Dynamic contrast-enhanced MRI shows altered blood-brain barrier function of deep gray matter structures in neuroborreliosis: a case-control study.

BACKGROUND: Main aim was assessment of regional blood-brain barrier (BBB) function by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in patients with neuroborreliosis. Secondary aim was to study the correlation of BBB function with biochemical, clinical, and cognitive parameters. METHODS: Regional ethical committee approved this prospective single-center case-control study. Within 1 month after diagnosis of neuroborreliosis, 55 patients underwent DCE-MRI. The patient group consisted of 25 males and 30 females with mean age 58 years, and the controls were 8 males and 7 females with mean age 57 years. Pharmacokinetic compartment modelling with Patlak fit was applied, providing estimates for capillary leakage rate and blood volume fraction. Nine anatomical brain regions were sampled with auto-generated binary masks. Fatigue, severity of clinical symptoms and findings, and cognitive function were assessed in the acute phase and 6 months after treatment. RESULTS: Leakage rates and blood volume fractions were lower in patients compared to controls in the thalamus (p = 0.027 and p = 0.018, respectively), caudate nucleus (p = 0.009 for both), and hippocampus (p = 0.054 and p = 0.009). No correlation of leakage rates with fatigue, clinical disease severity or cognitive function was found. CONCLUSIONS: In neuroborreliosis, leakage rate and blood volume fraction in the thalamus, caudate nucleus, and hippocampus were lower in patients compared to controls. DCE-MRI provided new insight to pathophysiology of neuroborreliosis, and can serve as biomarker of BBB function and regulatory mechanisms of the neurovascular unit in infection and inflammation. RELEVANCE STATEMENT: DCE-MRI provided new insight to pathophysiology of neuroborreliosis, and can serve as biomarker of blood-brain barrier function and regulatory mechanisms of the neurovascular unit in infection and inflammation. KEY POINTS: • Neuroborreliosis is an infection with disturbed BBB function. • Microvessel leakage can be studied with DCE-MRI. • Prospective case-control study showed altered microvessel properties in thalamus, caudate, and hippocampus.

Antibiotic therapy of neuroborreliosis: A survey among infectious disease specialists and neurologists in Norway, Sweden, and Denmark.

INTRODUCTION: Neuroborreliosis (NB) is a prevalent tick-borne neuroinfection in Europe. To delineate current practice in antimicrobial management of adults with NB and to prioritize future trials needed to optimize treatment recommendations, a questionnaire-based survey was performed. METHODS: A self-administered Internet-based survey of NB treatment practices among specialists in infectious diseases and neurology based in Norway, Sweden, and Denmark was carried out between October 2021 and February 2022. The participants were also asked to prioritize four pre-defined research questions for randomized controlled trials (RCTs) on therapy for NB. RESULTS: In total, 290 physicians (45% female) from Norway (30%), Sweden (40%), and Denmark (30%) participated in the survey. Of the responders, 230 (79%) were infectious disease specialists and 56 (19%) were neurologists. The preferred antibiotic treatment for patients with early NB was oral doxycycline (n = 225, 78%). Intravenous (IV) penicillin, ceftriaxone, or cefotaxime for the full treatment course was favored by 12%. A preferred treatment duration of 10-14 days for patients with NB was reported by 245 respondents (85%), most common among participants from Sweden (97%). A total of 170 (59%) responders reported having local hospital guidelines on the treatment of NB, most often with recommendation of oral doxycycline (92%) for 10-14 days (90%) as first line treatment. The prioritization score for future RCTs was highest for adjunctive prednisone therapy in NB patients with facial palsy (median 5; IQR 4-6) and for placebo versus repeated antibiotics in patients with persistent symptoms after completed antibiotic therapy for NB (median 5, IQR 3-6). CONCLUSION: In Sweden, all respondents preferred treating NB with oral doxycycline for 10-14 days, whereas 5% in Norway and 19% in Denmark still treat NB with IV antibiotics for the entire treatment course. RCTs to define the role of adjunctive prednisolone in NB patients with facial palsy and repeated antibiotics in patients with persistent symptoms are prioritized for future research.

Enhancement of cranial nerves in Lyme neuroborreliosis: incidence and correlation with clinical symptoms and prognosis.

PURPOSE: Symptoms of cranial neuritis are a common presentation of Lyme neuroborreliosis (LNB). Imaging studies are scarce and report contradictory low prevalence of enhancement compared to clinical studies of cranial neuropathy. We hypothesized that MRI enhancement of cranial nerves in LNB is underreported, and aimed to assess the prevalence and clinical impact of cranial nerve enhancement in early LNB. METHODS: In this prospective, longitudinal cohort study, 69 patients with acute LNB were examined with MRI of the brain. Enhancement of cranial nerves III-XII was rated. MRI enhancement was correlated to clinical findings of neuropathy in the acute phase and after 6 months. RESULTS: Thirty-nine of 69 patients (57%) had pathological cranial nerve enhancement. Facial and oculomotor nerves were most frequently affected. There was a strong correlation between enhancement in the distal internal auditory canal and parotid segments of the facial nerve and degree of facial palsy (gamma = 0.95, p < .01, and gamma = 0.93, p < .01), despite that 19/37 nerves with mild-moderate enhancement in the distal internal auditory canal segment showed no clinically evident palsy. Oculomotor and abducens nerve enhancement did not correlate with eye movement palsy (gamma = 1.00 and 0.97, p = .31 for both). Sixteen of 17 patients with oculomotor and/or abducens nerve enhancement had no evident eye movement palsy. CONCLUSIONS: MRI cranial nerve enhancement is common in LNB patients, but it can be clinically occult. Facial and oculomotor nerves are most often affected. Enhancement of the facial nerve distal internal auditory canal and parotid segments correlate with degree of facial palsy.

Tick-borne Pathogens Detected in the Blood of Immunosuppressed Norwegian Patients Living in a Tick-endemic Area.

BACKGROUND: The knowledge regarding the occurrence and the clinical implications of tick-borne infections in immunosuppressed patients living in tick-endemic areas is limited. METHODS: Adult patients with autoimmune conditions requiring immunosuppressive treatment such as infliximab and rituximab were invited to participate in the study when they attended the hospital for treatment and/or control of the disease. Whole-blood samples were analyzed by real-time polymerase chain reaction for Borrelia burgdorferi sensu lato, Borrelia miyamotoi, Anaplasma phagocytophilum, Rickettsia spp., Candidatus Neoehrlichia mikurensis, and Babesia spp. RESULTS: The occurrence of tick-borne pathogens in the blood of patients (n = 163) with autoimmune conditions requiring immunosuppressive treatment was evaluated. Pathogen DNA was detected in 8.6% (14/163) of the patients. The predominant pathogen was Ca. Neoehrlichia mikurensis (12/14), which was carried in the blood of infected patients for 10-59 days until treatment with doxycycline. B. burgdorferi s.l. and Rickettsia spp. were detected in 1 patient each. The B. burgdorferi-infected patient presented with fever, whereas the remaining patients were judged to have subclinical infections. B. miyamotoi, A. phagocytophilum, and Babesia spp. were not detected in any patient. CONCLUSIONS: Patients treated with biologicals and living in a tick-endemic area seem to have a high risk of contracting Ca. Neoehrlichia mikurensis infection, which, if left untreated, could result in thromboembolic complications.

Serological diagnostics of Lyme borreliosis: comparison of assays in twelve clinical laboratories in Northern Europe.

Lyme borreliosis (LB), caused by spirochetes belonging to the Borrelia burgdorferi sensu lato complex, is the most common tick-borne infection in Europe. Laboratory diagnosis of LB is mainly based on the patients' medical history, clinical signs and symptoms in combination with detection of Borrelia-specific antibodies where indirect enzyme-linked-immunosorbent assay (ELISA) is the most widely used technique. The objective of the study was to evaluate and compare the diagnostic accuracy (sensitivities and specificities) of serological tests that are currently in use for diagnosis of LB in clinical laboratories in Northern Europe, by use of a large serum panel. The panel consisted of 195 serum samples from well-characterized and classified patients under investigation for clinically suspected LB (n = 59) including patients with Lyme neuroborreliosis, Lyme arthritis, acrodermatitis chronica atrophicans, erythema migrans or other diseases (n = 112). A total of 201 serum samples from healthy blood donors were also included. The panel (396 serum samples altogether) was sent to 12 clinical laboratories (using five different ELISA methods) as blinded for group affiliation and the laboratories were asked to perform serological analysis according to their routine procedure. The results from the study demonstrated high diagnostic concordance between the laboratories using the same diagnostic assay and lower diagnostic concordance between laboratories using different diagnostic assays. For IgG, the results were in general rather homogenous and showed an average sensitivity of 88% (range 85-91%) compared to IgM which showed lower average sensitivity of 59% (range 50-67%) and more heterogeneous results between assays and laboratories.

Imaging in Lyme neuroborreliosis.

Lyme neuroborreliosis (LNB) is a tick-borne spirochetal infection with a broad spectrum of imaging pathology. For individuals who live in or have travelled to areas where ticks reside, LNB should be considered among differential diagnoses when clinical manifestations from the nervous system occur. Radiculitis, meningitis and facial palsy are commonly encountered, while peripheral neuropathy, myelitis, meningoencephalitis and cerebral vasculitis are rarer manifestations of LNB. Cerebrospinal fluid (CSF) analysis and serology are key investigations in patient workup. The primary role of imaging is to rule out other reasons for the neurological symptoms. It is therefore important to know the diversity of possible imaging findings from the infection itself. There may be no imaging abnormality, or findings suggestive of neuritis, meningitis, myelitis, encephalitis or vasculitis. White matter lesions are not a prominent feature of LNB. Insight into LNB clinical presentation, laboratory test methods and spectrum of imaging pathology will aid in the multidisciplinary interaction that often is imperative to achieve an efficient patient workup and arrive at a correct diagnosis. This article can educate those engaged in imaging of the nervous system and serve as a comprehensive tool in clinical cases. KEY POINTS: • Diagnostic criteria for LNB emphasise exclusion of an alternative cause to the clinical symptoms. • MRI makes a crucial contribution in the diagnosis and follow-up of LNB. • MRI may have normal findings, or show neuritis, meningitis, myelitis, encephalitis or vasculitis. • White matter lesions are not a prominent feature of LNB.

Does more favourable handling of the cerebrospinal fluid increase the diagnostic sensitivity of Borrelia burgdorferi sensu lato-specific PCR in Lyme neuroborreliosis?

BACKGROUND: Tests for direct detection of Borrelia burgdorferi sensu lato (Bb) in Lyme neuroborreliosis (LNB) are needed. Detection of Bb DNA using PCR is promising, but clinical utility is hampered by low diagnostic sensitivity. We aimed to examine whether diagnostic sensitivity can be improved by the use of larger cerebrospinal fluid (CSF) volumes and faster handling of samples. METHODS: Patients who underwent CSF examination for LNB were included. We collected two millilitres of CSF for PCR analysis, extracted DNA from the pellets within 24 h and analysed the eluate by two real-time PCR protocols (16S rRNA and OspA). Patients who fulfilled diagnostic criteria for LNB were classified as LNB cases and the rest as controls. RESULTS: Bb DNA in CSF was detected by PCR in seven of 28 adults with LNB. Two were Bb antibody negative. No Bb DNA was detected in CSF from 137 controls. Diagnostic sensitivity was 25% and specificity 100%. There was a non-significant trend towards larger CSF sample volume, faster handling of the sample, shorter duration of symptoms, and higher CSF cell count in the PCR-positive cases. CONCLUSION: We did not find that optimized handling of CSF increased diagnostic sensitivity of PCR in adults with LNB. However, our case series is small and we hypothesize that the importance of these factors will be clarified in further studies with larger case series and altered study design. PCR for diagnosis of LNB may be useful in cases without Bb antibodies due to short duration of symptoms.

Selective intrathecal enrichment of G1m1-positive B cells in multiple sclerosis.

Immunoglobulin gamma (IgG) heavy chain genes are associated with susceptibility to multiple sclerosis (MS) and IgG levels in the cerebrospinal fluid (CSF). However, how these variants are implicated in disease mechanisms remains unknown. Here, we show that proliferating plasmablasts expressing the G1m1 allotype of IgG1 are selectively enriched in CSF of G1m1/G1m3 heterozygous MS patients, whereas plasmablasts expressing either G1m1 or G1m3 are evenly distributed in blood. Moreover, there was a preferential intrathecal synthesis of oligoclonal IgG1 of the G1m1 allotype in heterozygous patients, whereas controls with Lyme neuroborreliosis displayed oligoclonal IgG1 of both allotypes. This points to a disease-specific mechanism involved in B-cell establishment within the central nervous system in MS.

Lyme neuroborreliosis: do we treat according to guidelines?

Evidence-based guidelines, published in 2010, equate the efficacy of oral and intravenous antibiotics and recommend treatment duration of 2 weeks in early Lyme neuroborreliosis (LNB) without encephalitis or myelitis. Further, the Norwegian health authorities give a general advice to choose oral rather than intravenous administration when proven effective, due to lower costs, fewer risks, and reduced patient inconvenience. In this study we aimed to chart LNB treatment practice in Norway and compare it to these recommendations. Adult patients diagnosed with definite LNB between 2007 and 2013 in 11 different hospitals in the four health regions in Norway were invited to answer a questionnaire regarding duration and administration of antibiotic treatment. A total of 253 patients answered. Median age at diagnosis was 59 years (range 19-83), and 125 (49%) were women. Duration of treatment was 1 week in 7 (3%) patients, 2 weeks in 81 (32%), 3 weeks in 62 (25%), 4 weeks in 48 (19%), 5 weeks in 12 (5%), ≥6 weeks in 29 (12%), and unknown in 14 (6%). Treatment was given orally in 77 (30%) patients, intravenously in 110 (44%), both orally and intravenously in 65 (26%), and unknown in one. Treatment practices differed between the health regions (p = 0.002). During the study period, there were no significant time trend neither with respect to proportion of patients treated for only 2 weeks (OR 0.899, p = 0.109) nor with respect to proportion of patients treated exclusively with oral antibiotics (OR 1.131, p = 0.074). In conclusion, there seem to be a gap between evidence-based recommendations and treatment practice of LNB in Norway.

Late onset myasthenia gravis is associated with HLA DRB1*15:01 in the Norwegian population.

BACKGROUND: Acquired myasthenia gravis (MG) is a rare antibody-mediated autoimmune disease caused by impaired neuromuscular transmission, leading to abnormal muscle fatigability. The aetiology is complex, including genetic risk factors of the human leukocyte antigen (HLA) complex and unknown environmental factors. Although associations between the HLA complex and MG are well established, not all involved components of the HLA predisposition to this heterogeneous disease have been revealed. Well-powered and comprehensive HLA analyses of subgroups in MG are warranted, especially in late onset MG. METHODOLOGY/PRINCIPAL FINDINGS: This case-control association study is of a large population-based Norwegian cohort of 369 MG patients and 651 healthy controls. We performed comprehensive genotyping of four classical HLA loci (HLA-A, -B, -C and -DRB1) and showed that the DRB1*15:01 allele conferred the strongest risk in late onset MG (LOMG; onset ≥ 60 years) (OR 2.38, p(c)7.4 × 10(-5)). DRB1*13:01 was found to be a protective allele for both early onset MG (EOMG) and LOMG (OR 0.31, p(c) 4.71 × 10(-4)), a finding not previously described. No significant association was found to the DRB1*07:01 allele (p(nc) = 0.18) in a subset of nonthymomatous anti-titin antibody positive LOMG as reported by others. HLA-B*08 was mapped to give the strongest contribution to EOMG, supporting previous studies. CONCLUSION: The results from this study provide important new information concerning the susceptibility of HLA alleles in Caucasian MG, with highlights on DRB1*15:01 as being a major risk allele in LOMG.

Importance of human leukocyte antigen (HLA) class I and II alleles on the risk of multiple sclerosis.

Multiple sclerosis (MS) is a complex disease of the central nervous system of unknown etiology. The human leukocyte antigen (HLA) locus on chromosome 6 confers a considerable part of the susceptibility to MS, and the most important factor is the class II allele HLA-DRB1*15:01. In addition, we and others have previously established a protective effect of HLA-A*02. Here, we genotyped 1,784 patients and 1,660 healthy controls from Scandinavia for the HLA-A, HLA-B, HLA-C and HLA-DRB1 genes and investigated their effects on MS risk by logistic regression. Several allele groups were found to exert effects independently of DRB1*15 and A*02, in particular DRB1*01 (OR = 0.82, p = 0.034) and B*12 (including B*44/45, OR = 0.76, p = 0.0028), confirming previous reports. Furthermore, we observed interaction between allele groups: DRB1*15 and DRB1*01 (multiplicative: OR = 0.54, p = 0.0041; additive: AP = 0.47, p = 4 × 10(-06)), DRB1*15 and C*12 (multiplicative: OR = 0.37, p = 0.00035; additive: AP = 0.58, p = 2.6 × 10(-05)), indicating that the effect size of these allele groups varies when taking DRB1*15 into account. Analysis of inferred haplotypes showed that almost all DRB1*15 bearing haplotypes were risk haplotypes, and that all A*02 bearing haplotypes were protective as long as they did not carry DRB1*15. In contrast, we found one class I haplotype, carrying A*02-C*05-B*12, which abolished the risk of DRB1*15. In conclusion, these results confirms a complex role of HLA class I and II genes that goes beyond DRB1*15 and A*02, in particular by including all three classical HLA class I genes as well as functional interactions between DRB1*15 and several alleles of DRB1 and class I genes.

Polymorphisms of the BDNF gene show neither association with multiple sclerosis susceptibility nor clinical course.

Brain-derived neurotrophic factor (BDNF) has been proposed a protective role in multiple sclerosis (MS) in several studies. The val(66)met polymorphism alters the function of the BDNF protein, and has along with rs56164415 previously been reported to be associated with MS. We genotyped BDNF SNPs val(66)met and rs56164415 in 2149 Norwegian MS patients and 2747 healthy controls. No association was found for any of the SNPs to disease susceptibility or any clinical or demographic parameters including sex, age at onset, disease course, disease severity and cognitive impairment.

[New gene map for multiple sclerosis]. / Nytt genkart for multippel sklerose.

BACKGROUND: Multiple sclerosis (MS) is a demyelinating, inflammatory disease of the central nervous system which affects young adults with a relapsing or progressive disease course. The etiology of the disease is unknown, but both environmental and genetic factors contribute to the risk of developing MS. MATERIAL AND METHODS: We give an overview of new knowledge of the genetic risk factors for MS, based on our own work as well as on literature in this field. RESULTS: Through genome-wide association studies and subsequent replication studies a series of novel MS genes have recently been identified, in addition to the HLA association previously described. The International MS Genetics Consortium in collaboration with the Wellcome Trust Case Control Consortium recently published a genome-wide study of 9,722 MS patients and 17,376 controls. Genome-wide significant association (p < 10-8) was observed for 29 new as well as 23 previously identified gene regions, in addition to the HLA-DRB1 and -A loci .The majority of these MS-associated regions encode immune-related molecules. CONCLUSION: Genetic studies of large patient and control samples obtained through international and national collaborations have identified a list of more than 50 MS risk-gene regions, in addition to HLA-DRB1 and -A loci. The risk associated with each of these loci is low, however, they collectively point to the importance of immune-related pathways in the etiology of MS.

No influence on disease progression of non-HLA susceptibility genes in MS.

Recently, several non-HLA loci have been shown to be convincingly associated with Multiple Sclerosis (MS) susceptibility, assumingly indicating important pathways in the pathogenesis. A genotype influence on disease outcome measures by these genes would support a role of these pathways in ongoing tissue damage. Here, however, we report a consistent dissociation between causation and progression for five non-HLA genotypes (IL7R, IL2RA, CLEC16A, CD226 and SH2B3) in 1776 Scandinavian MS patients.

Association to the Glypican-5 gene in multiple sclerosis.

Multiple sclerosis (MS) is an inflammatory, demyelinating disease affecting the central nervous system. MS-associated variants have been reported at both HLA and non-HLA loci, the latter including chromosome 13q31-32 and the Glypican-5 and Glypican-6 genes. In order to further explore the 13q31-32 region in MS, we genotyped 33 SNPs in 1355 Norwegian MS patients and 1446 Norwegian controls. An intronic SNP in the Glypican-5 gene (rs9523787) showed association with MS (p(corr)=0.006). Thus, this study supports that MS susceptibility at 13q31-32 may localize to the Glypican-5 gene, which should lead to further fine-mapping, replication and functional studies of this gene.

Two HLA class I genes independently associated with multiple sclerosis.

OBJECTIVE: The risk of multiple sclerosis (MS) is influenced by HLA-DRB1, while protective effects have been proposed for HLA-A*02 and HLA-C*05. Our aim was to further understand the role of HLA class I in MS through a comprehensive investigation. METHODS: 1529 MS patients and 1814 controls from Sweden and Norway were genotyped for HLA-DRB1, HLA-A, and HLA-C. Simultaneous analysis of all alleles while adjusting for confounding was achieved using logistic regression. RESULTS: We observed independent effects of all three genes. We confirm the HLA-A*02 (OR=0.73, p=9.2 x 10(-4)) association and report a novel effect of HLA-C*08 (OR=1.85, p=0.0093). CONCLUSIONS: The HLA class I region contains two factors modulating MS risk, characterized by independent associations with HLA-A and HLA-C.

A rare variant of the TYK2 gene is confirmed to be associated with multiple sclerosis.

A rare functional variant within the TYK2 gene (rs34536443) has been reported as protective in multiple sclerosis (MS) in recent studies. However, because of the low frequency of the minor allele (minor allele frequency=0.04), genome-wide significant association has been hard to establish. We genotyped 5429 Nordic MS cases and 6167 healthy controls for this TYK2 non-synonymous single-nucleotide polymorphism (ns-SNP), and combined the Nordic genotype data with raw genotypes from previous studies. The combined Nordic analysis showed significant association with MS (P=5 x 10(-4), odds ratio (OR) 0.78), and by mega-analysis of 10 642 MS patients, 10 620 controls and 2110 MS trios, the association at genome-wide significance level (P=5.08 x 10(-9), OR 0.77) was shown.

Killer immunoglobulin-like receptor ligand HLA-Bw4 protects against multiple sclerosis.

OBJECTIVE: Multiple sclerosis (MS) is a chronic inflammatory disease affecting the central nervous system. A human leukocyte antigen (HLA) class II association is well established (DRB1*1501-DQB1*0602), but more recently HLA class II-independent associations with HLA class I variants have also been reported. The HLA class I (HLA-A, -B, -C) molecules serve as ligands for both T-cell receptors and killer immunoglobulin-like receptors (KIRs). We investigated the HLA class I alleles defined by their KIR binding motifs and the KIR genes to evaluate whether these genes could influence MS susceptibility or severity, alone or in combination. METHODS: We typed Norwegian MS patients (n = 631) and controls (n = 555) for HLA-A, -B, -C and -DRB1 alleles as well as the presence or absence of genes encoding inhibitory (KIR2DL1, KIR2DL2, KIR2DL3, KIR2DL5, KIR3DL1, KIR3DL2, KIR3DL3) and activating (KIR2DS1, KIR2DS2, KIR2DS3, KIR2DL4, KIR2DS4, KIR2DS5, KIR3DS1) KIRs. RESULTS: The frequency of the HLA-Bw4 specificity, which is the ligand for the inhibitory KIR3DL1, was significantly reduced in MS patients as compared with controls (41.4% vs 55.1%, p(uncorrected (uc)) = 4.6 x 10(-6)). Also after stratifying for known HLA class II associations, the HLA-Bw4 association was seen (p(uc) = 0.002). No significant differences in gene carrier frequencies of inhibitory and activating KIRs were observed. However, our data indicate that MS patients who carry the activating KIR2DS2 and the inhibitory KIR2DL2 genes have more severe disease than patients not carrying these genes. INTERPRETATION: Carriage of the ligand of the inhibitory KIR3DL1 receptor, HLA-Bw4, was found to protect against MS in an HLA-DRB1 independent manner.

Replication analysis identifies TYK2 as a multiple sclerosis susceptibility factor.

In a recent genome-wide association study (GWAS) based on 12,374 non-synonymous single nucleotide polymorphisms we identified a number of candidate multiple sclerosis susceptibility genes. Here, we describe the extended analysis of 17 of these loci undertaken using an additional 4234 patients, 2983 controls and 2053 trio families. In the final analysis combining all available data, we found that evidence for association was substantially increased for one of the 17 loci, rs34536443 from the tyrosine kinase 2 (TYK2) gene (P=2.7 x 10(-6), odds ratio=1.32 (1.17-1.47)). This single nucleotide polymorphism results in an amino acid substitution (proline to alanine) in the kinase domain of TYK2, which is predicted to influence the levels of phosphorylation and therefore activity of the protein and so is likely to have a functional role in multiple sclerosis.