Whipple's disease and "Tropheryma whippelii"

Abstract

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.

FIG. 1

PAS staining. (A) PAS-positive, diastase-resistant “T. whippelii” bacteria in IL-4-deactivated cultures of human peripheral blood mononuclear cells. (Copyright Gabriele Schoedon, Department of Internal Medicine, University Hospital of Zurich.) (B) Macrophages with PAS-positive inclusions in cerebrospinal fluid of a patient with proven neurologic Whipple's disease. (Copyright Gabriele Schoedon.) (C) Right basal ganglion biopsy specimens filled with numerous PAS-positive inclusions from a patient with clinically proven neurologic Whipple's disease. (Copyright Sebastian Brandner, Institute of Neuropathology, University Hospital of Zurich.)

FIG. 1

PAS staining. (A) PAS-positive, diastase-resistant “T. whippelii” bacteria in IL-4-deactivated cultures of human peripheral blood mononuclear cells. (Copyright Gabriele Schoedon, Department of Internal Medicine, University Hospital of Zurich.) (B) Macrophages with PAS-positive inclusions in cerebrospinal fluid of a patient with proven neurologic Whipple's disease. (Copyright Gabriele Schoedon.) (C) Right basal ganglion biopsy specimens filled with numerous PAS-positive inclusions from a patient with clinically proven neurologic Whipple's disease. (Copyright Sebastian Brandner, Institute of Neuropathology, University Hospital of Zurich.)

FIG. 1

PAS staining. (A) PAS-positive, diastase-resistant “T. whippelii” bacteria in IL-4-deactivated cultures of human peripheral blood mononuclear cells. (Copyright Gabriele Schoedon, Department of Internal Medicine, University Hospital of Zurich.) (B) Macrophages with PAS-positive inclusions in cerebrospinal fluid of a patient with proven neurologic Whipple's disease. (Copyright Gabriele Schoedon.) (C) Right basal ganglion biopsy specimens filled with numerous PAS-positive inclusions from a patient with clinically proven neurologic Whipple's disease. (Copyright Sebastian Brandner, Institute of Neuropathology, University Hospital of Zurich.)

FIG. 2

Electron micrograph of Whipple's disease bacilli cultured with HEL cells. (Copyright Didier Raoult, Unité des Rickettsies, CNRS: UPRESA 6020, Faculté de Médicine, Université de la Méditerranée, Marseille, France.)

FIG. 3

Amplification systems used to analyze the 16S and the 16S-23S rDNA spacer region of “T. whippelii.” Expected product sizes are given. The position numbering is based on the reference sequence of Maiwald et al. (110).

FIG. 4

Phylogenetic tree showing the relation of the Whipple's disease bacterium “T. whippelii” to other representatives of the actinomycetes. Reproduced from reference with permission of the publisher.

FIG. 5

Nucleotide sequence of the “T. whippelii” 16S-23S rDNA internal transcribed spacer. The base numbering is that of the reference sequence (X99636) of Maiwald et al. (110); dots and hyphens symbolize identity and alignment gaps, respectively.

FIG. 6

Representative results of nested PCR assays for direct detection of “T. whippelii” 16S-23S rDNA spacer types in clinical specimens on ethidium bromide-stained agarose gels. PCR products derived from amplification using primer pair tws3 and tws4 (83) were reamplified with various type-specific primer combinations: twsA1 and twsB1 (for spacer type 1) (A), twsA2 and twsB2 (for types 2 and 3) (B), twsA1 and twsC1 (for type 1) (C), twsA2 and twsC1 (for type 2) (D), and twsA2 and twsC2 (for type 3) (E). The expected products are indicated by arrows. Lanes 1 to 10 show clinical specimens positive for “T. whippelii” spacer type 1 (lanes 1, 2, 5, and 8), spacer type 2 (lanes 4 and 9), and spacer type 3 (lane 7) and negative controls (lanes 3, 6, and 10). Lane 11 shows molecular mass markers (50-bp ladder; Boehringer, Mannheim). Reproduced from reference with permission of the publisher.