Leptospira spp. Infection: Leptospirosis
Leptospirae defy attempts at logical nomenclature and classification. Prior to 1989, the genus Leptospira was divided into two species, Leptospira interrogans, which contained all pathogenic strains, and Leptospira biflexa, which contained saphrophytic strains.
These were divided into over 200 L. interrogans and 60 L. biflexa serovars, and serovars were clustered into related serogroups. Genome analysis has resulted in an alternative classification scheme, with nearly 20 genomospecies, but these groups do not correlate in any way with former species, serovar, or pathogenicity. Thus, the serological classification still prevails. Individual serotypes tend to prefer a single maintenance host, but may infect many different host species. Mice can be infected with a number of Leptospira serotypes, but Leptospira ballum is the most common. Leptospirosis is a zoonotic disease and is the most geographically widespread zoonotic disease in the world. Human infections have been acquired from both pet and laboratory mice infected with L. ballum. Clinical manifestations of leptospirosis in humans are highly varied, including the most severe icteric form of infection, Weil's disease, characterized by renal and liver failures. Humans can become infected when handling sub- clinically infected mice, and infection is usually acquired through abraded skin and conjunctiva.Pathology
Infection of wild mice is frequent, but disease is typically silent. Infection of laboratory mice appears to be rare, but testing for this bacterium is seldom performed. Mice do not become clinically ill when naturally infected and develop persistent infections with intermittent shedding of organisms in the urine throughout life. Lesions are absent in naturally acquired infections, but mice are experimentally susceptible to disease. Experimental inoculation of C3H/He mice with L. interrogans serovar Icterohaemorrhagiae results in pulmonary fibrinoid vasculitis, thrombosis, and hemorrhage, as well as renal tubular necrosis and interstitial nephritis. T-cell deficiency (CD4 and CD8) increased susceptibility to disease. Infection of C3H/HeJ and C3H-scid mice with L. interrogans serovar Copenhageni results in lethal disease, characterized by discohesion of hepatic cords, hyperplasia of Kuppfer cells and macrophages, focal hepatic necrosis, interstitial nephritis, and tubular damage, with spirochetes visible in the renal interstitium.
Diagnosis
Leptospirae can be isolated by kidney culture, which should be performed on serial 10-fold dilutions of tissue homogenates because growth inhibition can occur in undiluted samples. PCR can be used for detection of Leptospira in tissues and urine and is more sensitive than culture. Serology is also possible; however, mice infected as neonates may become persistently infected but never seroconvert. Under natural conditions, this phenomenon is common.
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