Affects: Dogs
Leptospirosis is a blood infection caused by bacteria of the genus Leptospira that can infect humans, dogs, rodents, and many other wild and domesticated animals. Signs and symptoms can range from none to mild (headaches, muscle pains, and fevers) to severe (bleeding in the lungs or meningitis). Weil's disease ( VILES), the acute, severe form of leptospirosis, causes the infected individual to become jaundiced (skin and eyes become yellow), develop kidney failure, and bleed. Bleeding from the lungs associated with leptospirosis is known as severe pulmonary haemorrhage syndrome.
More than 10 genetic types of Leptospira cause disease in humans. Both wild and domestic animals can spread the disease, most commonly rodents. The bacteria are spread to humans through animal urine or feces, or water or soil contaminated with animal urine and feces, coming into contact with the eyes, mouth, or nose, or breaks in the skin. In developing countries, the disease occurs most commonly in pest control, farmers, and low-income people who live in areas with poor sanitation. In developed countries, it occurs during heavy downpours and is a risk to pest controllers, sewage workers, and those involved in outdoor activities in warm and wet areas. Diagnosis is typically by testing for antibodies against the bacteria or finding bacterial DNA in the blood.
Efforts to prevent the disease include protective equipment to block contact when working with potentially infected animals, washing after contact, and reducing rodents in areas where people live and work. The antibiotic doxycycline is effective in preventing leptospirosis infection. Human vaccines are of limited usefulness; vaccines for other animals are more widely available. Treatment when infected is with antibiotics such as doxycycline, penicillin, or ceftriaxone. The overall risk of death is 5–10%, but when the lungs are involved, the risk of death increases to the range of 50–70%.
Signs And Symptoms: The symptoms of leptospirosis usually appear one to two weeks after infection, but the incubation period can be as long as a month. 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. Additional symptoms develop in the second phase. The phases of illness may not be distinct, especially in patients with severe illness. About 90% of those infected experience mild symptoms, while 10% experience severe leptospirosis.
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. 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 diarrhoea may contribute to dehydration. The abdominal pain can be due to acalculous cholecystitis or inflammation of the pancreas. Rarely, the lymph nodes, liver, and spleen may be enlarged and palpable.
Resolution of symptoms occurs for one to three days. The immune phase starts after this and can last from four to 30 days, and can vary from brain to kidney complications. The hallmark of the second phase is inflammation of the membranes covering the brain. Signs and symptoms of meningitis include severe headache and neck stiffness. Kidney involvement is associated with reduced or absent urine output.
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. 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 Guillain-Barré syndrome are the complications. Signs of bleeding such as petechiae, ecchymoses, 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 manifestations. However, low platelet count is not associated with severe bleeding. 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%. 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.
Transmission: The survival of Leptospira bacteria is influenced by environmental factors, with transmission dynamics affected by climate change, extreme weather events, urbanisation, and interactions between human and animal populations. The bacteria thrive in warm and humid climates due to their preference for environments that maintain high moisture content and optimal temperatures for metabolic activity and motility. 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.
The number of cases of leptospirosis is directly related to the amount of rainfall, making the disease seasonal in temperate climates and year-round in tropical climates. The risk of contracting leptospirosis depends upon the risk of disease carriage in the community and the frequency of exposure. In rural areas, farming and animal husbandry are the major risk factors for contracting leptospirosis. Poor housing and inadequate sanitation also increase the risk of infection. In tropical and subtropical areas, the disease often becomes widespread after heavy rains or after flooding.
Leptospira bacteria are found mostly in mammals, but cold-blooded animals such as frogs, snakes, turtles, and toads have been shown to have the infection. Whether reservoirs of human infection exist is unknown. Rats, mice, and moles are important primary hosts, but other mammals, including dogs, deer, rabbits, hedgehogs, cattle, 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. Various mechanisms are known 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 leptospirosis, apparently from licking the urine of infected mice in the house. Leptospirosis can also be transmitted by the semen of infected animals. Bacteria can be consistently present in animal urine and may persist for years.
Humans are the accidental host of Leptospira. Humans become infected through contact with water or moist soil that contains urine and feces 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 leptospirosis 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 species 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.
Diagnostic Criteria: In 1982, the World Health Organization (WHO) proposed the Faine's criteria for the diagnosis of leptospirosis. It consists of three parts: A (clinical findings), B (epidemiological factors), and C (lab findings and bacteriological data). Since the original Faine's criteria only included culture and MAT in part C, which is difficult and complex to perform, the modified Faine's criteria were proposed in 2004 to include ELISA and slide agglutination tests, which are easier to perform. In 2012, modified Faine's criteria (with amendment) were proposed to include shortness of breath and coughing up blood in the diagnosis. In 2013, India recommended modifying Faine's criteria in the diagnosis of leptospirosis.
Treatment: Most leptospiral cases resolve spontaneously. Early initiation of antibiotics may prevent the progression to severe disease. Therefore, in resource-limited settings, antibiotics can be started once leptospirosis is suspected after history taking and examination.
For mild leptospirosis, antibiotic recommendations such as doxycycline, azithromycin, ampicillin, and amoxicillin were based solely on in vitro testing. In 2001, the WHO recommended oral doxycycline ([dose — ask your vet] up to [dose — ask your vet] every 12 hours) for five to seven days for those with mild leptospirosis. Tetracycline, ampicillin, and amoxicillin can also be used in such cases. However, in areas where both rickettsia and leptospirosis are endemic, azithromycin and doxycycline are the drugs of choice. Doxycycline is not used in cases where the patient suffers from liver damage as it has been linked to hepatotoxicity.
Based on a 1988 study, intravenous (IV) benzylpenicillin (also known as penicillin G) is recommended for the treatment of severe leptospirosis. Intravenous benzylpenicillin ([dose — ask your vet] up to [dose — ask your vet] every six hours) is used for five to seven days. Amoxicillin, ampicillin, and erythromycin may also be used for severe cases. Ceftriaxone ([dose — ask your vet] IV every 24 hours for seven days) is also effective for severe leptospirosis. Cefotaxime ([dose — ask your vet] IV every six hours for seven days) and doxycycline ([dose — ask your vet] initially followed by [dose — ask your vet] IV every 12 hours for seven days) are equally effective as benzylpenicillin (1.5 million units IV every six hours for seven days). Therefore, there is no evidence on differences in death reduction when benzylpenicillin is compared with ceftriaxone or cefotaxime. Another study conducted in 2007 also showed no difference in efficacy between doxycycline ([dose — ask your vet] initially followed by [dose — ask your vet] orally every 12 hours for seven days) or azithromycin ([dose — ask your vet] on day one followed by [dose — ask your vet] daily for two more days) for suspected leptospirosis. There was no difference in the resolution of fever, and azithromycin is better tolerated than doxycycline.
Outpatients are given doxycycline or azithromycin. Doxycycline can shorten the duration of leptospirosis by two days, improve symptoms, and prevent the shedding of organisms in their urine. Azithromycin and amoxicillin are given to pregnant women and children. Rarely, a Jarisch–Herxheimer reaction can develop in the first few hours after antibiotic administration. However, according to a meta-analysis done in 2012, the benefit of antibiotics in the treatment of leptospirosis was unclear, although the use of antibiotics may reduce the duration of illness by two to four days. Another meta-analysis done in 2013 reached a similar conclusion.
Prevention: Rates of leptospirosis can be reduced by improving housing, infrastructure, and sanitation standards. Rodent abatement efforts and flood mitigation projects can also help to prevent it. Proper use of personal protective equipment (PPE) by people who have a high risk of occupational exposure can prevent leptospirosis infections in most cases.
There is no human vaccine suitable for worldwide use. Only a few countries, such as Cuba, Japan, France, and China, have approved inactivated vaccines with limited protective effects. Side effects such as nausea, injection site redness and swelling have been reported after the vaccine was injected. Since the immunity induced by one Leptospiraserovar is only protective against that specific one, trivalent vaccines have been developed. They do not confer long-lasting immunity to humans or animals. Vaccines for other animals are more widely available. Vaccination of livestock and domestic animals, particularly dogs and cattle, is an effective measure in preventing both animal illness and zoonotic transmission to humans.
Doxycycline is given once a week as a prophylaxis and is effective in reducing the rate of leptospirosis infections amongst high-risk individuals in flood-prone areas. In one study, it reduced the number of leptospirosis cases in military personnel undergoing exercises in the jungles. In another study, it reduced the number of symptomatic cases after exposure to leptospirosis under heavy rainfall in endemic areas.
Prognosis: The overall risk of death for leptospirosis is 5–10%. For those with jaundice, the case fatality can increase up to 15%. For those infected who present with confusion and neurological signs, there is a high risk of death. Other factors that increase the risk of death include reduced urine output, age more than 36 years, and respiratory failure. With proper care, most of those infected will recover completely. Those with acute kidney failure may develop persistent mild kidney impairment after they recover. In those with severe lung involvement, the risk of death is 50–70%. Thirty percent of people with acute leptospirosis complained of long-lasting symptoms characterised by weakness, muscle pain, and headaches.