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Leptospirosis is
caused by the spirochete Leptospira interrogans.
The leptospires are 0.1 micrometer wide and 6 to 12
micrometer long , with 18 or more coils.
Of over 170 varieties, serovar
canicola is associated with dogs, serovar icterohemorrhagica with
rodents and serovar pomona with swine and cattle. Serovar
icterohemorrhagica grows in the lumen of renal tubules in the rat and
is shed in the urine for the life of the animal.
The leptospires
penetrate abraded skin or mucous membranes following contact with
infected rats, contaminated water, or mud.
Since worm, moist environments favour
survival of the spirochetes, the incidence is greater in the tropics.
Congenital infection causes fetal
death.
Symptoms begin 4 to 19 days after inoculation. Ninety percent of infections have a mild, anicteric course
with resolution of symptoms in about 1 week.
However, those with
severe infections have a sudden onset of fever, myalgia , headache , and
nausea and vomiting in the leptospiremic stage.
The symptoms abate
after 4 to 9 days and leptospires cease to circulate.
The second, or immune stage known as
Weil’s disease follows after a latent period of 1 to 3 days in 10% of
patients.
Fever, headache (which signals the onsetof meningismus), and the appearance of circulating IgM antibodies
are characteristic.
Severe myalgia, nausea, vomiting,
abdominal pains, conjunctivitis, and hemorrhage into the conjunctiva
are also features.
Eventually hepatic failure, renal
failure, and shock may lead to death.
At autopsy there is a bile
staining of tissues, hemorrhages in many organs, and pulmonary edema.
Microscopically, the liver shows dissociation of the liver cell
plates, erytrophagocytosis of the Kupffer cells, necrosis of
hepatocytes, neutrophils in sinusoids, and a mixed inflammatory cell
infiltrate in portal tracts.
In the kidney the tubular epithelium is
swollen and necrotic. Spirochetes are numerous in the lumen of the
tubules and particularly in bile-stained casts.
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In the first phase, culture of
blood and cerebrospinal fluid is the most effective means of
confirming the diagnosis.
PCR is a rapid,
sensitive and specific means of diagnosing leptospiral infection,
especially during the first few days of the disease.
Leptospires grow from urine after the second
week. Serologic tests are useful during the second phase.
Antibiotics
must be started within 4 days of onset. Large doses of penicillin and
tetracycline are useful.
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