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What is leptospirosis and its risk factors?

by Ishat Narain

Leptospirosis is an infectious disease that is transmitted from animals to humans. The infection can range from fever to multi-organ involvement, even causing death.

Leptospirosis is an infectious disease, universal distribution, transmitted naturally from animals to humans. It affects several domestic and wild animals, and humans can be infected by direct contact with an infected animal or an environment contaminated with the germ. Infection in humans can produce clinical pictures ranging from fever, cough, headache, muscle pain and chills, to the affection of multiple organs (kidneys, liver, spleen, brain, lungs), even causing death.

Leptospirosis is a zoonosis that affects many wild and domestic animal species; it has been described in more than 160. These animals constitute the reservoir (that is, the germ remains in them) and the infection source for humans. The most affected wild species are rodents, and the most affected domestic animals are dogs and cattle, horses, sheep, and pigs.

Infected animals shed leptospires in their urine. Humans become infected when they come into contact with these animals or with infected waters, especially stagnant waters and wetlands contaminated with these animals’ urine.

In the infected person, the immune system produces antibodies against the serotype (a microorganism category based on its antigens. Within the same type of bacteria – it also occurs with leptospires – there may be different serotypes or bacteria with different molecules on their surface; these are the molecules that the immune system detects as non-body antigens) of the leptospira that caused the infection.

A person who suffers from and recovers from a leptospira infection, even though they have created antibodies against that leptospira, is not protected against possible infections by other leptospires with another serotype; therefore, the same person is not free from another leptospirosis.

This disease is also known as Weil’s disease, enterohemorrhagic fever or hemorrhagic jaundice, pigsty disease, rice field fever, cane cutter fever, swamp or mud Stuttgart disease, and in some cases, Leptospira canicola fever.

Leptospirosis Causes and Risk Factors

The causes of leptospirosis are a type of bacteria, leptospirosis or bacteria of the genus Leptospira, which are part of the Leptospiraceae family, which are within the order of bacteria known as Spirochaetales. The latter group different bacteria that are similar in their morphology: gram-negative bacteria (that is, they show a characteristic appearance with Gram stain ), thin, helix-shaped, and measure 0.1 to 0.5 μm X 5 to 20 μm. The Spirochaetales order is subdivided into three families and 13 genera, of which only three cause disease in humans; these three genera are Leptospira, Treponema, and Borrelia.

As mentioned, this microbiological classification only attends to the bacteria’s morphological characteristics and not to the type of disease that they originate or to how it is acquired. Thus, bacteria are grouped within this order, such as, for example, the one responsible for syphilis, Treponema pallidum, which is transmitted by sexual contact; or infections caused by various types of Borrelia, which are transmitted through ticks or lice; or the diseases caused by Leptospira described below.

The leptospires are thin bacteria and winding, with a look at one or both ends. They have two flagella (like two threads) that give the bacteria more length and help it move. These bacteria can be cultured in the laboratory from samples obtained from infected patients. That is, they multiply if they are put in the media and under the conditions in which they grow best: between 28 and 30 ºC, and in media containing vitamins (B 1 and B 12 ), ammonium salts, and long-chain fatty acids.

In nature, leptospires can survive for quite a long time in the water or humid, temperate environments, as long as the pH is neutral or slightly alkaline (i.e., the opposite of acidic). Still, they only multiply in the animal that hosts them.

Recently, a group of scientists from the Venezuelan Institute for Scientific Research (Ivic) has found a bacterium, which they have named Leptospira venezuelensis, which can also cause this disease.

Risk factors for leptospirosis

Leptospirosis is an occupational disease associated with jobs that come into contact with animals or products contaminated by them. For example, it happens to veterinarians, ranchers, field, or sewer workers. Also, with increasing frequency, there are cases of infections acquired due to the practice of recreational activities in tropical and subtropical humid areas (for use when swallowing water, swimming in reservoirs, or practicing kayaking).

Leptospires enter the human being through a wound in the skin, no matter how small, and through the mucous membranes of the eyes and nose, from where they easily pass into the blood, where they begin to multiply, producing the first phase of the disease (leptospiremia or febrile phase).