IN HUMANS
Notified leptospirosis cases to National Notifiable Disease Surveillance System: (a) cases per year; (b) mean cases per month (2010-2020) – accessed 25 Jan 2021
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PREVALENCE AND RISK FACTORS • Occupational exposure or recreational activities that involve contact with contaminated water or soil is the
• Leptospirosis is a biphasic disease, with an initial infectious phase followed by an immune-mediated phase. Activation of host innate immunity and cytokine storm contribute to severe disease. Severe leptospirosis is characterised by dysfunction of multiple target organs and it is estimated that approximately 5 to 10% of human patients will develop severe signs of hepatic and renal disease (classically called Weil’s disease), and up to 15% of these patients die as a result. 15 • Some patients present with pulmonary involvement, a more common presentation of severe leptospirosis combined with Weil’s disease. Pulmonary infection can progress from mild illness, to bilateral lung infiltrates, to an acute respiratory distress syndrome. Pulmonary haemorrhage can occur in some patients, also known as severe pulmonary haemorrhage syndrome (SPHS), with reported mortality rates from 50 to 70%. 16 • Severity of disease is related to the infecting serovar (e.g. more severe with those of the Icterohaemorrhagiae serogroup) and host factors (age, immunocompetence etc.). • Other than conjunctival suffusion that is frequently seen during the initial leptospiraemic phase, ocular inflammation, particularly in the form of uveitis, is well-described during the recovery phase of illness. • Infection during pregnancy may result in abortion. Leptospires can be shed in breast milk.
most common source of human infection. 13 • The risk of zoonotic infection is highest for people that work outdoors (banana plantation workers, sugar cane harvesters, sewage workers) or with animals (farmers, abattoir workers and veterinary staff). 14,15 Leptospirosis can also be a recreational hazard for campers, bushwalkers and those involved in a range of water sports. 14,15 • Leptospirosis in humans is a nationally notifiable disease in Australia. Most cases are reported in young and middle-aged males. Increased incidence is associated with flooding events. Most cases occur in northern Australia. 14 CLINICAL DISEASE • Incubation period in humans is typically 5-14 days, but can be variable, with a range of 2-30 days reported. 14 In many cases, infection is subclinical or results in a non-specific flu-like illness (fever, headaches, muscle pain, nausea and vomiting). 15 Due to the mild and non-specific nature of infection, as is the case in dogs, human infections are also thought to be underdiagnosed. Aseptic meningitis may occur, more commonly in children and young adults. 15 • Generalised conjunctival erythema – called conjunctival suffusion – is a useful clinical sign in leptospirosis, occurring in up to 50% of cases of clinical leptospirosis while being rare in other “flu-like” illnesses.
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Companion Animal Zoonoses Guidelines 61
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