334
Leptospiral Infections
Some of these methods are impracticable as
routine measures and they adopted as a sero-
logical test the microscopic agglutination test,
using living suspensions of leptospira as antigens.
Because animals once affected may possess signi-
ficant serological titres years after the symptoms
have subsided they considered an animal to be
infective only if it showed: (a) typical or atypical
symptoms with a rising titre or (b) typical or
atypical symptoms with a positive culture.
Some of the positive cases dealt with by these
authors were also examined for a change in their
blood picture and all showed a neutrophile
leucocytosis. There was no difference between
the symptoms and lesions of the icteric cases due
to Lept. canicola and the active cases of Lept.
icterohaemorrhagiae infection. They see no basis
for the idea that there is a different symptom-
atology for the two infections.
Epidemiologically there is, however, a wide
difference for with Lept. icterohaemorrhagiae
the reservoir of infection is the rat, whereas not
only has Lept. canicola not been found in rats,
but it has so far been found impossible to make
the rat a carrier [Walch-Sorgdrager, 1939].
In Lept. canicola
infection there is a
host to host infection aided by uncleanliness
and contact with the urine of clinical, convalescent
and chronic cases.
There is little doubt that Lept. canicola is com-
moner than Lept. icterohaemorrhagiae in dogs
though the difference varies throughout the world.
In Holland [Klarenbeek, 1938] there is a record of
94 cases of Lept. canicola and 57 of Lept. ictero-
haemorrhagiae infection. Of the former 8 per
cent were in dogs under one year of age, 3 per
cent were jaundiced and 41 per cent were fatal.
In the latter 20 per cent were under one year,
82 per cent were jaundiced and 51 per cent were
fatal. In U.S.A. Meyer et al. investigated 88
cases of canine leptospirosis and all of the dog
strains of leptospirae which were examined were
Lept. canicola. Of the 88 cases studied 41
presented jaundice in varying degrees. Coffin
and Stubbs [1942] diagnosed 15 cases in Philadel-
phia, 13 of which were caused by Lept. canicola
and two by Lept
icterohaemorrhagiae. Gray
[1942] has recovered Lept. icterohaemorrhagiae
from four cases in Australia, where the isolation
of Lept. canicola has not been recorded. Sero-
logical tests of samples of dog sera present a
similar distribution. Meyer et al. found 16 of 47
dogs from San Francisco, four of 28 dogs from
Santa Rosa and 13 of 111 dogs from New York
City to possess antibodies for leptospirae. Van
der Walle [1939] examined 100 dogs in Antwerp
and was able to demonstrate leptospira infection
in 44. The percentage infected apparently in-
creased with age and Lept. canicola was found in
a proportion of about two to one of Lept. ictero-
haemorrhagia. Raven [1941] tested 105 sera
from dogs in rural communities of Pennsylvania
and 50 from dogs in Philadelphia by the agglu-
tination lysis reaction. Of these 38 per cent of
the former and 28 per cent of the latter were
positive either against Lept. canicola or Lept.
icterohaemorrhagiae. A greater number were
positive and had higher titres for the former than
the latter. Greene [1941] demonstrated anti-
bodies against Lept. canicola in the sera of from
19.4 to 46.7 per cent of dogs in Southern Cali-
fornia and none in 100 sera from cats; one sample
of cat serum agglutinated Lept. icterohaemor-
rhagiae to a titre of 1 : 90. Coffin and Stubbs
showed that 20 of 105 city and suburban dogs
brought to the veterinary hospital of the Univer-
sity of Pennsylvania reacted and only one of 59
hounds. In 86 per cent of the positive cases the
reaction was stronger with Lept. canicola.
The incidence of latent infection of the rat with
Lept. icterohaemorrhagiae is well documented
and evidence has been adduced by direct observa-
tion of leptospirae, animal inoculation and sero-
logical tests. Buchanan [1927] examined 166
wild rats in Scotland and 61 were shown to be
infected; other observers have recorded similar
findings in other countries. Schüffner [1941]
examined tame rats and finding about 40 per
cent infected, has emphasised the danger to which
workers who handle rats are exposed. The
presence of wounds on the hands is important
and human volunteers were immunised with killed
cultures of leptospirae.
The interest in canine leptospirosis throughout
the world is largely due to the fact that Lept.
canicola as well as Lept. icterohaemorrhagiae may
infect man. The latter type is well known as
a human pathogen and although commonly spread
through the agency of rats and mice there are on
record four human cases of true leptospiral jaun-
dice due to Lept. icterohaemorrhagiae transmit-
ted directly by dogs [Petersen and Jacobsen,
1937]. So far 22 human infections with Lept.
canicola have been recorded [Raven, 1941], 12
in Holland, one in Austria, six in Denmark, two
in California and one in Copenhagen. Of the
12 reported from Holland none died and four
showed meningitic symptoms.
Severe symp-
toms were not always recorded and jaundice
hardly ever, although there was evidence of bile
pigments in the blood serum. The serious renal
symptoms and uraemic conditions so typical
in dogs were not found in the human cases. Most
of the patients had a dog and in several cases the
dog was ill and in six of the cases the dog was
shown to be infected with Lept. canicola. Often