NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
41
R. capensis, R. simus, A. hebræum, A. variegatum, and Ixodes pilosus, and it
holds good in R. sanguineus, R. bursa, H. flava, and two species of Aponomma
common on reptiles in Madras.
Two species, R. evertsi and H. ægyptium, are described by Lounsbury and
Theiler as remaining throughout the first two stages on the same host.
It appears that it is the usual habit of ticks to leave their host at each stage
and that the passing of one or more metamorphoses on the same host is a
special adaptation.
In the different stages a host of the same or a different species may be selected,
H. leachi and the Indian dog tick attach themselves in all their stages to the
same host, which may often be the same dog, and R. appendiculatus behaves
similarly upon cattle. Other species feed as larvæ or nymphs on different hosts
to those selected by them as adults, and in I. hexagonus and I. reduvius in
Europe the nymphs and larvæ are found on lizards, birds, and upon small
mammals such as squirrels, moles, etc. As a rule the immature ticks are less
particular in their choice of hosts than the adult, but in certain South African
species Lounsbury has found the larvæ very difficult to satisfy in this respect and
he suggests that they normally choose some particular host at this stage.
As the genus Rhipicephalus is that to which the Indian dog tick belongs
it will require some mention. Many of the species of this group have so close
a general resemblance that their differentiation requires great care and the
question of two or more species being present on dogs in Madras has been
considered. The genus Boophilus created by Curtice for R. annulatus though
not considered by Neumann in his memoirs as sufficiently distinct to be
maintained as a separate genus undoubtedly contains a group of the
Rhipicephali very distinct from those ticks of which R. sanguineus may be
taken as the type. Mr. Lounsbury makes the remark that Neumann has since
considered the separation of this latter group as the Eurhipicephali, a
distinction which has much to recommend it.
Variation in size is considerable, but this is frequent in ticks and may
depend upon the food supply in the larval or nymphal stage. It is also
dependent upon the state of the tick, for a male, whose vasa differentia are
swollen with spermatozoa produces the impression of being a much larger tick
than one in which these structures are empty. The apparent size of an unfed
female also varies according to the period of fasting.
In R. appendiculatus and some other ticks a tail appears after the tick has
fed for a certain time. A slight prominence may sometimes be seen in males
of the Madras dog tick, but it rarely is sufficient to deserve the name of a tail
nor does it approach in character that figured by Lounsbury in R. appendi-
culatus.
G
In spite of certain slight variations among my specimens I have been
unable to satisfy myself that there is more than a single species which corre-
sponds with Neumann's description of R. sanguineus (Latreille).
R. SANGUINEUS (LATREILLE).
R. sanguineus drops from its host after engorgement in each of its three
stages, and whether in these it attacks the same or different dogs is determined
by chance.
The fully replete female after dropping from the dog at once proceeds to
crawl away, climbing, if it can, upwards sometimes to a height of over fifteen feet
from the ground. Sooner or later it inserts the anterior portion or the whole of
its body into some crack. Very often the crack is an extremely narrow one,
much narrower than one would suppose it possible for the tick to enter; yet the
ticks will be found firmly wedged within it having become very flattened in the
process. The ova are laid by preference in some such situation, and where
ticks are kept in captivity in tubes with crumpled paper they always choose a
place to deposit their eggs where the paper lies against the glass or against
another piece of paper, the eggs being deposited under these circumstances in a
more or less flat sheet. The period of oviposition commences a few days after
the female has dropped from the host, and the eggs are passed out continuously
until the tick (shrivelled to one-third or one-quarter of its original size) eventually
dies. Oviposition takes as a rule about four to seven days. The larvæ hatch
in three or four weeks and crawl away, leaving the mass of empty egg-shells
behind. By degrees the larvæ collect into swarms, which at first sight resemble
masses of ova. These swarms are often of very great size and must be
composed of many thousands of individuals. In nature the larvæ collect near
the bottom of walls and when a dog brushes against this spot the larvæ transfer
themselves en bloc to the dog. The larvæ will not feed immediately they are
hatched, but require a period of some days' rest; hungry larvæ placed on a dog
become gorged and drop off in from three to four days, but some drop even
earlier. The larvæ care very little where they attach themselves, but usually
do so on the hairy parts of the body where they are not easily detected. The
gorged larvæ, which are little black seed-like bodies measuring about ¾ millimetre,
crawl away and secrete themselves in cracks. For a day or two if the gorged
larvæ are disturbed they crawl about, but eventually become quite inert and
apparently dead. After about 9 or 10 days the skin breaks posteriorly and the
nymph emerges.
The nymphs are light brown active creatures about the same size as the
gorged larvæ and except that they are only about one-fifth the size there is a
distinct general resemblance, even in the details of the rostrum, to the adult
43
tick. The nymphs crawl about and eventually find a host; they often are seen
in little clusters, but never in such number as are the larvæ. They attach
themselves chiefly to the skin of the body and may be seen and studied on the
bare skin of the belly. When fully gorged they are a repetition on a larger scale
of the gorged larva, and a forecast on a smaller scale of the gorged female adult.
They fall off and enter cracks, and like the larvæ become apparently lifeless.
The nymphs in this state can be collected and handled like seeds, to
which they have a strong resemblance. As they reach the time of eclysis
the front portion becomes of a dead white colour. A little later, about 15 days
after they have left their host, the nymphal skin cracks posteriorly and the adult
hatches out.
Both males and females hatch out about the same time. They are at first
quite soft and do not attach themselves for some days; then they get on portions
of straw, etc., and wait for their host with the front legs extended in the air. As
a rule the adult attaches itself to the ear and even quite deep in the meatus. It
is especially fond of a little pocket on the posterior border of the ear. They
also select the skin between the paws or that at the back of the neck. They may,
however, attach themselves to almost any part of the body.
Adult females take from a few days to a week or more to become fully
gorged and to drop off. The sexes attach themselves close together, the male
lying beneath the female and copulation no doubt takes place when so situated.
For the first 24 to 48 hours after attachment but little increase in size of the
female takes place; usually, however, by the end of the second or third day a
distinct increase in size is noticeable though the general colour of the tick is
still a dark brown. As the posterior portion of the female still further enlarges
it becomes a buff colour and eventually a slaty gray. When fully replete the
female measures 6 to 8 mm. in length.
The body of the tick is at first more or less uniformly distended, but after
some days when the eggs have accumulated in the extremely long oviducts the
anterior portion of the body is much swollen whilst the posterior parts are
flattened. During the first days after leaving the host the female is restless
and wanders about passing considerable quantities of the white malpighian
secretion. Once having settled down to oviposition she rarely again moves, or
if disturbed does not travel far.
The ova are lighter in colour than those of H. flava and more numerous,
but they are difficult to detect from those of many species of ticks. They
number some thousands and adhere loosely together on account of an oily cover-
ing which they receive from the "cephalic gland" described by me in a previ-
ous publ i c a t i on—a s t r uc t ur e whos e f unc t i on I f i nd ha d be e n a l r e a dy a s c e r t a i ne d
by Lounsbury.
G 2
44
The changes undergone at the metamorphoses are all important with refer-
ence to the development of the parasite and must be briefly referred to in order
to make intelligible the passage of piroplasma through the tick.
For the first twenty-four hours or somewhat longer after leaving the host
both larval and nymphal stages are active. At this time the organs are practi-
cally those of the unfed condition with the exception that the diverticula are
enormously distended with blood. After several days have passed the cuticle
becomes thicker and denser and the ticks exhibit no sign of life; but changes
in the tissues consisting in the formation of masses of undifferentiated embryo-
nic tissue are proceeding rapidly. After a certain time this embryonic tissue
forms a rough model of the future nymph or adult as the case may be, and this,
lying as it does loosely within the hard and rigid cuticle of the previous stage,
can with suitable manipulation be turned out upon the slide. In it can be made
out indications of the limbs, rostrum and other parts, all modelled in undifferen-
tiated tissue consisting of polygonal cells of about the same size and appearance.
Little by little the model becomes more exact and the cells differentiate to form
the cuticle, muscles, and organs of the future stage. It is necessary only to
follow in detail the formation of the salivary glands of the adult, since the changes
undergone in the larva are similar, but on account of the difficulty of manipulation
have not been followed so closely. In the embryonic adult each of the future
limbs is seen as a bud-like outgrowth merging at the base into a dense mass
of embryonic tissue. Quite early intercellular streaks which stain a reddish
colour with Romanowski stain appear. These are the rudiments of the future
intraglandular salivary ducts and they spread further and further among the
tissue cells as development proceeds. Closely applied to them are seen cells
which have smaller and darker staining nuclei than the rest of the tissue (Pl. III,
fig. 7, lower nucleus). These eventually form the ducts of the gland. The
acini are formed from cells lying at the side of the embryonic ducts (Pl. III,
fig. 7), each acinus originating from a cluster of cells which arrange themselves
regularly to form an embryonic acinus (Pl. III, figs. 2 and 3). In most of the
acini all these cells develop equally forming a multicellular acinus (fig 2),
but in the case of certain acini lying along the main ducts one cell takes on
growth out of all proportion to that of the rest resulting in the single celled
"poison" acini seen in the adult gland (figs. 3 and 9).
Of the apparently similar cells forming the mass of embryonic tissue at the
bases of the embryonic limbs some may be progenitors of cells of the salivary
acini whilst others eventually become muscular, fatty or tracheal tissue.
In the larva the salivary gland consists of only a few acini, some being of
the ordinary type and others of the poison type. In the nymph many more acini
exist, and in the final change a great portion of the embryonic tissue at the base
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of the legs becomes converted into salivary tissue, the salivary glands in the
adult occupying a comparatively enormous area in the body of the undistended
tick. The chance that any cell of the original embryonic tissue may in whole or
in part end by becoming salivary tissue is therefore considerable, and any para-
site embedding itself in one of these cells stands a very fair chance of eventually
finding itself in a salivary acinus. As will be seen later piroplasma makes still
further provision to this end.
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I V .
EXPERIMENTAL INFECTION.
The first successful investigations regarding the transmission of Piroplasma
canis by ticks were those of Lounsbury, who found that, though canine piroplas
-mosis, like Texas fever, is transmitted through the ovum, it is not induced by
the bite of larvæ hatched from ova of infected mothers, but by these only
after they had gone through two further metamorphoses and had reached the
adult state. These experiments of Lounsbury are so conclusive that there is
little necessity to consider them in detail. Experiments were also undertaken by
Lounsbury to see whether infection taken in at one stage of metamorphosis could
be transmitted at a later stage, as happens in the case of East Coast fever when
transmitted by R. appendiculatus. These experiments led Lounsbury to conclude
that such stage to stage transmission does not take place; but his experiments
in this respect are not so numerous or so conclusive as those connected with
hereditary transmission. Infection was later experimentally induced by Nuttall
in England by means of infected ticks ( H. leachi) sent to him by Lounsbury from
South Africa, a demonstration of a striking kind that canine piroplasmosis is a
tick-borne disease.
My own experiments have shewn that the tick R. sanguineus (Latreille) is
also capable of transmitting canine piroplasmosis and a demonstration similar to
that which has been given in the case of H. leachi also exists, since ticks ( R.
sanguineus ) taken home by Captain James, I.M.S., gave rise to a severe infec-
tion in a dog at the Lister Institute.
As in Lounsbury's experiments the hereditary method of transmission is
placed beyond doubt. Unfortunately conclusive experiments with regard to
stage to stage infection have not yet been carried out and the evidence for this
method of infection is at present based only on the microscopical observations
given in the next section.
My earlier experiments shewed that infection resulted from the bite of adults,
but they were not sufficiently closely watched to enable accurate deductions to
be drawn from them. This was rectified in later experiments given here where
every possible precaution was taken to exclude error and to follow the details of
the process.
The cages used were of iron and immediately before use they were plunged
into a vat of boiling water. The tables used were flooded with scalding water
48
and every crack thoroughly treated. In the laboratory the table legs were placed
in shallow trays filled with kerosene oil and separate tables were used for every
experiment.
The dogs used were of the best breed obtainable. Very young dogs though
advantageous in some respects were apt to die from other causes than
piroplasma and pups of medium size were therefore for the most part utilised.
Before being used in the experiments the dogs were quarantined in newly dipped
cages for a period of five days in order that any larvæ or nymphs they might
have upon them should drop off. The dogs were then removed to a fresh cage
until required. Control dogs from the litters used in the experiment were in a
proportion of cases kept under observation.
During the experiments the cages were kept surrounded with a muslin
sheet in each case fresh from the wash to enable fed ticks to be observed and
collected.
In some of the experiments the conditions were arranged to resemble what
takes place in nature, the sequence of the metamorphoses not being interfered
with. Under these circumstances cages became infective, every susceptible
dog placed in such cages contracting the disease. In others isolated feeding
experiments were made.
SERIES A.
Experiment 1 . — A batch of seven adults were collected from dog No. 97
in the early stages of an attack of piroplasmosis. Of these five were
dissected, four shewing club-shaped bodies in the ovaries. The larvæ from ova
laid by some of these and by the two remaining adults were on 25th October
1906 liberated in cage 5 containing dogs Nos. 100, 101, 102, 103 and 104, and
to these dogs the larvæ quickly attached themselves, fed larvæ being first seen
on 27th October 1906. On 27th October 1906 dogs Nos. 101, 102 and 104
were removed to a fresh cage and kept under observation. They all died from
malnutrition on the dates noted in the table, but lived long enough to shew that
the bite of the larvæ had not caused infection up to the 16th day. Dogs 100 and
103 died about the same time, no piroplasmata being found or any sign of
infection.
On 27th October 1906, dogs 111 and 112, both from the same litter, were
placed in the cage and were bitten by some of the larvæ which had not yet fed.
On the 4th November 1906 fully hatched nymphs derived from the original
larvæ were first seen and gorged specimens were abundant on 7th November
1906. So that nymphs almost certainly attached themselves to both dogs on
the 4th or 5th November 1906. Dog 111 died on 10th November 1906 and
dog 112 on 11th November 1906 with abundant piroplasma. These being
49
young dogs probably died 24 to 48 hours after the first appearance of parasites,
making the incubation period, supposing they were infected by the larvæ, about
13 days, or, as appeared to be the case if infected by the nymphs, 5 days. In
spite of the shortness of the latter mentioned time and the difference between
the time of incubation and that given by other observers it is probable, as will be
seen from later experiments, that it was the nymphs that gave rise to the
infection with a short incubation period. In the salivary glands of rather a
small proportion of nymphs from this cage the bodies shewn in Pl. III, fig. 6,
and Pl. II, fig. 30, and described later were at this time seen.
On 13th November 1906 dogs 121 and 122 were added to the cage. They
were at once attacked by nymphs which had not yet fed. On 16th November
1906 the blood was negative. On 17th November 1906 dog No, 121 had
scanty piroplasma and 122 was negative. On 20th November 1906 dog 121
died of the typical acute disease with hæmoglobinuria. Dog 122 on this date
was still free from piroplasma. On the 22nd November 1906 numerous adults
which had hatched from the nymphs were observed and some had attached
themselves to dog 122. On 28th November 1906 dog 122 shewed a scanty
infection afterwards developing a very severe form of the disease with paralysis
of the hind legs and hæmoglobinuria and dying on 30th November 1906. In
this case the number of nymphs available to feed on Nos. 121 and 122 were not
very many, and No. 122 appears to have escaped infection from this source,
but to have succumbed to infection derived from the numerous adults in whose
salivary glands parasites were detected by microscopic examination.
Control dog 113 of the same litter as 111 and 112 but not used for experi-
ment remained free from piroplasma.
Experiment 2.—Two dogs, Nos. 127 and 129, from a litter of four, the other
two dogs, 128 and 130, being kept as controls, were placed in a cage on 29th
November 1906 with adults removed from cage 5. On 4th December 1906 both
shewed abundant piroplasma, but eventually recovered after a mild attack.
Controls 128 and 130 up to and on 27th December 1906, on which date they
were destroyed, shewed no piroplasma.
Experiment 3.—Two dogs, 135 and 136, were placed in a cage on 10th
December 1906 along with adults collected from cage 5 kept up to this time in
test tubes in the laboratory. On 18th December 1906 both dogs were observed
to be ill and extremely numerous parasites were found in the blood of both.
Dog 135 died on the same day and 136 some days later.
In the series of experiments both nymphs and adults undoubtedly gave
rise to infection. The experiments as regards the non-infectivity of the larvæ
were not, however, so conclusive as could be wished owing to the dogs used at
the beginning being too young.
H
50
SERIES B.
Experiment 4.—A number of adults were collected on 18th September 1906 ;
from dog go four days after large numbers of parasites had been seen in the
blood. The larvæ hatched out from ova laid by these were placed on dogs 109
and 110 in cage No. 3. On 4th November 1906 newly hatched nymphs were
observed and gorged nymphs were seen on 7th November 1906. On 12th
November 1906 both dogs shewed swarming piroplasma, dog 109 dying on the
15th November 1906 and dog 110 being killed the same day. The same
remarks apply to these dogs as to 111 and 112 in experiment No. 1.
On 13th November 1906 dogs 105 and 107 from a litter of which the other
two dogs, 106 and 108, were used in experiment No. 6 were added to the cage.
Both dogs, but especially dog 107, were attacked at once by nymphs, in the sali-
vary glands of about half of which parasites were present. On 16th November
1906 dog 107 had scanty piroplasma and on 17th November 1906 both were
infected. Dog 107 died on 19th November 1906 with paralysis of the hind legs
and hæmoglobinuria and dog 105 recovered. A few adults were first seen in the
cage on 14th November 1906. The other dogs of the litter, 106 and 108, used
in the experiments with R. bursa remained free from infection. The incubation
period following the bite of the nymph in this case was four days.
On 11th December 1906 dogs 131 and 132 were placed in the cage. On
21st December 1906 both dogs were observed to have pallid tongues and piro-
plasmata were found in their blood.
Experiment 5.—On 10th December 1906 two dogs, 139 and 140, from a
litter of five healthy dogs of large English breed, of which 137 and 138 were
kept as controls, were placed in a cage with adults hatched from gorged nymphs
collected from cage 3. On 18th December 1906 both shewed a rise of temper-
ature and numerous piroplasmata were present in the blood. The control dogs
137 and 138 remained free from infection for many weeks.
Experiment 6.—An experiment on similar lines to Nos. 1 and 4 was carried
out with larvæ from adult R. bursa which had been fed on dog No. 86 when
parasites abounded in the blood. On 25th October 1906 dogs 106 and 108
were placed in cage 6 with very numerous larvæ. On 28th October 1906 two
other dogs, 118 and 119, were added to the cage. All the dogs were bitten by
nymphs of R. bursa, fed nymphs being seen in immense numbers. On 20th
November 1906 many adult R. bursa had attached themselves. None of the
dogs became infected throughout the whole course of the experiment.
These experiments shew conclusively that infection is passed on by the
mother tick to her progeny and that this infection is transmissible by the
nymphs.
51
As regards the continuance of the power of transmission to the adult one
cannot be so dogmatic for the following reasons. In R. sanguineus it is almost
certain from evidence given later that stage to stage transmission as well as
hereditarily transmitted infection takes place. Dealing then with so short an
incubation period the possibility of reinfection of at least some of the nymphs
and the passage of infection by this means to the adult cannot without special
precautions, not taken in these experiments, be rigidly excluded. In the experi-
ments of series B such a reinfection almost certainly took place and it cannot be
excluded in others. It is, however, from the nature of the development of the
parasite quite reasonable to suppose that a continuance of infectivity from the
nymph to the adult may take place.
Again as regards the larva the experiments are too few to determine with
certainty that the larva never transmits. That it did not do so in the heavily
infected ticks used in the present experiments is, however, suggestive that it is,
as in H. leachi, non-infective.
Further feeding experiments to determine a number of details are necessary,
but since the main facts for the demonstration of which they were designed are
quite clear and since they were undertaken mainly to enable observations to be
made upon the parasite they will for the present suffice.
H 2