NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
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The endemic
index.
The third method is the only one which can be completely relied upon. In
carrying it out it is best to examine only infants and children under ten
years of age. For this method it is necessary to take blood films from
30 or 40 infants and young children up to 10 years of age and after staining
the films to examine them for the presence or absence of malaria parasites.
The percentage of children of ages up to ten years who have malaria parasites
in their blood is called •'' the endemic index of malaria." When the blood of a
sufficiently large number of children has been examined the figure affords a true
index of the degree to which malaria prevails in a place and affords the most
satisfactory means of comparing the amount of malaria in different localities.
7.—How to investigate the factors upon which the prevalence of malaria
depends.
How to carry
out a
" malarial
survey.''
We will assume that we have visited a village and have found by an
examination of the blood of 30 or 40 children that the endemic index of malaria
in the village is, let us say, 80. We have now to investigate the conditions in
which this high endemic index occurs. The first thing to be done is to obtain
a map of the village on a large scale and to set down on it all the pooh,
streams, and other collections of water within a quarter of a mile from the
houses of the village. Having done this we should proceed systematically to
find out what species of Jnopheline mosquitoes are breeding in each collec-
tion of water. To do so we must carry with us each day bottles or test
tubes labelled with numbers or letters similar to those by which the different
collections of water marked on our map are known. We shall put the larvæ
caught in the different collections of water in the labelled tubes in order that
when they have developed into adults and can be identified we shall know
exactly what species are breeding in the different pools and streams. The
distances of the various breeding places from the houses will be shown in the
map. The next thing to do is to search for adult Anopheline mosquitoes in
the houses, outhouses, and stables of the village, and we must attempt to
form an estimate of the abundance of these insects as a whole and of the
relative abundance of different species. One way of estimating this
is to keep a record each day of the number of specimens caught in a given
time, say two hours. The number of specimens caught depends entirely,
of course, on the skill of the worker, but when a worker is well skilled his
daily records are quite fairly comparable with each other and with his records
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The Indian
malaria-
carrying
species.
of work in any other village. The observer will usually find that some species
are much more abundant in houses than others, and such an observation
is of great importance. This work of catching adult Anophelines would
occupy perhaps two or three hours each morning, and the expert malari-
ologist would spend the remainder of the day in identifying the specimens
caught and in dissecting them to ascertain which of the species is carrying
malaria at the time. But, on account of the time required, the dissection of
mosquitoes with the object of finding sporozoites in the salivary glands and
zygotes in the stomach wall is beyond the scope of practical work which can
be done by medical practitioners in India unless other duties are neglected,
and the methods of dissection and examination will not be described here.
It must suffice to say that by the dissection of large numbers of different
species of Anophelines in malarious places in India it has been proved that
not all species are equally good carriers of malaria in nature, so it is
obvious that the particular species of Anopheline which is present in the <
houses of a village is a very important factor in the prevalence of malaria.
Up to the present time only four species, namely, Myzomyia listoni.
Myzomyia culicifacies, Nyssorhynchus fuliginosus and Nyssorhynchus stephensi*
have been proved by dissection to be malaria-carriers in nature in India, and
it has been shown also that one species, namely Pseudomyzomyia rossii, very
probably does not act as a carrier of malaria in nature. For this reason it will
be seen that in making our " malarial survey " great attention must be paid to
the presence or absence in the houses of listoni, culicifacies, fuliginosus or
stephensi and to the character and distance of the breeding places of those
species.
In this way we shall have investigated the two chief factors that influence
the prevalence of malaria in any place, namely, (1) the prevalence of the " source
of infection," which means, practically speaking, the abundance of native
children with malaria parasites in their blood (because it has been proved
that such native children form always the chief source of infection); and (2)
the prevalence of the " carrier of infection," which means the prevalence of
the particular species of Anopheline which carries the zygote and sporozoite
stages of the parasite.
* The proof that N. stephensi is a malaria carrier in nature in India has been fur-
nished very recently by Captain Listen, I.M.S., in Bombay.
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Some pro-
blems for
solution.
It might be hoped that by such an investigation we should be able to
explain satisfactorily the reasons for the prevalence of malaria in every place,
and the reasons for its great prevalence in some places and its absence in
others. Unfortunately this is not so, and it has to be admitted that all the
factors upon which the prevalence of malaria depends are not yet known.
There are places in India, for example, where a malaria-carrying species of
Anopheline is abundant, where people suffering from malarial fever are con-
stantly arriving, and where the climatic conditions are favourable for the
development of the parasite in the mosquito, but yet where the disease has
not become endemic. The reason of this is one of the many problems in
malaria which await solution. Another factor about which little or nothing is
known is the influence of the abundance of Anophelines. There are places in
India, for example, where the endemic index of malaria is as high as 60 or 70, yet
where the malaria-carrying species of Anopheline is so rare that an experienced
searcher may occupy an hour or more before finding a specimen. There are
other places where the malaria-carrying species is so common that 20 or 30
specimens can easily be caught in an hour, but where the endemic index is not
more than 12 or 15. We know also that even a very marked reduction in
the number of Anophelines in a place might not necessarily affect the
prevalence of malaria if it were to happen, for example, that by the importa-
tion of infected people or by some other means the prevalence of the source
of infection were increased; we must always remember that the prevalence
of the source of infection is a factor of equal and sometimes perhaps of
greater importance than the prevalence of Anophelines. Another factor of
very great importance in the prevalence of malaria in a district where the
disease is already endemic is the constant importation of susceptible persons.
Recent work by Captain Christophers and Dr. Bentley goes to show that
where such importation is constantly occurring everyone becomes infected
with malaria in a very short time, no matter how few Anophelines there may
be—provided, of course, there are any Anophelines at all.
We see, then, that if we wish to ascertain all the factors which determine
the prevalence of malaria in a place and to gain an accurate notion of the
relative importance of each, the subject of Anophelines, though among the
most important, is by no means the only subject that must be investigated.
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CHAPTER III.
Symptomatology and diagnosis of the malarial fevers.
W E are now in a position to return more particularly to the subject of
the malarial fevers, and in this chapter we shall consider their
symptomatology and diagnosis.
Avoid the
danger of
regarding
every case, of
fever as
malaria.
It is well known that the most prominent symptom caused by an infection
with malaria parasites is fever of a very definite and peculiar character.
This character may be summed up in the words Intermittency and Periodicity.
By Intermittency is meant the fact that the fever ceases at intervals; the
temperature alternately falls to normal or below, and rises again. On this
account the name " Intermittent fevers " is well applied to malarial fevers.
By Periodicity is meant the habitual tendency of the fever to recur at stated
intervals of time. Thus the fever may recur at intervals of 24 hours (Quoti-
dian Periodicity) or at intervals of 48 hours (Tertian Periodicity) or at inter-
vals of 72 hours (Quartan Periodicity). It may be said that, almost without
exception, all cases of fever due to the presence of malaria parasites in the
blood will, if left untreated, sooner or later exhibit these two characteristics of
intermittency and periodicity. Unfortunately the terms " malaria " and
" ague " are often applied in a loose manner to many continued and irregular
fevers, the nature of which is not wholly clear, and at the outset I would
strongly urge you to guard against making a hasty diagnosis in any continued
or irregular fever; and would advise you to err on the side of those who do
not consider any case of fever as malarial, until the character of the tem-
perature chart, or an examination of the blood, plainly proves it to be so,
rather than on the side of those who regard every case of fever as " malaria "
until, after several weeks of ineffectual treatment, this diagnosis is proved
to be wrong.
Before describing the clinical types of malarial fevers we must say
a few words regarding the process by which the malaria parasite produces
fever.
I have already described how the parasites in the red blood corpuscles
gradually grow larger and larger until they attain their full size and divide
up into a number of segments or spores, which burst through the thin
remnant of the corpuscle and become free in the blood plasma, ready to
E
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enter other corpuscles. It has been found—and the observation may be
verified by any one who examines the blood of a typical case of malarial
fever—that the onset of the attacks of fever from which the patient suffers,
always corresponds in point of time with the stage of sporulation or
segmentation of the parasites. During the period of apyrexia, only young
and medium-sized parasites, enclosed within the red blood corpuscles, can be
found, and it is only when the parasites are in the segmenting stage and
escaping from the corpuscles that the attack of fever begins. There is thus
a very intimate connection between the sporulation of the parasite and
the attack of fever, and it is possible that during the growth of the parasite
in the red blood cell it produces a pyrogenetic or fever-producing chemical
substance, which, when the parasite bursts from the red cell in the act
of sporulation, is liberated into the plasma and so becomes able to
exert its influence and cause fever. As long as the parasite remains inside
the envelope of the corpuscle the pyrogenetic substance cannot
escape, so that during the time the parasite takes to grow to its full
size the patient does not suffer from fever. As soon as the parasite divides
and bursts from the corpuscle the pyrogenetic substance escapes and causes
fever.
From this you will readily understand that a parasite which sporulates
every 24 hours will produce Quotidian fever, one which sporulates every 48
hours will produce Tertian fever, and one which sporulates every 72 hours
will produce Quartan fever.
It will be apparent that if a parasite should, for some reason or other,
complete its asexual cycle in a less period than 24, 28, or 72 hours, a
different clinical type of fever will result, and also that a different clinical
type may be produced by the presence in the blood of two or more groups of
parasites which sporulate at different times or at the same time on different
days. If, for example, a patient were infected with two groups of Benign
Tertian parasites, one group being due to sporulate about 10 A.M. on the 1st,
3rd, 5th, etc., of August and the other group being due to sporulate at the
same time on the 2nd, 4th, 6th, etc.. the patient would have a paroxysm of
fever every morning, and his temperature chart would be said to be of the
"double Tertian type. "
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I shall describe first the results of an infection with Benign Tertian
parasites, because this is the species most commonly met with in India,
and afterwards note the differences which result from infections with the
other two forms.
Symptoms of
Benign
Tertian fever.
1. Benign Tertian infection.—Supposing a man to have been bitten
by a mosquito infected with the sporozoites of the Benign Tertian parasite,
he will probably not feel any ill effects until about twelve or fourteen
days afterwards. This is the incubation period during which the parasites
have been gradually multiplying in his blood, but have not been present
in sufficient numbers to cause symptoms. Towards the end of the period
he may feel some aching of the bones, headache, or other premonitory
symptoms, and his temperature may be somewhat raised. After these
indefinite symptoms have gone on for a day or two the regular attacks of
" ague " begin. The attacks of fever recur, in infections with the Simple
or Benign Tertian parasite, at definite intervals of 48 hours.
Each
attack is represented clinically by a
"cold" stage, a
"hot"
stage, and a " sweating" stage. At the beginning of the cold stage
the patient feels chilly; after a short time the feeling of cold
spreads all over his body and becomes so intense that his teeth chatter,
and he shakes from head to foot. His temperature, however, in spite
of the feeling of cold, begins to rise. After a time the shivering stops and
the patient begins to feel hot, the skin becomes dry and burning, and
the temperature rapidly rises to 103°F. or 104°F. or more. After an hour
or so the hot stage passes off, the patient begins to perspire profusely, the
fever quickly declines, and in a short time all the acute symptoms have
disappeared, and the patient feels almost well. As a rule he is able to get
up and go about his occupation until the next day but one, when he will
again have another attack of fever similar to the first one. If untreated,
these attacks may recur every other day for many weeks, gradually de-
clining in severity as time goes on. In the meantime the patient's spleen
has become enlarged, and he has become pale and anæmic. After the fever has
left him apparently for good it may return at irregular intervals for many
months (Relapses). These relapses of fever may be brought on by almost
any exciting cause such as chill, over-fatigue, over-anxiety exposure to the
Relapses.
E 2
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sun, etc., and have no connection whatever with mosquitoes. One explanation
of their cause is that all the asexual parasites of the first infection have
not died out, and when the patient's resisting power is lessened by any of
the conditions just mentioned, the parasites are able to develop rapidly
again and produce their ill effects. Another explanation has already been
mentioned under the heading parthenogenesis. (Page 3.) In this view it is
assumed that all the asexual parasites have died out, but that some of the
sexual (female) forms, which are very resistant even to the action of large
doses of quinine, persist and that under influences similar to those just men-
tioned a crop of asexual forms can be produced from these female parasites.
The relation of the parasites to the different clinical stages.—If the patient's
blood be examined at the onset of fever, that is a little time before the cold
or rigor stage, it will always be found that (as we have already noted) the
majority of the parasites are in the stage of division or sporulation. The
onset of fever and the rigor correspond in point of time to the sporulation of
the asexual forms of the parasite. From the point of view of treatment this
is an important point to remember. By the time the hot stage approaches
all the parasites have divided up and are entering, or have already entered,
fresh corpuscles. During the last part of the hot stage, during the sweating
stage, and during the period of apyrexia. the parasites are enclosed in the
red blood corpuscles, growing and developing pigment. Between any two
similar stages of the parasite an interval of 48 hours elapses, i.e., the Benign
Tertian parasite takes 48 hours to complete its asexual cycle.
These points and the clinical characters of Benign Tertian malarial fever
are-illustrated in Chart. I.
This chart shows three typical paroxysms of ague occurring at the same
time on alternate days. Each attack lasted from about 11 A.M. until about
8 P.M. At 12 noon, during the shivering stage, sporulating forms were found
in the blood, and at 7 P.M. very young forms, which had lately entered the
corpuscles, were present. The sudden rise of the fever and its quick fall are
characteristic of Benign Tertian infections. The administration of thirty
grains of quinine at 7 A.M. on the 26th. though it did not prevent the onset
of the attack on that day, stopped all future paroxysms and practically cured
the case. (See page 72.)
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CHART No. I.
Malarial fever. Renign Teitian infection.
Name.—Gunner T, Age.—25 years.
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After the attacks of fever have gone on for some time, sexual forms of
the parasite which, in the case of the Benign Tertian parasite, are spherical
hi shape, will be seen in the blood as well as the asexual sporulating forms.
These sexual forms, however, do not cause fever except in the circumstances
when parthenogenesis occurs.
2. Quartan infection.—The symptoms produced by an infection with the
Quartan form of the malaria parasite are similar to those produced by the
Benign Tertian form, except that the interval between the onset of the
attacks of fever is one of 72 hours instead of 48 hours. The reason of this
is that the Quartan parasite takes 72 hours to complete its asexual cycle
instead of only 48 hours as is the case with the Tertian parasite.
Chart II illustrates the result of an infection with Quartan parasites.
CHART No. II.
Malarial fever. Quartan infection.
Name.—Chetty. Age.—10 years.
( 55 )
On the 10th young Quartan parasites were found in the blood of this
patient ; on the 11th medium-sized forms, and on the 12th at 5 P.M. pre-
segmenting and segmenting forms.
Symptoms of
Malignant
Tertian fever.
Malignant Tertian infection.— There are marked differences between infec-
tions with the Malignant Tertian form of the malaria parasite and those with
Benign Tertian or Quartan parasites, and the term " malignant " has been
applied to this species of parasite in opposition to the term " benign," which
is applied to the parasites of Benign Tertian and Quartan fevers, because
dangerous symptoms, such as hyperpyrexia, coma, delirium, etc., are much
more liable to arise in the course of an infection with this form of parasite
than with the others. The Malignant Tertian parasite, like the simple or
Benign Tertian, as a rule takes 48 hours to complete its asexual cycle, and for
the first few days of a case this fact is often apparent from the temperature
chart (see Chart III). With this form of parasite, however, there is a great
tendency for the parasites to complete their cycle in a shorter time than
48 hours, often indeed in as short a time as 24 hours, so that after a day or
two the patient usually has an attack of fever every day (Quotidian fever).
Again there is a tendency for the individual parasites to complete their cycles in
different periods of time instead of all doing so at the same time as in the
case of Benign Tertian and Quartan infections. As a result of this it not
infrequently happens that the temperature does not fall quite to normal for
several days together, and the chart may be remittent in character.
In untreated cases the fever continues in this way for about a week or
ten days and then ceases, leaving the patient weak and anæmic but otherwise
apparently well. After an interval of apyrexia varying from six days to a week
or more, a second series of attacks of fever, exhibiting a Tertian or Quotidian
periodicity exactly similar to the first attacks, occurs. These relapses may
be repeated at more or less constant intervals of a week or more for two or
three months, gradually getting shorter and less severe until they die out
altogether, leaving the patient very anaemic and with an enlarged spleen.
These points are well illustrated in Chart III, which is from a case of
Malignant Tertian fever in a child.
For the first four days this chart shows a definite Tertian periodicity.
Then follow daily paroxysms until the 9th, after which an interval of six
days' apyrexia occurs. This is followed by a series of relapses occurring at
CHART No. III.
Malarial fever. Malignant Tertian infection.
Name.—Rangu. Age.— 1½ years.
( 57 )
varying intervals, and in this case the relapses were still occurring at fairly
definite intervals four months after the primary attack. The temperature
is intermittent throughout. It should be noted that, as the temperatures in
this case were taken only twice daily, they are not by any means a record
of the highest temperature reached on any particular day. In order to
obtain a correct temperature chart it is necessary for the temperature to be
recorded at least every four hours and preferably every two hours. If in a
case of Malignant Tertian fever the temperature is carefully recorded at fre-
quent intervals it will be found that the chart presents very characteristic
features which in the absence of a microscopic examination of the blood are
of service in diagnosis. They are shown in Chart IV. In each febrile
paroxysm there is, as was first described by Marchiafava and Bignami, an
initial rise of temperature, then a pseudo crisis, then a second rise of tempera-
ture (called the precritical elevation ) and finally a true crisis.
CHART No. IV.
Malarial fever. Malignant Tertian infection.
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The Malignant Tertian parasites are much smaller than those of the Benign
group of fevers. Their amoeboid movements are very active, and it is very
common to see several parasites in one corpuscle. Only the young forms of
the parasite arc seen in the peripheral blood, segmentation occurring for the
most part in the deeper viscera, such as the spleen and bone-marrow. To-
wards the end of the first series of attacks of fever, that is, about a week
after the commencement of the disease, sexual forms (crescents) appear in the
blood. Their number gradually increases, and they are very abundant after
the fever has quite left the patient.
Mixed infections.*—Combined infections, with different species of the
malaria parasite, occur not infrequently in India, and may produce irregular
charts. A combined infection of Benign and Malignant Tertian parasites is
perhaps most commonly met with, but combinations of Benign Tertian and
Quartan parasites are also seen. Chart V illustrates a mixed infection of this
nature in a child.
CHART No. V.
Malarial fever. Combined infection with Benign Tertian and Quartan parasites.
Name,.—Uligarnmak. Age.—4 years.
* " Mixed" infections must not be confused with "double " or "triple " infections.
The latter terms are used to define infections with two or three groups of the same
species of parasite. (See page 50.)