Epidemiology
• Leptospirosis- most widespread of zoonoses
• Present in all continents, except Antartica
• Pathogenic leptospires survive for long periods in (the convoluted tubules of) the kidneys in natural hosts, multiply and are shed in urine
• Animal carriers excrete upto 100 million leptospires per ml of urine
• Infected urine contaminates mud/water that is neutral or slightly alkaline-leptospires survive for weeks
• People come into contact with such water-leptospires enter the body through abraded skin or mucosa and initiate infection
• Certain occupational groups-agricultural workers in rice/cane fields, miners, sewage cleaners exposed to infection-more common in them
• Leptospires can be shed through milk of lactating animals-die rapidly in milk
• Human infection through milk unknown
• Not shed in saliva-animal bites not infectious; Arthropods do not transmit the infection
• Animals as carriers- rats-ubiquitous, carry the most pathogenic serotype icterohemorrhagiae
• Field mice carry grippotyphosa, pigs carry pomona, dogs carry canicola serotypes
• Generally nonpathogenic in the reservoir animal
• Of veterinary importance since infection in cattle/pigs cause economic loss
• Infection among animals- transmitted by contaminated water/fodder
• Human beings are an aberrant/end host- no transmission to other humans
• Was a rural disease of agricultural workers- Now, an urban problem in developing countries- overcrowding, insanitation, increasing rat population and habit of walking barefoot
Laboratory diagnosis
Leptospires
are seen in the blood during the acute phase of the disease but can seldom be
demonstrated after 8-10 days. They persist in the internal organs, and most
abundantly in the kidneys, so may be demonstrated in the urine in the later
stages of the disease.
v Microscopic
Demonstration in blood/urine
v Isolation
in culture
v Inoculation
in Guinea pigs
v Serological
tests
Examination
of Blood
• Helpful
in early stages of the disease (before antibiotics are given)
• Leptospires
disappear from blood after the first week
1)
Examination of blood under dark field microscope/by immunofluorescence;
but of little practical value
2)Three
or four drops of blood are inoculated
into EMJK or similar medium-
incubated at 370C for two days and left at room temperature in the
dark for two weeks
• Samples
from the cultures are examined every third day for the presence of
Leptospires under dark ground
illumination
• Primary
isolation may be delayed and may take many weeks to months
• Chances
of isolation are increased by culturing blood daily at the early stage
of the disease
• Leptospires
may be isolated from CSF also
3)
The blood from the patient is inoculated intraperitoneally into young guinea pigs
With
virulent serotypes- icterohemorrhagiae, the animals develop fever, die
within 8-12 days with jaundice and hemorrhage into the lungs and serous
cavities
With
other serotypes- canicola or pomona, animal may not become
ill-Leptospires should be demonstrated in the peritoneal fluid, by blood
culture or by serology
From
the third day after inoculation, the peritoneal fluid is examined daily
under dark ground illumination
When
Leptospires are detected the blood withdrawn by cardiac puncture is
inoculated into culture media
Urine
Examination
- Leptospires
appear in the urine in the second week of the disease and intermittently
thereafter for 4-6 weeks
- Urine
should be examined immediately - Leptospires readily undergo lysis in
acid urine
1)
Centrifuged deposit of urine is examined
under dark field microscope
2)
Direct culture of urine seldom successful
due to contamination but isolation is possible by inoculation into guinea
pigs
Serological tests
- Antibodies
appear in serum towards the end of the first week of the disease, increase
till the fourth week, then reduces.
- Antibodies/Agglutinins
are demonstrable years after the infection
- Serological
tests can be- broadly reactive
genus specific screening tests and the serotype specific tests
v Genus
specific/ Broadly reactive tests -identify Leptospiral infection
without identifying the exact serotype
• The
antigens for these tests are prepared from the nonpathogenic L. biflexa
Patoc 1 strain
• Sensitized
erythrocyte lysis (SEL), complement fixation, agglutination and indirect immune
florescence, ELISA
• ELISA to
detect IgM and IgG separately, to determine the stage of infection can be done
• Simple
and rapid dip stick assays for detecting Leptospira specific IgM
antibody in human sera available
v Serotype
specific tests
• Identify
the infecting serotype by macroscopic and microscopic agglutination tests
• Macroscopic
agglutination tests done with inactive formalinized
suspensions of Leptospiral serotypes with serial dilutions of the test serum
• Microscopic
agglutination tests (MAT) use live cultures of different
serotypes and agglutination is observed under the low power dark field
microscope- more specific- done in reference laboratories
Prophylaxis
• Leptospirosis
results from contact of skin or mucosa with contaminated water
Ø Rodent
control
Ø Disinfection
of water
Ø Wearing
of protective clothing
• Vaccination
of high risk groups such as agricultural workers encouraged. Immunity is serotype specific
Ø Vaccination
of dogs, cattles, pigs
Therapy
• Sensitive
to penicillin and tetracyclines
• Treatment
should be started early in the course of the disease
• Penicillin
given as IV : 1-2 million units 6 hourly for 7 days, for serious cases
• A mild Jarish Herxheimar reaction seen
in some
• Doxycycline
200 mg orally given once in a week effective for prophylaxis
• Jarish
Herxheimar reaction - common detoxification response of the
body to the increased toxins released during a treatment for pathogens
• the
amount of toxins released into the circulation is more than what our body can
safely handle quickly
• lot
of stress on internal organs, especially the colon, liver and kidneys that are
involved in filtering toxins in the body
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