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Leptospirosis is caused by the Leptospira bacterial genus. These coiled, gram-negative aerobic bacteria are motile with hooked ends and paired flagella, which allows them to burrow into tissues. Both humans and animals can be infected by these bacteria. Leptospirosis is one of the most common infectious diseases that can be transmitted naturally to humans from animals.
Sources of infection are the urine or urine-contaminated media (e.g., water, food, and soil) of infected animals such as rats, cattle, cats, dogs, and wild animals. Approximately 90% of those affected present with mild flu-like symptoms, while a small percentage may experience life-threatening conditions. This severe presentation of leptospirosis is known as Weil’s disease.
The disease has a biphasic clinical presentation. There is first an acute or septicemic phase that is followed by a secondary stage or immune phase. The acute phase lasts for about a week, whereas the immune phase is characterized by the production of antibodies and the shedding of leptospires in the urine. The complications that arise because of the disease are largely in part to the localization of the pathogen within tissues throughout the body. This occurs during the immune phase of the illness.
After an incubation period that ranges anywhere between 2 and 30 days, typically 5 and 14 days, the onset of clinical illness is abrupt. A patient with acute disease may present with varying degrees of headache, high fever, muscle pain, rigors, anorexia, nausea, vomiting, diarrhea, pharyngitis, dry cough, and non-pruritic rash. These are generally considered to present as a mild flu-like illness that is in many cases self-limited and is also known as anicteric leptospirosis.
In the immune phase of anicteric leptospirosis, aseptic meningitis may be seen and may account for a significant minority of all aseptic meningitis causes. Those who develop aseptic meningitis tend to be younger in comparison to those who develop the more severe presentation of leptospirosis. Important differential diagnoses include influenza, HIV, and tropical mosquito-borne diseases such as dengue. Other conditions that leptospirosis can mimic include infectious mononucleosis, malaria, encephalitis, glandular fever, pneumonitis, and viral hepatitis.
The acute phase of the disease tends to lasts between 5 and 7 days. This phase is then followed by a short 1 to 3-day period, which shows clinical improvement. The fever drops and may even go away. Moreover, the patient may become relatively asymptomatic. The period may lead to a regression of the disease to an asymptomatic illness or progression to Weil’s disease, also known as icteric leptospirosis, which is characterized by internal hemorrhaging and multiple organ dysfunction and/or failure.
Weil’s disease often has a severe and very rapidly progressive clinical course. It is estimated that up to 15% of patients with leptospirosis may develop the icteric manifestation of the disease. The jaundice that occurs with the icteric presentation is not due to liver cell death and liver function returns to normal with disease regression. Weil’s disease may lead to acute renal failure (ARF) with significantly elevated serum amylase levels and hematuria (blood in urine). Thrombocytopenia is a significant predictor of ARF development, while pre-renal azotemia is a significant predictor of death.
The incidence of lung involvement with Weil’s disease varies, but symptoms include mild to severe hemoptysis (coughing up blood) and adult respiratory distress syndrome, which may lead to death. Alveolar infiltrates seen on radiographic imaging and dyspnea are relatively poor prognostic factors. In addition to the lungs, cardiac involvement is common, but may very well be underestimated. Cardiac abnormalities are seen with abnormal T waves on ECG due to myocarditis and are poor prognostic factors.
Icterus of the sclera together with conjunctival suffusion is pathognomonic of Weil’s disease. Following recovery from the acute illness, a minority of patients may experience anterior uveitis. Furthermore, there have been reports of chronic visual disturbances 2 decades or more post acute illness. Other complications of leptospirosis include abortion in pregnancy and rare ones such as aortic stenosis, epididymitis, reactive arthritis, Kawasaki syndrome, and Guillain-Barre syndrome.