NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
CONTENTS.
D. Previous history of plague cases as regards contact with
other plague cases . . . . .
. . .
E. Relative frequency of the occurrence of single and multiple
cases of plague in houses and buildings
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PART V. — Relation of insanitary conditions to the spread of plague.
A. Influence of insanitary conditions, considered without reference
to rat-plague, upon the spread of the epidemic .
B. Influence of insanitary conditions upon the spread of rat-
plague and upon the transference of infection from rats
to man
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1. The conditions which favour the spread of rat-plague
over a city, e.g., Bombay, or through a village,
e.g., in the Punjab
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2. The conditions which favour the spread of rat-plague into
and throughout inhabited buildings .
C. Incidence of plague on different classes of the community
PART VI. — The recurrence of plague in houses in successive
epidemics
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PART VII. — The importation of infection from an infected to an
uninfected locality
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A. Conveyance of infection by rats
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B. Conveyance of infection by infected rat-fleas
PART VIII. — The recrudescence and seasonal prevalence of plague .
A. The existence of the plague bacillus in nature during the non-
epidemic season
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1. Saprophytic existence of the bacillus in the soil
2. The existence' of the bacillus in man
3. The existence of the bacillus in the rat
B. The factors which influence the rise and fall of the
epidemic .
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1. Temperature
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2. The number and susceptibility of the rats .
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3. Variation in the number of
fleas
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C. Conclusion
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PART IX. — General conclusions
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THE
ETIOLOGY AND EPIDEMIOLOGY OF PLAGUE:
A SUMMARY OF THE WORK OF THE PLAGUE COMMISSION.
PART I.—INTRODUCTION.
The first duty of the Commission was by study of the liter-
ature and by careful enquiry from workers in India to ascertain
the main conclusions which had been already formed regarding
the epidemiology of plague. In the first progress report to the
Advisory Committee these conclusions were set forth and may
be briefly summarised as follows :—
(1) Plague, with the exception of the pneumonic form,
which, however, is uncommon (2 5 per cent. of all
cases), is not particularly infectious or contagious and
man to man infection plays no important part in the
spread of epidemics in India. The disease may, how-
ever, be introduced into a new locality and so ultimately
occasion a new outbreak by the agency of man.
For this to occur it is not necessary that the human
agent himself should be suffering from the disease.
(2) Definite localities, huts, rooms or houses, in which
plague has occurred amongst rats or man, are during
an epidemic highly infectious. Further, the infection
seems to cling to these localities for a long time.
(3) While plague can exist and spread under a great range
of climatic conditions, it exhibits a marked seasonal
prevalence, which is the most striking feature of the
epidemiology of the disease,
(4) In the great majority of instances plague in man is
associated with an epizootic among rats : and
there seemed to be the strongest reasons for regarding
the epizootic amongst rats as by far the most import-
ant cause of the epidemic spread of the disease.
It is necessary to state that, although the work of the
present Commission has demonstrated the part played by the
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rat and the rat-flea in the spread of plague, this demonstration did
not surprise plague workers in India. On the contrary, the obser-
vations, both epidemiological and experimental, which had been
made in India pointed to this conclusion. Lieutenant-Colonel
W. B. Bannerman, I.M.S., has put on record the state of know-
ledge as regards the spread of plague prior to the commencement of
work by the Commission in a paper published in the Journal of
Hygiene of April 1906. This paper is a digest of "many very
valuable reports made by officers of the Indian Medical Service
who have dealt personally with plague epidemics, which reports
existing in the archives of the various local Governments are not
available for reference by the public." Colonel Bannerman
shows that the trend of opinion amongst workers in India was,
that plague is disseminated through rats and that its spread to
man is occasioned by the agency of fleas. In this connection
Captain W. Glen Liston, I.M.S. (Indian Medical Gazette,
February 1905) had shown that the common rat-flea in India
was Pulex cheopis and that this flea would bite man. In fact
he had taken many specimens of this flea on human beings in a
plague-infected house. He had also used guineapigs as traps
for P. cheopis in plague-infected houses and had on several
occasions observed that these animals became infected with
plague when exposed in this way. He had made the further
observation that numerous plague bacilli were to be found
in the stomach contents of rat-fleas taken on guineapigs in
plague-infected houses. Finally, so convinced were Colonel
Bannerman and Captain Liston of the truth of the flea transmission
theory that they had designed and built at the Plague Research
Laboratory. Parel, special godowns or cabins, in which it was
proposed to carry out large series of experiments to prove this
theory. These godowns had just been completed when the
Plague Commission began work and, as we shall see, the experi-
ments which were made in them by the Commission went far
to prove that the rat-flea is the only agent of transmission of
plague infection from animal to animal.
It is not then too much to say that the work of the
Commission has been a cope-stone to careful and tedious inves-
tigations already carried out in India—and of course elsewhere—
rather than an original building, and that to the preliminary work
and to the ready and whole-hearted assistance which the Commis-
3
sion received in India from all concerned the success of their
labours is largely due.
The work of the Commission consisted of both epidemiological
observations and experimental investigations. The epidemiological
observations were made in the City of Bombay itself, in four
villages in the north of the Island of Bombay within easy
distance of the Parel Laboratory and in two isolated villages in
the Amritsar district of the Punjab. The experimental work was
carried out at the head-quarters of the Commission, namely,
the Plague Research Laboratory, Parel, Bombay.
B 2
5
PART II.—EPIDEMIOLOGICAL
OBSERVATIONS
ON
PLAGUE IN THE RAT AND IN MAN AND ON THE
RELATION BETWEEN THE EPIZOOTIC AND THE
EPIDEMIC.
A.—Methods of investigation which were adopted.
B.—Observations on the rat population.
C.—Observations on plague in the rat—the epizootic.
D.—Observations on plague in man—the epidemic.
E.—Relation of the. epizootic to the epidemic :—
1. Relation in time :—
2. Relation in place.
3. Relation in quantity.
A.—METHODS OF INVESTIGATION WHICH WERE ADOPTED.
The methods which were adopted for studying the disease
in rats and in man were practically the same in the various
places where the observations were made ; they differed only in
the agencies which were used.
In the first place, an endeavour was made to obtain daily as
many rats, alive and dead, as possible and to examine these in as
full detail as possible.
In Bombay City the collection of the rats was in the hands
of the staff of the Sanitary and Cleansing Department of the Muni-
cipality, which is under the direction of the Health Officer. With
this department arrangements were made for a daily supply of
several hundred rats (alive and dead) from all over the City.
In the four villages around Bombay and in the two Punjab
villages the collection of rats was in the hands of the Commission
staff, assistance being obtained from the village officials.
Every evening many traps were set in various situations and
were collected every morning. To evey trap was attached a label
giving the exact locality where it had been set, e.g., street, house,
ground-floor, first-floor, etc., godown, stable, gully. In this
way it was possible to allocate each trap containing rats to a par-
ticular part of a building. In the case of rats picked up dead a
ticket was attached to each rat indicating the exact place where it
6
had been found. While it cannot be denied that by these
methods, which were the best available, only a percentage of the
dead rats were obtained, it is certain that this percentage was a
fairly large one and was a good sample.
In Bombay all the rats were examined at the Parel Laboratory
in the Punjab villages a small laboratory for the purpose was
fitted up in a bungalow adjoining both villages. Elaborate arrange-
ments were made for this examination, so that in Bombay
it was easily possible to deal with from 1,000 to 2,000 rats daily.
A flea census of the live rats was first made, the rats being
chloroformed to death for this purpose. They were then dealt
with in the same way as the rats brought to the laboratory dead.
A record of all rats was kept stating their weight, species and
sex ; if female, whether pregnant or not; and if pregnant, the num-
ber of young present. Further, all rats were examined to ascertain
whether they were plague infected or not, the diagnosis of such
infection ultimately resting in the hands of one of the members
of the Commission. A careful post-mortem examination of all
plague-infected rats was made and the results described on a form
specially drawn up for the purpose. In Bombay this detailed
examination was stopped after about 5,000 post-mortem records
had been obtained, but in the Punjab it was continued throughout
the observations. As the accuracy of the statistics depends on
the accuracy of the diagnosis of plague in the rats, particular
attention was paid to this point. Reference will be made to diagnosis
later on.
In the second place, as complete an investigation as possible
was made of every plague case which came to light.
In Bombay City the Commission relied for this infor-
mation on the staff of the Health Department. For purposes
of administration Bombay is divided by this department into ten
districts and each district into two or more sections. In charge
of each district there is a qualified Health Officer, the Registrar,
who has under him a staff of sub-registrars, inspectors and menials.
All the senior officers have an unusually wide experience of plague
on its clinical -side and besides have a particularly thorough and
extensive knowledge of their districts. This superior staff was
trained by the Commission to fill up special plague case cards,
7
which contained all the necessary information. In addition to
the cards outline maps of each section were distributed to the
several offices and each plague case with the date of report was-
dotted on the map. The whole organisation was supervised on
the Commission's behalf by two selected medical officers of the-
Health Department and was daily superintended by members
of the Commission.
In the villages, both in Bombay and in the Punjab, a complete
census was made, full particulars for each house being recorded
on special census cards. These particulars included name, age,
sex, caste and occupation of every inhabitant. In the Punjab
villages, with a view to ascertaining how far plague tends to-
recur in particular houses, full particulars of the prev ous inci-
dence of plague in each house were noted on the cards. Every
plague case, and in fact every case of illness, was visited by a mem-
ber of the Commission. The same system of detailing the infor-
mation on cards and of spot maps was used as in Bombay.
Further, in order to gain the confidence of the villagers and thus,
obtain early information and avoid concealment of cases a
free dispensary was opened in each village and placed in charge
of a competent medical man. At first an endeavour was made
to confirm the diagnosis by means of a bacteriological examina-
tion. t was soon recognised, however, that any attempt to
obtain material for examination as a routine measure would
defeat its own object by leading to concealment of cases. The
procedure was therefore abandoned and the diagnosis based on
clinical features, which are usually sufficiently typical.
In the third place, the relation of the rat epizootic to the
epidemic was investigated.
As regards time and quantity the relation was easily ascertained
from an analysis of the daily returns of plague-infected rats and of
plague cases.
As regards place relationship, we have already seen that the
information concerning each plague case was recorded on a special
card and that each case with its date was dotted on a map. The
plague-infected rats were treated in practically the same way.
Special plague-rat cards were prepared, which in the case of the
villages were filled up by a member of the Commission, who at the
same time indicated on the map the place where the rat was found-
8
In Bombay a list of the rats found plague infected was sent each
evening from the laboratory to the collecting agency and to the
district registrar's office. Accompanying this list were sent
the corresponding plague-rat cards to be filled up. The locality,
where each rat had been found, was marked on the nearest wall by
the collecting agency, while the cards were filled up and the locality
and date dotted on the map by the senior officials of the district
registrar's office. The cards were then returned to the laboratory.
B.—OBSERVATIONS ON THE RAT POPULATION.
In the City of Bombay five species of rodents were found,
namely, Mus rattus (the black rat), Mus decumanus (the grey rat),
Mus musculus (the mouse), Nesokia bengalensis and Nesokia bandi-
cota (the bandicoot). It is unnecessary here to enter into the minute
differentiation of these species. It was found always possible
to distinguish rats of the type of M. ratius from rats of
the type of M. decumanus, but no distinction could be made
between the large number of varieties of M. rattus, which have
been described. Briefly, it may be said that from a practical
point of view the important points which ought to be taken into
account in differentiating between M. rattus and M. decumanus
are the character of the tail and the relative size of the ears. These
features, together with the shape of the head and the general colour
of the fur, serve to distinguish Nesokia bengalevsis from M.
decumanus. The tail in M. rattus is always longer than the body
and head together, it is dark in colour and has well marked rings.
The ears in this species are larger in proportion to the size of the
rat than in M. decumanus; in the latter the tail is shorter than the
body and head together and the ventral aspect is lighter coloured
than the dorsal aspect. In Nesokia bengalensis the tail is shorter
than the head and body together, but in appearance resembles
that of M. rattus, i.e., the rings are well marked. Further, the
hairs on the tail are shorter and less numerous in N. bengalensis
than in M. decumanus and there is no brush of hairs pro-
jecting beyond the tip of the tail, as there is in this latter species.
The head of 2V. bengalensis, looked at from above, is broader and
shorter than that of M. decumanus and the cars are somewhat
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larger in proportion to the size of the animal. The colour
of the fur of N. bengalensis is uniformly darker than in M.
decumanus ; it is also coarser and with well-marked spines on the
back. There is no difficulty in distinguishing M. musculus (the
mouse) and the ordinary bandicoot (Nesokia bandicota) from the
other species.
Mus rattus and Mus decumanus are by far and away the
commonest rodents in Bombay. N. bengalensis is comparatively
rare, making up only about; 1 per cent. of the total. The mouse
appears not to be a common animal in Bombay.
Mus rattus, which is found in large numbers in every part of
Bombay City, is essentially a house rat; it may almost be called
a domesticated animal, living and breeding as it does in the houses
where the people live. While it is typically a climbing rat. it is
also able to burrow, e.g., in earthen floors and walls. Its nests
axe as a rule to be found in little-disturbed accumulations of
material, such as stacks of firewood, cotton-waste, etc., and in
recesses, such as cupboards.
There is no doubt that the rat infestation of houses in Bombay
is very great. There is, however, a definite relation between the
rat infestation of the building and the character of the building,
the features which especially favour rat infestation being earthen
floors and country tiled roofs, a state of disrepair, accumulations
of rubbish and food, such as stores of grain, etc.
It was found that, while M. rattus breeds all the year round
in Bombay, breeding was most vigorous during the months June
to October, so that the hottest months of the year represent
the breeding season. The mean number of young per rat was
found to be 5 2, while the largest number noted in a single rat
was 9.
Mus decumanus, which is numerous in every quarter of Bombay
and especially numerous in the native town, lives for the
most part outside houses, in sewers, storm water drains,
stables, etc. While it is a burrowing animal with remarkable
power of gnawing through hard materials, e.g., brick and
concrete, it is also a good climber. Its nest is to be found in one
of the burrows which it makes. The breeding season corres-
ponds closely with that of M. rattus, except that there is apparently
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a second breeding season in March. This species, however, like
M. rattus, breeds all the year round. The average number of young
per pregnant female is 8 1, the largest number found in a single rat
being 14.
As regards the relative numbers and haunts of Mus rattus and
Mus decumanus, the following statements are founded on the
trapping of nearly 12,000 rats of these two species in the native-
city.
M. rattus is apparently much more common in Bombay
than M. decumanus, as, taking all traps set, seven of the former-
species to every three of the latter were caught. They are found
in this proportion on ground floors of houses, but M. rattus in-
creases relatively to M. decumanus as one ascends the building. M.
decumanus has never been found above the third floor, so that on the
fourth floor and upwards M. rattus is alone present. In gullies,
compounds of houses, stables, godowns and food and tea
shops the number of M. decumanus relatively increases, so much
so in the case of compounds, that in traps set in them twice as many
of this species as of M. rattus were taken. Further, it is evident
that these two species of rats are closely associated with each other—
gullies, the lower floors of the houses and godowns appearing to
be their common meeting ground.
The Commission have observed nothing to show that the rats
of Bombay, even during the epizo otic season, are in the habit of
migrating from one quarter of the city to another. There
may be desertion of infected buildings, but there is certainly no
general migration.
Finally, it is necessary to emphasise two important facts con.
cerning the rats of Bombay which, as we shall see, have a great
significance in relation to plague. The first fact is the widespread
distribution of M. rattus in buildings in the city. The Commis-
sion do not think it an exaggeration to state that every inhabited
building in Bombay City and Island, not excepting even the better
class bungalows, shelters its colony of M. rattus. The second
important fact is that to a certain extent M. decumanus, as we have-
seen, is a house rat and even forms extensive burrows in the floors-
and walls of buildings.
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As regards the other rodents in Bombay little need be said
as they do not influence the plague epidemic.
Nesokia bengalensis is not common as it appears to be in
Calcutta. It was taken in those sections of Bombay city where there
are fairly large areas of waste ground and was trapped in the
ground-floors of houses, in gullies, in stables and in godowns
The bandicoot is now an extremely rare animal in Bombay.
It was caught only in the open country and palm groves in the
northern part of the Island.
Mice were taken on all the floors of buildings, in stables and in
godowns.
In none of the villages in the neighbourhood of Bombay,
with the exception of Parel, was M. decumanus obtained during
the year they were under observation. A few of this species
were taken in Parel, a village, in which the buildings are very
similar to those of Bombay and where there are a certain number
of sewers and storm water drains.
A few specimens of Nesokia bengalensis were taken in these
villages.
M. rattus was found to be very common in the villages.
Its
habits and haunts were the same as in Bombay. In two of
the villages, namely, Parel and Worli, a very thorough and
systematic, examination of the rat infestation was made
during the period they were under observation.
This was
done by setting daily a number of traps in the different houses
and recording the number of rats caught in each trap. The traps
were sent in the houses in rotation according to the census num-
bering.
In Parel 2,195 M. rattus, a number equal to two-thirds of the
human population, were captured during the year. This number
gives an average of 15 rats per building. From one building,
which was divided into 16 tenements and sheltered 70 inhabitants,
as many as 393 rats were taken. At the beginning of the opera-
tions 65 rats per 100 traps set were captured, while at the end of the
year this number had been reduced to 34 rats per 100 traps set—
not a very great reduction. We can conclude, then, that the rat
infestation of Parel is very considerable, and that, despite the capture
and removal from the village during the year's operations of a
12
large number of rats, equivalent to two-thirds of the human popu-
lation, the number at the end of the year was apparently not very
greatly diminished.
Very similar observations were made in Worli. This is an
isolated village on the west coast of the Island and is chiefly inha-
bited by fisher folk The buildings are huts constructed of rough
stones. The roofs of the huts are generally covered with palm
leaves and offer excellent shelter for M. rattus. During the
year's operations 2,603 rats of this species were taken in the village,
a number larger than the human population (2,508). At the
beginning of the trapping as many as 70 rats per 100 traps were
caught, while at the end of the year this number had been reduced,
only 17 rats per 100 traps set being taken. There is no doubt that
the rat population had been considerably diminished. The inhabi-
tants themselves recognised this fact and five months after
the operations had been stopped begged that the routine setting
of traps might be continued, as the rats had again become a
nuisance.
It would appear, then, that the fecundity of M. rattus is so great
that nothing but extensive and persistent efforts to destroy it
can materially reduce its numbers in any village. The same con-
clusion was arrived at as the result of the observations in the Punjab,
which we shall now consider.
From November 1905 to December 1900 continuous observation?
on the rat population were carried out in the Punjab villages of
Dhund and Kasel. Four species of rats were found, namely. M.
rattus. M. decumanus, Nesokia bengalensis and Gerbillus adieus
(the Indian field rat).
Only five mice were taken. This small number may be due
to the traps being unsuitable for catching them. Twenty-
five N. bengalensis were captured, all in the fields at harvest
time. Of 9 Gerbilli two were taken in the fields and the remaining
seven in the villages, most of them in houses on the outskirts.
Mus ralias, therefore, is the common rat of the Punjab villages
and is the only one which has any influence on the plague epidemic.
In all 7.525 specimens were examined during the year. The type
very closely resembles that found in Bombay. The colour of the
dorsal fur is usually brown, while the belly is Greyish, dirty yellow or