NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
81
in different places in the Punjab and though every other species was represented
no larvæ of M. rossi were taken. In April many hundreds of adults were collected
from the houses in all parts of the city and specimens of all the plains species except
M. turkhudi were found, but not a single specimen of M. rossi was among
them. At Delhi in April though anopheles were not abundant, specimens of
all other species were obtained, but there were no M. rossi. Such complete
disappearance of the commonest of all the species for so many months is very
remarkable.
In regard. to N. fuliginosus we again have a very clearly defined tendency to a
marked seasonal prevalence. This species being, as Adie described it at Fcroze-
pore, the common cold weather anopheles. Its period of greatest preponderance
is unconnected with the monsoon and depends largely upon the amount of water
left standing from th e previous year and showers falling in the early months. It
shows little tendency to increase until the season for the autumn species is passing
away.
The species C. pulcherrima follows the habits of N. fuliginosus, but in the
eastern portion of the Punjab is relatively unimportant. Its seasonal prevalence
in the western districts requires to be worked out.
N. stephensi in Amritsar, Atari, Beas and Delhi is a species which comes into
prominence in the early summer. And though. it is found at other times of the
year it does not seem to increase much in the autumn.
Upon M. culicifacies further observations seem called for, especially in view
of the great importance this species possesses as the chief carrier of malaria in the
Punjab. In 1909 the numbers of M. culicifacies at Amritsar in the autumn
certainly underwent no rise at all comparable with that of M. rossi at this time.
I have found the adults of this species in fact as numerous in April as at any time
of the year. The larvæ of M. culicifacies however at Mian Mir undoubtedly
underwent an increase which commenced in August and continued throughout the
autumn. The numbers caught in Delhi were also highest in October.
With the cessation of the rain the land more or less rapidly dries, the smaller
pools disappear and the pits and more permanent collections of water only remain
as breeding places. It is very noticeable that under these circumstances in the
absence of fresh rain many pools cease to be suitable for breeding and the number
of larvæ therefore tends to be diminished out of proportion to a e extent of
desiccation.
Adults however continue to be caught in very large numbers even though
breeding places are greatly reduced and larvæ scanty. N. fuliginosus, N. stephensi
and M. culicifacies still retaining about the same prevalence for a time again
assume relatively greater prominence with the disappearance of M. rossi. But in
October the night temperature begins to fall considerably and by November the
M
82
average is usually under 60°F. In December it has fallen to 50°F. or thereabouts
and the cold weather conditions we have described supervene.
I.—PERMANENT BREEDING PLACES.
Probably the best general division of breeding places is that used by Dr. Bently
in regard to the breeding places in Bombay city. This division is into:
—
(a) Permanent.
(b) Temporary.
Permanent breeding places in the Punjab are often more important as a means
of enabling a species to maintain itself through periods of drought than as a source
of malaria.
During the months May and June anopheles are put to great stress. A morn-
ing's search for example in June 1910 in one of the most malari ous parts of Amritsar
yielded only three anopheles and no breeding places were found in the neighbour-
hood,.
And to the west of Delhi city on the land away from the neighbourhood of
the river I failed in April to find even a single source of anopheles. Similarly in
November only one place was found in which a few larvæ were present. But how-
ever hard pushed the genus may be as a result of drought we can generally find
some place in the neighbourhood where the different species are breeding more or
less freely. At Delhi for example N. stephensi and, M. culicifacies were found breed-
ing freely in the bed of the Jumna. At Amritsar anopheles were still a bundant in
certain tanks to the n orth of the city long after they have become greatly reduced
elsewhere. At Atari a series of excavations filled with water have always yielded
several species no . matter what time of the year th ey were visited. When suitable
temporary breeding places form in the neighbourhood of permanent breeding
places a species can at once extend itself over a wide area. A large permanent
source of anopheles may exert in fact a very important indirect effect, as is shown
by Dr. Bentley for Bombay, by its power of at once stocking temporary breeding
places. Thus at Delhi it is reasonable to believe that in the case of rair falling and
creating numerous temporary breeding places th e species would propagate them-
selves in greatest numbers first in the areas bordering the river, and this might
explain to some extent the distribution of malaria in the city without our having to
suppose that the Jumna bed was the source of the actual anopheles which reached
the city. In Amritsar small pools on the outskirts were immediately stocked
with larvæ, but further within the city they remained often a fortnight or more
without becoming infected, there being no adults at the time in the neighbourhood
to make use of them.
In a country so dry and so exposed to drought as the Punjab, large areas in
which anopheles can continue to exist, however adverse the conditions be elsewhere,
83
are thus important and may almost be termed anopheles sanctuaries. The follow-
ing conditions in the Punjab may be considered as always acting to a greater or
less extent in this way—
(1) Large river beds like that of the Jumna, Beas, etc.
(2) Jheels and large tanks filled with aquatic vegetation with their asso-
ciated swamps and pools.
(3) Extensive brick fields and large excavated tracts such as exist near
most large towns and even some villages.
(4) Irrigation systems.
Apart from such sources larvæ of anopheles are not abundant in the dry
months. That a particularly dry year seems to exert no permanent reduction
in the genus is rather grimly shown later when we discuss the effect of " dry "
years upon malaria. ( Vide Chapter XIII.)
IV.—TEMPORARY BREEDING PLACES.
During and after the rains when breeding of most species is at its maximum
the chief sources of anopheles are—
(1) Pits and excavations which surround almost every village and town.
(2) Shallow accumulations of rain water.
(3) Irrigation channels.
(4) Other miscellaneous sources.
The larger pits contain water all the year round but are more often than not
unsuitable for breeding purposes and no larvæ are found in them. The small pools
whose numbers may be great during the rains are undoubtedly the most important
source of M. rossi.
Of all sources during this time the second type are the most interesting. In
some cases after the rains, sheets of water can be seen stretching for miles. In March,
when investigating some sheets of water of this kind lying in the Gherinda thana,
I was greatly struck with the numbers of anopheles such sheets must give rise
to. The larvæ of M. culicifacies and of N. fuliginosus were in immense number
everywhere quite irrespective of houses or any obvious source of food supply. It
was also very noticeable that in tile Case of M. culicifacies the larvæ and the adults
which hatched out from them were very large specimens suggesting that the con-
ditions were peculiarly favourable to this species. When such waters last any
time aquatic weeds very rapidly grow and for the time being a village may for all
practical purposes come to be situated in a marsh.
In other cases very extensive sheets of water may be hidden in the grass and
vegetation, and may escape notice unless search be made for such a condition,
or acres of land may be covered with small puddles lying in furrows and invisible
84
even a few yards off, or again such collections may be of such a temporary nature
as to seem unlikely to breed anopheles. But very commonly though a small shallow
pool of this kind may appear to have dried up, it is surprising how often one finds
on close inspection that one or two hoof marks of cattle or some other small hollows
still contain a little water and that crowds of larva are here collected together.
Even if the water entirely dries up the larva still retain, so long as the mud
remains moist, the power to continue their development when more rain falls.
One may thus find pools of a very temporary nature acting as important
breeding places.
The part played by irrigation channels is well shown by the work done at
Mian Mir in 1901—03. The number of larvæ of M. culicifacies after August was
always very great ; so much so that, as this species was not found breeding in any
numbers in the pools, its breeding places were considered to be almost confined to
the canals. But the abolition and filling up of the canals have not reduced the
numbers of this species which was very numerous in October 1909. Very pro-
bably large numbers still breed in shallow rain pools such as I have described,
many of them obscured by and hidden among grass. In addition to the breeding
which goes on in the actual water channels there are often escapes in connection
with canals which may be important breeding places. In the canal district
south of the Jhelum, where apart from the canals there is practically no water, I
found in one such situation so many larvæ of M. culicifacies that the edges of
the pools appeared black and the larva formed a scum visible at a distance of
several yards.
Many kinds of breeding places frequently mentioned as sources of anopheles
are relatively not very important in the Punjab. Water near standpipes I have
rarely found with more than at most a very few and usually small larva. Tins
and receptacles also, though they may be found containing anopheles larva, are not
an important source of anopheles in the Punjab.
Wells at Delhi are a source of N. stephensi, but at Amritsar the amount of
breeding in wells seems almost negligible.
V.—RELATIVE PROPORTIONS OF MALE AND FEMALE ANOPHELES.
The proportion of male and female adults caught has shown a constant rela-
tion to :
—
(a) The distance of the breeding places.
(b) The absence or presence of breeding places.
At Amritsar males were found not to have penetrated to a greater distance
than about 100 yards into the more solid portions of the town. Even beyond
the first row or two of houses their numbers had already become reduced in com-
parison with that of the females. When breeding places had been reduced in
85
numbers (April to June) the proportion of males also diminished and in June
nearly every anopheles caught was a female.
The following tabulated statement of recorded catches illustrates this
point:—
Anopheles caught in houses on
the immediate outskirts of Amritsar.
Anopheles caught in a zone lying interior
to the extreme outskirts.
MARCH.
(a ) At Hakiman with few or no breeding places
in the neighbourhood.
N. fuliginosus male
.
.
.
.
0 No anopheles found.
„ f e ma l e
.
.
.
. 11
N. stephensi male
.
.
.
. 1
„ female
.
.
.
.
1
( b) At Jalewlayan many breeding places.
N. fuliginosus male
.
.
.
.
35 N. fuliginosus male
.
.
.
. 0
„ female
.
.
.
. 44
„ female .
.
.
. 21
(c) Houses immediately behind above.
N. fuliginosus male
.
.
.
. 10
„ female
.
.
.
. 37
APRIL.
Breeding places disappearing.
N. fuliginosus male
.
.
.
. 9 N. fuliginosus male
.
.
.
.
1
„ female
.
.
.
. 38
„ female .
.
.
. 103
M. culicifacies male
.
.
.
.
3 M. culicifacies male
.
.
.
.
0
„ f e m a l e .
.
.
. 15
„ f e m a l e
.
.
.
. 3
N. stephensi
male
.
.
.
.
3 N. stephensi male
. .
.
. 0
„ f e m a l e .
.
.
.
6
„ f e m a l e .
.
.
.
4
C. pulcherrima male
.
.
.
.
0
„ f e m a l e .
.
.
.
2
JUNE.
(a ) Before extensive breeding places formed by
rains.
N. fuliginosus male
.
.
.
. 0 N. fuliginosus male
.
.
.
.
0
„
female .
.
.
.
6
„ female
.
. .
.
1
M. culicifacies male
.
.
.
.
0
„ female
.
.
.
. 4
N. stephensi
male
.
.
.
. 0
„ female
.
.
.
. 9
86
(b ) After rains had started.
N. fuliginosus male
.
.
.
. 2
„
female .
.
.
. 10
M. rossi
male
.
. abundant
M. rossi
male .
.
.
1
„
female .
.
„
„
female .
.
.
. 29
NOVEMBER.
N. fuliginosus male
.
.
.
. 1
„
female
.
.
. 49
M. culicifacies male
.
.
.
. 0
„
female .
.
.
. 2
Anopheles caught at Delhi near
breeding places:
Anopheles caught in the town
away from any local breeding places :
APRIL.
M. cul i ci f aci es male
.
.
.
. 2
„
female .
. .
. 3
N. stephensi male
.
.
.
. 1
„
female .
.
.
. 2
NOVEMBER.
N. fuliginosus male .
.
.
. 0
„
female .
.
.
. 6
M. culicifacies male .
.
.
. 1
„
female .
.
. . 11
N. stephensi male .
. . . 0
„
female .
.
. . 3
M. rossi
male .
.
. .
0
„
female .
. .
. 4
Though these observations show that in towns the males penetrate only a
short distance, they do not necessarily show that males are confined to the
immediate neighbourhood of breeding places. At Atari males were numerous in
the village though this was at a distance of 400 yards from the breeding places.
They therefore seem able to traverse considerable distances in the open.
VI.—SPECIES OF WHICH THE ADULTS ARE FOUND IN THE OPEN.
At Atari it has been mentioned that there exist extensive breeding grounds.
These consist of excavations perennially filled with water which is for some reason
always in a state very suitable for breeding. In the beginning of November 1909
there were no other important source of larvæ than the pools referred to. In
these the most numerous larvæ were those of M. rossi. Larvæ of N. fuliginosus
and C. pulcherrima were also present in large numbers.
87
In the evening anopheles could be seen hatching out from the pupal skin
and after resting a short time flying ofd to the low bushes which grew at the edge
of the water.
During the day therefore various bushes and tufts of grass which lay on the
plain around this source of anopheles were covered with a large mosquito net and
beaten vigorously with a stick. (It was found difficult to dislodge mosquitoes
during the day but easier towards evening.)
Immediately on the banks the result of a number of beatings yielded—
M. rossi
male
.
.
.
. 13
„
female
.
.
.
.
5 None contained blood.
C. pulcherrima male
.
.
.
.
1
„
female
.
.
.
.
2 Both were fully gravid, neither containing
blood, i.e., they were on the point of ovi-
position.
N. f uliginosus male
.
.
.
.
0
„
female .
.
.
.
1 Fully gravid, no blood in the gut, i.e., it was
on the point of oviposition.
This operation of beating bushes, etc., was then carried out over a wider area.
Between the breeding place and the village, on what seemed a dried and sunbaked
plain with little or no shelter, the following yield was given :—
N. fuliginosus male
.
.
.
.
2
„
female .
.
.
.
7 5 specimens contained recentm ammalian
blood and the ovaries more or less devel-
oped.
1 contained old blood, the ovaries nearly
fully developed.
1 containing no blood, the spermatheca was
empty and the ovaries undeveloped.
C. pulcherrima male
.
.
.
2
„
female .
.
.
. 1 No blood, ovaries undeveloped.
M. rossi
male
.
.
.
.
1
Anopheles were in this case found not only small bushes and in tufts of tall
grass but in a low scrubby plant growing somewhat like heather and even small
depressions in the ground formed by the partial sinking in of some recently-made
graves.
In a direction away from the village and away from any other houses at a dis-
tance of 500 yards from the breeding place the catch was as follows :—
M. rossi
femal
. .
. . 1 No blood in gut, undeveloped ovaries, sper-
matheca empty, glands immature.
N. fuliginosus femal
.
.
. .
2 1 showed old mamm alian blood in gut.
Ovaries partly developed, spermetheca full.
1 showed no blood, ovaries fully developed.
C. pulcherrima female
. .
.
.
1 Recent mammalian blood, ovaries slightly
developed.
88
It will be seen that except on the borders of the excavations the species M.
rossi, though the Commonest in its larval form, was not nearly so frequently found
in the bushes, etc., as N. fuliginosus.
Of very great interest was the condition of the females caught in different
places. Those caught away from the pools had in many cases blood in the
gut and showed ovaries undergoing development just as would have been the case
in anopheles caught in a village. Yet in this position it is difficult to see how
they got any blood. The females of species other than M. rossi caught near the
edge of the pool, being fully gravid and having got rid of every trace of blood,
must have been ready at any moment to lay their eggs. It is reasonable to
suppose that they had found their way back to the water for this purpose.
Up to the present no tests have been made as to the nature the blood found in
these mosquitoes, but the fact that most of the females had succeeded. in obtaining
blood shows that the species N. fuliginosus and C. pulcherrima can live quite well
even on a bare plain with a few tufts of grass and a few small bushes for shelter.
In the village a catch of anopheles gave—
M. rossi females 40.
There were also numerous males
and a few N. fuliginosus
and C. pulcherrima.
The females showed an ovarian formula indicating steady infiltration ( vide
next section).
VII.—AGE COMPOSITION OF ANOPHELES COMMUNITIES.
The method of ascertaining the age of an anopheles and ether bionomical
facts regarding the genus will form the subject of a later report, but brief mention
may be made of what I have termed the ovarian index of a community.
Roughly speaking there is an ovarian index characteristic of anopheles com-
munities near active breeding places and corresponding with a high relative pre-
valence of males. There is another ovarian index characteristic of communities,
remote from breeding places or those existing after breeding places have dis-
appeared, in this case associated with an absence of males or their occurrence in
very small numbers.
A third type of communities exist in which large numbers of specimens are at
about the same stage of development, but all stages are not represented. This
seems to suggest the spasmodic flights of anopheles on particular nights.
VIII.—RELATION TO MALARIA.
Of the long list of Punjab anopheles four species only, M. culicilacies, N.
stevhenssi, M. fuliginosus have been recorded as having been
89
found in nature carrying the sporozoites of malaria. M. culicifacies was first shown
to carry malaria at Mian Mir by the Royal Society's Commission N. stephensi is
recorded by Liston and later by Bentley as actively concerned in the transmission
of malaria at Bombay. The power of N. fuliginosus to carry malaria is shown
by Adie who found one of 200 specimens dissected at Ferozeporo with sporozoites.
In this I am able to confirm Colonel Adie as sporozoites were found in this species
from a village near Amritsar in April. It is worthy of note that at the same time
the dissection of hundreds of this species caught in Amritsar city gave a negative
result. Major Robertson, I.M.S., informs me that N. maculipalpis, which is the
common species in the Terai below Naini Tal, also acts as a carrier in nature in this
locality.
With the exception of M. rossi the power of the remaining species of anopheles
in the Punjab to transmit malaria in nature is unknown.
Even more important than the question whether the rarer species transmit
malaria or not is the question as to what part if any is taken by M. rossi. The
results obtained with this species by Stephens, Christophers and James have been
lately confirmed by Bentley who, dissecting M. rossi and N. stephensi caught
together in Bombay, found the former with sporozoites and the latter entirely
negative. But the very strongest evidence is required before this species can be
considered never to act as a carrier.
IX.-RELATION OF ANOPHELES TO EPIDEMIC CONDITIONS.
No actual observations as to the relative prevalence of anopheles during
epidemic times exists. Enough has been said to show that this would be an
extremely important subject of enquiry.
N
90
CHAPTER XI.
Rainfall and Temperature in Relation to Epidemic Malaria.
The statement is very generally made in the Punjab that following an
unusually heavy monsoon, fever is especially prevalent. By this is meant
undoubtedly that the chief determinant of epidemic malaria is rainfall. It remains
for us to see to what extent epidemic malaria is related to rainfall.
I.—THE RAINFALL OF 1908.
According to the Meteorological report the following were the most notice-
able features of the weather for this year—
(1) The only marked feature noted in regard to the rains in the early part
of the year was an excess of rain in April most marked in the south-
east of the Punjab.
(2) The monsoon was not properly established in the Punjab until July,
the fall in June being below the average.
(3) The weather in April and May was cooler than usual, but in June the
temperature was in excess.
Regarding the Monsoon the following points are drawn attention to
—
(1) Owing to the monsoon current being directed to a greater extent than
usual to Upper India, the rainfall for the whole monsoon period in
the Punjab was very largely in excess.
(2) Unusually heavy rain fell in. the western districts in September. In
this month rainfall in the eastern districts, especially in the Delhi
Division, was in defect.
Total Monsoon Rain.
Map IV shows the monsoon rainfall in 1908 for each recording station in a
graphic manner. The chief feature is an area of comparatively heavy rainfall
covering the central districts. It will be observed that this latter area corresponds
roughly with the northern epidemic area.
The strip of heavy rainfall extending down to Ferozepore and the area of
epidemic intensity at Fazilka is significant. The distribution of heavy rainfall
over Gujrat and Jhelum is also in keeping with what we know of the distribution
of the epidemic.
Gurdaspur, which has curiously enough just missed having a monsoon rain-
fall of 30 inches, was also passed over by the epidemic. In the meteorological
summary it will be seen that whilst in Amritsar the departure from the normal was
15.54 and in Gujrat 18.5, in Gurdaspur it was only 4.94.