Handbook of Medical Entomology Part 7

Most recent writers agree that, on man, they do not bore into the skin, as is generally supposed, but enter a hair follicle or sebaceous gland and from the bottom of this, pierce the cutis with their elongate hypopharynx. According to Braun, there arises about the inserted hypopharynx a fibrous secretion--the so-called "beak" which is, in reality, a product of the host. Dr. J. C. Bradley, however, has made careful observations on their method of attack, and he a.s.sures us that the mite ordinarily remains for a long time feeding on the surface of the skin, where it produces the erythema above described. During this time it is not buried in the skin but is able to retreat rapidly into it through a hair follicle or sweat gland. The irritation from the mites ceases after a few days, but not infrequently the intolerable itching leads to so much scratching that secondary infection follows.

Relief from the irritation may be afforded by taking a warm salt bath as soon as possible after exposure or by killing the mites by application of benzine, sulphur ointment or carbolized vaseline. When they are few in number, they can be picked out with a sterile needle.

Much may be done in the way of warding off their attacks by wearing gaiters or close-woven stockings extending from ankle to the knee. Still more efficacious is the sprinkling of flowers of sulphur in the stockings and the underclothes from a little above the knee, down. The writers have known this to make it possible for persons who were especially susceptible to work with perfect comfort in badly infested regions. Powdered naphthalene is successfully used in the same way and as Chittenden (1906) points out, is a safeguard against various forms of man-infesting tropical insect pests.

The question of the destruction of the mites in the field is sometimes an important one, and under some conditions, is feasible. Chittenden states that much can be accomplished by keeping the gra.s.s, weeds, and useless herbage mowed closely, so as to expose the mites to the sun. He believes that in some cases good may be done by dusting the gra.s.s and other plants, after cutting, with flowers of sulphur or by spraying with dilute kerosene emulsion in which sulphur has been mixed. More recently (1914) he calls attention to the value of cattle, and more especially sheep, in destroying the pests by tramping on them and by keeping the gra.s.s and herbage closely cropped.

IXODOIDEA OR TICKS

Until recently, the ticks attracted comparatively little attention from entomologists. Since their importance as carriers of disease has been established, interest in the group has been enormously stimulated and now they rank second only to the mosquitoes in the amount of detailed study that has been devoted to them.

[Ill.u.s.tration: 45_a_. Argus persicus. Capitulum of male. After Nuttall and Warburton.]

The ticks are the largest of the Acarina. They are characterized by the fact that the hypostome, or "tongue" (fig. 45) is large and file-like, roughened by sharp teeth. They possess a breathing pore on each side of the body, above the third or fourth c.o.xae (fig. 45_b_).

[Ill.u.s.tration: 45_b_. Left spiracle of nymph of _Argas persicus_. After Nuttall and Warburton.]

There are two distinct families of the IXODOIDEA, differing greatly in structure, life-history and habits. These are the ARGASIDae and the IXODIDae. We shall follow Nuttall (1908) in characterizing these two families and in pointing out their biological differences, and shall discuss briefly the more important species which attack man. The consideration of the ticks as carriers of disease will be reserved for a later chapter.

Argasidae

In the ticks belonging to the family ARGASIDae, there is comparatively little s.e.xual dimorphism, while this is very marked in the Ixodidae. The capitulum, or so-called "head" is ventral, instead of terminal; the palpi are leg-like, with the segments subequal; the scutum, or dorsal s.h.i.+eld, is absent; eyes, when present, are lateral, on suprac.o.xal folds.

The spiracles are very small; c.o.xae unarmed; tarsi without ventral spurs, and the pulvilli are absent or rudimentary.

In habits and life history the Argasidae present striking characteristics. In the first place, they are long-lived, a factor which counts for much in the maintenance of the species. They are intermittent feeders, being comparable with the bed-bug in this respect. There are two or more nymphal stages, and they may molt after attaining maturity.

The female lays comparatively few eggs in several small batches.

Nuttall (1911) concludes that "The Argasidae represent the relatively primitive type of ticks because they are less constantly parasitic than are the Ixodidae. Their nymphs and adults are rapid feeders and chiefly infest the habitat of their hosts. * * * Owing to the Argasidae infesting the habitats of their hosts, their resistance to prolonged starvation and their rapid feeding habits, they do not need to bring forth a large progeny, because there is less loss of life in the various stages, as compared with the Ixodidae, prior to their attaining maturity."

[Ill.u.s.tration: 46. Argus persicus. Dorsal and ventral aspects. (4).

After Ha.s.sell.]

Of the Argasidae, we have in the United States, several species which have been reported as attacking man.

_Argas persicus_, the famous "Miana bug" (fig. 46), is a very widely distributed species, being reported from Europe, Asia, Africa, and Australia. It is everywhere preeminently a parasite of fowls. According to Nuttall it is specifically identical with _Argas america.n.u.s_ Packard or _Argas miniatus_ Koch, which is commonly found on fowls in the United States, in the South and Southwest. Its habits are comparable to those of the bed-bug. It feeds intermittently, primarily at night, and instead of remaining on its host, it then retreats to cracks and crevices.

Hunter and Hooker (1908) record that they have found the larva to remain attached for five or eight days before dropping. Unlike the Ixodidae, the adults oviposit frequently.

[Ill.u.s.tration: 47. Otiobius (Ornithodoros) megnini, head of nymph. After Stiles.]

[Ill.u.s.tration: 48. Otiobius (Ornithodoros) megnini, male. (_a_) dorsal, (_b_) ventral aspect. After Nuttall and Warburton.]

The most remarkable feature of the biology of this species is the great longevity, especially of the adult. Hunter and Hooker report keeping larvae confined in summer in pill boxes immediately after hatching for about two months while under similar conditions those of the Ixodid, _Boophilus annulatus_ lived for but two or three days. Many writers have recorded keeping adults for long periods without food. We have kept specimens in a tin box for over a year and a half and at the end of that time a number were still alive. Laboulliene kept unfed adults for over three years. In view of the effectiveness of sulphur in warding off the attacks of Trombidiidae, it is astonis.h.i.+ng to find that Lounsbury has kept adults of _Argas persicus_ for three months in a box nearly filled with flowers of sulphur, with no apparent effect on them.

We have already called attention to the occasional serious effects of the bites of this species. While such reports have been frequently discredited there can be no doubt that they have foundation in fact. The readiness with which this tick attacks man, and the extent to which old huts may be infested makes it especially troublesome.

_Otiobius (Ornithodoros) megnini_, the "spinose ear-tick" (figs. 47, 48), first described from Mexico, as occurring in the ears of horses, is a common species in our Southwestern States and is recorded by Banks as occurring as far north as Iowa.

The species is remarkable for the great difference between the spiny nymph stage and the adult. The life history has been worked out by Hooker (1908). Seed ticks, having gained entrance to the ear, attach deeply down in the folds, engorge, and in about five days, molt; as nymphs with their spinose body they appear entirely unlike the larvae. As nymphs they continue feeding sometimes for months. Finally the nymph leaves the host, molts to form the unspined adult, and without further feeding is fertilized and commences oviposition.

The common name is due to the fact that in the young stage the ticks occur in the ear of their hosts, usually horses or cattle. Not uncommonly it has been reported as occurring in the ear of man and causing very severe pain. Stiles recommends that it be removed by pouring some bland oil into the ear.

Banks (1908) reports three species of _Ornithodoros_--_O. turicata_, _coriaceus_ and _talaje_--as occurring in the United States. All of these attack man and are capable of inflicting very painful bites.

Ixodidae

The ticks belonging to the family IXODIDae (figs. 49 and 50) exhibit a marked s.e.xual dimorphism. The capitulum is anterior, terminal, instead of ventral as in the Argasidae; the palpi are relatively rigid (except in the subfamily Ixodinae), with rudimentary fourth segment; scutum present; eyes, when present, dorsal, on side of scutum. The spiracles are generally large, situated well behind the fourth c.o.xae; c.o.xae generally with spurs; pulvilli always present.

In habits and life history the typical Ixodidae differ greatly from the Argasidae. They are relatively short-lived, though some recent work indicates that their longevity has been considerably under-estimated.

Typically, they are permanent feeders, remaining on the host, or hosts, during the greater part of their life. They molt twice only, on leaving the larval and the nymphal stages. The adult female deposits a single, large batch of eggs. Contrasting the habits of the Ixodidae to those of the Argasidae, Nuttall (1911) emphasizes that the Ixodidae are more highly specialized parasites. "The majority are parasitic on hosts having no fixed habitat and consequently all stages, as a rule, occur upon the host."

[Ill.u.s.tration: 49. Ixodes ricinus; male, ventral aspect. After Braun and Luehe.]

As mere parasites of man, apart from their power to transmit disease, the Ixodidae are much less important than the Argasidae. Many are reported as occasionally attacking man and of these the following native species may be mentioned.

[Ill.u.s.tration: 50. Ixodes ricinus, var. scapularis, female. Capitulum and scutum; ventral aspect of capitulum; c.o.xae; tarsus 4; spiracle; genital and a.n.a.l grooves. After Nuttall and Warburton.]

_Ixodes ricinus_, the European castor bean tick (figs. 49, 50), is a species which has been often reported from this country but Banks (1908) has shown that, though it does occur, practically all of the records apply to _Ixodes scapularis_ or _Ixodes cookei_. In Europe, _Ixodes ricinus_ is very abundant and very commonly attacks man. At the point of penetration of the hypostome there is more or less inflammation but serious injury does not occur unless there have been introduced pathogenic bacteria or, unless the tick has been abruptly removed, leaving the capitulum in the wound. Under the latter circ.u.mstances, there may be an abscess formed about the foreign body and occasionally, serious results have followed. Under certain conditions the tick, in various stages, may penetrate under the skin and produce a tumor, within which it may survive for a considerable period of time.

_Ixodes cookei_ is given by Banks as "common on mammals in the Eastern States as far west as the Rockies." It is said to affect man severely.

_Amblyomma americanum_, (fig. 158c), the "lone star tick," is widely distributed in the United States. Its common name is derived from the single silvery spot on the scutum of the female. Hunter and Hooker regard this species as, next to _Boophilus annulatus_, the most important tick in the United States. Though more common on cattle, it appears to attack mammals generally, and "in portions of Louisiana and Texas it becomes a pest of considerable importance to moss gatherers and other persons who spend much time in the forests."

_Amblyomma cajennense_, noted as a pest of man in central and tropical America, is reported from various places in the south and southwestern United States.

_Dermacentor variabilis_ is a common dog tick of the eastern United States. It frequently attacks man, but the direct effects of its bite are negligible.

The "Rocky Mountain spotted fever tick" (_Dermacentor andersoni_ according to Stiles, _D. venustus_ according to Banks) is, from the viewpoint of its effects on man, the most important of the ticks of the United States. This is because, as has been clearly established, it transmits the so-called "spotted fever" of man in our northwestern states. This phase of the subject will be discussed later and it need merely be mentioned here, that this species has been reported as causing painful injuries by its bites. Dr. Stiles states that he has seen cases of rather severe lymphangitis and various sores and swellings developing from this cause. In one case, of an individual bitten near the elbow, the arm became very much swollen and the patient was confined in bed for several days. The so-called tick paralysis produced by this species is discussed in a preceding chapter.

There are many other records of various species of ticks attacking man, but the above-mentioned will serve as typical and it is not necessary to enter into greater detail.

TREATMENT OF TICK BITES--When a tick attaches to man the first thing to be done is to remove it without leaving the hypostome in the wound to fester and bring about secondary effects. This is best accomplished by applying to the tick's body some substance which will cause it to more readily loosen its hold. Gasoline or petroleum, oil or vaseline will serve. For removing the spinose ear-tick, Stiles recommends pouring some bland oil into the ear. Others have used effectively a pledget of cotton soaked in chloroform.

In general, the treatment recommended by Wellman for the bites of _Ornithodoros moubata_ will prove helpful. It consists of prolonged bathing in very hot water, followed by the application of a strong solution of bicarbonate of soda, which is allowed to dry upon the skin.

He states that this treatment is comforting. For severe itching he advises smearing the bites with vaseline, which is slightly impregnated with camphor or menthol. Medical aid should be sought when complications arise.

The DERMANYSSIDae are Gamasid mites which differ from others of the group in that they are parasitic on vertebrates. None of the species normally attack man, but certain of them, especially the poultry mite, may be accidental annoyances.

[Ill.u.s.tration: 51. Dermanyssus gallinae, female. After Delafond.]

_Dermanyssus gallinae_ (fig. 51), the red mite of poultry, is an exceedingly common and widespread parasite of fowls. During the day it lives in cracks and crevices of poultry houses, under supports of roosts, and in litter of the food and nests, coming out at night to feed. They often attack people working in poultry houses or handling and plucking infested fowls. They may cause an intense pruritis, but they do not produce a true dermatosis, for they do not find conditions favorable for multiplication on the skin of man.

Tarsonemidae