Research Article: Human Leptospirosis Caused by a New, Antigenically Unique Leptospira Associated with a Rattus Species Reservoir in the Peruvian Amazon

Date Published: April 2, 2008

Publisher: Public Library of Science

Author(s): Michael A. Matthias, Jessica N. Ricaldi, Manuel Cespedes, M. Monica Diaz, Renee L. Galloway, Mayuko Saito, Arnold G. Steigerwalt, Kailash P. Patra, Carlos Vidal Ore, Eduardo Gotuzzo, Robert H. Gilman, Paul N. Levett, Joseph M. Vinetz, Mathieu Picardeau

Abstract: As part of a prospective study of leptospirosis and biodiversity of Leptospira in the Peruvian Amazon, a new Leptospira species was isolated from humans with acute febrile illness. Field trapping identified this leptospire in peridomestic rats (Rattus norvegicus, six isolates; R. rattus, two isolates) obtained in urban, peri-urban, and rural areas of the Iquitos region. Novelty of this species was proven by serological typing, 16S ribosomal RNA gene sequencing, pulsed-field gel electrophoresis, and DNA-DNA hybridization analysis. We have named this species “Leptospira licerasiae” serovar Varillal, and have determined that it is phylogenetically related to, but genetically distinct from, other intermediate Leptospira such as L. fainei and L. inadai. The type strain is serovar Varillal strain VAR 010T, which has been deposited into internationally accessible culture collections. By microscopic agglutination test, “Leptospira licerasiae” serovar Varillal was antigenically distinct from all known serogroups of Leptospira except for low level cross-reaction with rabbit anti–L. fainei serovar Hurstbridge at a titer of 1∶100. LipL32, although not detectable by PCR, was detectable in “Leptospira licerasiae” serovar Varillal by both Southern blot hybridization and Western immunoblot, although on immunoblot, the predicted protein was significantly smaller (27 kDa) than that of L. interrogans and L. kirschneri (32 kDa). Isolation was rare from humans (2/45 Leptospira isolates from 881 febrile patients sampled), but high titers of MAT antibodies against “Leptospira licerasiae” serovar Varillal were common (30%) among patients fulfilling serological criteria for acute leptospirosis in the Iquitos region, and uncommon (7%) elsewhere in Peru. This new leptospiral species reflects Amazonian biodiversity and has evolved to become an important cause of leptospirosis in the Peruvian Amazon.

Partial Text: Leptospirosis is a zoonotic disease of world-wide distribution caused by pathogenic spirochetes of the genus Leptospira[1]–[3]. The disease cannot be diagnosed on clinical grounds alone because its clinical presentations are diverse, ranging from undifferentiated fever to fulminant disease typified by various combinations of jaundice, renal failure, hemorrhage, and shock as well as involvement of other organs such as gallbladder, pancreas, myocardium, and central nervous system. The diagnosis of leptospirosis is made even more difficult by the lack of sensitive and readily accessible diagnostics.

Here we report isolation of a new species of Leptospira with novel biological characteristics that caused in humans a non-specific syndrome of undifferentiated fever. We showed definitively through serological and molecular analysis using 16S rRNA gene sequencing and pulsed field gel electrophoresis that this new leptospire, provisionally named “Leptospira licerasiae” serovar Varillal strain VAR 010T, is antigenically unique, is a significant cause of acute leptospirosis in the Peruvian Amazon region of Iquitos, and has a Rattus reservoir. Recognition of “Leptospira licerasiae” serovar Varillal strain VAR 010T as a new serovar is supported by the lack of agglutination of this strain by any serogroup reference serum and the lack of reactivity of anti- VAR 010T serum raised in rabbits against the serovars of Leptospira strains representing the nearly comprehensive and standard panel of leptospiral serogroups. A similar situation was found with L. fainei serovar Hurstbridge, where the following evidence was adduced in support of this novel serovar: lack of significant cross-agglutination was observed with reference antisera representing the 24 pathogenic serogroups and the main saprophytic ones; lack of agglutination by antiserum raised against one of the strains against any serogroup [19]. The serological characterization of the new serovar, Varillal, was conducted in two laboratories, one of which was the WHO/FAO/OIE Collaborating Centre for Reference and Research on Leptospirosis, Australia and Western Pacific Region, fulfilling the requirements for recognition of new serovars by the International Committee on Systematics of Prokaryotes, Subcommittee on the Taxonomy of Leptospiraceae[28].



Leave a Reply

Your email address will not be published.