chafeensis, E. canis and the so called human granulocytic agent (HGE) have been identified in human diseases following a tick bite. The ehrlichiosis is characterized, in human, by a mild fever associated with lymphoadenopathy. The diagnosis is made on the identification of morulae (the intracytoplasmatic inclusion of the growing rickettsiae) in the white cells of peripheral blood. In addition the molecular diagnosis is also possible by PCR. Tick-borne encephalitis (TBE) is the only viral arthropod-borne encephalitis in Europe: it is caused by a flavivirus and it can also be transmitted by the ingestion of goat raw milk. The more relevant epidemiological figure is limited to the Alps, in particular to the Northern side (Austria). Isolated cases have been reported also in Italy. TBE is a benign self-limiting illness that usually recovers without any reliquate. The laboratory diagnosis is obtained by isolating the virus in cell cultures from the CSF or blood of acute phase patients. Serology is anyway the main laboratory tool to perform this diagnosis. Complement fixation and EIA IgM are the most used methods: the latter technique is particularly sensitive in early infection.

Origins, evolution, and vector/host coadaptations within the genus Flavivirus

Although viruses in the genus Flavivirus share complex antigenic interrelationships, they can be divided into four phylogenetic/ecological groups: two mosquito-borne groups, a tick-borne group, and nonvectored viruses. These divisions largely reflect the selective constraints imposed on the viruses by the vertebrate hosts, the invertebrate vectors, and the associated ecologies. Phylogenetic trees based on the flavivirus genetic sequence show characteristic branching patterns that reflect these groupings. This review describes the evolution and possible origins of individual flaviviruses, correlating ecological and epidemiological characteristics with their phylogenies and geographic dispersal. It will also become apparent that many of the phylogenetic lineages that define species diverged relatively recently, and the subsequent dispersal and epidemiology of these viruses have therefore been significantly influenced by increasing human population densities and activities such as recreation, urbanization, land reclamation, transportation, and deforestation. This review also considers some of the likely implications of persistent/chronic infections in relation to virus dispersal and recombination between related flaviviruses on phylogenetic analysis and vaccine development strategies.