They may not have any symptoms Signs and symptoms
A schematic of the human body showing the symptoms and signs of leptospirosis
Schematic depiction of the symptoms and signs of leptospirosis. Human eye showing symptomatic red and yellow patches on the white of the eye
Conjunctival suffusion (red conjunctiva) together with jaundice is a specific feature of leptospirosis. The symptoms of leptospiros
is usually appear one to two weeks after infection,[7] but the incubation period can be as long as a month.[18] The illness is biphasic in a majority of symptomatic cases. Symptoms of the first phase (acute or leptospiremic phase) last five to seven days. In the second phase (immune phase), the symptoms resolve as antibodies against the bacteria are produced.[8] Additional symptoms develop in the second phase.[19] The phases of illness may not be distinct, especially in patients with severe illness.[20] 90% of those infected experience mild symptoms while 10% experience severe leptospirosis.[21]
Leptospiral infection in humans causes a range of symptoms, though some infected persons may have none. The disease begins suddenly with fever accompanied by chills, intense headache, severe muscle aches and abdominal pain.[5][18] A headache brought on by leptospirosis causes throbbing pain and is characteristically located at the head's bilateral temporal or frontal regions. The person could also have pain behind the eyes and a sensitivity to light. Muscle pain usually involves the calf muscle and the lower back. The most characteristic feature of leptospirosis is the conjunctival suffusion (conjunctivitis without exudate) which is rarely found in other febrile illnesses. Other characteristic findings on the eye include subconjunctival bleeding and jaundice. A rash is rarely found in leptospirosis. When one is found alternative diagnoses such as dengue fever and chikungunya fever should be considered. Dry cough is observed in 20–57% of people with leptospirosis. Thus, this clinical feature can mislead a doctor to diagnose the disease as a respiratory illness. Additionally, gastrointestinal symptoms such as nausea, vomiting, abdominal pain, and diarrhoea frequently occur. Vomiting and diarrhea may contribute to dehydration. The abdominal pain can be due to acalculous cholecystitis or inflammation of the pancreas.[18] Rarely, the lymph nodes, liver, and spleen may be enlarged and palpable.[8]
There will be a resolution of symptoms for one to three days.[7] The immune phase starts after this and can last from four to 30 days and can be anything from brain to kidney complications.[22] The hallmark of the second phase is inflammation of the membranes covering the brain.[7] Signs and symptoms of meningitis include severe headache and neck stiffness.[7] Kidney involvement is associated with reduced or absent urine output.[7]
The classic form of severe leptospirosis, known as Weil's disease, is characterised by liver damage (causing jaundice), kidney failure, and bleeding, which happens in 5–10% of those infected.[7] Lung and brain damage can also occur. For those with signs of inflammation of membranes covering the brain and the brain itself, altered level of consciousness can happen. A variety of neurological problems such as paralysis of half of the body, complete inflammation of a whole horizontal section of spinal cord, and muscle weakness due to immune damage of the nerves supplying the muscles are the complications. Signs of bleeding such as non-traumatic bruises at 1 mm (0.039 in), non-traumatic bruises more than 1 cm (0.39 in), nose bleeding, blackish stools due to bleeding in the stomach, vomiting blood and bleeding from the lungs can also be found. Prolongation of prothrombin time in coagulation testing is associated with severe bleeding manifestation. However, low platelet count is not associated with severe bleeding.[18] Pulmonary haemorrhage is alveolar haemorrhage (bleeding into the alveoli of the lungs) leading to massive coughing up of blood, and causing acute respiratory distress syndrome, where the risk of death is more than 50%.[18] Rarely, inflammation of the heart muscles, inflammation of membranes covering the heart, abnormalities in the heart's natural pacemaker and abnormal heart rhythms may occur.[8]
Cause
Bacteria
A scanning electron micrograph of several lepitospira bacteria on a filter
Scanning electron micrograph of a number of Leptospira sp. bacteria atop a 0.1 µm polycarbonate filter
Leptospirosis is caused by spirochaete bacteria that belong to the genus Leptospira, which are aerobic,[8] right-handed helical,[12] and 6 –20 micrometers long.[7] 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.[23] In addition, Leptospira have a flagellum located in the periplasm, associated with corkscrew style movement.[7] Chemoreceptors at the poles of the bacteria sense various substrates and change the direction of its movement.[12] The bacteria are traditionally visualised using dark-field microscopy without staining.[7]
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.[24] The 19 members of the P1 subclade include the 8 species that can cause severe disease in humans: L. borgpetersenii, L. interrogans, L. kirschneri, L. mayottensis, L. noguchii, L. santarosai, and L. weilii.[12][24] 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).[24] 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 50 °C (122 °F) and can be inactivated by 70% ethanol, 1% sodium hypochlorite, formaldehyde, detergents and acids.[25]
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.[12] Over 250 pathogenic serovars of Leptospira are recognised, with closely related serovars gathered into over 26 pathogenic serogroups.[8] 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.[12]
Transmission
The bacteria can be found in ponds, rivers, puddles, sewers, agricultural fields and moist soil.[7] Pathogenic Leptospira have been found in the form of aquatic biofilms, which may aid survival in the environment.[26]
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.[18]
Leptospira are found mostly in mammals.[5] However, reptiles and cold-blooded animals such as frogs, snakes, turtles, and toads have been shown to have the infection.[15] Whether they are reservoirs of human infection is unknown.[18][15] 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.[15] In Africa, a number of wildlife hosts have been identified as carriers, including the banded mongoose, Egyptian fox, Rusa deer, and shrews.[27] 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.[citation needed] House-bound domestic dogs have contracted leptospirosis, apparently from licking the urine of infected mice in the house.[citation needed] Leptospirosis can also be transmitted via the semen of infected animals.[15] The duration of bacteria being consistently present in animal urine may persist for years.[15]
Humans are the accidental host of Leptospira.[5] Humans become infected through contact with water or moist soil that contains urine from infected animals.[7] The bacteria enter through cuts, abrasions,[7] ingestion of contaminated food, or contact with mucous membrane of the body (e.g. mouth, nose, and eyes).[28] Occupations at risk of contracting leptospirosis include farmers, fishermen, garbage collectors and sewage workers.[5] The disease is also related to adventure tourism and recreational activities.[5] 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.[5] However, Leptospira are unlikely to pe*****te intact skin.[8] The disease is not known to spread between humans, and bacterial dissemination in recovery period is extremely rare in humans.[8] Once humans are infected, bacterial shedding from the kidneys usually persists for up to 60 days.[25]
Rarely, leptospirosis can be transmitted through an organ transplant.[29] Infection through the placenta during pregnancy is also possible.[30][31][32] It can cause miscarriage and infection in infants.[33]
