Biomedical subjects

O Kahl

Publications and source records attributed to O Kahl.

At least 19 recordsLinked to original sources

PubMed2006

Pathogens and host DNA in Ixodes ricinus nymphal ticks from a German forest.

Unfed nymphs of Ixodes ricinus were collected from vegetation in a forest on the outskirts of Berlin, Germany and were analyzed for host and pathogen DNA. Pathogens were detected in 47% of the ticks. Borrelia afzelii was the commonest pathogen detected, followed by Rickettsia helvetica. Other pathogens included B. valaisiana, B. garinii, B. burgdorferi sensu stricto, Anaplasma phagocytophilum, and a relapsing fever-like Borrelia. Most of the host DNA detected was of rodent origin and was associated with infection by B. afzelii, R. helvetica, and A. phagocytophilum. Bird DNA was associated with B. valaisiana and B. garinii, and ruminant DNA with A. phagocytophilum. B. afzelii was also found in two ticks that contained bird DNA.

Anaplasma phagocytophilum↗

PubMed1999

Chemoprophylaxis for Lyme borreliosis?

Chemoprophylaxis is a term which describes treatment with an antimicrobial chemotherapeutic before, during or shortly after an actual or suspected exposure to an infectious agent in order to prevent clinical disease, which may be severe or even fatal. Lyme borreliosis is considered the most frequent ixodid-tick-transmitted human bacterial infection in the northern hemisphere. For several years there has been a debate on the prophylactic application of antimicrobial chemotherapeutics after an attached Ixodes tick was removed. Would this measure prevent a subsequent borrelia infection and would it be practical? People are exposed to tick-bites mostly during leisure spent in recreational areas which are often tick infested. The proportion of I. ricinus ticks infected with B. burgdorferi s. l. varies from area to area and in a given area also from year to year (infection rate up to a maximum of 55%). The transmission rate strongly depends on the duration of feeding, but it could be shown that the critical time of feeding is much shorter for European I. ricinus than for the North American I. scapularis or I. pacificus ticks. Nevertheless, even the low risk of complications despite the very good chance of treating erythema migrans successfully seems to justify prophylactic treatment for some investigators whilst others do not see an argument for this. Double blinded studies in the USA showed a relatively low frequency of illness after vector tick-bite and absence of disseminated disease manifestations. The efficacy of prophylactic antibiotic treatment after tick-bites is not established. Suggestions to examine removed ticks for borrelia in order to obtain indication for prophylactic antibiotic treatment will fail in practice because of high costs and uncertainty in verifying the transmission. Do we need blinded studies in central Europe on a representative number of cases, although it is known that Lyme borreliosis can be treated effectively even in its second and third stage and has never caused a fatal outcome? We conclude that only a reliable diagnosis of symptoms is the basis for a rational antibiotic treatment, and that instead of chemoprophylaxis for Lyme borreliosis after a vector tick-bite the wait and watch policy is recommended.

Animals↗

PubMed1999

The pigeon tick (Argas reflexus): its biology, ecology, and epidemiological aspects.

The European pigeon tick, Argas reflexus (F.), is in central Europe predominantly an urban pest parasitizing wild and domesticated pigeons, Columba livia. Under certain circumstances, however, it also bites humans, occasionally causing an IgE-mediated type-I allergy. Control of A. reflexus is very difficult because of a number of remarkable morphological, physiological, and behavioural features of the tick. The present study aimed at elucidating the distribution and the frequency of occurrence of A. reflexus in Berlin and its possible vector role for Borrelia burgdorferi sensu lato (s. l.). Buildings reported by occupiers to be infested with A. reflexus were personally examined. In addition, the carrier status of this soft tick for B. burgdorferi (s. l.) was investigated in three German towns by an indirect immunofluorescence assay. A total of 188 Berlin buildings was found to be infested with A. reflexus between 1989 and 1998. Infestations were found in 17 out of the 21 districts, clustering in the inner city. There was only a single Borrelia-positive tick out of 800 sampled in Berlin, Leipzig, and Hannover using the genus specific antibody H9724. The same tick was PCR-negative for B. burgdorferi outer surface protein A. Neither these results nor those of other studies on the occurrence of antibodies against B. burgdorferi in pigeons suggest that field populations of A. reflexus and/or pigeons in central Europe harbour the causative agent of Lyme borreliosis.

Animals↗

PubMed1999

Borrelia burgdorferi sensu lato in Ixodes ricinus ticks and rodents in a recreational park in south-western Ireland.

Ixodes ricinus ticks infected with Borrelia burgdorferi sensu lato were numerous on the edges of paths and roads in a recreational park in south-western Ireland. The abundance of ticks at different sites was related to the presence of deer, but a negative relationship was shown between tick abundance and tick infection rates. This is thought to be due to the deposition of large numbers of uninfected ticks by deer, which are apparently not good reservoir hosts of B. burgdorferi s.l. Blood meal analysis only detected deer DNA in uninfected nymphs. Reservoir competent rodents, Apodemus sylvaticus and Clethrionomys glareolus, were abundant at all sites and a high proportion of captured specimens were infested with larval ticks. However, very few rodents were infected with B. burgdorferi s.l. and none of the unfed infected nymphs analysed for the identity of their larval blood meal had fed on rodents. The spirochaetes detected in I. ricinus in the study area may be poorly adapted to rodents or are not transmitted readily because of the absence of nymphal infestation. The majority of spirochaetes in these ticks were apparently acquired from non-rodent hosts, such as birds.

Animals↗

PubMed1998

Ixodes ricinus strains in Europe.

An analysis of cuticular hydrocarbons (CH) of unfed adult Ixodes ricinus ticks collected throughout Europe showed that there are 10 distinct I. ricinus groups. Studies on the seasonal and annual consistency of CH composition and possible effects of host and environmental factors suggested that CHs may be used as a genuine genetic marker for I. ricinus. Preliminary studies compared the vector competence of ticks from three of the most separated I. ricinus groups and the results suggested that there may be significant differences in tick susceptibility to Borrelia afzelii.

Animals↗

PubMed1998

European reservoir hosts of Borrelia burgdorferi sensu lato.

Existing knowledge on reservoir hosts of Borrelia burgdorferi sensu lato was collated and reviewed and several species, particularly birds, were identified as reservoir competent. At the present time, 9 small mammals, 7 medium-sized mammals and 16 bird species, including passerines, sea birds and pheasants, appear to be capable of transmitting spirochaetes to ticks and thus of participating in the natural circulation of B. burgdorferi s.l. in Europe. The house mouse, Mus musculus is strongly suspected of reservoir competence and many other small rodent species, particularly in eastern Europe and Russia, have been implicated. Ungulates are not thought to play a major role as reservoir hosts, though co-feeding transmission may permit some tick infection. The criteria for establishment of reservoir status are outlined and a method for identification of host blood meals of previous instars of unfed ticks, developed in a participant laboratory, is briefly described.

Animals↗

PubMed1998

Detection of Borrelia burgdorferi sensu lato in ticks: immunofluorescence assay versus polymerase chain reaction.

Immunofluorescence (IFA) and polymerase chain reaction (PCR) were examined as methods for detecting Borrelia burgdorferi sensu lato spirochaetes in unfed Ixodes ricinus nymphs. Although similar results were produced in some cases, a great deal of variation occurred. Furthermore, in both the highly controlled initial laboratory study, involving 252 shared samples, and the study on field-collected ticks (n = 460), the IFA tended to detect more infected ticks than the PCR. The basis for these findings are as yet undetermined. The development of a quality assurance scheme is recommended so that laboratories can validate their methods and a preliminary feasibility study suggested that such a scheme is practical.

Animals↗

PubMed1998

Lyme borreliosis habitat assessment.

Tick ecologists throughout Europe provided descriptions of Lyme borreliosis habitats according to a standardised format and data for 105 habitats in 16 countries were received. The data showed that high risk situations, as defined by the presence of large numbers of B. burgdorferi sensu lato-infected nymphal I. ricinus, occur in heterogeneous deciduous woodland, usually with a recreational function and with a diverse fauna, usually including deer. Large numbers of ticks occurred in some other habitats, but infection prevalence was usually low. The situation for adult I. ricinus was similar but less clearly defined. Tick infection rates were found to be lower in western Europe than in the east, and the infection rate in I. persulcatus, the most easterly vector species, was markedly higher than in I. ricinus. In the vast majority of habitats the infection rate in adult I. ricinus was greater than in nymphs. Larvae were rarely found to be infected.

Animals↗

PubMed1998

Lyme borreliosis awareness.

A Lyme borreliosis information leaflet has been produced to promote awareness amongst the general public. It was designed to provide a framework for similar material throughout Europe and complements a questionnaire produced to measure awareness of Lyme borreliosis. This questionnaire can be used to determine the impact of educational campaigns using material such as the leaflet. Feasibility studies showed that the questionnaire successfully highlighted predictable differences between sample groups and also that the leaflet performed well in increasing knowledge in low-awareness groups.

Blood Donors↗

PubMed1998

Risk of infection with Borrelia burgdorferi sensu lato for a host in relation to the duration of nymphal Ixodes ricinus feeding and the method of tick removal.

The objectives of the present study were to investigate the risk of B. burgdorferi s.1. (Bb)-transmission by I. ricinus-nymphs to a host (i) after different periods of feeding, and (ii) with regard to the particular method of tick removal. On each of 72 Mongolian gerbils 3 tick nymphs taken from a highly infected batch were allowed to feed in a small capsule. Feeding ticks were removed 16.7, 28.9, 47.0, and 65.2 hrs post-attachment. In each of these 4 groups 3 sub-groups with 6 gerbils each were deticked by (a) pulling ticks out with forceps without any pretreatment, (b) pulling ticks out after 3 min of intensive squeezing, and (c) applying nail polish to ticks 1.1 hrs before removal. The infection status in each gerbil was subsequently determined by larval xenodiagnosis. All gerbils with ticks removed > or = 47 hrs post-attachment were found to be infected. After 16.7 hrs as well as after 28.9 hrs of tick feeding, approximately 50% of the gerbils had acquired a transmissible infection, thus Bb-transmission to a host may even occur in the early phases of I. ricinus feeding. There is no evidence from this study that the tick removal method used has any significant influence on a host's Bb-infection risk.

Animals↗

PubMed1998

Water balance of Dermatophagoides pteronyssinus (Acari: Pyroglyphidae) maintained by brief daily spells of elevated air humidity.

A facility was constructed to expose cultured Dermatophagoides pteronyssinus (Trouessart) to 24-h cycles of changing relative humidity; low humidity was interrupted every day by a period of high humidity. The temperature was kept at 16 degrees C, a common temperature on the ground floor of Dutch houses. Partially dehydrated mites were exposed to various humidity regimes in the absence of food and liquid water. Some mites gained weight when moist air was given for only 1.5 h every day. In the presence of food, egg production was recorded when moist air was given for at least 3 h daily, whereas the average relative humidity was quite low and less than the critical equilibrium humidity of D. pteronyssinus. Brief spells of elevated humidity allowed populations to survive much longer in a microclimate that was otherwise too dry, and may be decisive for survival during the winter months. We found that average relative humidity was misleading as an indicator of mite survival and growth conditions.

Acari↗

PubMed1997

Tick-borne encephalitis virus (TBEV)-specific RT-PCR for characterization of natural foci of TBE and for other applications.

An effective detection system for TBEV-RNA sequences using a RT-PCR technique has been developed. In our system, specific oligonucleotide primers corresponding to the 5'-terminal noncoding region were successfully used to identify TBEV sequences in ticks. To prove the specificity of the PCR products, Southern blot hybridization with an internal digoxigenin-labelled probe was carried out. In this paper, we present some potential applications of this technique. The primers were used to identify 21 TBEV strains isolated in different years, in different geographic regions and from different sources. 22313 Ixodes ricinus ticks from north-east Germany were analyzed for TBEV-specific sequences in order to characterize the viral activity in natural foci of TBE. In the new Federal Länder, only 6 samples gave positive PCR-results, showing that the natural foci of TBE had not been extinguished but remained in a state of endemic latency. We also used the RT-PCR to develop an animal model to investigate the temporal pattern of viraemia in the Mongolian gerbil (Meriones unguiculatus) through xenodiagnosis (sequential tick feeding on an infected host and subsequent RT-PCR testing of the resultant engorged ticks).

Animals↗

PubMed1995

The spatial distribution of Borrelia burgdorferi-infected Ixodes ricinus in the Connemara region of County Galway, Ireland.

Studies were carried out in the Connemara area of County Galway in the west of Ireland in order to determine the abundance and distribution of the tick, Ixodes ricinus and the prevalence of its infection with Borrelia burgdorferi. The tick was very abundant locally, in particular when associated with cattle, sheep and enclosed red deer. Large numbers of ticks not only occurred on the pastures, but also on adjacent roadside verges. No infections with B. burgdorferi could be demonstrated when nymphal ticks were sampled from central areas of the pastures, suggesting that livestock and red deer are probably not significant reservoirs of the spirochaete. Small numbers of infected nymphal and adult ticks were associated with hedges, dry stone walls, the margins of woodland adjoining infested pastures and in woodland from which livestock were excluded. Woodmice (Apodemus sylvaticus) were most numerous in such habitats and the majority were infected with B. burgdorferi.

Animals↗

PubMed1994

Acquisition of Borrelia burgdorferi by Ixodes ricinus ticks fed on the European hedgehog, Erinaceus europaeus L.

A hedgehog, Erinaceus europaeus, was found to be heavily infested with larval and nymphal Ixodes ricinus in a forest park in Co. Galway, Ireland. A large proportion of the ticks that engorged and detached were infected with the spirochaete, Borrelia burgdorferi, the causative agent of human Lyme borreliosis. The identity of these spirochaetes was confirmed by immunofluorescent assay with B. burgdorferi-specific monoclonal antibody and by polymerase chain reaction test and they were transmitted from the hedgehog to laboratory-reared ticks and from the ticks obtained from the hedgehog to gerbils (Meriones unguiculatus). The high infection rate of the larvae that fed on the hedgehog in comparison with unfed larvae from the same habitat was interpreted as strong evidence that this host species is reservoir competent. Since hedgehogs can evidently feed adult ticks as well as many immature stages, they may well have an important role in the ecology of Lyme borreliosis in some habitats.

Animals↗

PubMed1992

Studies on the ecology of Lyme disease in a deer forest in County Galway, Ireland.

The abundance of the tick Ixodes ricinus (L.) and the infection rate of ticks with Borrelia burgdorferi (Johnson et al.) were compared on either side of a deer fence in a forest park in County Galway, Ireland, in an attempt to elucidate the role of fallow deer, Dama dama, and woodmice, Apodemus sylvaticus, in determining the population density of I. ricinus and the transmission of B. burgdorferi. The results showed that tick numbers were much higher on the deer side of the fence, although the density of mice was similar on both sides. This suggests that, in the absence of other obvious factors, deer rather than mice are responsible for tick abundance in this habitat. Tick infection rates, determined by immunofluorescence, were consistently higher outside the deer fence than inside it. It is suggested, therefore, that mice rather than deer may be the important reservoir hosts of B. burgdorferi in this habitat and that deer, by feeding many larvae, probably contribute large numbers of uninfected ticks to the population. If this is the case, there will not be a direct relationship between deer abundance and tick infection rates. This has important implications for risk assessment.

Animals↗

PubMed1992

Tick infection rates with Borrelia: Ixodes ricinus versus Haemaphysalis concinna and Dermacentor reticulatus in two locations in eastern Germany.

Unfed nymphal Ixodes ricinus, Haemaphysalis concinna, and adult Dermacentor reticulatus were collected in two locations of Saxony in July and September 1991 by flagging. In July, the abundance of nymphal I. ricinus was about 2-3 times higher than that of nymphal H. concinna, a time of the year when nymphs of both species are reported to have a seasonal peak of activity. No D. reticulatus were flagged concurrently. In September, host-seeking activity of nymphal I. ricinus was again quite high as was that of adult D. reticulatus but only low numbers of nymphal H. concinna were collected. The flagged ticks were individually examined for Borrelia by an indirect immunofluorescence assay (I. ricinus: n = 414; H. concinna: n = 96; D. reticulatus: n = 116). The prevalence of Borrelia (probably B. burgdorferi) in I. ricinus varied from 12.1% to 21.0%. No borreliae were found in H. concinna. Of the examined D. reticulatus from one site (n = 97) 11.3% contained either B. burgdorferi or a related Borrelia. This may be the first finding of Borrelia in an Eurasian Dermacentor species.

Animals↗

PubMed1990

Gross morphological changes in the salivary glands of Ixodes ricinus (Acari, Ixodidae) between bloodmeals in relation to active uptake of atmospheric water vapour.

The gross morphological changes in the salivary glands of Ixodes ricinus (L.) were investigated at the light microscopic level in various phases off the host with emphasis on the engorged nymph, in order to relate the capability of active vapour uptake in the course of postembryonal development to degeneration and regeneration of salivary-gland alveoli. Agranular alveoli in engorged immatures of I. ricinus, from detachment to the following early pharate phase, do not appear different from those of the unfed instars. This is also true for the female up to approximately the end of oviposition. During moulting, the agranular alveoli of the immatures degenerate and new ones are formed which are apparently already functional in teneral nymphs and adults. In contrast, granular alveoli, much enlarged in freshly detached immature I. ricinus, shrivel in the early post-repletion period and soon reach a highly reduced state which is maintained until apolysis. Subsequently, they disintegrate completely. The finding that engorged and detached immatures of I. ricinus with markedly atrophied granular alveoli are capable of active vapour uptake until some days after initiation of apolysis suggests that only agranular alveoli are responsible for producing the primary secretion involved in vapour uptake.

Animals↗

PubMed1989

Prevalence of Borrelia burgdorferi in Ixodes ricinus ticks in Berlin (West).

In 1986, 1711 nymphal and adult Ixodes ricinus orginating from Berlin (West) forests were examined individually or in pools of up to 10 ticks for the presence of Borrelia burgdorferi, the etiologic agent of Lyme borreliosis. Detection of borreliae was carried out by means of a culture method using modified Barbour-Stoenner-Kelly-Medium (BSK II). Tick populations from 14 out of 15 locations contained positive specimens. The calculated minimal infection rate of pooled ticks was 2.5% in nymphs (n = 1365), 10.2% in females (n = 59), and 5.3% in males (n = 114). Among those ticks examined individually, none of the nymphs (n = 49) proved to be positive but B. burgdorferi was isolated from 8.2% of the females (n = 73) and 7.8% of the males (n = 51). Fifty-five out of 56 isolates were identified as B. burgdorferi by means of an indirect immunofluorescence test (IFT) using monoclonal antibody H 5332. From these results B. burgdorferi must be considered as being present in the Berlin area.

Animals↗