NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
THE ANATOMY AND HISTOLOGY OF TICKS.
INTRODUCTION.
W HILE the external characters of ticks have, especially of late, received a
good deal of attention from observers, the memoirs of Neumann 23
forming, for example, a complete systematic work on the subject, it is otherwise in
the case of the internal structure. This has been scarcely touched upon by
most authors, and, so far as I am aware, no full or systematic account of the
anatomy of the tick exists. Even isolated observations upon the subject are
curiously meagre and very difficult of access.
Yet the existence, almost proved, of a developmental cycle of Piroplasma
in the tick, and the probability that some spirochætes of the blood of man
and animals also undergo developmental changes in the tick, have made it most
desirable that we should have at least a general knowledge of the tissues of these
blood-suckers.
The following account of the anatomy and histology of Ornithodoros
savignyi (Audouin) has been written, therefore, with the hope that, by supplying
the want already alluded to, it will assist future research upon the development
in the tick of the spirochaætes of " tick fever " and of other spirilloses. At the
same time I have endeavoured to make the work applicable to the investigation
of Piroplasma by studying a species of Rhipicephalus (R. annulatus) and one
of Hyalomma(H. ægyptium), examples of theRhipicephalinæandIxodinæ
respectively.
A close study of these two species and a more general investigation of a num-
ber of species of different genera, viz. Hæmaphysalis, Ixodes, and Aponomma,
has demonstrated in the different scutum-bearing ticks a very close similarity in
the structure and arrangement of the organs. Even the differences between the
Ixodidæ and the Argasidæ, are by no means great. I have found it sufficient
therefore to describe a single type only, i.e. Rhipicephalus to represent the
Ixodidæ, whilst Ornithodoros has been taken as representing the Argasidæ.
The two types will subserve our present purpose of elucidating the structure of
ticks, and one or other type will probably be found applicable, with but few
modifications, to any species investigated.
In addition to observations relating to the structure of ticks, I have also
added some others upon the life processes, regarding many of which there is
This paper was received on September 12th, 1905.
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2
scope for investigation, and upon the embryology of ticks, a matter of obvious
importance, where the production of disease involves hereditary transmission
of the virus.
For the opportunity of studying Ornithodoros I am entirely indebted to
Dr. Oliver of the South Indian Railway, who first drew my attention to the
presence of this tick in Southern India, and has kept me supplied with material.
3
I.
TICKS AS TRANSMITTERS OF DISEASE.
O N account of its great economic importance and also from its intrinsi
interest, the reaction of ticks to the piroplasmoses of cattle has been the
subject of much work, and has led to the accumulation of a large literature.
Smith and Kilborne 1 demonstrated the transmission by ticks of the disease
known as Texas Fever of cattle so long ago as 1893. The researches of Koch 2,
Theiler 3, and others have since shown that it is possible to distinguish several,
apparently distinct, piroplasmoses in cattle, all of which, it would appear, are
conveyed by some or other species of tick. Donitz 4, in a résumé of the subject
gives twelve species of Rhipicephalus, which are at present known, or suspected,
to be concerned in the spread of these cattle diseases in various parts of the
world. It will be sufficient for our present purpose to note that, from the first,
it has been recognised, that transmission occurs, not by ticks, which have
themselves fed on an infective animal, but by their progeny.
Ticks ( Rhipicephalus bursa) have been shewn by Motas 5, to convey
piroplasmosis in sheep, and Bowhill 6 remarks, that it is more than probable,
that piroplasmosis in horses (P. equi) is also spread in this way.
Recently Lounsbury 7 has shown that ticks (Hæmaphysalis leachi), are in-
s t r u m e n t a l i n t h e t r a n s m i s s i o n of a piroplasmosis in dogs (Malignant Jaundice of
the Dog). Nuttall8 confirms Lounsbury in this respect, and gives some very con-
vincing results, since he succeeded in producing the disease in dogs in England,
by means of ticks infected in South Africa. According to Lounsbury, the method
of transmission in the case of the dog disease differs from that in Texas fever,
in that neither the larvæ, nor the nymphs, from an infected mother are patho-
genic. In malignant jaundice of the dog, only the adult ticks derived from
an infected mother are capable of giving rise to the disease. Nuttall's results
confirm this, inasmuch as his successful cases were obtained with adult ticks,
whose mothers alone had fed on infected dogs. There is, therefore, at present a
good deal of diversity in the evidence, as to when ticks are infective. The very
definite results in the case of the dog disease seems to show clearly, that adults
of the second generation may transmit infection, though as larvæ and nymphs
they only harbour it. What mechanism is involved in a process apparently so
complex cannot at present even be guessed at.
Whilst ticks have been known for some time as carriers of the Piroplasmata,
it has only recently been ascertained that they are agents in the transmission of
certain spirochætæ. The first indication that this is the case was given by the
researches of Marchoux and Salimbeni 9, who found a tick, Argas miniatus,
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4
concerned in the spread of an epidemic spirillosis among domestic fowls in Brazil.
This important discovery had the immediate result of focussing attention upon
the subject of tick-borne disease in man, which had, up to this time, been mainly
conjectural.
That ticks will at times attack man has been noted by several observers.
Anderson 10and Wilson and Chowning11even attribute the transmission of a
human piroplasmosis ( P. hominis) to a species of Dermacentor, though Stiles 1 2
throws grave doubts upon the accuracy of these observations. It would appear
that in most cases these ticks are species, whose usual host is some other animal
and the only species which at present are actually known to attack man
habitually, are certain ticks, which have been made known to us in the first place
by travellers. Such ticks have been described as occurring in Persia, and in parts
of Africa, but they are also reported from Mexico and elsewhere. Their habits
resemble those of the common bed bug, and they appear to be veritable human
parasites.
Quite recently our knowledge of these ticks has become more precise, though
it is still far from being complete. The differentiation and nomenclature of the
species is in some confusion, but they all belong to the Argasidæ, and have up to
the present been included in two genera, Argas and Ornithodoros. The species
so far known are :
—
Argas persicus (Fischer).
Argas tholozani (Lab. et Meg).
Ornithodoros moubata (Murray).
Ornithodoros savignyi (Andouin).
Ornithodoros savignyi var. cæca (Neumann).
It is probable that the list will require expansion, especially as recently
ticks of this nature have been reported from parts of the world where their
presence was not previously known. Ornithodoros moubata is an African
species, apparently identical with O. savignyi var. cæca (Neumann), O. savignyi
(Andouin) also has a wide distribution in Africa, being found in the Cape and
in Egypt. A species resembling O. moubata is reported from Brazil by
Christy 13.Argas turicata(Duges) andA. megnini(Duges) are said by Duges
to attack man freely in Mexico, and a similar readiness to feed on human blood
is noted by Hassal 19in the case of the American fowl tickA. miniatus,and
by Gibert 18for the pigeon tick,A. reflexus.
The chief interest in regard to these ticks lies in the fact that their bite is
credited with causing, not only acute local symptoms, but also at times severe con-
stitutional disturbance, and even death, an effect which it is difficult to imagine
could arise from the normal secretions of the tick. A disease attributed to the
bite of the Tete tick ( O. moubata) is described by both Livingstone and Sir John
5
Kirk. Daniels14 has given a description of a case seen by him at Tete
and considered the evidence for such a disease convincing. Ross and
Milne 15, whilst drawing attention to a so-called "Tick fever" in Uganda,
state that, in eight out of eight cases, they have found spirochætes in the blood.
Dutton and Todd 16, who had been working independently and in ignorance of
the results of the last-mentioned observers, shortly afterwards announced that
"tick fever" on the Congo was due to infection with a spirochæte resembling,
but not identical with, the S. obermeieri, and that it could be transmitted to
monkeys by means of the bite of infected ticks. Wellman 20 describing a case of
relapsing fever in Angola, considers it probable that "tick fever" is merely
infection with S. obermeieri, and doubts whether it is conveyed only by ticks.
The results of Dutton and Todd, who succeeded in infecting monkeys with young
ticks* of the second generation, certainly suggest that the parasite passes
through some developmental cycle in the tick, in which case it is probable that
the tick acts as the specific agent in its dissemination. At any rate there would
appear to be no reason to doubt that such a disease as "tick fever" exists, and
it can serve no useful purpose to discuss here the relationship of the spirochæte
of tick fever, since at present practically nothing is known concerning human
spirillosis.
"Tick fever," as described by the African observers, has a somewhat ob-
scure symptomatology. It has a tendency to relapse, as in the disease due to the
S. obermeieri. There is extreme constitutional depression, though apparently not,
as a rule, high fever. A characteristic symptom is diarrhœa. The spirillum
is usually present only in small numbers in the peripheral blood, and is easily
overlooked. The disease is therefore not one which is likely to obtrude itself
where attention is not specially directed to its diagnosis. So far the disease is
known to occur in the Zambesi valley, in Uganda, and at Entebbe on the Congo.
It seems not unlikely that it will be found elsewhere.
In India there is no recognised disease of the nature of the "tick fever" of
Africa. Captain Browse, I.M.S. 17, has reported spirilla in the blood of man in
Northern India, but at present it is impossible to say whether such bodies are
S. obermeieri, or other spirochætes. As previously remarked, tick fever may,
in practice, be readily overlooked, and the disease may still turn out to be of
importance in connection with the many obscure fevers, which are so common
in Indian hospitals. Even the well-known "Relapsing fever" might well repay
more study from the ætiological point of view than it has yet received.
That human ticks are not absent from India was brought to my notice by
* NOTE.—In the case of O. savignyi (Andouin) the larva, as will be seen later, is inactive and apparently
quite incapable of sucking blood. If a similar condition hold good in the case of O. savignyi var. cæca
(Neumann), infection can take place only after the casting of the larval skin and by the nymph.
6
Dr. Oliver, who has been, so far as I am aware, the first to note their existence.
After telling me of a tick known to him as the Tiripati tick, which appeared to be
of this nature, he forwarded a number of specimens, which have been identified
by Mr. Pocock as 0. savignyi (Audouin). Afterwards Major Donovan, I.M.S.,
through one of his students was able to get many specimens from Kalahasti, whilst
I have also received several hundreds sent by Dr. Oliver's Assistant, M. P. Vera-
swamy Naidu, from Tiripati West, Yerfed, Gekakur, and Vendod. I have since
received specimens sent by Dr. Chandra Sekar of the Madras Medical College
from Tanjore and Conjeeveram. Human ticks are therefore widely distributed
in the Madras Presidency and probably elsewhere in India.
Dr. Oliver obtained his specimens from the gravelly floor of the third class
passenger sheds, a situation in which many natives are accustomed to spend the
night. I have been informed, from another source, that the ticks are also
common in Tiripati town, some miles away from the railway station. Dr. Oliver
informs me that "ulcers" and severe fever are popularly supposed to result from
the bite of the ticks. So far, I have not succeeded in infecting monkeys by
means of ticks sent from Tiripati. Most of these were large specimens, and it
is possible that younger ticks are necessary for the purpose. Even though the
species has not yet been found to transmit the spirochæte of tropical spirillosis,
the possible significance of such a blood-sucking parasite of man cannot be
overlooked, and it is very desirable that its distribution and comparative pre-
valence in India should be ascertained.
It is of interest that specimens of the camel tick of Aden sent to me by
Captain Patton, I.M.S., are a species of Ornithodoros, probably O. savignyi.
Captain Patton tells me that these ticks are very common and attack man
freely.
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II.
THE BIONOMICS OF TICKS.
T HE life processes of ticks have been observed chiefly in the case of species
infesting domestic animals. Hart 3 0 , H a s s a l
2 6
, L o u n s b u r y
3 1
a n d o t h e r s h a v e
also made observations upon the Argasidæ. It is evident that considerable
scope for investigation, especially in regard to the natural history of the latter
family, still exists.
The habits of the Ixodidæ and of the Argasidæ are by no means similar.
The Ixodidæ.—A number of species of Rhipicephalus have been closely
observed, as regards their habits, notably R. Annulatus by Salmon and Stiles2 8
and R. Decoloratus by Lounsbury. 29 Theiler 3 and others have described the
habits of species of Amblyomma and Hyalomma. Lounsbury and Nuttall have
described very fully the life processes in Hæmaphysalis leachi a dog tick.
In the main, the habits of the different species are similar, but differences,
especially in certain particulars, exist.
The ova of the I xodi dæa r e l a i d i n m a s s e s r e s e m b l i n g f i s h - r o e i n a p p e a r a n c e .
Lounsbury gives 2,000 to 4,000 as the number of ova laid by a single gravid
female of H. leachi. An equally large number is the rule in the family. The
eggs are oval in shape and of a light yelldw, brown, or red colour. They
measure approximately 400 μ b y 3 0 0
μ i n d i a m e t e r . H a t c h i n g t a k e s p l a c e ,
as a rule, only after some considerable time (weeks or months). Many of
the ova laid by fully gorged females, which I have at various times removed
from naturally infested animals, have failed to hatch out at all. Lounsbury
notes a similar heavy mortality in the larvæ. Gravid females of cattle ticks will
generally deposit their ova in any situation where they may be confined, but
it is very possible that in nature they crawl to some suitable place for the
purpose. Lounsbury notes that the dog tick, H. leachi, probably, in nature,
deposits its ova in cracks, rather than upon the earth. The same habit is very
noticeable in the case of the dog tick of Madras, a species of rhipicephalus, which
climbs to a height of fifteen feet or more in search for a suitable spot to lay its
eggs. Females removed from their host when fully gorged, crawl for two or
three days over the bottom of the vessel in which they are confined. Some
species readily climb the vertical surface of the glass vessel, but others do
not attempt this. Sooner or later the female becomes quiescent and remains
at one spot without movement. The plump and distended appearance which
the tick exhibits on its first removal from the host gradually becomes less
conspicuous, whilst certain very characteristic bright yellow areas appear and
increase rapidly in size. These areas are due to the distension of the malpighian
8
tubules with their products, which at this time accumulate rapidly. At this
time also, ticks pass large quantities of a dead white material, which is derived
from the malpighian tubules, and cannot be regarded as fæces in the true sense
of the term. Coincidently with these changes ova are passed from the genital
pore. In ticks at this time, the anterior portion of the body, lying between the
first pair of legs, is usually depressed, so as to form a more or less cup-shaped
hollow. The lateral edges are accentuated in some instances ( Hyalomma
ægyptium ) by a thickening of the chitin. Within the hollow are situated the
head and the genital orifice. As the ova are laid, the tick moves slightly back-
wards, so that the eggs are deposited in a heap in front of it. After the process,
which takes several days at least to complete, is over, the tick gradually shrivels
up and dies.
On hatching from the ovum, the young larval ticks are minute hexapod
creatures. They differ considerably in general appearance from the adult tick,
and are without sexual organs. The newly-hatched larvæ attach themselves, as
soon as possible, to some vertebrate and suck blood. The larva then gorges
itself and after a few days casts its skin. It emerges as an octopod nymph
which differs from the mature form mainly in the absence of any sexual opening.
The nymph, again becomes engorged, moults, and emerges as the adult tick.
The habits at these times vary greatly in the case of different species.
R. annulatus remains attached to the same host throughout all the changes
(Nuttall8). According to Theiler3 the same occurs in the case of R. decoloratus
(Koch). Ixodes reduvius, according to Kossel and Weber 27, leaves its host
before becoming adult, as also does R. evertsi and Hyalomma ægyptium (Theiler).
Finally some species leave their host at each change, namely, H. leachi
(Lounsbury), R. appendiculatus, R. simus and Amblyomma hebraeum (Theiler).
Donitz4 proposes to revive the genus Boophilus, founded in 1890 by Curtice, for
those Rhipicephali which go through development on the same animal, without
detaching themselves at any time, since he finds that such habits are accom-
panied by certain anatomical characters. Thus, according to this writer, the
two first mentioned species R. annulatus and R. decoloratus would be contained
in the genus Boophilus.
After casting the nymphal skin, pairing takes place. The males and
females may at this time often be found attached close together, and the male is
often covered by the more bulky female. The males, according to Lounsbury,
move about and may fertilise several females. Donitz 4 has observed the act of
copulation in Ixodes ricinus, R. appendiculatus, and R. evertsi. The proboscis
of the male, with the exception of the palps, is inserted into the vulva of the
female. The legs of the male, which are used as clasping organs, lie behind the
corresponding legs of the female. Donitz was unable to ascertain how the
9
seminal fluid reached the palps which, judging from their analogy with those
of spiders, should be accessory organs of copulation. From anatomical
considerations which are discussed later, there can be no doubt that the male
passes into the vulva of the female one or more spermatophores, or sacs
containing a large number of spermatozoa (see Sect. V, p. 24).
The female, after finally attaching herself, steadily distends with blood.
The time during which she remains on the host varies with the species. In the
case of some species it may be as short as twenty-four hours. During this time
the tick increases enormously in size, the body becoming enlarged out of all
proportion to the rostrum and legs. If an attempt be made to remove a tick at this
time, considerable force is necessary and the mouth parts are practically torn
from their situation in the tissues. When fully gorged the female tick drops to
the ground and shortly deposits her ova. After or during this act the female
dies. The males do not become gorged in the same manner as the female and
are therefore less conspicuous.
The Argasidæ.—The habits of the family have been described in the case
of A. miniatus, the American fowl tick, A. reflexus,the pigeon tick,O. savignyi
(Audouin), O. moubata and a few others. The different species show in the
main the same characteristics. My own observations have been made upon
O. savignyi (Audouin).
The general behaviour of these ticks is quite unlike that of the cattle ticks.
As would be gathered from the accounts of travellers, ticks of the genus are
mainly nocturnal in their habits, and conceal themselves by day. The specimens
from Tiripati buried themselves partly or wholly in the gravel during the day, but
issued forth at evening-time, and ran quickly about. At times, especially if one
breathes upon or gently disturbs the gravel, the ticks display considerable
excitement. If handled they at once sham death. In this condition the legs are
closely applied to the body and the tick is readily overlooked among fragments
of stick and stone. When running about, the ticks often exhibit a curious habit
of raising the first pair of legs, as though receiving in this way information as
regards their surroundings. When ticks were placed in glass or porcelain
vessels, a rapid tapping sound was sometimes heard. This appeared to be
due to a vibration of the hinder portion of the body, which was seen to occur
from time to time.
Ornithodorus savignyi is exceptionally hardy and can live many months
without food or moisture. Specimens are sent to me in perforated tin cannisters,
together with a quantity of the gravel in which they are found. Although the
journey by post takes forty-eight hours, the ticks invariably arrive in a living
condition. Placed in a dish with a little gravel, many of the ticks have lived
without food for over four months.
C