Leptospira interrogans; Leishmania donovani; Legionella pneumophila
Leptospira interrogans are flexible, gram-negative spirochetes (spiral or cork-screw bacteria) with internal flagella that they use to propel themselves by twisting back and forth 1. “They are motile, with hooked ends and paired axial flagella (one on each end), enabling them to burrow into tissue. Motion is marked by continual spinning on the long axis” 2. Leptospira cells are encased in a three to five layer membrane and have relatively simple nutritional needs. The only known organic compounds necessary for its growth are vitamins B1 and B12. L. interrogans is one of two species of Leptospira, and contains over 200 pathogenic strains, the most prevalent being canicola, grippotyphosa, hardjo, icterohaemorrhagiae, and pomona. These pathogenic bacteria, which are referred to as Leptospires, are the infectious agents that cause the zoonotic disease Leptospirosis. This disease is known to affect both humans and animals, and is considered the most common zoonosis in the world 2. It has the potential to become even more prevalent with global warming. The primary hosts for this disease are wild and domestic animals, and the disease is a major cause of economic loss in the meat and dairy industry. Humans acquire the infection by contact with the urine of infected animals, but human-to-human transmission is extremely rare 1. Mucous membranes and broken skin are most likely the sites of entry for this bacterium, but they are also believed to enter the host through sodden and waterlogged skin, through the lungs (after inhalation of aerosolized body fluid), or through the placenta during pregnancy. “Virulent organisms in a susceptible host gain rapid access to the bloodstream through the lymphatics, resulting in leptospiremia and spread to all organs. The incubation period is usually 5-14 days but has been described from 72 hours to a month or more” 2. A generalized infection may develop, but no lesion develops at the site of entry. The host responds by producing antibodies that rapidly eliminate the leptospires from all tissues except the brain, eyes, and kidneys. Leptospires surviving in the brain and eyes multiply slowly if at all; however, in the kidneys they multiply in complex tubules and are shed in the urine 1. The leptospires can stay in the host for weeks to months, and in rodents they may be shed in the urine for its entire lifetime. Exotic-pet trade further increases the likelihood of transmission. In 2005, leptospirosis was transmitted from southern flying squirrels imported from Miami, Florida, to two Japanese animal handlers employed by an importer of exotic pets. Endemic canine leptospirosis is becoming more common in the United States, and California has seen a re-emergence of disease since 2000 2. The first recorded case was in 1886 and was referred to as Weil’s disease, which could be deadly. It was initially believed to be related to the plague, but not as contagious. These days, however, most human cases of leptospirosis are not life threatening. Case fatality is low but increases with advancing age and may reach 20% or more in those with jaundice or kidney damage 3. The mortality rate in severe leptospirosis has been described as ranging from 5-40%, but the mild form of the illness is rarely fatal. The elderly and people with impaired immune systems are at the highest risk of mortality. “No evidence suggests that leptospirosis affects persons of various races, ages, or sexes differently. However, because occupational exposure constitutes a major risk for development of disease, a disproportionate number of working-aged males seem to be affected” 2. Clinical manifestations of the disease are associated with a general fever, headache, muscle pain, and nausea, and therefore are often misdiagnosed as meningitis or hepatitis. Jaundice has been seen in more severe infections 1. In the early course of infection, leptospires...
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