Last month’s Part 1 of the leptospirosis review, which addressed
the etiology, geographic distribution, transmission, infection reservoir and
infection in humans, included some information on the recent leptospirosis
epidemic in flooded territories of the Philippines. As of Oct. 26, 2,158 cases
– including 167 deaths – were recorded. On Nov. 16, WHO reported that
the number of cases increased to 3,382 individuals, with an estimate of 249
deaths. To compare, during all of 2008, 769 cases were reported throughout the
The Filipino government and the humanitarian community had distributed
leptospirosis prophylaxis to nearly 338,000 individuals in the National Capital
Region as of Nov. 16. This has become the world’s second largest
leptospirosis epidemic on record, the largest being the 2008 Sri Lanka
post-flooding outbreak (4,500 cases, of which 1,150 reportedly were fatal).
The WHO-coordinated Global Outbreak Alert and Response Network (GOARN),
a pool of experts on permanent standby to identify, respond and assist with
disease outbreaks around the world, presented in mid-November the results from
its three-week technical assessment of the leptospirosis situation in the
Philippines. It reported that the GOARN lab continued the testing of
leptospirosis samples from infected patients in the Philippines to determine
the particular disease strain. According to the GOARN experts, the testing
requires significant time and effort due to the fragility of the samples and
the complicated nature of the disease.
Infections in animals
All mammals appear to be susceptible to at least one species of
Leptospira. Disease is rare in cats and less common in sheep than
Serovars associated with disease in cattle include L. hardjo,
L. pomona, L. grippotyphosa, L. canicola and L.
icterohaemorrhagiae. In sheep and goats, serovars associated with disease
include L. hardjo, L. pomona, L. grippotyphosa and L.
ballum. Serovars associated with disease in pigs include L. pomona,
L. grippotyphosa, L. bratislava, L. canicola, L.
icterohaemorrhagiae, L. tarassovi and L. muenchen. Serovars
associated with disease in horses include L. hardjo, L. pomona,
L. canicola, L. icterohaemorrhagiae and L. sejroe. In
dogs, the serovars associated with the disease include L. pomona, L.
grippotyphosa, L. canicola, L. icterohaemorrhagiae, L.
pyrogenes, L. paidjan, L. tarassovi, L. ballum and
The risk of infection is highest in hunting dogs, show dogs and dogs
with access to water such as ponds. The severity of disease is affected by the
dog’s age, previous leptospirosis vaccinations and the serovar, route of
exposure and dose of organisms.
The primary reservoir hosts for most Leptospira serovars are wild
mammals, particularly rodents. Reservoir hosts among domestic animals include
cattle, pigs, sheep and dogs.
The specific reservoir hosts vary with the serovar and the geographic
region. Disease in reservoir hosts is more likely to be asymptomatic, mild or
chronic. Reservoir hosts include:
- Rats serogroups: L. icterohaemorrhagiae and L.
- Mice serogroup: L. ballum;
- Cattle serovars: L. hardjo, L. grippotyphosa and L.
- Sheep serovars: L. hardjo and L. pomona;
- Pigs serovars: L. pomona, L. tarassovi and L.
- Dogs serovars: L. canicola and L. bataviae.
The incubation period is four to 12 days in dogs. Abortions usually
occur three to 10 weeks after infection in cattle and 15 to 30 days after
infection in pigs.
Leptospira infections may be asymptomatic, mild or severe and
acute or chronic. The clinical signs are often related to kidney disease, liver
disease or reproductive dysfunction. Chronically-infected animals are often
In cattle, acute leptospirosis occurs mainly in calves. The symptoms may
include fever, anorexia, conjunctivitis, diarrhea and, in severe cases,
jaundice, hemoglobinuria, anemia, pneumonia or signs of meningitis. Some calves
may die within three to five days. The clinical signs vary with the serovar.
Infections with serovar L. hardjo, for example, are not usually
associated with hemolytic anemia. In adult cattle, the most prominent signs of
infection are abortions, decreased fertility or decreased milk yield. Some
serovars also cause increased neonatal mortality; others can cause sudden
agalactia or decreased milk production; the milk may be thick, yellow and
blood-tinged but there is typically little evidence of mammary inflammation.
In swine, clinical leptospirosis is most often characterized by
reproductive signs, including late-term abortions, infertility, stillbirths,
mummified or macerated fetuses and increased neonatal mortality. Subclinical
infections are common. In piglets, there may be fever, anorexia, depression,
diarrhea, jaundice, hemoglobinuria and gastrointestinal disorders, as well as
signs of meningitis.
In horses, many infections are subclinical. Ocular disease is the most
common syndrome. During the acute phase, ocular signs may include fever,
photophobia, conjunctivitis, miosis and iritis. Periodic ophthalmia may be
sequelae of acute infections. In the chronic phase, there may be anterior and
posterior adhesions of the eye, a turbid vitreous body, cataracts, uveitis and
other ocular abnormalities.
Canine leptospirosis is clinically highly variable. Some infections are
asymptomatic or mild, while others are severe or fatal. The initial signs are
usually nonspecific and may include fever, depression, anorexia, stiffness,
myalgia, shivering and weakness. The mucus membranes are often injected. These
symptoms may be followed by signs of kidney disease, including anuria,
hematuria, polyuria, vomiting, dehydration and oral ulceration. Hemorrhagic
syndromes occur in some dogs; some die peracutely without clinical signs.
Chronic kidney disease can be a sequela.
In dogs, the serovar L. icterohaemorrhagiae usually causes fever,
hemorrhage, anemia and jaundice. L. grippotyphosa tends to cause severe
acute kidney failure and/or chronic active hepatitis. Dogs infected with
serovar L. pomona are often asymptomatic and chronic carriers; serovar
L. canicola often causes chronic interstitial nephritis.
Leptospira spp. are shed in the urine of acutely infected
animals. Chronic carriers may excrete them for months or years. In addition,
organisms can be found in aborted or stillborn fetuses, as well as in normal
fetuses or vaginal discharges after calving. Rarely, leptospira is
transmitted through rodent bites.
Leptospirosis can be diagnosed by culture, detection of antigens or
nucleic acids, or serology. The location of the organisms varies with the form
of the disease. In acute infections, Leptospira may be found in the
blood, milk, and cerebrospinal, thoracic or peritoneal fluids. During chronic
infections, they are sometimes found in the urine. The liver, lung, brain and
kidney are collected at necropsy from acute cases, and the kidney and genital
tract are tested in chronic cases. Organisms can also be found in the body
fluids or tissues of aborted fetuses.
Leptospira species can be cultured on a variety of media but are
fastidious and grow slowly on primary isolation. Special transport media may be
required for shipment to the laboratory. Depending on the serovar, culture may
take up to 13 to 26 weeks. Identification to the species, serogroup and serovar
level is done by reference laboratories, using genetic and immunologic
techniques. Leptospira can also be identified in clinical samples by
immunofluorescence and immunhistochemical staining, as well as DNA probes and
polymerase chain reaction techniques. Silver staining is sometimes useful as an
adjunct technique. Antigen- detection techniques include enzyme-linked
Serology is also used for diagnosis. Paired acute and convalescent
samples are preferred from most animals, but a single positive sample from an
aborted fetus is diagnostic.
Herd tests are often used in ruminants. The most commonly used
serological tests are the microscopic agglutination test and ELISAs.
Serovar-specific ELISAs are available in veterinary medicine, and
cross-reactions are less common in animals than in humans.
A milk ELISA can detect antibodies in samples from individual cows or in
bulk milk. Titers may become undetectable in chronically-infected dogs that are
still shedding organisms.
Leptospirosis vaccines are available for pigs, cattle and dogs. Although
the vaccines prevent disease, they do not completely prevent infection or the
shedding of the organisms.
Immunity is largely serovar specific: vaccines are protective only
against the included serovars or closely related serovars. Prophylactic
treatment of exposed animals with antibiotics can also prevent disease.
Sanitation and preventing contact with contaminated environments or
infected wildlife, particularly rodents, can decrease infection. Animals should
not be allowed to drink from or enter contaminated water. Good sanitation can
reduce the risk of infection in kennels and in areas where livestock are bred
or give birth.
In cattle, control measures include vaccination, isolation and treatment
of infected animals, rodent control, prevention of contact with wildlife, sheep
and pigs, and prevention of access to contaminated bodies of water.
Preventive treatment of animals with streptomycine before their export
or to their introduction into other herds has been practiced by many countries
as a standard requirement.
To read Part 1 of this column, click here.
Arnon Shimshony, DVM, is Associate Professor at the Koret School of
Veterinary Medicine Hebrew University of Jerusalem, Rehovot, and is the
ProMED-mail Animal Diseases Zoonoses Moderator. Dr. Shimshony was Chief
Veterinary Officer, State of Israel, from 1974 to 1999.