NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
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The breeding places of anopheles larvæ.
It is now well known that anopheles larvæ may occasionally be found
in almost any collection of water of whatever nature it may be. This fact
has an important application when any practical measures at extermination of
larvæ are attempted, in that it leads us not to overlook even the most unlikely
places in our search for larvæ ; for unless we search systematically every
collection of water, temporary or permanent, we may easily allow an important
breeding place to remain, when we think all possible breeding places have been
done away with.
Under favourable conditions, however—that is, abundance of breeding
places of all kinds near at hand— anopheles will not, as a rule, lay their eggs in an
unsuitable collection of water, and there is no doubt, I think, that under such cir-
cumstances, not only do anopheles select their breeding places, but that each
species has a particular kind of breeding ground that it prefers over any other.
This observation, which was first made by Dr. Christophers at Jalpaiguri in
Bengal, is a very important one.
At Jalpaiguri two species of anopheles were common viz.:—A. Rossii (Giles),
and A. Sinensis sub-species Nigerrimus . The breeding places of A. Rossii
were invariably found to be small, shallow, muddy puddles and pools close
to, and among the native huts. A. Nigerrimus, on the contrary, was breeding
entirely at some distance from the village in the deep natural pools of a swampy
marsh. The larvæ of A. Rossii were never found in these pools and those of
A. Nigerrimus never in the shallow muddy pools near the huts.
In the Duars, the same selection of breeding places by A. Rossii and
A. Fluviatilis was found to exist, the larvæ of A. Rossii being found only in the
shallow muddy pools near the coolie huts, and the larvæ of A. Fluviatilis (the
adults of which were nevertheless more common in the huts than those of
A. Rossii ) being found at some distance from the lines only in the small clear
pools formed by a mountain stream, and in the water among the grass and weed
at the edge of the stream itself.
This selection of particular breeding places extends to all the species of
Indian anopheles , and in September of last year I found an excellent example of
its application to the three species, A. Culicifacies (Giles), A. Fuliginosus
(Giles) and A. Rossii in one of the isolated bazaars at Mian Mir. This bazaar is
surrounded by an irrigation channel about four feet wide and three feet deep.
At the upper end of this watercourse and about ten yards from it are a number
of broad, shallow muddy pools. At the lower end of the watercourse and about
thirty yards from the bazaar is a swampy piece of land covered with thick trees
53
and shrubs and containing a number of deep clear pools in which water plants
and weed have grown.
The adults of the three species, A. Rossii, A. Culicifacies, and
A. Fuliginosus, were present in the houses of the bazaar, and we should have
expected that the larvæ of all the species would have been found together in any and
all of the breeding places. This, however, was not the case. In the irrigation
channel no other larvæ than those of A. Culicifacies were ever found, in the
shallow muddy pools no other larvæ than those of A. Rossii, and in the clear deep
pools under the trees no other larvæ than those of A. Fuliginosus .
It is evident, therefore, that each of these species had selected a particular
kind of breeding place.
In another part of Mian Mir an example of selection of breeding places by
another species of anopheles was found. In this place several species of ano
-pheles were present in the barracks of the native troops, and there were abun
-dance of breeding places of different kinds near. The larvæ of only one species,
however ( viz., A. Stephensii), were found in the gumlahs of water kept in the
lines in case of fire, and the larvæ of this species were never found in any of
the other breeding places—a good example of selection of a breeding place by
this species.
At Mian Mir the breeding grounds of the species of anopheles were in ac
-cordance with what we had found for the same species in other parts of India ; and
it is possible to divide the Indian anopheles as regards their breeding grounds into
at least three groups, viz ., (I) those which breed almost exclusively in running
water (the members of Group I, page 3o), (2) those which breed in shallow muddy
pools in the vicinity of dwellings and in tins and gumlahs of water (the members
of Group IV, page 44) and (3) those which breed at some distance from houses in
deep natural pools with much aquatic vegetation and in marshes (the members
of Group II and some of those of Group III, .page 35).
The favourite breeding grounds of some of the species of Indian anopheles
may be summed up as follows :—
GROUP I.—A. Fluviatilis . The larvæ of this species are found most fre
- q u e n t l y i n q u i c k l y r u n n i n g s t r e a m l e t s w i t h g r a s s y e d g e s .
Their presence in a stream can be detected only by
dipping with a tin among the grass and vegetation at the
edge of the stream and in the pools and backwaters.
A. Culicifacies . This species is essentially a breeder in slowly
moving water. It will be found in canals, ditches and
streams when quite absent from neighbouring shallow,
stagnant pools. Irrigation canals are its favourite breed-
ing place in the Punjab. In places where there is no
running water it may be found in clear pools as at Ennur
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near Madras, where it was breeding in the borrow-pits by
the side of the railway. It has also been found in rocky
pools in the bed of a river.
GROUP II —A. Nigerrimus. The larvæ of this species are found chiefly
in deep dark natural waters with much aquatic vegetation.
Favourite breeding places are deep overgrown canals,
swamps in the jungle and ponds with water weeds. Their
breeding places are not as a rule found near houses.
The larvæ are generally scattered singly among the
water plants at the edges of the pool and can be caught
only by dipping with a tin or muslin net among the
plants and weed.
A. Barbirostris. The breeding places of this species are
practically the same as those of A. Nigerrimus. In
Lahore the larvæ were present in the lily ponds in the
public gardens until the end of November.
GROUP III.—A. Fuliginosus (Giles). The larvæ of this species are often
found along with those of A. Nigerrimus. As a rule,
however, they prefer more open water and more sunlight.
In Madras and in the Central Provinces they were
common in the large open tanks with grassy edges.
A. famesii (Theobald). In the Central Provinces the larvæ
of this species were found among the grass and water
weeds at the edge of a large open lake ; and in Travancore
(Quilon) in a large sandy tank.
GROUP IV .—A. Rossii. The breeding places of this species have already
been sufficiently referred to. Its larvæ are never found
at any distance from houses. Shallow muddy pools are
its favourite breeding ground and hundreds of larvæ are
usually present in the same small pool, and being easily
seen t he l ar væ of t hi s speci es ar e t he ones whi ch ar e
most frequently found by observers. The larvæ of most
other species have to be fished for with a tin or net.
In Madras, the larvæ of A. Rossii are common in the
irrigated rice fields and in the muddy tanks, as well
as in pools made by digging for building purposes, in
brick-fields, and in cultivated areas.
A. Stephensii. In Mian Mir (Punjab) this species was
found to be breeding only in the earthenware g u m l a h s
and tins kept full of water in the line of the native troops
in case of fire. In Madras I found it breeding only in
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the disused wells in the courtyards of the Native and
Eurasian houses. It is probable that since the introduction
of a pipe-water-supply into Madras City the numbers of
this species, at any rate, have largely increased, for its
larvæ are only found in those wells which, since the
introduction of the pipe-water-supply, have been unused.
A. Maculata. The larvæ of this species may be found
further from houses than those of A. Rossii, and whereas
the larvæ of A. Rossii are usually found in muddy water,
the larvæ. of A. Maculata prefer clear sandy or rocky
pools. In the Duars its larvæ were found in clear pools
on a rice field. In Hong-Kong (China) I found the
larvæ of this mosquito in the small marshy pools on the
granite soil of Kowloon.
Sufficient observations have not been made with regard to the remaining
.species of anopheles to enable their favourite breeding places to be stated with
certainty.
Under unfavourable conditions the selection of suitable breeding places by
the different species is not of course so apparent, and many instances might be
given which show that if all the suitable breeding places near a village are
dried up the anopheles will lay their eggs on any collection of water. The
“ test pool ” experiment of Stephens and Christophers in Africa is sufficient to
prove this, and the same expedient for finding out whether adult anopheles are
really present in a place or not, when all the natural breeding places have dis-
appeared, has been frequently resorted to by us in India.
Even without making artificial pools or placing large gumlahs of water in
a village, many examples may be found in nature. Thus in one part of Calcutta
(Hastings) in June, when no breeding place could be found anywhere near, and
no adults could be caught in the houses, we were able to prove that adults were
really present by finding their larvæ in the cisterns of water on the roofs of the
houses—the only place where at that time we were able to find larvæ in this part
of Calcutta. Again, during the hot weather in Mian Mir, when the irrigation
channels had been stopped for a long time and there were no natural breeding
places of any kind, I was able to find larvæ in very curious situations, as, for in-
stance, in the water of the swimming bath, in the horse troughs, in tins of water
which had been accidentally left about, in many of the small drains which take off
the waste water of the standpipes, wash houses, etc., and in the small stone
reservoirs in the gardens.
These facts point to the necessity of a very thorough search in every
collection of water when any efforts at extermination of larvæ are attempted, and
although under favourable conditions we may certainly say that we are more
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likely to find anopheles larvæ in certain collections of water than in others, no,
hard and fast rule, which might perhaps prevent us from searching a particular
place, can be made.
The enemies of larvæ and the effect of running water on larvæ.
We have made a good many experiments which show that many small
water animals and young fish feed voraciously on mosquito laræ, but I do not
think so much importance attaches to this subject as is generally supposed. It
is of course true that a number of small water animals, larvæ, and young fish
eat mosquito larvæ, but it is equally true that under natural conditions anopheles
larvæ may always be found in the same pools in which the most voracious fish
or water animals are living, and experiments on this subject carried out under
artificial conditions are apt to be misleading. A kind of young fish, for ex
ample, is very common in the irrigation watercourses at Mian Mir : if a few
specimens of this fish are put into a basin of water with twenty or thirty ano
pheles larvæ, in an hour or two the fish will have devoured all the larvæ. Under
natural conditions, however, the number of larvæ in the watercourses does not
appear to be lessened by the presence of the fish, and I have watched a natural
pool of water containing these fish and anopheles larvæ for some days without
the number of larvæ having appreciably diminished.
In other parts of India, too, it is not at all uncommon to find larvæ in pools
containing fish and other water animals which will devour the larvæ readily if
placed along with them in a bottle or basin.
Another point to which I am not inclined to attach much importance is
the effect of running water on larvæ. If it were possible in all the streams and
canals of India to make the water run as swiftly at the sides as it does in the
centre they would of course afford poor breeding grounds, but however swiftly a
stream runs in the centre there are almost always many small bays and back
- w a t e r s w h e r e t h e l a r v æ c a n l i v e s h e l t e r e d b y w e e d s a n d g r a s s , s o t h a t i t i s
possible to find anopheles larvæ by dipping at the edges of almost every stream,
however swiftly it may appear to be running. The effect of running water on
larvæ is not to kill them, but simply to carry them on with it until they find some
sheltered bay or backwater where they can develop unmolested. This is the
case in the more swiftly running irrigation channels at Mian Mir. If a length
between two bridges of one of these water channels be examined, a large number
of very young larvæ which are evidently being carried onwards with the stream
will be found. At the bridges, however, where the water is collected into a
comparatively still pool before it passes under the narrow bridge, full grown larvæ
and pupæ will invariably be found. The inference is that the young larvæ have
been carried down by the stream to develop in the comparatively still waters.
near the bridges.
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The distance of flight of anopheles mosquitoes .
At the present time practically all observers are agreed that anopheles do
not fly to any great distance from their breeding places in search of food, and
although it is of course possible to find anopheles larvæ in jungles several miles
from any human habitation, the inference is that the adults of these larvæ feed
either on the blood of animals or on vegetable juices.
The importance of ascertaining the usual distance of flight of those species
which habitually feed on the blood of man is very great, because unless this is
known it is impossible to state the safe distance for a residence from a focus of
infection.
There are three groups of rain-formed pools in Mian Mir which afford a
good opportunity for observation in connection with this important subject.
One of these groups of pools is 450 yards away from any habitation, the second
group is 750 yards away and the third is over three-quarters of a mile away.
With each shower of rain these pools are filled and remain full for over a week
as a rule.
On every occasion I have found the first group of pools to contain many
larvæ within a week of a shower of rain : on three out of four occasions the
second group of pools has contained larvæ, and on no occasion have larvæ been
found in the pools of the third group. This shows, I think, that mosquitoes will
readily fly to a breeding place a quarter of a mile away, that they will less
readily fly to a breeding place half a mile away, and that they will never (except
perhaps under exceptional circumstances) fly over three-quarters of a mile. In
these instances the larvæ found were those of A. Rossii.
In an indirect way also the usual distance of flight of mosquitoes can be
determined and the safe distance from a focus of infection ascertained.
In Mian Mir, for example, there are two groups of syce lines, one of which
is 150 yards and the other 500 yards from the same and only breeding place of
the malaria-carrying species of anopheles. In the nearer syce lines numerous
adult anopheles were caught, and in the further syce lines we were not able, at
the time of our examination, to catch any adult anopheles. The endemic index
of the nearer syce lines was 56 per cent., and that of the further lines only 20
per cent. This is sufficient to prove that the majority of the anopheles did not
fly the 500 yards to the further syce lines.
The following examples will show, however, that it is not unusual for ano-
pheles to fly a quarter of a mile. In the village of Anjini in the Central Provinces
three species of anopheles were abundant, the endemic index was 25 per cent.,
and the nearest breeding places were a quarter of a mile away. Three species
were also present, though scanty, in the village of Takli, with the nearest breeding
places the same distance away and an endemic index of 15 per cent. Above 1
a quarter of a mile, however, from a breeding place the amount of malaria rapidly
diminishes, and over half a mile away safety from anopheles is practically
assured as the following examples show:-
Names of places.
Presence of adult
anopheles.
Distance of nearest
breeding grounds.
Endemic index.
Lawa
None found.
Half mile.
5%
Wadi
None found.
Half mile.
5%
Chintarapelly
None found.
Over half mile.
o%
We may say, therefore, that the usual distance of flight of anopheles mos-
quitoes rarely if ever exceeds half a mile, and that at this distance from a focus
of infection we are practically safe from malaria.
The following table shows the percentage of infected children in the
different places we have visited :—
TABLE I.—To SHOW THE MALARIAL INFECTION OF NATIVE CHILDREN
IN INDIA.
District.
Name of Locality.
Percentage of infected children
(=Endemic Index).
Calcutta
o
Madras
5
P l a i n s o f B e n g a l
Belgureiah
7 . 3
Jalpaiguri
1 6 . 1
Mainaiguri
24.3
The Duars .
Rungamutty
43
Naigaisurie
55
Nagrakata
72
Sam Sing
28
Darjeeling hills
Kurseong
o
Seypudura
o
Tonetta
o
Mian Mir (Punjab)
Infantry Bazaar
52
Artillery Bazaar
35
Syce lines A.
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Syce lines B.
20
Cavalry Lines
24
Central Provinces
Phutala Village
45
S a h a d a r a V i l l a t g e i
15
D i d g o h V i l l a g e
20
Seendra Village
20
Ambigheri Village
25
Angin i Vi l l age
25
Takli Village
1
T e l e n k e r i
10
K a m a l
7
Sunegaon Vi l l age
8
Bighori Village
3o
Lawa
Village
5
Wadi
5
Vizagapatam District.
Vizagapatam
o
Tapara
10
Chintarapalli
o
Fishing village
27
Jeypur State
Sukni
5 0
Patungi
35
Koraput
20
Bodawalasa
86
Kanaputty
5o
Sisagoda
70
K oomba
60
Madras
Ennur
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From the above table it will be seen that the proportion of infected child-
ren varies greatly in different places. In very malarious districts a large per-
centage of the young children have malaria parasites in their blood, in places
which are less malarious a smaller proportion of infected children is found, and in
places where malaria is rare or absent, few or none of the children are found
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infected. The percentage of infected children affords, in fact, a very true test
of the endemicity of malaria in different places, and the figure representing
this percentage may, therefore, be termed the "Malarial Endemicity Index,"
or shortly the "Endemic Index."
It would of course be possible to arrive at a rough estimate of the amount
of malaria and the liability to infection at different places by other methods
than this, as, for example, by an examination of the statistics of admissions into
hospitals for malarial fever, or by an estimation of the number of people with
enlarged spleens, but by neither of these methods can we arrive at an accurate
result, for neither of them will give us any information regarding the prevalence
of malarial parasites at the time of our examination. It is obvious that a
knowledge of the prevalence of parasites among the general population, and a
knowledge of the number of infected anopheles mosquitoes are the only reliable
data on which we can form an estimate of the amount of malaria and the
danger of infection.
The reasons for the great differences in the malarial endemicity of different
places in India shown in the above table will be discussed later: at present it is
necessary to refer to the significance of the infection of native children, and to
the relative immunity of the adult native.
The great importance of the infection of native children lies in the fact
that they form undoubtedly the chief source from which anopheles mosquitoes
become infected. This is a point of the greatest practical importance and one
which cannot be too clearly recognised. That this must be so, is easily under
-
stood when we remember that practically all the cases of malarial fever occurring
in native children are untreated, and go on for many months without it being
recognised by anyone that the children are suffering from malarial fever, and
have malaria parasites in their blood. A further proof is given in the fact that
the highest proportion of infected anopheles is found in the places where we
find the largest number of infected children; and in places where there are
no infected children it is difficult or impossible to find infected anopheles.
This is shown in the following table.
TABLE II.—TO SHOW THE CONNECTION BETWEEN INFECTED CHILDREN
AND INFECTED ANOPHELES MOSQUITOES.
Locality. Percentage of infected children.
Percentage of infected a n o p h e l e s .
Calcutta
Nil (140 examined)
Nil ( 3 5 2 e x a m i n e d ) .
Mian Mir
55-60
4 . 6 ( o n e s p e c i e s ) .
The Duars (Rungamutty)
45-50
6 . 2 5 ( o n e s p e c i e s ) .
Ennur (Madras)
60-65
8 . 8 ( o n e s p e c i e s ) .
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It is apparent from the above table that the greatest liability to infection of
any new corner exists in those places which contain the largest number of in-
fected children, and in places, such as Calcutta, where there are no infected
children, there is practically no danger of infection with malarial fever.
We have seen that two other important points were brought out by Koch,
and Stephens and Christophers, in Africa, in connection with the infection of
native children, viz., (1) that a diminished infection of the children occurred with
advancing age, and (2) that the adult negro in Africa was relatively immune
to malarial infection.
For certain malarious districts of India these same rules will apply, as the
following table shows:—
TABLE III.-To SHOW DIMINISHED INFECTION WITH INCREASING AGE
OF NATIVE CHILDREN IN MALARIOUS DISTRICTS OF INDIA.
Locality.
infected
children up to 3
years of age.
Infected
children up to 5
years of age.
Infected
children up to 10
years of age.
Infected
children over
to years of age.
Infected
children over 15 years
and adults.
Mian Mir (Punjab).
80%
66%
50%
. . . None in 25 examined.
Ennur (Madras).
65%
51%
4 6 %
16%
None in 10 examined.
Rungamutty (Duars)
. . .
48.3%
43%
...
None in 33 examined.
I t i s e v i d e n t , t h e r e f o r e , t h a t n a t i v e s l i v i n g i n s u c h p l a c e s a s t h e a b o v e a c q u i r e
a relative immunity with advancing age. This immunity is probably an acquired
one, due to repeated infection and re-infection occurring during childhood, for,
in less malarious districts than the above, the relative immunity enjoyed by the
adult native is not so marked, and the diminished infection of the children at
advancing age periods is not shown.
The following is an example of this:—
TABLE IV.—TO SHOW THAT IN LESS MALARIOUS PLACES VERY LITTLE,
IF ANY, IMMUNITY OCCURS WITH ADVANCING AGE.
L o c a l i t y .
Infected
children up to
5 years.
Infected
children up to
10 years.
Infected
children up to
15 years.
Infected
children up to
18 years.
Infected
adults.
Jalpaiguri (Bengal).
Rare
13.3%
15.2%
16 %
Not uncommon.
It is probable, therefore, that in Africa, as well as in India, it is only in the
very malarious parts that the adult acquires a marked immunity. In Africa,
however, malaria appears to be almost equally prevalent in all the parts that
have been examined, and at the same time to be almost equally prevalent