A zoonotic infection is a type of infection transmitted from a vertebral animal to man. Among the soonotic infections that is transmitted to man is Leptospirosis.

Leptospirosis, also called canicola fever, is a worldwide zoonotic infection with greater incidence in tropical regions. The epidemiology of leptospirosis has been modified by changes in animal husbandry, climate, and human behavior. Early treatment with antibiotics is important in acute disease. The offending microorganism is a spirochete.

Leptospirosis is identified as one of the emerging infectious diseases, exemplified by the recent outbreaks in Nicaragua, Brazil, India, Southeast Asia, the United States, and most recently in Sabah, Malaysia. Interest surged up from large clusters of cases which have occurred in Central and South America following flooding.

This type of infection with zoonosis ranges fom subclinical infection to a severe syndrome of multi-organ infections with high mortality. This syndrome, icteric leptospirosis with renal failure, was first reported over 100 years ago by Adolf Weil. Thus, it is also called Weil’s disease. It has been suggested that Leptospira interrogans serovar icterohaemorrhagiae was introduced to Western Europe in the 18th century by the westward extension of the range of Rattus norvegicus from Eurasia.

The etiology of Leptospirosis was demonstrated in 1915 in Japan and Germany. Spirochetes were found and specific antibodies in the blood of Japanese miners with infectious jaundice. In Germany, soldiers affected with French disease, were found to be afflicted with Leptospirosis, L.interrogans. The spirochetes had hooked ends, and the role of the rat as a source of human infection was discovered in 1917, while the potential for leptospiral disease in dogs was recognized.

In 1989, the genus Leptospira was divided into two species: L. interrogans, comprising all pathogenic strains; and the L. biflexa, containing the saprophytic strains isolated from the environment.

Microscopic examination show leptospires as tightly coiled spirochetes, usually 0.1 um by 6 to 0.1 by 20 um, but occasional cultures may contain much longer cells. The helical amplitude is approximately 0.1 to 0.15 um, and the wavelength is approximately 0.5 um. The cells have pointed ends, either or both of which are usually bent into a distinctive hook. Two axial filaments with polar insertions are located in the periplasmic space.

Leptospires exhibit two distinct forms of movement, translational and nontranslational. Letospires have a double membrane structure common to spirochetes.Leptospires are obligate aerobes with an optimum growth temperature of 28 to 30 degrees centigrade. They produce both catalase and oxidase.

Leptospires are phylogenetically related to other spirochetes. Presumed to be the most widespread zoonosis in the world and the source of infection in humans is usually either direct or indirect contact with the urine of an infected animal. The incidence is relatively higher in warm-climate countries than in temperate regions. This is due mainly to the longer survival of leptospires in the environment in warm, humid conditions.

The disease is seasonal, with peak incidence occurring in summer or fall in temperate regions, where temperature is the limiting factor in survival of leptospires, and during rainy seasons in warm-climate regions.The usual portal of entry is through abrasions or cuts in the skin or via the conjuntiva.

Infection may take place via intact skin after prolonged immersion in water, but this usually occurs when abrasions are likely to occur and is thus difficult to substantiate. Water-borne transmission has been documented and contamination of water supplies has resulted in several outbreaks of leptospirosis. Inhalation of aerosols or water also may result in infection of the mucous membranes of the repiratory tract. Rarely, infection may follow animal bites. Direct transmission between humans has been demonstrated rarely. However, excretion of leptospires in human urine months after recovery has been recorded. Transmission by sexual intercourse during convalescence has also been reported.

Animals including humans can be divided into maintenance hosts and accidental hosts. A maintenance host is defined as a species in which infection is endemic and is usually transferred from animal to animalbhy direct contact. Other animals including humans may become infected by indirect contact with the maintenance host, which may cause severe or fatal disease.

The clinical presentation of leptosirosis is biphasic, with acute or septicemic phase lsting ablut a week, followed by the immune phase, characterized by antibody production and excretion of leptospires in the urine. Most of the complications lof leptospirosis are associated with localization of leptospires within the tissues during the immune phase and thus occur during the second week of the illness.

Anicteric Leptospirosis

The great majority of infections caused by leptospires are either subclinical or of very mild severity, and patients will probably not seek medical attention. A smaller proportion of infections, but the overwhelming majority of the recognized cases, present with a febrile illness of sudden onset. Other symptoms include chills, headache, myalgia, abdominal pain, conjunctival suffusion, and less often a skin rash. If present, the rash is often transient, lasting less than 24 h.

This anicteric syndrome usually lasts for about a week, and its resolution coincides with the appearance of antibodies. The fever may be biphasic and may recur after a remission of 3 to 4 days. The headache is often severe, resembling that occurring in dengue, with retro-orbital pain and photophobia. Myalgia affecting the lower back, thighs, and calves is often intense.

Aseptic meningitis may be found in 25% of all leptospirosis cases and may account for a significant minority of all causes of aseptic meningitis. Mortality is almost nil in anicteric leptospirosis, but death resulting from massive pulmonary hemorrhage occurred in 2.4% of the anicteric patients in a Chinese outbreak.

The differential diagnosis must include common viral infections, such as influenza, human immunodeficiency virus seroconversion, and, in the tropics, dengue, in addition to the bacterial causes of fever of unknown origin, such as typhoid.

Icteric Leptospirosis

This is a much more severe disease in which the clinical course is often very rapidly progressive. Severe cases often present late in the course of the disease, and this contributes to the high mortality rate, which ranges between 5 and 15%. Between 5 and 10% of all patients with leptospirosis have the icteric form of the disease.

The jaundice occurring in leptospirosis is not associated with hepatocellular necrosis, and liver function returns to normal after recovery. Serum bilirubin levels may be high, and many weeks may be required for normalization. There are moderate rises in transaminase levels, and minor elevation of the alkaline phosphatase level usually occurs.

The complications of severe leptospirosis emphasize the multisystemic nature of the disease. Leptospirosis is a common cause of acute renal failure, which occurs in 16 to 40% of cases. A distinction may be made between patients with prerenal azotemia, and those with acute renal failure. Patients with prerenal azotaemia may respond to rehydration, and decisions regarding dialysis can be delayed for up to 72 h. In patients with acute renal failure, oliguria was a significant predictor of death.

Serum amylase levels are often raised significantly in association with acute renal failure but clinical symptoms of pancreatitis are not a common finding. Necrotizing pancreatitis has been detected at autopsy.

Thrombocytopenia, platelet count of <100 × 109/liter occurs in 50% of cases and is a significant predictor for the development of acute renal filure. However, thrombocytopenia in leptospirosis is transient and does not result from disseminated intravascular coagulation.

Patients may present with a spectrum of symptoms, ranging from cough, dyspnea, and hemoptysis (which may be mild or severe) to adult respiratory distress syndrome. Intra-alveolar hemorrhage was detected in the majority of patients, even in the absence of overt pulmonary symptoms. Pulmonary hemorrhage may be severe enough to cause death.

Cardiac involvement in leptospirosis is common but may be underestimated. Fatal myocarditis was first described in 1935. Clinical evidence of myocardial involvement, including abnormal T waves, was detected in 10% of 80 severe icteric cases in Louisiana , while similar electrocardiographic abnormalities were detected in over 40% of patients in China, India, Sri Lanka, and the Philippines, including both icteric and nonicteric cases.

Treatment of leptospirosis differs depending on the severity and duration of symptoms at the time of presentation. Patients with mild, flu-like symptoms require only symptomatic treatment but should be cautioned to seek further medical help if they develop jaundice. Patients who present with more severe anicteric leptospirosis will require hospital admission and close observation. If the headache is particularly severe, a lumbar puncture usually produces a dramatic improvement.

The management of icteric leptospirosis requires admission of the patient to the intensive care unit initially. Patients with prerenal azotemia can be rehydrated initially while their renal function is observed, but patients in acute renal failure require dialysis as a matter of urgency. This is accomplished satisfactorily by peritoneal dialysis. Cardiac monitoring is also desirable during the first few days after admission.

Oxytetracycline was also used. Doxycycline 100 mg twice a day for 7 days was shown to reduce the duration and severity of illness in anicteric leptospirosis by an average of 2 days.