Immunogenicity of a DNA and Recombinant Protein Vaccine Combining LipL32 and Loa22 for Leptospirosis Using Chitosan as a Delivery System.

Leptospirosis is a worldwide zoonotic disease caused by pathogenic Leptospira, a genus of which more than 250 serovars have been identified. Commercial bacterin vaccines are limited in that they lack both cross-protection against heterologous serovars and long-term protection. This study investigated in mice the immunogenicity of an anti-leptospirosis vaccine, using the outer membrane proteins LipL32 and Loa22 as antigens. The immunogenicity of this vaccine formulation was compared with those induced by vaccines based on LipL32 or Loa22 alone. A DNA-encapsulated chitosan nanoparticle was used for in vivo DNA delivery. Using a unique DNA plasmid expressing both lipL32 and loa22 for vaccination, higher antibody responses were induced than when combining plasmids harboring each gene separately. Therefore, this formulation was used to test the immunogenicity when administered by a heterologous prime (DNA)-boost (protein) immunization regimen. The specific antibody responses against LipL32 (total IgG and IgG1) and Loa22 (IgG1) were higher in mice receiving two antigens in combination than in those vaccinated with a single antigen alone. Although no significant difference in splenic CD4+ T cell proliferation was observed among all groups of vaccinated mice, splenocytes from mice vaccinated with two antigens exhibited higher interferon-γ and IL-2 production than when using single antigens alone upon in vitro restimulation. Taken together, the immunogenicity induced by LipL32 and Loa22 antigens in a heterologous primeboost immunization regimen using chitosan as a DNA delivery system induces higher immune response, and may be useful for developing a better vaccine for leptospirosis.

An outbreak of leptospirosis, Thailand--the importance of the laboratory.

The reported incidence of leptospirosis increased 30-fold in Thailand between 1995 and 2000. Despite many hypotheses to explain the increase, the true etiology remains unknown. We conducted a review of the national surveillance system for leptospirosis, examining the reporting practices, system attributes, and utilization of laboratory confirmation in two northeastern provinces. Using standard guidelines for evaluation of public health surveillance systems, we assessed the timeliness, completeness, and accuracy of data; the sensitivity and specificity of case ascertainment; and the overall usefulness of the Thai leptospirosis surveillance system. Physicians were interviewed to assess compliance and understanding of the case definition. Capacity for confirmation of leptospirosis by a Thai latex agglutination test was assessed. Completeness for variables critical for linking epidemiologic and laboratory data for leptospirosis was 69%. Twenty-eight percent of 208 provincial surveillance reports were considered timely. Interviewed physicians indicated that the national case definition was difficult to understand and apply, and that laboratory confirmation was infrequently used. Compared to a standardized microscopic agglutination test (MAT) panel, the Thai test was specific, but relatively insensitive. We found that a lack of a standardized case definition for leptospirosis, the infrequent use of confirmatory laboratory testing, and the inability to link clinical, epidemiologic, and laboratory data hindered system utility. This surveillance system for leptospirosis highlights difficulties with surveillance of febrile illnesses in general, and the importance of laboratory confirmation for infections that are difficult to diagnose clinically.