Leptospirosis: causes, symptoms, diagnosis, and treatment

Leptospirosis is an acute fever caused by various Leptospira.


Causes

The pathogen is Leptospira. Wild animals and domesticated animals, such as cats, dogs, pigs, cattle, and mice, are the natural hosts. Leptospira parasitic in rodents are mainly Leptospira icterohaemorrhagica, which can infect humans and cause Weil's disease, also known as icterohaemorrhagic fever, while pretibial fever, also known as Fort Bragg fever, sometimes characterized by symmetrical skin lesions on the anterior tibia and splenomegaly, is caused by Leptospira autumnalis. The parasites of cats and dogs are predominantly Leptospira canicola, and the parasites of pigs and cattle is mostly Leptospira pomona.

Leptospira are excreted through the urine of the animal hosts. Human mucous membranes or scratched skin in contact with the urine or water or soils contaminated by the urine, ingestion of the contaminated water, or swimming in the contaminated water can cause this disease.


Signs and Symptoms

The incubation period is 2 - 20 days, usually 7 - 13 days.

The first stage is the sepsis period, and is characterized by sudden onset, headache, severe myalgia, rigors, fever, cough, pharyngitis, and chest pain. Hemoptysis may occur in some patients. Conjunctival suffusion usually occurs on the 3rd or 4th day. Hepatosplenomegaly are uncommon. This stage can last for 4 - 9 days, with repeated rigors and fever, and the body temperature is often up to >39°C. Subsequently, the body temperature drops.

The second stage is an immunologic stage, occurs between the 6th and 12th days of the disease, and is related to the presence of serum antibodies. Fever and early symptoms reoccur, and meningitis may occur. Iridocyclitis, optic neuritis, and peripheral neuropathy may occur in few patients.

Skin lesions are present in less than 50% of patients. Solitary or fused, slightly raised, 2 - 5cm in diameter erythema may occur on the 4th day. Petechiae or purpura may be on the skin and mucous membranes in some patients. There are symmetrically distributed erythema on the anterior tibia, but also extensively elsewhere.

If the disease occurs in pregnancy, even in the recovery period, miscarriage may occur.

Weil’s disease is a severe manifestation of leptospirosis. Hemolytic jaundice is usually accompanied by azotemia, anemia, obnubilation, and persistent fever. The onset is similar to that of other mild leptospirosis. However, due to capillary damage, hemorrhage can occur, including epistaxis, petechiae, purpura, and ecchymosis. Subarachnoid, adrenal or gastrointestinal bleeding is less common. Thrombocytopenia can also occur. Liver dysfunction and kidney dysfunction occur on the 3rd to 6th day. Abnormal renal function is manifested by proteinuria, pyuria, hematuria, and azotemia. Hepatic lesions are mild and can completely recover.

The fatality rate of patients without jaundice is zero, while the fatality rate of patients with jaundice is 5% - 10%, and the fatality rate is higher in patients aged >60 years.


Diagnosis

If there are clinical presentations and pathogen cultured and isolated from the blood or cerebrospinal fluid, the disease can be diagnosed.


Treatment

In severe patients, the treatment regimen is penicillin G 5 - 6 million units intravenously q6h, or ampicillin 500 - 1000mg IV q6h.

In mild patients, the treatment regimen is doxycycline 100mg po q12h, ampicillin 500 - 750mg po q6h, or amoxicillin 500mg orally once every 6 hours, for 5 - 7 days.

Supportive therapy for critically ill patients includes supplementation of fluids and electrolytes.

In the epidemic area, doxycycline 200mg orally once a week can be used to prevent this disease.