The Beta Poisson dose-response model is not a single-hit model

The choice of a dose-response model is decisive for the outcome of quantitative risk assessment. Single-hit models have played a prominent role in dose-response assessment for pathogenic microorganisms, since their introduction. Hit theory models are based on a few simple concepts that are attractive for their clarity and plausibility. These models, in particular the Beta Poisson model, are used for extrapolation of experimental dose-response data to low doses, as are often present in drinking water or food products. Unfortunately, the Beta Poisson model, as it is used throughout the microbial risk literature, is an approximation whose validity is not widely known. The exact functional relation is numerically complex, especially for use in optimization or uncertainty analysis. Here it is shown that although the discrepancy between the Beta Poisson formula and the exact function is not very large for many data sets, the differences are greatest at low doses--the region of interest for many risk applications. Errors may become very large, however, in the results of uncertainty analysis, or when the data contain little low-dose information. One striking property of the exact single-hit model is that it has a maximum risk curve, limiting the upper confidence level of the dose-response relation. This is due to the fact that the risk cannot exceed the probability of exposure, a property that is not retained in the Beta Poisson approximation. This maximum possible response curve is important for uncertainty analysis, and for risk assessment of pathogens with unknown properties.

Relationship between pathogenesis of Guillain-Barre syndrome and Penner's serotypes of Campylobacter jejuni

OBJECTIVE

To investigate the relationship between the pathogenesis of Guillain-Barre syndrome (GBS) and Campylobacter jejuni (C. jejuni) in China.

METHODS

C. jejuni strains were isolated from fresh stools of 47 GBS patients in Beijing area from 1995 to 1997 by modified Skirrow's method. Serotyping of C. jejuni was performed with Penner's method in 47 GBS patients and 171 patients with C. jejuni enteritis in our hospital during the same period. The stools from which no C. jejuni strains could be isolated were typed by PCR-RFLP (restriction fragment length polymorphism) method.

RESULTS

Six C. jejuni strains were isolated by Skirrow's method, including 3 strains of Penner serotype 2, 1 Penner serotype 4, 1 Penner serotype 19 and 1 Penner serotype 26. Three strains of DNA-I, which was equal to the same type of Penner serotype 19, were found by PCR-RFLP method.

CONCLUSION

C. jejuni isolated from Beijing area are similar to those reported in literature, which once more confirms the molecular mimicry pathogenetic theory of GBS caused by C. jejuni infection in China. The similarities of serotypes between C. jejuni strains from GBS patients and those from C. jejuni enteritis patients may explain the high incidence of GBS following C. jejuni infection in China.

[Campylobacter jejuni enteritis and Guillain-Barré syndrome]

Guillain-Barré syndrome (GBS) is the most common cause of acute neuromuscular paralysis. Sera from patients with GBS following Campylobacter jejuni infection frequently have autoantibody to GM 1 ganglioside in the acute phase of the illness. We revealed that the lipopolysaccharide (LPS) of C. jejuni that was isolated from a GBS patient has the oligosaccharide structure [Gal beta 1-3 GalNAc beta 1-4 (NeuAc alpha 2-3) Gal beta 1-], which is identical to the terminal tetrasaccharide of GM 1 ganglioside. (1) Infection by C. jejuni that bears the GM 1-like lipopolysaccharide associated with the serotypic determinant of PEN 19 induces high production of IgG 1 and IgG 3 anti-GM 1 antibodies with help of T cells. (2) IgG anti-GM 1 antibody binds to motor nerve terminal axons, inhibits motoneuron excitability, and produces the development of GBS.

[Pathophysiology and therapeutic approach in inflammatory demyelinating polyneuropathy--recent advances]

Recent advances on pathogenetic mechanism and therapeutic approach for Guillain-Barré syndrome (GBS) and chronic inflammatory demyelinating polyneuropathy (CIPD) were briefly reviewed. As for GBS, an axonal form has been recognized as a clinicopathological variant, in which Campylobacter jejuni infection and elevated anti-GM1 antibody tires are frequently observed. Other anti-glycolipid antibodies to GQ1b, GD1b and GM2 would also be significant as a determinant factor for a clinical phenotype. Beneficial effects of IVIg therapy and plasmapheresis have been established. Although CIDP has also been considered to be demyelinating neuropathy, axonal pathology is frequently noted, and in such cases, a substantial motor neuron loss is present. Clinical recovery in the cases with high anti-MAG and anti-SGPG titers is not necessarily favorable. Corticosteroid therapy, plasmapheresis and IVIg have been all established as therapies beneficial for CIDP.

[A case of acute multifocal motor neuropathy with conduction block after Campylobacter jejuni enteritis]

The patient was a 25-year-old male with acute multifocal motor neuropathy with conduction block (MMNCB) after Campylobacter jejuni enteritis. After having suffered from diarrhea for 3 days, he rapidly developed asymmetrical distal-dominant muscle weakness in all extremities. Sensory disturbance was unremarkable except for slight disturbance in deep sensation. Deep tendon reflexes were normal throughout the course of present illness. CSF analysis revealed increased protein up to 66 mg/dl without pleocytosis. In electrophysiological examinations, persistant multifocal conduction blocks in the motor nerves were predominantly noted in the distal part of the extremities. Serum titers of anti-Campylobacter jejuni antibody, anti-GM1 antibody and anti-GalNAc-GD1a antibody were elevated. Muscle weakness resolved completely within 7 weeks. The sural nerve biopsy did not reveal either axonal degeneration, nor demyelination. These clinical and laboratory findings suggested that this case was most likely an acute type of MMNCB after Campylobacter jejuni enteritis.

[A case of isolated tricuspid valve endocarditis caused by Campylobacter fetus]

We reported a rare case of isolated tricuspid valve endocarditis in a non-addict with no underlying cardiac disease. A 48-year-old man was presented with high fever and newly developed leg edema. The diagnosis of tricuspid endocarditis was established following detection of a large vegetation (3.0 cm) on the tricuspid valve on echocardiography. One blood culture showed positive for Campylobacter fetus. At operation, a large and a small vegetation were found attached to the anterior leaflet of the tricuspid valve, and the septal leaflet was also found to be involved by the infective endocarditis. These leaflets were therefore removed and the tricuspid valve was replaced with CarboMedics valve. He has remained free of endocarditis for nineteen months after surgery.

[A case of axonal form of Guillain-Barré syndrome associated with anti-GM1b IgG antibody following Penner 4 Campylobacter jejuni infection]

A 41-year-old woman was admitted to the hospital because of diarrhea followed by progressive weakness of all extremities and dysphagia. On neurological examination, she showed facial diplegia, bulbar palsy, flaccid quadriplegia, and absence of all deep tendon reflexes in addition to Laségue's sign. The Campylobacter jejuni Penner type 4 was isolated from the culture of stool. The test of anti-GM1b antibody (IgG) was positive in the serum. The protein content was elevated in the cerebrospinal fluid without pleocytosis. The studies of motor nerve conduction velocity showed a pattern of the axonal neuropathy. This is a case of Guillain-Barré syndrome presenting with the axonal neuropathy possibly due to the immune response directed to GM1b which is triggered by the Campylobacter jejuni Penner type 4 infection.

[Axonal Guillain-Barré syndrome associated with anti-GalNAc-GD1a antibody subsequent to Campylobacter jejuni (PEN 43) enteritis]

We reported a 16-year-old boy who had Guillain-Barré syndrome (GBS) after suffering diarrhea. Campylobacter jejuni was isolated from his stool, and the serotype belonged to PEN 43. Neurologic examination revealed distal-dominant muscle weakness atrophy, and mild sensory disturbance. Motor and sensory nerve conduction velocities were normal, but compound muscle action potentials were markedly reduced. Serum from the patient had high titers of anti-FalNAc-GD1a antibodies. He had HLA-A24, B51, DRB1*04 and DRB1*09. His elder sister showed diarrhea and serum anti-C. jejuni antibody, but did not showed GBS and serum anti-ganglioside antibody. Her HLA types were A24, B51, DRB1*09 and DRB1*14.

GM1 antibody in Guillain-Barre syndrome after Campylobacter jejuni infection

Fecal culture of Campylobacter jejuni was prepared by the method of Skirrow, and serum class specific antibodies (IgG, IgM and IgA) to Campylobacter jejuni and serum class specific antibodies (IgG IgM) to GM1 were prepared with solid phase enzyme linked immunasorbent assay in 16 cases of Guillain-Barre syndrome (GBS), 32 controls with other neurological diseases (disease controls) and 90 normal controls. The results showed that the incidence of Campylobacter jejuni infection, especially recent infections, in the group with Guillain-Barre syndrome was much higher than that in the two control groups, and that the positive rate of GM1 antibody was also much higher in the GBS group than in the two control groups. The results suggest that Campylobacter jejuni infection may be one of the important precipitating factors of Guillain-Barre syndrome and play an important role in the epidemiological pattern of Guillain-Barre syndrome in China. It damages the myelin of peripheral nerves through induction of GM1 antibody production.

Immunopathogenesis and treatment of the Guillain-Barré syndrome--Part II

In the second part of our review the role of antecedent infections in the pathogenesis of GBS is discussed. The association with Campylobacter jejuni (C. jejuni) is highlighted and the concept of molecular mimicry, i.e., sharing of epitopes between microbes and peripheral nerve, explained. Alternative mechanisms to relate an infection with the immune-mediated neuropathy are elaborated. Current therapies of the GBS include plasma exchange, high-dose intravenous immunoglobulins, and supportive treatment directed to secondary complications. Published therapeutic trials are reviewed and future approaches are outlined. Principles of general care are also summarized.

A longitudinal study of calprotectin as an inflammatory marker in patients with reactive arthritis

OBJECTIVE

To examine the value of calprotectin, a major granulocyte protein with bactericide properties, as an inflammatory marker in patients with reactive arthritis.

METHODS

Twenty-five patients with Chlamydia-induced and 27 patients with enterobacteria-induced reactive arthritis were analysed. At the first visit and after 3, 12, 24, 52 and 104 weeks, calprotectin concentrations were measured in plasma and when possible, in synovial fluid. C-reactive protein (CRP) and the erythrocyte sedimentation rate (ESR) were analysed and clinical assessments of disease activity were performed.

RESULTS

Of the inflammatory markers, the plasma calprotectin concentrations were the first to normalize during recovery. Calprotectin concentrations in the plasma were highly correlated with CRP and ESR, and calprotectin was found to have high correlation coefficients with the clinical assessments of disease activity. High calprotectin concentrations were found in the synovial fluid.

CONCLUSION

The high correlations between calprotectin in plasma and clinical and laboratory markers of inflammation, as well as the rapid normalization following clinical improvement, demonstrate that calprotectin may be used as an inflammatory marker in patients with reactive arthritis.

[A patient with Guillain-Barré syndrome in association with Campylobacter jejuni enteritis (PEN19:LIO7) in a patient with HLA-B52 antigen]

We report a 15-year-old boy with Guillain-Barré syndrome (GBS) in association with Campylobacter jejuni enteritis. A neurologic examination revealed distal-dominant weakness and areflexia. Compound muscle action potentials were markedly reduced in amplitude, but the decrease in motor conduction velocities was slight. C. jejuni was isolated from his stool culture and the serotype belonged to PEN19:LIO7. Thin-layer chromatography-immunostaining showed that his serum IgG reacted strongly with GM1 and weakly with GD1b. The patient had HLA-B52 antigen, whose epitope is very similar to that of B35 antigen.

Pathogenesis of axonal Guillain-Barré syndrome: hypothesis

Pathologic studies of acute motor axonal neuropathy show strong evidence of the presence of primary axonal Guillain-Barré syndrome (GBS). The pathogenesis of axonal GBS is speculated to be as follows: (1) Infection by an organism induces the high production of a cross-reactive antibody between an infectious agent and the motor nerve axon in patients with a particular immunogenetic background. (2) The antineural antibody binds to the motor nerve terminals, thereby inhibiting motoneuron excitability and causing muscular weakness. (3) Binding of the antineural antibody, or subsequent functional impairment of the motoneurons, causes the motor axon to degenerate from the terminals. (4) In severe cases, extensive axonal loss and central chromatolysis of the motoneurons occur. These inhibit recovery and lead to a poor functional prognosis.