Bacteria Scanning electron micrograph of a number of Leptospira sp. bacteria atop a 0.1 µm polycarbonate filter<unk>  is caused by spirochaete bacteria that belong to the genus Leptospira, which are aerobic, right-handed helical, and 6 –20 micrometers long. Like Gram-negative bacteria, Leptospira have an outer membrane studded with lipopolysaccharide (LPS) on the surface, an inner membrane and a layer of peptidoglycan cell wall. However, unlike Gram-negative bacteria, the peptidoglycan layer in Leptospira lies closer to the inner than the outer membrane. This results in a fluid outer membrane loosely associated with the cell wall. In addition, Leptospira have a flagellum located in the periplasm, associated with corkscrew style movement. Chemoreceptors at the poles of the bacteria sense various substrates and change the direction of its movement. The bacteria are traditionally visualised using dark-field microscopy without staining. A total of 66 species of Leptospira has been identified. Based on their genomic sequence, they are divided into two clades and four subclades: P1, P2, S1, and S2. The 19 members of the P1 subclade include the 8 species that can cause severe disease in humans: L. alexanderi, L. borgpetersenii, L. interrogans, L. kirschneri, L. mayottensis, L. noguchii, L. santarosai, and L. weilii. The P2 clade comprises 21 species that may cause mild disease in humans. The remaining 26 species comprise the S1 and S2 subclades, which include "saprophytes" known to consume decaying matter (saprotrophic nutrition). Pathogenic Leptospira do not multiply in the environment. Leptospira require high humidity for survival but can remain alive in environments such as stagnant water or contaminated soil. The bacterium can be killed by temperatures of and can be inactivated by 70% ethanol, 1% sodium hypochlorite, formaldehyde, detergents and acids. Leptospira are also classified based on their serovar. The diverse sugar composition of the lipopolysaccharide on the surface of the bacteria is responsible for the antigenic difference between serovars. Over 250 pathogenic serovars of Leptospira are recognised, with closely related serovars gathered into over 26 pathogenic serogroups. Strains of different species of Leptospira may be members of the same serogroup because of horizontal gene transfer of LPS biosynthetic genes between different species. Transmission The bacteria can be found in ponds, rivers, puddles, sewers, agricultural fields and moist soil. Pathogenic Leptospira have been found in the form of aquatic biofilms, which may aid survival in the environment. Leptospira live in the kidneys of various wild and domestic animals. When animals ingest the bacteria, they circulate in the bloodstream, then lodge themselves into the kidneys through the glomerulular or peritubular capillaries. The bacteria then pass into the lumens of the renal tubules and colonise the brush border of the proximal convoluted tubule. This causes the continuous shedding of bacteria in the urine without the animal experiencing significant ill effects. This relationship between the animal and the bacteria is known as a commensal relationship, and the animal is known as a reservoir host. Leptospira are found mostly in mammals. However, reptiles and cold-blooded animals such as frogs, snakes, turtles, and toads have been shown to have the infection. Whether there are reservoirs of human infection is unknown. Rats, mice, and moles are important primary hosts, but other mammals including dogs, deer, rabbits, hedgehogs, cows, sheep, swine, raccoons, opossums, and skunks can also carry the disease. In Africa, a number of wildlife hosts have been identified as carriers, including the banded mongoose, Egyptian fox, Rusa deer, and shrews. There are various mechanisms whereby animals can infect each other. Dogs may lick the urine of an infected animal off the grass or soil, or drink from an infected puddle. House-bound domestic dogs have contracted<unk> , apparently from licking the urine of infected mice in the house.<unk>  can also be transmitted via the semen of infected animals. The duration of bacteria being consistently present in animal urine may persist for years. Humans are the accidental host of Leptospira. Humans become infected through contact with water or moist soil that contains urine from infected animals. The bacteria enter through cuts, abrasions, ingestion of contaminated food, or contact with mucous membrane of the body (e.g. mouth, nose, and eyes). Occupations at risk of contracting<unk>  include farmers, fishermen, garbage collectors and sewage workers. The disease is also related to adventure tourism and recreational activities. It is common among water-sports enthusiasts in specific areas, including triathlons, water rafting, canoeing and swimming, as prolonged immersion in water promotes the entry of the bacteria. However, Leptospira are unlikely to penetrate intact skin. The disease is not known to spread between humans, and bacterial dissemination in recovery period is extremely rare in humans. Once humans are infected, bacterial shedding from the kidneys usually persists for up to 60 days. Rarely,<unk>  can be transmitted through an organ transplant. Infection through the placenta during pregnancy is also possible. It can cause miscarriage and infection in infants.<unk>  transmission through eating raw meat of wildlife animals have also been reported (e.g. psychiatric patients with allotriophagy).
Leptospirosis
Rickettsiosis
Bartonellosis
Dengue fever
Typhoid fever
Malaria
Blackwater fever
Murine typhus