What is the Leptospira?
Leptospira is a genus of spiral-shaped bacteria belonging to the phylum Spirochetes. Named for its slender, coiled appearance, this bacterium is responsible for a widespread zoonotic disease known as Leptospirosis, which can lead to severe health problems in both humans and animals.
Firs discovered in the 20th century, the Leptospira bacteria were initially isolated from rats and subsequently linked to Weil's disease, a severe human infection form. The bacterium was formally named 'Leptospira' in 1917, with its species designation derived from its discoverers, Inada, and Ito's, who were conducting investigations on yellow fever at that time.
Leptospira Structure
Leptospira is a thin, tightly coiled bacteria featuring a distinctive double-membrane structure that sets it apart from the typical Gram-negative bacteria. This double membrane envelops the bacterial cytoplasm and provides the bacteria with a level of physiological adaptation to counter hostile environments. The bacteria usually move in corkscrew-like rotations propelled by the two endoflagella located in the periplasmic space between these membranes.
Symptoms of Leptospira Infection
With fluctuating onset times, Leptospira infection symptoms range from mild to severe. The early phase often resembles the flu, characterized by symptoms like fever, vomiting, muscle pain, and red eyes. However, if left untreated, the disease can advance to cause jaundice, kidney failure, and meningitis. In rare cases, it may lead to complications such as Weil's disease or pulmonary hemorrhagic syndrome, which can prove fatal without prompt treatment.
Proteins in Leptospira
Leptospira bacteria are composed of proteins playing various roles in the survival and pathogenesis of the bacterium. Some proteins, such as LipL41 and LipL32, are abundantly present on the outer surface and serve as antigens when the bacterium infects the host. These antigenic proteins can trigger an immune response in the host. Research has outlined LipL32 as a major protein, which could be pursued as an optional antigen.
Leptospira Antigen Structure
The structure of Leptospira's antigenic proteins is key to their functionality. For instance, LipL32, a surface-exposed lipoprotein, has a distinctive amphipathic structure - with one hydrophobic region for integration into the bacterial membrane and a hydrophilic region for interaction with the host immune system. This enables the protein to have a high immunogenic capacity.
Leptospira Antigen-Related Signaling Pathways
The interaction of Leptospira and its antigenic proteins with the host initiates several signaling pathways. For instance, the encounter with LipL32 protein can activate the host's Toll-like receptors, such as TLR2 and TLR4. This interaction triggers downstream signaling pathways leading to the upregulation of inflammatory cyto- and chemokines, as well as interferons. This activation often influences the outcome of the disease, with the host immune response contributing to the severity of leptospirosis.
Leptospira-Related Vaccines
Given the critical nature of leptospirosis, efforts have been made towards developing effective vaccines. Presently available vaccines are chiefly bacterin-type, based on whole-killed cells of the bacteria. However, these vaccines exhibit limitations, including short-term immunity and serovar-specific protection, and are typically ineffective against Leptospira.
Therefore, newer vaccines based on antigenic proteins are being developed. Attention is on the antigenic outer surface proteins like LipL32 due to its high immunogenicity, with experimental vaccines eliciting strong and potentially long-lasting immune responses.
