Influence of saturation deficit and temperature on Ixodes ricinus tick questing activity in a Lyme borreliosis-endemic area (Switzerland).

Questing Ixodes ricinus ticks were sampled monthly in a periurban mixed forest at Neuchâtel, Switzerland, in 1996, 1997, and 1998. A total of 5,530 I. ricinus nymphs and 1,385 adults were collected. The emergence of questing tick populations in spring varied among years in relation to the air temperature. The monthly variation in questing nymph density was negatively correlated with the saturation deficit; there was a strong decrease in tick numbers in late spring and summer as soon as the saturation deficit increased. A variation in tick density in relation to the saturation deficit was also observed between years; the tick density was high when the saturation deficit was low during spring and summer (1997) and was low when the saturation deficit was high (1998). During the 3-year study period, marked climatic differences among years highlighted the influence of temperature and saturation deficit on the phenology of ticks.

Multi-step-ahead prediction using dynamic recurrent neural networks.

A method for the development of empirical predictive models for complex processes is presented. The models are capable of performing accurate multi-step-ahead (MS) predictions, while maintaining acceptable single-step-ahead (SS) prediction accuracy. Such predictors find applications in model predictive controllers and in fault diagnosis systems. The proposed method makes use of dynamic recurrent neural networks in the form of a nonlinear infinite impulse response (IIR) filter. A learning algorithm is presented, which is based on a dynamic gradient descent approach. The effectiveness of the method for accurate MS prediction is tested on an artificial problem and on a complex, open-loop unstable process. Comparative results are presented with polynomial Nonlinear AutoRegressive with eXogeneous (NARX) predictors, and with recurrent networks trained using teacher forcing. Validation studies indicate that excellent generalization is obtained for the range of operational dynamics studied. The research demonstrates that the proposed network architecture and the associated learning algorithm are quite effective in modeling the dynamics of complex processes and performing accurate MS predictions.

Transmission of Borrelia afzelii from Apodemus mice and Clethrionomys voles to Ixodes ricinus ticks: differential transmission pattern and overwintering maintenance.

This study deals with the ecology of Lyme borreliosis in Europe. The relationships between Borrelia burgdorferi sensu lato spirochetes, Clethrionomys and Apodemus rodent reservoirs and the Ixodes ricinus tick vector were investigated during 16 consecutive months in an enzootic area in Switzerland. Cultivation of ear skin biopsies was used to isolate spirochetes from C. glareolus, A. sylvaticus, A. flavicollis and Glis glis. Borrelia infection was more frequently observed in Clethrionomys than in Apodemus. Tick xenodiagnosis was used to determine the infectivity of rodents. The infection rate in ticks fed on Clethrionomys was higher than that in ticks fed on Apodemus, but Apodemus yielded more infected ticks than Clethrionomys because of a better tick moulting success. Xenodiagnostic ticks were placed into BSK medium to obtain isolates. Isolates from rodents and rodent-feeding ticks were all identified as B. afzelii. The follow-up of the infectivity status of repeatedly recaptured rodents clearly demonstrated that these hosts remained infective for ticks during winter till the following spring. Comparing C. glareolus and A. sylvaticus, each rodent species showed different host infection, different host infectivity and contributed differently to the moulting success of feeding ticks. These factors influence differentially the pattern of transmission of B. afzelii from Clethrionomys voles and Apodemus mice to I. ricinus ticks.

Efficient transmission of Borrelia burgdorferi between cofeeding Ixodes ricinus ticks (Acari: Ixodidae).

Feeding ticks are generally spatially distributed in clusters on vertebrate hosts. To test the effect of clustering on transmission of a tick-borne pathogen, Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner-infected Ixodes ricinus L. nymphs and uninfected I. ricinus larvae were allowed to feed together in retaining chambers on uninfected AKR/N mice. Engorged infective nymphs dropped off at days 5, 6, and 7, and the 1st infected larvae that fed in the chambers together with the infected nymphs dropped off at day 5. In contrast, ear biopsies and xenodiagnostic larvae placed on the head remained negative during that period. These results suggest that a cofeeding transmission occurred between B. burgdorferi-infected ticks and noninfected ones in the absence of a disseminated infection. Further investigations are being undertaken to determine whether the mechanism responsible for this cofeeding transmission is similar to that described previously with virus-infected ticks.

Immunization of mice by recombinant OspA preparations and protection against Borrelia burgdorferi infection induced by Ixodes ricinus tick bites.

The wide distribution of Borrelia burgdorferi, the spirochete causing Lyme borreliosis, represents a human health hazard in many areas of the world. Vaccination has been proposed as an effective prevention strategy. Vaccination experiments were conducted with preparations of recombinant outer surface protein A (OspA) derived from Borrelia burgdorferi strain ZS7. Mice received three doses (1 microgram each) of the antigens adsorbed to aluminum hydroxide. A strong immune response to the vaccine antigen was observed. Mice were challenged after immunization, using Ixodes ricinus nymphal ticks infected with Borrelia burgdorferi strain ZS7. Infection was investigated by ear biopsy culture, xenodiagnosis with uninfected larvae and serological response to Borrelia burgdorferi antigens. All unimmunized control animals were found to be infected, while all immunized animals were found to be protected against infection by Borrelia burgdorferi. In addition, most adult ticks derived from nymphs that fed on immunized mice were found to be free of spirochetes.

Passage of hemolysins through the midgut epithelium of female Ixodes ricinus L. fed on rabbits infested or reinfested with ticks.

Antibodies considered in this study are hemolysins synthesized by rabbits against sheep red blood cells. Ingested with the blood meal, they cross the tick midgut epithelium and retain their immunological properties in the hemolymph. During a reinfestation of rabbits, more ticks present these antibodies, and titres are generally higher than during a first infestation. Hemolysins are only found in ticks weighing 180 mg or more.

Familial occurrence of abdominal aortic aneurysms.

The occurrence of clinically diagnosed and ruptured abdominal aortic aneurysms (AAAs) in the family was studied retrospectively among 200 consecutive patients with AAAs treated at the Surgical Clinic, University Hospital of Umeå, in the north of Sweden, during the period 1965 to 1981. A standardized questionnaire was sent to the 89 patients who were still alive when the study was performed, and 87 patients answered it. In 14 of these families there was one blood relative with AAA, and in two families there were two blood relatives with AAAs, apart from the proband. In nine cases AAAs occurred among the 468 brothers and sisters of the probands (1.9%), and in five cases among cousins. Seven of the 204 deceased brothers and sisters (3.4%) had died of ruptured AAAs. No questionnaires were sent to the families of the 111 deceased patients, but at least 11 of these patients had AAAs in the family. Pedigrees of the families with aggregation of aneurysms are presented, and fortuitous familial aggregation or predisposition to the development of AAAs is discussed.

Intermittent claudication and muscle fiber fine structure: correlation between clinical and morphological data.

Bilaterally obtained muscle biopsies (anterior tibial muscle) from 22 patients with unilateral peripheral arterial insufficiency (intermittent claudication) were qualitatively and quantitatively analyzed by means of enzyme histochemistry and electron microscopy. In a majority of the biopsies from the symptomatic legs, two different patterns of morphological deviations were seen in the abnormal muscles: one suggested primary muscle fiber damage and the other indicated denervation. Biopsies from the asymptomatic legs were often only slightly changed or normal. Significant correlations were found in both legs between the relative number of type 1 (slow twitch, highly oxidative) fibers and the age of the subjects. In symptomatic legs, furthermore, a relation could be demonstrated between the relative number of type 1 fibers and (1) the initial walking tolerance (walking distance covered before pain occurred), (2) duration of symptoms, and (3) occlusion or stenosis at high level (i.e., above the deep femoral artery). Finally, the diameters of both type 1 and type 2 fibers in the symptomatic leg were correlated to the initial walking tolerance. The importance of circulatory disturbances as differential diagnostic points (arteriovasculo-occlusive myopathy) in the diagnosis of neuromuscular diseases is stressed.

Effects of thoracic epidural block and prenalterol on coronary vascular resistance and myocardial metabolism in patients with coronary artery disease.

A thoracic epidural block from T1 to T12 was performed with plain prilocaine in four patients with coronary artery disease who were scheduled for abdominal aortic aneurysm surgery. The hemodynamic effects of the block consisted of marked reduction in arterial blood pressure due to impairment of cardiac performance and reduction in systemic vascular resistance. The heart rate decreased moderatetly. The epidural block induced a marked reduction in coronary vascular resistance with only a moderate decrease in coronary sinus blood flow. The myocardial oxygen and lactate utilization decreased in parallel to the decrease in cardiac work. In spite of the absence of arrhythmias and ST-T-segment changes following the epidural block, regional myocardial dysoxia could not be ruled out with the present methods. Administration of the cardioselective beta 1-adrenoreceptor agonist prenalterol increased cardiac performance and thereby arterial blood pressure, but did not affect the systemic or coronary vascular resistance.

Hemodynamic and cardiometabolic effects of infrarenal aortic and common iliac artery declamping in man--an approach to optimal volume loading.

Nineteen patients undergoing abdominal aortic aneurysm surgery were randomly assigned to two groups and investigated to elucidate the mechanisms of declamping hypotension. The control group of nine patients was kept at an average mean pulmonary artery occlusion pressure (MPAOP) of 11 mmHg (1.46 kPa) before declamping. The other group was volume loaded to a MPAOP of 16 mmHg (2.13 kPa) shortly before declamping. Following declamping there was a significantly greater decrease in mean arterial pressure in the control group, with the same reduction of MPAOP in both groups. In parallel, cardiac and stroke volume indices decreased in the control patients, but remained unchanged in the volume-loaded patients. In the control group there was a reduction in myocardial substrate utilization which was not seen in the volume-loaded patients. No signs of myocardial ischemia could be demonstrated in any of the groups. The results indicate that mismatching between intravascular volume and blood volume is the main cause of infrarenal aortic or common iliac artery declamping hypotension. Volume loading before declamping to a slightly elevated MPAOP can effectively prevent hypotension, while a normal MPAOP does not guarantee a stable hemodynamic situation after declamping.

Effects of thoracic epidural block and the beta-1-adrenoreceptor agonist prenalterol on the cardiovascular response to infrarenal aortic cross-clamping in man.

Sixteen patients scheduled for abdominal aortic resection and grafting were randomly assigned to two groups to study the cardiovascular effects of infrarenal aortic cross-clamping. The patients in the first group had received a thoracic epidural block followed by intravenous administration of the selective beta-1-adrenoreceptor agonist prenalterol prior to induction of general anaesthesia. The patients in the second group served as controls and received no specific treatment prior to general anaesthesia. In both groups, aortic cross-clamping was followed by an equal rise in pulmonary artery diastolic pressure and mean systemic arterial pressure. There was a significant difference in systemic vascular resistance, as the control group had a 46% increase 30 s after cross-clamping, while the pretreated patients had only a 7% increase at the same time. Moreover, the patients given the thoracic epidural block followed by prenalterol increased their stroke volume and cardiac indices, as compared to the patients in the control group who showed a significant decrease in these parameters. Possible mechanisms for the mode of action of the combined thoracic epidural block and beta-1-adrenoreceptor agonist pretreatment are discussed.

Aorto-iliac arterial thrombosis in young women. Report of 3 cases.

Three cases of young women with thrombotic arterial occlusion in the aorto-iliac region are described. All were smokers and used oral contraceptives. Both these factors must be regarded to be of etiological importance.

Bilateral aneurysm of dacron graft following aorto-femoral graft operation. A case report.

A case of bilateral aneurysmatic widening of the Dacron graft after aorto-femoral bypass is described. The probable cause of an aneurysm in Dacron graft without any involvement of the host vessels may be the rupture of the Dacron fibres due to fatigue of the material. Furthermore, a contributory cause of aneurysm in our case may be the fact that both anastomoses were performed at nearly right angles causing turbulence.