Legionella longbeachae Is Immunologically Silent and Highly Virulent In Vivo.

BACKGROUND: Legionella longbeachae (Llo) and Legionella pneumophila (Lpn) are the most common pneumonia-causing agents of the genus. Although both species can be lethal to humans and are highly prevalent, little is known about the molecular pathogenesis of Llo infections. In murine models of infection, Lpn infection is self-limited, whereas Llo infection is lethal. METHODS: We used mouse macrophages, human macrophages, human epithelial cells, and mouse infections in vivo to evaluate multiple parameters of the infection. RESULTS: We determined that the Llo Dot/Icm secretion system is critical for virulence. Different than Lpn, Llo disseminates and the animals develop a severe pulmonary failure, as demonstrated by lung mechanics and blood oxygenation assays. As compared to Lpn, Llo is immunologically silent and fails to trigger the production of cytokines in human pulmonary epithelial cells and in mouse and human macrophages. Infections in Tnfr1-/-, Ifng-/-, and Il12p40-/- mice supported the participation of cytokines for the resistance phenotype. CONCLUSIONS: Both Lpn and Llo require the Dot/Icm system for pathogenesis, but the infection outcome is strikingly different. Llo is immunologically silent, highly virulent, and lethal. The differences reported herein may reflect unappreciated clinical differences in patients infected with Lpn or Llo.

Legionella bozemanii, an elusive agent of fatal cavitary pneumonia.

A 67-year-old patient died of Legionella bozemanii pneumonia with negative urinary antigen and negative serology. Cystic lesions in pneumonia of unknown origin should lead to the differential diagnosis of L. bozemanii infections.

Legionellosis from Legionella pneumophila serogroup 13.

We describe 4 cases of Legionella pneumophila serogroup 13-associated pneumonia. These cases originate from a broad geographic range that includes Scotland, Australia, and New Zealand. L. pneumophila serogroup 13 pneumonia has a clinically diverse spectrum that ranges from relatively mild, community-acquired pneumonia to potentially fatal severe pneumonia with multisystem organ failure. All cases were confirmed by culture and direct fluorescent antibody staining or indirect immunofluorescent antibody tests. Proven or putative sources of L. pneumophila serogroup 13 infections in 2 patients included a contaminated whirlpool spa filter and river water. An environmental source was not found in the remaining 2 cases; environmental cultures yielded only other L. pneumophila serogroups or nonpneumophila Legionella species. We describe the clinical and laboratory features of L. pneumophila serogroup 13 infections. L. pneumophila serogroup 13 pneumonia is rarely reported, but it may be an underrecognized pathogenic serogroup of L. pneumophila.

Legionella species infection in adult febrile respiratory tract infections in the community.

Legionella spp. (Lsp) are well recognized as etiologic factors in pneumonia but less so in respiratory tract infections (RTI) in the community. The objective of the present study was to characterize febrile RTI patients with a documented Legionella etiology, in terms of specific serogroups, clinical manifestations of the disease, disease course and the effect of antibiotic therapy. Ambulatory adults with febrile RTI (n = 250) were included in a prospective study in which the etiological causes of the infection were identified using sophisticated serological techniques. Paired sera were obtained for each of the patients and were tested for 41 different serotypes of Lsp using micro-immuno-fluorescence (MIF) serology. Only a significant change in IgG and/or IgM antibody titers was considered diagnostic. In 28 patients (11.2%) there was serological evidence of acute infection with 1 of the types of Lsp. The infections were manifested clinically as upper RTI in 9 patients and as lower RTI in the other 19 patients (community-acquired pneumonia in 2 of these). L. pneumophila serogroup 1 was identified in 3 patients, L. pneumophila serogroups higher than 1 were identified in 13 patients and L. non-pneumophila serogroups in 18 patients. The clinical and laboratory findings in patients with acute Lsp infection were not significantly different from those in patients without evidence of this infectious agent. The length and course of the disease were similar in the 12 patients treated with specific antibiotics for Lsp and in those who were not. We conclude that Lsp can be identified in a significant percentage of patients with acute febrile RTI. No specific clinical or laboratory features were observed for these patients and specific antibiotic therapy does not affect the course of the disease.

Legionella: from environmental habitats to disease pathology, detection and control.

Studies on Legionella show a continuum from environment to human disease. Legionellosis is caused by Legionella species acquired from environmental sources, principally water sources such as cooling towers, where Legionella grows intracellularly in protozoa within biofilms. Aquatic biofilms, which are widespread not only in nature, but also in medical and dental devices, are ecological niches in which Legionella survives and proliferates and the ultimate sources to which outbreaks of legionellosis can be traced. Invasion and intracellular replication of L. pneumophila within protozoa in the environment play a major role in the transmission of Legionnaires' disease. Protozoa provide the habitats for the environmental survival and reproduction of Legionella species. L. pneumophila proliferates intracellularly in various species of protozoa within vacuoles studded with ribosomes, as it also does within macrophages. Growth within protozoa enhances the environmental survival capability and the pathogenicity (virulence) of Legionella. The growth requirements of Legionella, the ability of Legionella to enter a viable non-culturable state, the association of Legionella with protozoa and the occurrence of Legionella within biofilms complicates the detection of Legionella and epidemiological investigations of legionellosis. Polymerase chain reaction (PCR) methods have been developed for the molecular detection of Legionella and used in environmental and epidemiological studies. Various physical and chemical disinfection methods have been developed to eliminate Legionella from environmental sources, but gaining control of Legionella in environmental waters, where they are protected from disinfection by growing within protozoa and biofilms, remains a challenge, and one that must be overcome in order to eliminate sporadic outbreaks of legionellosis.

La neumonía atípica por Legionella pneumophila: informe del segundo caso en México / Atypical pneumonia caused by Legionella pneumophila: second case report in Mexico

En 1977 se informó de 34 muertes por neumonía en 221 asistentes a la Convención de la Legión Americana en Filadelfia. El agente causal fue identificado y llamado Legionella pneumophila. La legionellosis es una enfermedad de distribución mundial, pero en México sólo hay un caso informado, posiblemente por no considerarse en el diagnóstico diferencial de las neumonías adquiridas en la comunidad. Informamos el caso de una paciente previamente sana en la que se diagnosticó una neumonía secundaria a Legionella pneumophila

Pityriasis rosea Gibert: detection of Legionella micdadei antibodies in patients.

Some epidemiological and clinical characteristics of Pityriasis rosea Gibert has led us to hypothesize that this disease may be the clinical manifestation of an infection caused by legionellas. We have thus tested the sera of 36 patients ill with Pityriasis rosea and 19 controls for Legionella pneumophila serogroup 1-6 and Legionella micdadei antibodies. These, who had the same age and sex distribution as study patients, were receiving treatment for other diseases in the same ward. Also tested were 200 sera from the voluntary blood donors from the same region as study patients. Legionella micdadei antibodies were detected in 12 (33.3%) Pityriasis rosea cases and in one (5.2%) control. They were significantly more common in Pityriasis rosea cases than in either controls or voluntary blood donor population. The findings to date encourage continued research into the causative relationship between the Legionella micddadei infection and the onset of Pityriasis rosea Gibert.

Legionella myositis.

Neuromuscular involvement in patients with legionnaires' disease is common, with serum CK elevations in up to 78% of patients. A few cases have been associated with neuropathy. The mechanism of injury to the neuromuscular system is unknown, but organisms have not previously been found in nerve or muscle. We report the clinical, electrophysiologic, and pathologic findings in a patient with Legionella myositis and motor neuropathy, the first case to demonstrate direct muscle invasion by the Legionella organism.