Pathogenic mechanisms of Bartonella henselae infections

An uncommon presentation of Bartonella-associated neuroretinitis

BACKGROUND

This article documents a case of neuroretinitis initially presenting with ocular pain, 20/20 visual acuities, optic disc edema, and macular serous detachment without macular star formation in the absence of a history of exposure to pets or cats or symptoms suggestive of Bartonella infection. This initial clinical presentation appeared unilateral, but later became bilateral.

CASE REPORT

Physical and neuroophthalmologic consultation, neuroimaging studies, blood chemistry, and serologic analysis were requested. Positive serologic (IGG) titers to Bartonella henselae and Bartonella quintana were detected. Treatment was instituted initially with oral tetracycline (250 mg) qid and subsequently with doxycycline (100 mg) bid and prednisone (20 mg) qd.

CONCLUSION

Bartonella infection may cause optic disc edema and serous detachment without macular star formation. This presentation may occur without the generally characteristic signs and symptoms of Bartonella-associated neuroretinitis. A bilateral involvement may follow an initial unilateral presentation during the affliction period of this disorder.

Do plant and human pathogens have a common pathogenicity strategy?

Recently, a novel 'two-step' model of pathogenicity has been described that suggests host-cell-derived vasculoproliferative factors play a crucial role in the pathogenesis of bacillary angiomatosis, a disease caused by the human pathogenic bacterium Bartonella henselae. The resulting proliferation of endothelial cells could be interpreted as bacterial pathogens triggering the promotion of their own habitat: the host cell. Similar disease mechanisms are well known in the plant pathogen Agrobacterium tumefaciens, which causes crown gall disease. There are notable similarities between the pathogenicity of A. tumefaciens leading to tumourous disease in plants and to the B. henselae-triggered proliferation of endothelial cells in humans. Here, we hypothesize that this pathogenicity strategy might be common to several bacterial species in different hosts owing to shared pathogenicity factors.

A heat-stable component of Bartonella henselae upregulates intercellular adhesion molecule-1 expression on vascular endothelial cells

Bartonella henselae upregulated the expression of intercellular adhesion molecule-1 (ICAM-1) on human umbilical vein endothelial cells (HUVECs). The induction level of ICAM-1 depended on the inoculation bacterial dose. ICAM-1 expression began increasing 4 h after infection and reached a sustained peak beginning at 12 h after B. henselae infection; this time course was similar to that of lipopolysaccharide (LPS) of Escherichia coli. The stimulatory effect was abolished when live B. henselae were separated from HUVECs by a filter membrane. The nonpiliated strain, which is unable to invade endothelial cells, induced ICAM-1 expression to the same extent as the piliated strain. Inactivation of B. henselae by ultraviolet (UV) irradiation, heat (56 degrees C, 30 min), or sonication did not alter its stimulatory activity. Polymyxin B, which strongly inhibited the effect of LPS, did not exert any influence on the stimulatory activity of B. henselae. Furthermore, the effect of sonicated B. henselae was not inhibited even by boiling, which was also the case with LPS. Our data suggest that some heat-stable component of B. henselae binds to the endothelial cell surface, inducing ICAM-1 expression. Though the participation of LPS could not be completely ruled out, we suppose that some unidentified heat-stable proteins, lipids, or polysaccharides may be the stimulatory factor(s). The ability of B. henselae to enhance the expression of adhesion molecules on endothelial cells may be an important mechanism in the pathogenesis of B. henselae infection.

Recent Advances in Diagnosis and Treatment of Cat Scratch Disease

The cause of cat scratch disease (CSD), first described in France in 1950 and in the United States in 1951, was unknown until 1983 when the bacterium in lymph nodes was detected using a Warthin-Starry silver stain. Afipia felis has been an infrequent cause of CSD since1988, when this gram-negative bacterium was first isolated from 10 patients with CSD. In 1992 Bartonella organisms were isolated from immunocompetent and immunocompromised patients. An indirect fluorescent antibody test to detect bartonella-specific serum immunoglobulins was developed in 1992. Since then multiple studies have shown that three Bartonella species may produce either CSD in humans, usually Bartonella henselae or Bartonella clarridgeiae, or bacteremia in healthy cats. Also, these two bacteria and Bartonella quintana cause bacillary angiomatosis, bacillary peliosis, or relapsing bacteremia in humans. Cats are healthy carriers of Bartonella organisms and may be bacteremic for months to years. Cat-to-cat transmission of Bartonella organisms involves the cat flea in absence of direct contact transmission. CSD is the most common cause of regional lymphadenitis in children and adolescents. Present knowledge on the etiology, clinical features, epidemiology, pathogenesis, diagnosis, and management of CSD are presented. Also, brief comments about the etiology, clinical presentation, and treatment of bacillary angiomatosis and bacillary peliosis are provided.

Ocular manifestations of cat-scratch disease

Bartonella henselae has only recently been isolated, characterized, and found to be the principal cause of cat-scratch disease (CSD). The availability of specific serologic investigations has allowed the recognition of a spectrum of ocular CSD syndromes that previously were ill defined and considered idiopathic. The primary inoculation complex causing regional lymphadenopathy is represented in the eye by Parinaud's oculoglandular syndrome; B. henselae is the most common cause. Leber's neuroretinitis has been identified for 80 years, and new data suggest that it is commonly a manifestation of CSD; the extent of the association remains to be determined. CSD optic neuritis is also described. The vitreoretinal manifestations include anterior uveitis, vitritis, pars planitis, focal retinal vasculitis, a characteristic retinal white spot syndrome, Bartonella retinitis, branch retinal arteriolar or venular occlusions, focal choroiditis, serous retinal detachments, and peripapillary angiomatous lesions. The pattern of ocular disease in AIDS-associated B. henselae infections is poorly delineated; unusual manifestations include conjunctival and retinal bacillary angiomatosis. The benefit of antimicrobial therapy for CSD in immunocompetent individuals has been difficult to establish, partly because most infections are self limited. Empirically, azithromycin, ciprofloxacin, rifampin, parenteral gentamicin, or trimethoprim-sulfamethoxazole provide the best therapeutic choices to minimize damage to the eye.

Interactions of Bartonella henselae with vascular endothelial cells

The emerging human pathogen Bartonella henselae has the remarkable capacity to colonise vascular tissues and to stimulate vasoproliferative tumour growth. Although the molecular principle of bacterium-induced neovascularisation (angiogenesis) is still unclear, recent studies have indicated a novel mechanism of endothelial colonisation that involves the formation, engulfment and uptake of a large bacterial aggregate.

Parinaud syndrome caused by Bartonella henselae: case report

The authors report a case of Parinaud syndrome (conjunctivitis with pre-auricular satellite adenitis) caused by Bartonella henselae, the etiologic agent of Cat Scratch Disease. The etiologic assessment of this case was performed by serum indirect immunofluorescence reaction and allowed for a better therapeutics and follow up, avoiding ineffective antibiotics and surgical interventions.