Alonzo, Abigail S.
B.S. Bio 3
February 21, 2013 LEPTOSPIROSIS
Leptospirosis is a bacterial infection caused by long, thin, motile spirochetes belonging to the genus Leptospira, family Leptospiraceae, and order Spirochaetales. These spirochetes are finely coiled, thin, motile, obligate, slow-growing anaerobes. Their flagella allow them to burrow into tissue. More recent work has identified 7 distinct species of pathogenic leptospires, which appear as more than 250 serologic variants (serovars). They may be free-living or associated with animal hosts and survive well in freshwater, soil, and mud areas where they can live for weeks or months. They can thrive in hot, humid environments but not in acidic environments. They are primarily contained in the genital and urinary tract. The disease is known as the most common zoonosis in the world, that is, it is the most common disease carried by animals and affects animals, including humans. The incidence varies from sporadic in temperate zones to endemic in a few tropical countries. The disease is often referred to as swineherd’s disease, or swamp fever, mud fever, Icterohemorrhagic fever, Rice-field fever, Cane-cutter fever, Hemorrhagic jaundice, Stuttgart disease, or Canicola fever. Wild mammals are known to be the main reservoir of the leptospiral serovars. About 160 mammals including fats, skunks, raccoon, and cattle, have been termed as vectors or carriers of the disease. Rats are considered to be the most important reservoir. Transmission occurs by contamination of soil, water, or vegetation by urine excreted from infected animals. Humans can become infected upon contact of the contaminated material with abraded skin, mucous membranes such as conjunctiva or alimentrary tract, or ingestion of the contaminated material. Occasionally, the organism may even enter the body through intact skin. Infection has occurred after animal and rodent bites, after contact with abortion products of infected animals, and after ingestion of contaminated food and water. The latter route of infection is believed to occur via the mucosa of the mouth and the esophagus because leptospires cannot survive in an acidic environment. Leptospires may persist for long periods in the renal tubules of animals by establishing a symbiotic relationship with no evidence of disease or pathological changes in the kidney. As a result, animals that serve as reservoirs of host-adapted serovars can shed high concentrations of the organism in their urine without showing clinical evidence of disease. Leptospiruria in humans is more transient, rarely lasting more than 60 days. Humans and nonadapted animals are incidental hosts. With rare exceptions, man represents a dead end in the chain of infection because person-to-person spread of the disease is rare. Most cases occur in the warm season and in rural areas because leptospires can persist in water for many months. The leptospires from infected animals contaminate the warm lake water. They survive best in freshwater, damp alkaline soil, vegetation, and mud with temperatures higher than 22°C. Mucous surfaces of the mouth, pharynx, and esophagus may be crossed easily by pathogenic leptospires, as are mucous membranes of the bronchial tree and lung alveoli. Transmission via laboratory accidents may occur but is rare. The bacterium usually invades through the mucosa, multiplies in the blood and tissue. The resulting leptospiremia can spread to any part of the body but particularly affects the liver and kidney. After the organism gains access to the kidney, it migrates to the interstitium, renal tubules, and tubular lumen, causing interstitial nephritis and tubular necrosis. When renal failure develops, it is usually due to tubular damage, but hypovolemia from dehydration and from altered capillary permeability can also contribute to renal failure. Liver involvement is seen as centrilobular necrosis with proliferation of Kupffer cells. Jaundice may...
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