LEPTOSPIROSIS DEFINITION

Leptospirosis is a febrile disease (fever) caused by infection with the bacteria Leptospira interrogans. The disease can range from very mild and symptomless to a more serious, even life threatening form, that may be associated with kidney (renal) failure.

An infection by the bacterium Leptospira interrogans goes by different names in different regions. Alternate names for leptospirosis include mud fever, swamp fever, sugar cane fever, and Fort Bragg fever. More severe cases of leptospirosis are called Weil's syndrome or icterohemorrhagic fever. This disease is commonly found in tropical and subtropical climates but occurs worldwide.

As of the mid 1980s, there were 35-60 cases of leptospirosis reported in the United States each year. Most cases occur in Hawaii, followed by the south Atlantic, Gulf, and Pacific coastal states. However, because of the nonspecific symptoms of leptospirosis, it is believed that the occurrence in the United States is actually much higher. Leptospirosis occurs year-round in the United States, but about half of the cases occur between July and October.

Leptospirosis is a disease of animals and can be a very serious problem in the livestock industry. Leptospira bacteria have been found in dogs, rats, livestock, mice, voles, rabbits, hedgehogs, skunks, possums, frogs, fish, snakes, and certain birds and insects. Infected animals will pass the bacteria in their urine for months, or even years. In the United States, rats and dogs are more commonly linked with human leptospirosis than other animals.

Humans are considered "accidental hosts" and become infected with Leptospira interrogans by coming into contact with urine from infected animals. This is either through direct contact with urine, or through contact with soil, water, or plants that have been contaminated by animal urine. Leptospira interrogans can survive for as long as six months outdoors under favorable conditions. Leptospira bacteria can enter the body through cuts or other skin damage or through mucous membranes (such as the inside of the mouth and nose). It is believed that the bacteria may be able to pass through intact skin, but this is not known.

Once past the skin barrier, the bacteria enter the blood stream and rapidly spread throughout the body. The infection causes damage to the inner lining of blood vessels. The liver, kidneys, heart, lungs, central nervous system, and eyes may be affected.

There are two stages in the disease process. The first stage is during the active Leptospira infection and is called the "bacteremic," or "septicemic," phase. The bacteremic phase lasts from three to seven days and presents as typical flu-like symptoms. During this phase, bacteria can be found in the patient's blood and cerebrospinal fluid. The second stage, or "immune phase," occurs either immediately after the bacteremic stage or after a 1-3 day symptom-free period. The immune phase can last up to one month. During the immune phase, symptoms are milder but meningitis (inflammation of spinal cord and brain tissues) is common. Bacteria can be isolated only from the urine during this second phase.