Use of molecular epidemiology to trace transmission pathways for infectious salmon anaemia virus (ISAV) in Norwegian salmon farming.

BACKGROUND: Infectious Salmon Anaemia (ISA) is a disease affecting farmed Atlantic salmon, and most salmon producing countries have experienced ISA outbreaks. The aim of the present study was to use epidemiological and viral sequence information to trace transmission pathways for ISA virus (ISAV) in Norwegian salmon farming. METHODS: The study covers a period from January 2007 to July 2009 with a relatively high rate of ISA outbreaks, including a large cluster of outbreaks that emerged in Northern Norway (the North-cluster). Farms with ISA outbreaks and neighbouring salmon farms (At-risk-sites) were tested for the presence of ISAV, and epidemiological information was collected. ISAV hemagglutinin-esterase (HE) and fusion (F) protein genes were sequenced and phylogenetic analyses were performed. Associations between sequence similarities and salmon population data were analysed to substantiate possible transmission pathways. RESULTS: There was a high degree of genetic similarity between ISAV isolates within the North-cluster. ISAV was detected in 12 of 28 At-risk-sites, and a high proportion of the viruses were identified as putative low virulent genotypes harbouring the full length highly polymorphic region (HPR); HPR0 of the HE protein and the amino acid glutamine (Q) in the F protein at position 266. The sequences from HPR0/F (Q(266)) genotypes revealed larger genetic variation, lower viral loads and lower prevalence of infection than HPR-deleted genotypes. Seaway distance between salmon farms was the only robust explanatory variable to explain genetic similarity between ISAV isolates. DISCUSSION: We suggest that a single HPR-deleted genotype of ISAV has spread between salmon farms in the North-cluster. Furthermore, we find that HPR0/F (Q(266)) genotypes are frequently present in farmed populations of Atlantic salmon. From this, we anticipate a population dynamics of ISAV portrayed by low virulent genotypes occasionally transitioning into virulent genotypes, causing solitary outbreaks or local epidemics through local transmission.

A Monte Carlo simulation model for assessing the risk of introduction of Gyrodactylus salaris to the Tana river, Norway.

The Tana river in northern Norway, the most productive salmon river in Europe, is free of Gyrodactylus salaris. Currently there is one salmon farm in operation on the Tana fjord. Because of the strong association between stocking of rivers with salmon and infestations with G. salaris there is national and international concern that the existing farm might lead to the introduction of the parasite to the Tana river. In response to these concerns a quantitative analysis of the risk of introduction of G. salaris to the Tana river was undertaken. A scenario tree, the Monte Carlo simulation model and results of the simulations including sensitivity analyses are presented and discussed. Results show that the probability of introduction of G. salaris to the Tana river via transfer of smolt to the existing salmon farm is extremely low primarily due to the low probability that the transferred smolt become infested. The total risk was very sensitive to changes in the salinity of the water at the sea site.

Prolonged I-III interwave interval in cerebellar astrocytoma.

We are reporting the case of a 41-year-old female diagnosed with a cerebellar astrocytoma. The tumor was detected after the patient was referred for MRI scan because of an abnormal ABR. The ABR was unusual as the I-V interwave intervals (IWIs) were within normal limits bilaterally, but the I-III IWI was prolonged by .40 msec on the left ear in comparison to the right ear. This case report illustrates the importance of the I-III IWI in the detection of retrocochlear pathology and the nonsequential generation of the components of the ABR.

Aminoglycoside ototoxicity in pediatric patients receiving long-term peritoneal dialysis.

We evaluated 14 children on long-term peritoneal dialysis for ototoxicity associated with aminoglycoside (AG) therapy. Baseline evaluation of all patients and 7 controls included pure-tone audiometry (PTA) and click-evoked auditory brain stem response (ABR). Nine patients had repeat PTA and ABR evaluations and vestibular testing 1 year after study entry. Five patients had an additional assessment following intraperitoneal AG therapy. The baseline auditory function of the patients was significantly poorer than controls at 6.0 and 8.0 kHz by PTA (P < 0.05), whereas the results of ABR testing were not different. Of the 14 patients, 4 (28%) had hearing loss, 3 of whom had a history of intravenous AG therapy. In contrast, none of the patients who received intraperitoneal AG therapy only, or without a history of AG therapy, had hearing loss (P < 0.005). There was no evidence of progressive loss of hearing acuity with time or associated with intraperitoneal AG therapy. One patient had findings of vestibular dysfunction. We conclude that children receiving peritoneal dialysis are at risk of AG ototoxicity. While intraperitoneal administration of AG may be associated with less ototoxicity than intravenous administration, further study is necessary to verify this finding and close monitoring of AG levels remains mandatory irrespective of the route of administration. PTA rather than click-evoked ABR appears to be the best indicator of abnormal hearing acuity in this population.

The effect of stimulus duration using the Brookler-Grams closed-loop caloric irrigator.

Nystagmic responses to traditional 40-sec, 30 degrees C water calorics were recorded and compared to those obtained with the Brookler-Grams closed-loop irrigator using 30 degrees C, 40-, 50-, and 60-sec irrigations. Significant differences were noted between the responses to the water irrigator and the 40- and 50-sec closed-loop irrigations. The 60-sec closed-loop irrigation produced responses that were equivalent to the responses obtained with the water irrigation in slow component velocity, amplitude, frequency, latency, and duration. The 30 degrees C 60-sec closed-loop irrigation is an acceptable stimulus in electronystagmographic caloric testing.

Comparison of responses to air, water, and closed-loop caloric irrigators.

Three types of commercially available caloric irrigation units--air, water, and closed-loop--were evaluated for nystagmus response patterns and comfort. Electronystagmographic recordings were analyzed for slow-phase velocity, response duration, amplitude, frequency, and test-retest reliability. Significant differences were found among the three types of irrigators, between warm and cool irrigators, and between male and female subjects. Test-retest reliability was adequate for all three units. Subjects clearly favored the closed-loop system over the water and air irrigators, but the water irrigator yielded the most robust caloric response.

Treatment of tinnitus with electrical stimulation: an evaluation of the Audimax Theraband.

Several treatment forms exist for tinnitus. These multiple treatments speak to the elusive etiology of tinnitus. Many authors have reported tinnitus reduction or elimination with electrical stimulation. This study evaluates a new device (Audimax Theraband) which delivers inaudible, transdermal, mastoid electrical stimulation. Thirty patients suffering from chronic tinnitus were evaluated in a single-blind crossover fashion. Since the electrical stimulation is inaudible, each patient served as his or her own control. Patients received actual or placebo stimulation over a period of 2 weeks. They rated their tinnitus levels and the effectiveness of the device before and after using the Theraband. Only 2 subjects out of 30 (7%) obtained true positive results. Side effects were minimal and reversible.

The effects of age, sex, hearing loss and water temperature on caloric nystagmus.

Seventy five subjects ranging in age from 18 to 87 years received warm and cool caloric irrigations. Nystagmus was recorded and latency, duration, amplitude, frequency and speed of the slow component were measured. The effects of age, hearing loss, sex and water temperature were evaluated. Significant differences were found in cool water durations. Significant differences were found as a function of age for all parameters in warm water calorics. Response duration was not found to be significantly correlated to speed of the slow component in cool calorics.

Effects of six conditions of ocular fixation on caloric nystagmus.

Caloric tests were performed on 20 normal volunteers under the following six conditions of ocular fixation: (1) eyes open with lighted +20-diopter lenses; (2) eyes open with lighted +20-diopter lenses plus strobe lighting; (3) eyes open in darkness; (4) eyes closed in darkness; (5) eyes closed in a dimly lighted room; and (6) eyes open with unlighted +20-diopter lenses plus strobe lighting. Latency, amplitude, frequency, duration, and speed of the slow component were measured from a permanent recording. Significant differences were found between the lighted +20-diopter lens conditions and all others for all variables except latency. Tests performed with lighted +20-diopter lenses should be cautiously interpreted due to the noticeable response suppression noted in these conditions. The present procedure of performing caloric tests with the eyes closed in a dimly lighted room was found to be unqeustionably preferable.

An evaluation of speech audiometry by bone conduction in hearing-impaired adults.

Pure-tone thresholds, speech reception thresholds (SRT), and speech discrimination scores (DS) were obtained by ac and bc on 20 normal-hearing and 30 hearing-impaired adults. Correlations between the SRT and pure-tone thresholds (ave. of .5, 1, and 2 kc/s) were significant by both ac and bc. Correlations between DS by ac and bc were also highly significant, indicating the value of the bc DS in specific difficult cases. The clinical observation was confirmed statistically of decreasing DS with increasing sensorineural hearing loss.

A study of five parameters of calorically-induced nystagmus in the clinical situation.

Latency, duration, and amplitude of response, frequency of nystagmic beats, and speed of the slow component of calorically-induced nystagmus were studied by ENG in 14 normal-hearing adults. Attention was directed toward differences as a function of stimulus temperature (30 degrees C vs 44 degrees C) and side of stimulation. Nystagmus amplitudes were significantly larger from R ear as compared to L ear irrigations, and from cool as compared to warm. Ssc's from cool irrigations were also significantly larger than from warm. A series of t-tests computed for correlated samples indicated that the R ear 30 degrees irrigation, which was the first stimulus for all Ss, was responsible for the significant differences. Implications of the need for research on caloric interstimulus intervals and vestibular response fatigue were presented, and a procedure outlined to avoid erroneous results in caloric testing.

Analysis of optokinetic and eye tracking data on normal subjects.

This study was undertaken to determine the incidence of abnormal eye tracking patterns in normal subjects and to compare the optokinetic (OPK) response of normal subjects using a nystagmographic gonioscope (Nystagmotrac) and Coats's type of OPK drum. Eye movement was recorded by means of an electronystagmographic (ENG) recorder, and the speed of the slow component was computed for the OPK response. The eye tracking test showed a high rate of abnormality among our subjects. Optokinetic testing revealed highly symmetrical responses for all subjects.