Tropheryma whippelii in peripheral blood mononuclear cells and cells of pleural effusion

Tropheryma whipplei Infection (Whipple Disease) in the USA

BACKGROUND

Whipple disease (WD) is an infection caused by the bacterium Tropheryma whipplei (TW). Few cases have been reported in the USA.

AIMS

To report on the demographics, clinical manifestations, diagnostic findings, treatment, and outcomes of TW infection.

METHODS

Cases of TW infection diagnosed from 1995 to 2010 were identified in three US referral centers and from 1995 to 2015 in one. Definite classic WD was defined by positive periodic acid-Schiff (PAS) staining and probable WD by specific positive TW polymerase chain reaction (PCR) of intestinal specimens. Localized infections were defined by a positive TW PCR result from samples of other tissues/body fluids.

RESULTS

Among the 33 cases of TW infections, 27 (82%) were male. Median age at diagnosis was 53 years (range 11-75). Diagnosis was supported by a positive TW PCR in 29 (88%) and/or a positive PAS in 16 (48%) patients. Classic WD was the most frequent presentation (n = 18, 55%), with 14 definite and 4 probable cases. Localized infections (n = 15, 45%) affected the central nervous system (n = 7), joints (n = 4), heart (n = 2), eye (n = 1), and skeletal muscle (n = 1). Blood PCR was negative in 9 of 17 (53%) cases at diagnosis. Ceftriaxone intravenously followed by trimethoprim and sulfamethoxazole orally was the most common regimen (n = 23, 70%). Antibiotic therapy resulted in clinical response in 24 (73%).

CONCLUSIONS

TW infection can present as intestinal or localized disease. Negative small bowel PAS and PCR do not exclude the diagnosis of TW infection, and blood PCR is insensitive for active infection.

Tropheryma whipplei infection and Whipple's disease

Recent advances in medical microbiology, epidemiology, cellular biology, and the availability of an expanded set of diagnostic methods such as histopathology, immunohistochemistry, PCR, and bacterial culture have improved our understanding of the clinical range and natural course of Tropheryma whipplei infection and Whipple's disease. Interdisciplinary and transnational research activities have contributed to the clarification of the pathogenesis of the disorder and have enabled controlled trials of different treatment strategies. We summarise the current knowledge and new findings relating to T whipplei infection and Whipple's disease.

Constrictive pleuropericarditis: a dominant clinical manifestation in Whipple's disease

Background

Whipple’s disease is a rare, multisystemic, chronic infectious disease which classically presents as a wasting illness characterized by polyarthralgia, diarrhea, fever, and lymphadenopathy. Pleuropericardial involvement is a common pathologic finding in patients with Whipple’s disease, but rarely causes clinical symptoms. We report the first case of severe fibrosing pleuropericarditis necessitating pleural decortication in a patient with Whipple’s disease.

Case presentation

Our patient, an elderly gentleman, had a chronic inflammatory illness dominated by constrictive pericarditis and later severe fibrosing pleuritis associated with a mildly elevated serum IgG4 level. A pericardial biopsy showed dense fibrosis without IgG4 plasmacytic infiltration. The patient received immunosuppressive therapy for possible IgG4-related disease. His poor response to this therapy prompted a re-examination of the diagnosis, including a request for the pericardial biopsy tissue to be stained for Tropheryma whipplei.

Conclusions

Despite a high prevalence of pleuropericardial involvement in Whipple’s disease, constrictive pleuropericarditis is rare, particularly as the dominant disease manifestation. The diagnosis of Whipple’s disease is often delayed in such atypical presentations since the etiologic agent, Tropheryma whipplei, is not routinely sought in histopathology specimens of pleura or pericardium. A diagnosis of Whipple’s disease should be considered in middle-aged or elderly men with polyarthralgia and constrictive pericarditis, even in the absence of gastrointestinal symptoms. Although Tropheryma whipplei PCR has limited sensitivity and specificity, especially in the analysis of peripheral blood samples, it may have diagnostic value in inflammatory disorders of uncertain etiology, including cases of polyserositis. The optimal approach to managing constrictive pericarditis in patients with Whipple’s disease is uncertain, but limited clinical experience suggests that a combination of pericardiectomy and antibiotic therapy is of benefit.

Tropheryma whipplei tricuspid endocarditis: a case report and review of the literature

INTRODUCTION

The main clinical manifestations of Whipple's disease are weight loss, arthropathy, diarrhea and abdominal pain. Cardiac involvement is frequently described. However, endocarditis is rare and is not usually the initial presentation of the disease. To the best of our knowledge, this is the first reported case of a patient with Tropheryma whipplei tricuspid endocarditis without any other valve involved and not presenting signs of arthralgia and abdominal involvement.

CASE PRESENTATION

We report a case of a 50-year-old Caucasian man with tricuspid endocarditis caused by Tropheryma whipplei, showing signs of severe shock and an absence of other more classic clinical signs of Whipple's disease, such as arthralgia, abdominal pain and diarrhea. Tropheryma whipplei was documented by polymerase chain reaction of the blood and pleural fluid. The infection was treated with a combined treatment of doxycycline, hydroxychloroquine and sulfamethoxazole-trimethoprim for one year.

CONCLUSION

Tropheryma whipplei infectious endocarditis should always be considered when facing a blood-culture negative endocarditis particularly in right-sided valves. Although not standardized yet, treatment of Tropheryma whipplei endocarditis should probably include a bactericidal antibiotic (such as doxycycline) and should be given over a prolonged period of time (a minimum of one year).

[Tonsillar hypertrophy and mesenteric adenopathies as the main manifestations in a patient with Whipple's disease]

Whipple's disease is an infrequent chronic infection caused by Tropheryma whipplei, identified in 1992. Intestinal, articular, central nervous system and cardiac involvement is common. The presence of abdominal adenopathies, especially mesenteric adenopathies, without peripheral adenopathies or gastrointestinal, articular, neurological or cardiac symptoms is rare. We present the case of a male patient with tonsillar hypertrophy, mesenteric adenopathies, fever and constitutional syndrome, leading to suspicion of lymphoma. Biopsy findings of the lingual tonsil and mesenteric adenopathies were compatible with Whipple's disease. The diagnosis was confirmed by blood polymerase chain reaction.

Diagnosis of Wihipple disease by immunohistochemical analysis: a sensitive and specific method for the detection of Tropheryma whipplei (the Whipple bacillus) in paraffin-embedded tissue

Whipple disease is a rare infection characterized clinically by diarrhea, fever, weight loss, arthralgia, malabsorption, and other systemic manifestations. The etiologic agent, Tropheryma whipplei, has been cultured only rarely. By using a polyclonal rabbit antibody produced against a cultured strain of T whipplei, tissue sections from 18 patients with Whipple disease were studied. Specimens from patients with histologic mimics and other infections served as control specimens. Immunostaining was identified in all 18 patients. Granular immunostaining was observed similar to that in periodic acid-Schiff (PAS) stains. In 2 patients, immunostaining was identified in specimens negative by H&E and PAS stains. In 4 patients studied before and after antibiotic therapy, immunostaining was retained but diminished in intensity and quantity. Immunostaining was not identified in any control specimen. Immunohistochemical analysis is a sensitive and specific method for the diagnosis of Whipple disease in paraffin-embedded tissue and may provide new opportunities to investigate the pathogenesis of the infection.

Whipple's disease

Whipple's disease is a chronic systemic bacterial infection that predominantly affects middle-aged men. Antimicrobial therapy is curative. The causative agent has been identified as Tropheryma whippelii. A PCR-based diagnostic test is now available and is particularly useful in patients with early-stage or atypical disease. The test can detect bacterial nucleic acids in tissues and body fluids, including joint fluid. Studies using this test found no evidence that T. whippelii may be a common cause of unexplained seronegative oligoarthritis or polyarthritis. Further work is needed to identify the patient subsets most likely to benefit from T. whippelii PCR testing in joint specimens. Isolation of the organism has been achieved recently. This will probably allow development of a serological test, which may facilitate the diagnosis. Weight loss and diarrhea are the most common symptoms of Whipple's disease. Joint manifestations antedate the intestinal complaints in three-fourths of patients, the mean interval being 6 years. In most patients, duodenal and jejunal biopsy specimens contain macrophages filled with PAS-stained granules corresponding to bacteria. Nevertheless, some patients have no intestinal symptoms, and a few have normal intestinal histological findings. Before the onset of intestinal symptoms, several clinical patterns should suggest Whipple's disease. Unexplained, chronic, seronegative oligoarthritis or polyarthritis affecting the large limb joints is the most common presentation. A characteristic feature is the intermittent occurrence of the joint manifestations, at least early in the disease. Other patterns are destructive polyarthritis and spondyloarthropathy. The major advances made recently in techniques for detecting and isolating the causative agent may show that Whipple's disease is more common and has a broader clinical spectrum than was previously thought. Another hope is that the diagnosis will be made earlier, before the development of potentially fatal systemic complications.

Neurologic manifestations of gastrointestinal disease

Although previously considered rare, neurologic manifestations of gastrointestinal diseases are increasingly recognized. Understanding of Whipple disease and gluten sensitivity is in transition and these conditions are becoming the province of neurologists. Recent improvements in diagnostic testing have improved our understanding and case finding for vitamin B12 deficiency. Many patients with these conditions present with neurologic manifestations alone. Therefore, these conditions are becoming the province of neurologists, and neurologic manifestations of gastrointestinal disease are becoming a more common part of neurologic practice.

Whipple's endocarditis: review of the literature and comparisons with Q fever, Bartonella infection, and blood culture-positive endocarditis

Whipple's disease is a systemic infection sometimes associated with cardiac manifestations. Recently, there has been an increase in the number of reported cases of Whipple's endocarditis. The purpose of our study was to describe this entity. Data from 35 well-described cases of Whipple's endocarditis were collected and compared with those of blood culture-positive endocarditis, Q fever endocarditis, and Bartonella endocarditis. Some patients with generalized Whipple's disease presented with cardiac involvement, among other symptoms. Others presented with a nonspecific, blood culture-negative endocarditis with no associated symptoms. In comparison with cases of endocarditis due to other causes, congestive heart failure, fever, and previous valvular disease were less frequently observed in the cases of Whipple's endocarditis. Without examination of the excised valves, the diagnosis of infective endocarditis could not have been confirmed in most cases. Treatment is not well established. Whipple's endocarditis is a specific entity involving minor inflammatory reactions and negative blood cultures, and its incidence is probably underestimated.

Whipple's disease and "Tropheryma whippelii"

Whipple's disease is a rare bacterial infection that may involve any organ system in the body. It occurs primarily in Caucasian males older than 40 years. The gastrointestinal tract is the most frequently involved organ, with manifestations such as abdominal pain, malabsorption syndrome with diarrhea, and weight loss. Other signs include low-grade fever, lymphadenopathy, skin hyperpigmentation, endocarditis, pleuritis, seronegative arthritis, uveitis, spondylodiscitis, and neurological manifestations, and these signs may occur in the absence of gastrointestinal manifestations. Due to the wide variability of manifestations, clinical diagnosis is very difficult and is often made only years or even decades after the initial symptoms have appeared. Trimethoprim-sulfamethoxazole for at least 1 year is usually considered adequate to eradicate the infection. The microbiological diagnosis of this insidious disease is rendered difficult by the virtual lack of culture and serodiagnostic methods. It is usually based on the demonstration of periodic acid-Schiff-positive particles in infected tissues and/or the presence of bacteria with an unusual trilaminar cell wall ultrastructure by electron microscopy. Recently, the Whipple bacteria have been characterized at the molecular level by amplification of their 16S rRNA gene(s). Phylogenetic analysis of these sequences revealed a new bacterial species related to the actinomycete branch which was named "Tropheryma whippelli." Based on its unique 16S ribosomal DNA (rDNA) sequence, species-specific primers were selected for the detection of the organism in clinical specimens by PCR. This technique is currently used as one of the standard methods for establishing the diagnosis of Whipple's disease. Specific and broad-spectrum PCR amplifications mainly but not exclusively from extraintestinal specimens have significantly improved diagnosis, being more sensitive than histopathologic analysis. However, "T. whippelii" DNA has also been found in persons without clinical and histological evidence of Whipple's disease. It is unclear whether these patients are true asymptomatic carriers or whether differences in virulence exist among strains of "T. whippelii" that might account for the variable clinical manifestations. So far, six different "T. whippelii" subtypes have been found by analysis of their 16S-23S rDNA spacer region. Further studies of the pathogen "T. whippelii" as well as the host immune response are needed to fully understand this fascinating disease. The recent cultivation of the organisms is a promising major step in this direction.

Whipple disease and arthritis

Whipple disease is a chronic, multisystem, curable, bacterial infection that usually affects middle-aged men and has a wide range of clinical manifestations. The most common symptoms are weight loss and diarrhea, preceded in three quarters of cases by arthritis for a mean of 6 years. In most patients, periodic acid-Schiff staining of proximal small bowel biopsy specimens reveals inclusions within the macrophages, corresponding to bacterial structures. However, patients with various manifestations of the disease may have no gastrointestinal symptoms and negative jejunum biopsy results. Before the onset of gastrointestinal symptoms, a strong index of clinical suspicion is the key to diagnosis. The classic setting is long-term, unexplained, seronegative oligoarthritis or polyarthritis with a palindromic or relapsing course, although chronic destructive polyarthritis and spondyloarthropathy have been repeatedly reported. Identification of the Whipple bacterium, Tropheryma whippelii, has led to the development of polymerase chain reaction as a diagnostic tool in patients in the early stages of the disease or with atypical Whipple disease. This technique can be used to detect the bacterium in many tissues and fluids, including synovial tissue and fluid. The recent cultivation of the Whipple bacillus should lead to the development of serologic tests, further facilitating diagnosis. These recent major advances may show that the infection is more frequent than previously suspected and may expand the clinical spectrum of the disease. It may also allow earlier diagnosis, thereby preventing the development of the severe systemic and sometimes fatal forms of the disease.

PCR analysis in the pathological diagnosis of Whipple's disease: emphasis on extraintestinal involvement or atypical morphological features

PCR analysis of species-specific bacterial 16S rRNA gene of Tropheryma whippelii was performed in biopsies from 10 cases of Whipple's disease (WD). In seven patients showing the typical clinical picture of WD, PCR was performed on the diagnostic intestinal biopsy. In the remaining three cases (an autopsy case of disseminated WD and two patients showing lymphadenopathy as the initial clinical presentation), PCR was done on lymph node specimens. In one of the lymph node biopsies, an unusual sarcoidlike granulomatous reaction had led to the diagnosis of sarcoidosis. The specific bacterial DNA was detected in all cases, both in intestinal biopsies and in lymph node specimens. Follow-up biopsies after antibiotic therapy were evaluated in two patients. The two follow-up biopsies were negative, although in both of them scattered nests of PAS-positive macrophages remained. The results of this study suggest that PCR analysis of species-specific sequences of the 16S rRNA of Tropheryma whippelii is a very useful tool for the pathological diagnosis of WD. It confirms the diagnosis of WD in intestinal biopsies as well as in extraintestinal sites, even when the morphological appearance is not typical. It is also the most precise technique for monitoring therapeutic effects.

Severe pulmonary hypertension reversed by antibiotics in a patient with Whipple's disease

The case is described of a 58 year old man with systemic Whipple's disease with pericardial and pleural effusions and severe pulmonary hypertension. After three months of antibiotic treatment there was a complete resolution, not only of the symptoms known to be associated with Whipple's disease (diarrhoea, arthralgia, pericardial and pleural effusions), but also of pulmonary hypertension.

Polymerase chain reaction-based detection of Tropheryma whippelii in central nervous system Whipple's disease

Whipple's disease of the central nervous system (CNS) may be associated with normal intestinal histology as a result of minimal or patchy involvement. The diagnosis is difficult and is frequently made post mortem. We studied 6 patients with clinically suspected CNS Whipple's disease; 2 had oculomasticatury myorhythmia (OMM) fitting criteria for a diagnosis of definite CNS Whipple's disease. One of the 2 had duodenal histology highly suggestive of Whipple's disease the other 5 patients had normal duodenal histology. DNA was extracted from paraffin-embedded duodenal tissues in all patients and frozen pontine tissue in 1. Two primer pairs (W3F-W4R, W3F-W2R) were used in separate polymerase chain reactions (PCRs) to amplify fragments of Tropberyma whippelii 16S rDNA from these tissue samples. PCR amplicons were detected only in the duodenal tissues from the 2 patients with OMM. The sequences of these amplicons were identical to the corresponding region of the previously published Tropheryma whippelii 16S rDNA sequence. PCR-based assays of intestinal or brain tissue may be of value for confirming, and possibly refuting, a clinical diagnosis of CNS Whipple's disease in a patient with any combination of dementia, supranuclear gaze palsy, hypothalamic manifestations, myoclonus, seizures, ataxia, or OMM, especially when tissue histology is unrevealing.

Whipple disease. Clinical review of 52 cases. The SNFMI Research Group on Whipple Disease. Société Nationale Française de Médecine Interne

Whipple disease is a rare, multiorgan disease with prominent intestinal manifestations. We report a retrospective clinical study of 52 patients recruited in various parts of France from 1967 to 1994. Seventy-three percent of the patients were male. Clinical manifestations preceding the diagnosis were articular for 35 patients (67%), digestive for 8 patients (15%), general for 7 patients (14%), and neurologic for 2 patients (4%). At a later stage of the disease, 44 patients (85%) presented diarrhea, weight loss, and malabsorption, while 8 patients (15%) did not show any gastrointestinal symptom throughout the development of the disease. Forty-three patients (83%) presented arthralgia or arthritis, and 11 (21%) had prominent neurologic symptoms. In addition, cardiovascular symptoms were present in 9 patients (17%); mucocutaneous symptoms, in 9 patients (17%); pleuropulmonary symptoms, in 7 patients (13%); and ophthalmologic symptoms, in 5 patients (10%). All patients but 1 were given a positive diagnosis on histopathologic criteria: jejunal biopsy for 46 patients (90%), lymph node biopsy for 3 patients (6%), brain biopsy for 1 patient (2%), postmortem jejunal and cerebral biopsy for 1 patient (2%). With treatment, the disease evolved favorably in 47 patients (90%), while 5 patients (10%) had unfavorable outcomes (2 deaths from neurologic involvement, 1 patient with chronic dementia, and 2 patients with digestive symptoms insensitive to antimicrobial therapy). Of the 41 patients initially treated successfully and whose treatment has been completed, clinical evolution after discontinuation of treatment was favorable in 34 cases (83%). Clinical relapses occurred in 7 patients. No relapse was observed after treatment by trimethoprim-sulfamethoxazole, alone or following a combination of penicillin and streptomycin, or after the combination of penicillin and streptomycin, whatever the oral follow-up treatment prescribed. The evolution of patients showing a relapse was favorable in all cases after reintroduction of antibiotic therapy. These results are discussed in the light of previously published series and case reports of Whipple disease. The diagnosis of the disease remains difficult at an early phase or when digestive symptoms are absent. It is noteworthy that proximal enteroscopy is sometimes misleading, considered normal on macroscopic examination and nonspecific on pathologic grounds. A normal erythrocyte sedimentation rate represents another pitfall. Histopathology is the key for positive and differential diagnosis, and may require multiple and repeated biopsies. Findings from molecular biology confirm the central role of an uncultured Gram-positive bacillus which was named in 1992 Tropheryma whippelii. A recent report suggests that polymerase chain reaction (PCR) analysis of peripheral blood might allow the diagnosis of Whipple disease in some cases. However, immunologic or cellular parameters such as macrophagic function may play an important, although not clearly elucidated, role in the pathogeny of the disease. Trimethoprim-sulfamethoxazole should be considered the antimicrobial agent of choice in the treatment of Whipple disease, minimizing the risk of cerebral involvement and relapses.

Molecular cloning, upstream sequence and promoter studies of the human gene for the regulatory subunit RII alpha of cAMP-dependent protein kinase

The gene for the regulatory subunit RII alpha of cAMP-dependent protein kinase is highly regulated during spermatogenesis and a strong signal from a distinct short mRNA form is observed postmeiotically during spermatid elongation. This report presents the isolation and characterization of the 5'-flanking region (1.2 kb) and exon 1 of the human RII alpha gene. S1 nuclease mapping and primer extension experiments revealed the presence of a major transcriptional start site located 208 nucleotides upstream of start for translation. The 5'-flanking region of the RII alpha gene did not contain a TATA box and was highly G/C-rich. A basal promoter directing high levels of chloramphenicol acetyl transferase (CAT) activity was identified in the 5'-flanking sequence. Several potential binding sites for transcription factors were identified in this region, which may be responsible for the germ cell-specific regulation of this gene. We have previously reported that the human testis RII alpha cDNA contains a region (amino acids 45-75) with little or no homology to the corresponding rat skeletal muscle cDNA (Oyen, O., Myklebust, F., Scott, J.D., Cadd, G.G., McKnight, G.S., Hansson, V. and Jahnsen, T. (1990) Biol. Reprod. 43, 46-54). We examined whether this difference could arise due to organ-specific splice mechanisms or represented a species difference. We show that the low homology region of the human RII alpha cDNA resides entirely within exon 1, and does not originate from a tissue-specific alternate splicing of this distinct region.

Arthralgia as an early extraintestinal symptom of Whipple's disease. Report of five cases

Five patients with Whipple's disease all suffered from arthralgia for a long time (15 years in one case) before developing gastrointestinal or other symptoms. In all patients, arthralgia was seronegative, and there was no evidence of joint destruction. Arthralgias were symmetric and migrating. Whipple's disease is part of the differential diagnosis of enteropathic arthralgia. Thereby, the polymerase chain reaction can be a helpful tool to prove Whipple's disease in difficult differential diagnosis.

Ophthalmoplegia and leg myorhythmia in Whipple's disease: report of a case

Whipple's disease (WD) is a rare disorder that is more common in males than in females. Progressive supranuclear ophthalmoplegia (SNO) in conjunction with oculomasticatory myorhythmia (OMM) or oculofacioskeletal myorhythmia are characteristic movement abnormalities when WD involves the nervous system. Limb myorhythmia without facial or ocular myorhythmia has not been reported in WD. We report such a case who had SNO and leg myorhythmia but no facial or ocular myorhythmia. She had onset of WD at age 28 and 16 years later developed SNO and leg myorhythmia. The neurological manifestations did not respond to antimicrobial agents or to the drugs used for parkinsonism or essential tremor. Valproate produced a remarkable improvement in leg myorhythmia, but the efficacy declined after 3 months. Because WD may infest as a neurological disorder without gastrointestinal symptoms, all SNO cases, with or without OMM, and those with skeletal myorhythmia should be suspected of WD. These patients should be treated vigorously and followed carefully since neurological involvement is the most disabling feature and it has a propensity to relapse.

Diagnostic guidelines in central nervous system Whipple's disease

Many cases of central nervous system (CNS) Whipple's disease are not diagnosed until postmortem. Few reviews of CNS Whipple's disease have delineated the frequencies of abnormalities on neurological examination, cerebrospinal fluid studies, neuroimaging, and intestinal biopsy studies. Guidelines for diagnosis and treatment have not been proposed. In this review we present 3 new cases of CNS Whipple's disease and summarize the literature to determine the frequencies of neurological signs and abnormalities on diagnostic testing. We propose guidelines for diagnostic screening, selection for biopsy, and treatment. Review of the 84 cases of CNS Whipple's disease (81 in the literature, 3 new) revealed that 80% of the patients had systemic signs. Cognitive changes were frequent (71%), and 47% with cognitive changes also had psychiatric signs. Oculomasticatory myorhythmia and oculo-facial-skeletal myorhythmia, pathognomic for CNS Whipple's disease, were present in 20% of patients, and were always accompanied by a supranuclear vertical gaze palsy. Tissue biopsy was a sensitive technique; 89% of those who had biopsies had positive biopsy results. Diagnosis and treatment of definite CNS Whipple's disease should be based on the presence of pathognomic signs (oculomasticatory myorhythmia or oculo-facial-skeletal myorhythmia) or positive biopsy or polymerase chain reaction results. Possible CNS Whipple's disease should be diagnosed in the setting of unexplained systemic symptoms and neurological signs (supranuclear vertical gaze palsy, rhythmic myoclonus, dementia with psychiatric symptoms, or hypothalamic manifestations). Those with possible CNS Whipple's disease should undergo small-bowel biopsy.

Sequence-based identification of microbial pathogens: a reconsideration of Koch's postulates

Over 100 years ago, Robert Koch introduced his ideas about how to prove a causal relationship between a microorganism and a disease. Koch's postulates created a scientific standard for causal evidence that established the credibility of microbes as pathogens and led to the development of modern microbiology. In more recent times, Koch's postulates have evolved to accommodate a broader understanding of the host-parasite relationship as well as experimental advances. Techniques such as in situ hybridization, PCR, and representational difference analysis reveal previously uncharacterized, fastidious or uncultivated, microbial pathogens that resist the application of Koch's original postulates, but they also provide new approaches for proving disease causation. In particular, the increasing reliance on sequence-based methods for microbial identification requires a reassessment of the original postulates and the rationale that guided Koch and later revisionists. Recent investigations of Whipple's disease, human ehrlichiosis, hepatitis C, hantavirus pulmonary syndrome, and Kaposi's sarcoma illustrate some of these issues. A set of molecular guidelines for establishing disease causation with sequence-based technology is proposed, and the importance of the scientific concordance of evidence in supporting causal associations is emphasized.