Handbook of Medical Entomology Part 2

OTHER VENOMOUS SPIDERS--While conclusive evidence regarding the venomous nature of spiders is meager and relates almost wholly to that of the genus _Latrodectus_, the group is a large one and we are not justified in dismissing arbitrarily, all accounts of injury from their bites.

Several species stand out as especially needing more detailed investigation.

_Chiracanthium nutrix_ is a common European species of the family Clubionidae, concerning which there is much conflicting testimony. Among the reports are two by distinguished scientists whose accounts of personal experiences cannot be ignored. A. Forel allowed a spider of this species to bite him and not only was the pain extreme, but the general symptoms were so severe that he had to be helped to his house.

The distinguished arachnologist, Bertkau reports that he, himself, was bitten and that an extreme, burning pain spread almost instantaneously over the arm and into the breast. There were slight chills the same day and throbbing pain at the wound lasted for days. While this particular species is not found in the United States, there are two other representatives of the genus and it is possible that they possess the same properties. We are unaware of any direct experimental work on the poison.

_Epeira diadema_, of Europe, belongs to a wholly different group, that of the orb-weavers, but has long been reputed venomous. Kobert was able to prepare from it an extract whose effects were very similar to that prepared from _Latrodectus_, though feebler in its action. Under ordinary circ.u.mstances this spider is unable to pierce the skin of man and though Kobert's results seem conclusive, the spider is little to be feared.

_Phidippus audax_ (_P. tripunctatus_) is one of our largest Attids, or jumping spiders. The late Dr. O. Lugger describes a case of severe poisoning from the bite of this spider and though details are lacking, it is quite possible that this and other large species of the same group, which stalk their prey, may possess a more active poison than that of web-building species.

SUMMARY--It is clearly established that our common spiders are not to be feared and that the stories regarding their virulence are almost wholly without foundation. On the other hand, the chances of secondary infection from the bites of some of the more powerful species are not to be ignored.

Probably all species possess a toxin secreted by the poison gland, virulent for insects and other normal prey of the spiders, but with little or no effect on man.

There are a very few species, notably of the genus _Latrodectus_, and possibly including the European _Chiracanthium nutrix_ and _Epeira diadema_, which possess, in addition, a toxalb.u.men derived from the general body tissue, which is of great virulence and may even cause death in man and the higher animals.

[Ill.u.s.tration: 10. A whip-scorpion (Mastigoproctus giganteus). Half natural size. After Comstock.]

THE PEDIPALPIDA OR WHIP-SCORPIONS

The tailed whip-scorpions, belonging to the family Thelyphonidae, are represented in the United States by the giant whip-scorpion _Mastigoproctus giganteus_ (fig. 10), which is common in Florida, Texas and some other parts of the South. In Florida, it is locally known as the "grampus" or "mule-killer" and is very greatly feared. There is no evidence that these fears have any foundation, and Dr. Marx states that there is neither a poison gland nor a pore in the claw of the chelicera.

THE SCORPIONIDA, OR TRUE SCORPIONS

The true scorpions are widely distributed throughout warm countries and everywhere bear an evil reputation. According to Comstock (1912), about a score of species occur in the Southern United States. These are comparatively small forms but in the tropics members of this group may reach a length of seven or eight inches. They are pre-eminently predaceous forms, which lie hidden during the day and seek their prey by night.

[Ill.u.s.tration: 11. A true scorpion. After Comstock.]

The scorpions (fig. 11) possess large pedipalpi, terminated by strongly developed claws, or chelae. They may be distinguished from all other Arachnids by the fact that the distinctly segmented abdomen is divided into a broad basal region of seven segments and a terminal, slender, tail-like division of five distinct segments.

The last segment of the abdomen, or telson, terminates in a ventrally-directed, sharp spine, and contains a pair of highly developed poison glands. These glands open by two small pores near the tip of the spine. Most of the species when running carry the tip of the abdomen bent upward over the back, and the prey, caught and held by the pedipalpi, is stung by inserting the spine of the telson and allowing it to remain for a time in the wound.

The glands themselves have been studied in _Prionurus citrinus_ by Wilson (1904). He found that each gland is covered by a sheet of muscle on its mesal and dorsal aspects, which may be described as the _compressor muscle_. The muscle of each side is inserted by its edge along the ventral inner surface of the chitinous wall of the telson, close to the middle line, and by a broader insertion laterally. A layer of fine connective tissue completely envelops each gland and forms the basis upon which the secreting cells rest. The secreting epithelium is columnar; and apparently of three different types of cells.

1. The most numerous have the appearance of mucous cells, resembling the goblet cells of columnar mucous membranes. The nucleus, surrounded by a small quant.i.ty of protoplasm staining with haematoxylin, lies close to the base of the cell.

2. Cells present in considerable numbers, the peripheral portions of which are filled with very numerous fine granules, staining with acid dyes such as methyl orange.

3. Cells few in number, filled with very large granules, or irregular ma.s.ses of a substance staining with haematoxylin.

The poison, according to Kobert (1893), is a limpid, acid-reacting fluid, soluble in water but insoluble in absolute alcohol and ether.

There are few data relative to its chemical nature. Wilson (1901) states that a common Egyptian species, _Buthus quinquestriatus_, has a specific gravity of 1.092, and contains 20.3% of solids and 8.4% ash.

The venom of different species appears to differ not only quant.i.tatively but qualitatively. The effects of the bite of the smaller species of the Southern United States may be painful but there is no satisfactory evidence that it is ever fatal. On the other hand, certain tropical species are exceedingly virulent and cases of death of man from the bite are common.

In the case of _Buthus quinquestriatus_, Wilson (1904) found the symptoms in animals to be hypersecretion, salivation and lachrymation, especially marked, convulsions followed by prolonged muscular spasm; death from asphyxia. The temperature shows a slight, rarely considerable, rise. Rapid and considerable increase of blood-pressure (observed in dogs) is followed by a gradual fall with slowing of the heart-beat. The coagulability of the blood is not affected.

An interesting phase of Wilson's work was the experiments on desert mammals. The condition under which these animals exist must frequently bring them in contact with scorpions, and he found that they possess a degree of immunity to the venom sufficient at least to protect them from the fatal effects of the sting.

As far as concerns its effect on man, Wilson found that much depended upon the age. As high as 60 per cent of the cases of children under five, resulted fatally. Caroroz (1865), states that in a Mexican state of 15,000 inhabitants, the scorpions were so abundant and so much feared that the authorities offered a bounty for their destruction. A result was a large number of fatalities, over two hundred per year. Most of the victims were children who had attempted to collect the scorpions.

The treatment usually employed in the case of bites by the more poisonous forms is similar to that for the bite of venomous snakes.

First, a tight ligature is applied above the wound so as to stop the flow of blood and lymph from that region. The wound is then freely excised and treated with a strong solution of permanganate of potash, or with lead and opium lotion.

In recent years there have been many attempts to prepare an antivenom, or antiserum comparable to what has been used so effectively in the case of snake bites. The most promising of these is that of Todd (1909), produced by the immunization of suitable animals. This antivenom proved capable of neutralizing the venom when mixed _in vitro_ and also acts both prophylactically and curatively in animals. Employed curatively in man, it appears to have a very marked effect on the intense pain following the sting, and the evidence so far indicates that its prompt use greatly reduces the chance of fatal results.

THE SOLPUGIDA, OR SOLPUGIDS

The SOLPUGIDA are peculiar spider-like forms which are distinguished from nearly all other arachnids by the fact that they possess no true cephalothorax, the last two leg-bearing segments being distinct, resembling those of the abdomen in this respect. The first pair of legs is not used in locomotion but seemingly functions as a second pair of pedipalpi. Figure 12 ill.u.s.trates the striking peculiarities of the group. They are primarily desert forms and occur in the warm zones of all countries. Of the two hundred or more species, Comstock lists twelve as occurring in our fauna. These occur primarily in the southwest.

[Ill.u.s.tration: 12. A solpugid (Eremobates cinerea). After Comstock.]

The Solpugida have long borne a bad reputation and, regarding virulence, have been cla.s.sed with the scorpions. Among the effects of their bites have been described painful swelling, gangrene, loss of speech, cramps, delirium, unconsciousness and even death. Opposed to the numerous loose accounts of poisoning, there are a number of careful records by physicians and zoologists which indicate clearly that the effects are local and though they may be severe, they show not the slightest symptom of direct poisoning.

More important in the consideration of the question is the fact that there are neither poison glands nor pores in the fangs for the exit of any poisonous secretion. This is the testimony of a number of prominent zoologists, among whom is Dr. A. Walter, who wrote to Kobert at length on the subject and whose conclusions are presented by him.

However, it should be noted that the fangs are very powerful and are used in such a manner that they may inflict especially severe wounds.

Thus, there may be more opportunity for secondary infection than is usual in the case of insect wounds.

The treatment of the bite of the Solpugida is, therefore, a matter of preventing infection. The wound should be allowed to bleed freely and then washed out with a 1:3000 solution of corrosive sublimate, and, if severe, a wet dressing of this should be applied. If infection takes place, it should be treated in the usual manner, regardless of its origin.

THE ACARINA, OR MITES AND TICKS

A number of the parasitic Acarina evidently secrete a specific poison, presumably carried by the saliva, but in most cases its effect on man is insignificant. There is an abundant literature dealing with the poisonous effect of the bite of these forms, especially the ticks, but until recently it has been confused by failure to recognize that various species may transmit diseases of man, rather than produce injury through direct poisoning. We shall therefore discuss the Acarina more especially in subsequent chapters, dealing with parasitism and with disease transmission.

Nevertheless, after the evidence is sifted, there can be no doubt that the bites of certain ticks may occasionally be followed by a direct poisoning, which may be either local or general in its effects. Nuttall (1908) was unable to determine the cause of the toxic effect, for, in _Argas persicus_, the species most often implicated, he failed to get the slightest local or general effect on experimental animals, from the injection of an emulsion prepared by crus.h.i.+ng three of the ticks.

It seems clearly established that the bite of certain ticks may cause a temporary paralysis, or even complete paralysis, involving the organs of respiration or the heart, and causing death. In 1912, Dr. I. U. Temple, of Pendleton, Oregon, reported several cases of what he called "acute ascending paralysis" a.s.sociated with the occurrence of ticks on the head or the back of the neck. A typical severe case was that of a six year old child, who had retired in her usual normal health. The following morning upon arising she was unable to stand on her feet. She exhibited paralysis extending to the knees, slight temperature, no pain, sensory nerves normal, motor nerves completely paralyzed, reflexes absent. The following day the paralysis had extended to the upper limbs, and before night of the third day the nerves of the throat (hypoglossal) were affected. The thorax and larynx were involved, breathing was labored, she was unable to swallow liquids, phonation was impossible and she could only make low, guttural sounds. At this stage, two ticks, fully distended with blood, were found over the junction of the spinal column with the occipital bones in the hollow depression. They were removed by the application of undiluted creoline. Though the child's life was despaired of, by the following morning she was very much improved. By evening she was able to speak. The paralysis gradually receded, remaining longest in the feet, and at the end of one week the patient was able to go home.

There was some doubt as to the exact species of tick implicated in the cases which Dr. Temple reported, although the evidence pointed strongly to _Dermacentor venustus_.[C] Somewhat later, Hadwen (1913) reported that "tick paralysis" occurs in British Columbia, where it affects not only man, but sheep and probably other animals. It is caused by the bites of _Dermacentor venustus_ and was experimentally produced in lambs and a dog (Hadwen and Nuttall, 1913). It is only when the tick begins to engorge or feed rapidly, some days after it has become attached, that its saliva produces pathogenic effects.

Ulceration following tick bite is not uncommon. In many of the instances it is due to the file-like hypostome, with its recurved teeth, being left in the wound when the tick is forcibly pulled off.

THE MYRIAPODA, OR CENTIPEDES AND MILLIPEDES

The old cla.s.s, Myriapoda includes the DIPLOPODA, or millipedes, and the CHILOPODA, or centipedes. The present tendency is to raise these groups to the rank of cla.s.ses.

The Diplopoda

The DIPLOPODA, or millipedes (fig. 13), are characterized by the presence of two pairs of legs to a segment. The largest of our local myriapods belong to this group. They live in moist places, feeding primarily on decaying vegetable matter, though a few species occasionally attack growing plants.

[Ill.u.s.tration: 13. A millipede. After Comstock.]