Handbook of Medical Entomology Part 28

CHAPTER XI

SOME POSSIBLE, BUT IMPERFECTLY ESTABLISHED CASES OF ARTHROPOD TRANSMISSION OF DISEASE

INFANTILE PARALYSIS OR ACUTE ANTERIOR POLIOMYELITIS

The disease usually known in this country as infantile paralysis or, more technically, as acute anterior poliomyelitis, is one which has aroused much attention in recent years.

The causative organism of infantile paralysis is unknown, but it has been demonstrated that it belongs to the group of filterable viruses. It gives rise to a general infection, producing characteristic lesions in the central nervous system. The result of the injury to the motor nerves is a more or less complete paralysis of the corresponding muscle. This usually manifests itself in the legs and arms. The fatal cases are usually the result of paralysis of the muscles of respiration. Of the non-fatal cases about 60 per cent remain permanently crippled in varying degrees.

Though long known, it was not until about 1890 that it was emphasized that the disease occurs in epidemic form. At this time Medin reported his observations on an epidemic of forty-three cases which occurred in and around Stockholm in 1887. Since then, according to Frost (1911), epidemics have been observed with increasing frequency in various parts of the world. The largest recorded epidemics have been those in Vermont, 1894, 126 cases; Norway and Sweden, 1905, about 1,500 cases; New York City, 1907, about 2,500 cases. Since 1907 many epidemics have been reported in the United States, and especially in the Northern States east of the Dakotas. In 1912 there were over 300 cases of the disease in Buffalo, N. Y., with a mortality of somewhat over 11 per cent.

In view of the sudden prominence and the alarming spread of infantile paralysis, there have been many attempts to determine the cause, and the manner in which the disease spreads and develops in epidemic form. In the course of these studies, the question of possible transmission by insects was naturally suggested.

C. W. Howard and Clark (1912) presented the results of studies in this phase of the subject. They dealt especially with the house-fly, bedbug, head, and body lice, and mosquitoes. It was found that the house-fly (_Musca domestica_) can carry the virus of poliomyelitis in an active state for several days upon the surface of the body and for several hours within the gastro-intestinal tract. Mosquitoes and lice were found not to take up or maintain the virus. On the other hand, the bedbug (_Cimex lectularius_) was found to take the virus from the infected monkeys and to maintain it in a living state within the body for a period of seven days. This was demonstrated by grinding up in salt solution, insects which had fed on poliomyelitic animals and injecting the filtrate into a healthy monkey. The experimenters doubted that the bedbug is a carrier of the virus in nature.

Earlier in the same year, Brues and Sheppard published the results of an intensive epidemiological study of the outbreak of 1911, in Ma.s.sachusetts. Special attention had been paid to the possibility of insect transfer and the following conclusion was reached:

"Field work during the past summer together with a consideration of the epidemiology of the disease so far as known, points strongly toward biting flies as possible carriers of the virus. It seems probable that the common stable-fly (_Stomoxys calcitrans_ L.) may be responsible to a certain extent for the spread of acute epidemic poliomyelitis, possibly aided by other biting flies, such as _Taba.n.u.s lineola_. No facts which disprove such a hypothesis have as yet been adduced, and experiments based upon it are now in progress."

As stated by Brues (1913), especial suspicion fell upon the stable-fly because:

1. The blood-sucking habits of the adult fly suit it for the transfer of virus present in the blood.

2. The seasonal abundance of the fly is very closely correlated with the incidence of the disease, rising rapidly during the summer and reaching a maximum in July and August, then slowly declining in September and October.

3. The geographical distribution of the fly is, so far as can be ascertained, wider, or at least co-extensive with that of poliomyelitis.

4. _Stomoxys_ is distinctly more abundant under rural conditions, than in cities and thickly populated areas.

5. While the disease spreads over districts quickly and in a rather erratic way, it often appears to follow along lines of travel, and it is known that _Stomoxys_ flies will often follow horses for long distances along highways.

6. In a surprisingly large number of cases, it appeared probable that the children affected had been in the habit of frequenting places where _Stomoxys_ is particularly abundant, i.e., about stables, barnyards, etc.

The experiments referred to were carried on during the summer of 1912 and in September Dr. Rosenau announced that the disease was transferred by the bite of the stable-fly.

A monkey infected by inoculation was exposed to the bites of upwards of a thousand of the _Stomoxys_ flies daily, by stretching it at full length and rolling it in a piece of chicken wire, and then placing it on the floor of the cage in which the flies were confined. The flies fed freely from the first, as well as later, after paralysis had set in.

Alternating with the inoculated monkey, healthy monkeys were similarly introduced into the cage at intervals. New monkeys were inoculated to keep a supply of such infected animals and additional healthy ones were exposed to the flies, which fed willingly and in considerable numbers on each occasion. "Thus the flies were given every opportunity to obtain infection from the monkeys, since the animals were bitten during practically every stage of the disease from the time of the inoculation of the virus till their death following the appearance of paralysis. By the same arrangement the healthy monkeys were likely to be bitten by flies that had previously fed during the various stages of the disease on the infected monkeys. The flies had meanwhile enjoyed the opportunity of incubating the virus for periods varying from the day or two which usually elapses between consecutive feedings, to the two or three-week period for which at least some (although a very small percentage) of the flies lived in the cage."

"In all, twelve apparently healthy monkeys of a small j.a.pan species were exposed to the flies in the manner described for the infected monkeys.

Some were placed in the cage only once or twice and others a number of times after varying intervals. These exposures usually lasted for about half an hour, but were sometimes more protracted. No results were apparent until two or three weeks after the experiment was well under way, and then in rather rapid succession six of the animals developed symptoms of poliomyelitis. In three, the disease appeared in a virulent form, resulting in death, while the other three experienced transient tremblings, diarrha, partial paralysis and recovery."--Brues, 1913.

Very soon after the announcement of the results of experiments by Rosenau and Brues, they were apparently conclusively confirmed by Anderson and Frost (1912), who repeated the experiments, at Washington.

They announced that through the bites of the _Stomoxys_ flies that had previously fed on infected monkeys, they had succeeded in experimentally infecting three healthy monkeys.

The results of these experiments gained much publicity and in spite of the conservative manner in which they had been announced, it was widely proclaimed that infantile paralysis was conveyed in nature by the stable-fly and by it alone.

Serious doubt was cast on this theory by the results of further experiments by Anderson and Frost, reported in May of 1913. Contrary to the expectations justified by their first experience, the results of all the later, and more extended, experiments were wholly negative. Not once were these investigators again able to transmit the infection of poliomyelitis through _Stomoxys_. They concluded that it was extremely doubtful that the insect was an important factor in the natural transmission of the disease, not only because of their series of negative results, "but also because recent experiments have afforded additional evidence of the direct transmissibility or contagiousness of poliomyelitis, and because epidemiological studies appear to us to indicate that the disease is more likely transmitted largely through pa.s.sive human virus carriers."

Soon after this, Kling and Levaditi (1913) published their detailed studies on acute anterior poliomyelitis. They considered that the experiments of Flexner and Clark (and Howard and Clark), who fed house-flies on emulsion of infected spinal cord, were under conditions so different from what could occur in nature that one could not draw precise conclusions from them regarding the epidemiology of the disease.

They cited the experiments of Josefson (1912), as being under more reasonable conditions. He sought to determine whether the inoculation of monkeys with flies caught in the wards of the Hospital for Contagious Diseases at Stockholm, where they had been in contact with cases of poliomyelitis, would produce the disease. The results were completely negative.

Kling and Lavaditi made four attempts of this kind. The flies were collected in places where poliomyelitics had dwelt, three, four and twenty-four after the beginning of the disease in the family and one, three, and fifteen days after the patient had left the house. These insects were for the greater part living and had certainly been in contact with the infected person. In addition, flies were used which had been caught in the wards of the Hospital for Contagious Diseases at Soderkoping, when numbers of poliomyelitics were confined there.

Finally, to make the conditions as favorable as possible, the emulsions prepared from these flies were injected without previous filtering, since filtration often causes a weakening of the virus. In spite of these precautions, all their results were negative, none of the inoculated animals having contracted poliomyelitis. They also experimented with bedbugs which had fed upon infected patients at various stages of the disease, but the results in these cases also were wholly negative.

Kling and Levaditi considered at length the possibility of transmission of the disease by _Stomoxys_. As a result of their epidemiological studies, they found that infantile paralysis continued to spread in epidemic form in the dead of winter, when these flies were very rare and torpid, or were even completely absent. Numerous cases developed in the northern part of Sweden late in October and November, long after snow had fallen. On account of the rarity of the Stomoxys flies during the period of their investigations they were unable to conduct satisfactory experiments. In one instance, during a severe epidemic, they found a number of the flies in a stable near a house inhabited by an infected family, though none was found in the house itself. These flies were used in preparing an emulsion which, after filtering, was injected into the peritoneal cavity of a monkey. The result was wholly negative.

As for the earlier experiments, Kling and Levaditi believe if the flies were responsible for the transmission of the disease in the cases reported by Rosenau and Brues, and the first experiments of Anderson and Frost, it was because the virus of infantile paralysis is eliminated with the nasal secretions of paralyzed monkeys and the flies, becoming contaminated, had merely acted as accidental carriers.

Still further evidence against the hypothesis of the transmission of acute anterior poliomyelitis by _Stomoxys calcitrans_ was brought forward by Sawyer and Herms (1913). Special precautions were used to prevent the transference of saliva or other possibly infectious material from the surface of one monkey to that of another, and to avoid the possibility of complicating the experiments by introducing other pathogenic organisms from wild flies, only laboratory-bred flies were used. In a series of seven carefully performed experiments, in which the conditions were varied, Sawyer and Herms were unable to transmit poliomyelitis from monkey to monkey through the agency of _Stomoxys_, or to obtain any indication that the fly is the usual agent for spreading the disease in nature.

The evidence at hand to date indicates that acute anterior poliomyelitis, or infantile paralysis, is transmitted by contact with infected persons. Under certain conditions insects may be agents in spreading the disease, but their role is a subordinate one.

Pellagra

PELLAGRA is an endemic and epidemic disease characterized by a peculiar eruption or erythema of the skin (figs 144 and 145), digestive disturbances and nervous trouble. Insanity is a common result, rather than a precursor of the disease. The manifestations of pellagra are periodic and its duration indeterminate.

[Ill.u.s.tration: 144. Pellagrous eruption on the face. After Watson.]

The disease is one the very name of which was almost unknown in the United States until within the past decade. It has usually been regarded as tropical, though it occurs commonly in Italy and in various parts of Europe. Now it is known that it not only occurs quite generally in the United States but that it is spreading. Lavinder (1911) says that "There are certainly many thousand cases of the disease in this country, and the present situation must be looked upon with grave concern."

It is not within the scope of this book to undertake a general discussion of pellagra. The subject is of such importance to every medical man that we cannot do better than refer to Lavinder's valuable precis. We can only touch briefly upon the entomological phases of the problems presented.

The most commonly accepted theories regarding the etiology of the disease have attributed it to the use of Indian corn as an article of diet. This supposed relationship was explained either on the basis of, (a) insufficiency of nutriment and inappropriateness of corn as a prime article of food; (b) toxicity of corn or, (c) parasitism of certain organisms--fungi or bacteria--ingested with either sound or deteriorated corn.

In 1905, Sambon proposed the theory of the protozoal origin of pellagra and in 1910 he marshalled an imposing array of objections to the theory that there existed any relationship between corn and the disease. He presented clear evidence that pellagra existed in Europe before the introduction of Indian corn from America, as an article of diet, and that its spread was not _pari pa.s.su_ with that of the use of corn. Cases were found in which the patients had apparently never used corn, though that is obviously difficult to establish. He showed that preventive measures based on the theory had been a failure. Finally, he believed that the recurrence of symptoms of the disease for successive springs, in patients who abstained absolutely from the use of corn, militated against the theory.

[Ill.u.s.tration: 145. Pellagrous eruption on the hand. After Watson.]

On the other hand, Sambon believed that the periodicity of the symptoms, peculiarities of distribution and seasonal incidence, and a.n.a.logies of the symptoms to those of other parasitic diseases indicated that pellagra was of protozoal origin, and that it was insect-borne.

The insect carriers, he believed to be one or more species of Simuliidae, or black-flies. In support of this he stated that _Simulium_ appears to effect the same topographical conditions as pellagra, that in its imago stage it seems to present the same seasonal incidence, that it has a wide geographical distribution which seems to cover that of pellagra, and that species of the genus are known to cause severe epizootics.

Concluding from his studies in Italy, that pellagra was limited almost wholly to agricultural laborers, he pointed out that the Simulium flies are found only in rural districts, and as a rule do not enter towns, villages, or houses.

[Ill.u.s.tration: 146. A favorite breeding place of Simulium. Ithaca, N.

Y.]

When Sambon's detailed report was published in 1910, his theory was seized upon everywhere by workers who were anxious to test it and who, in most cases, were favorably disposed towards it because of the wonderful progress which had been made in the understanding of other insect-borne diseases. In this country, the entomological aspects of the subject have been dealt with especially by Forbes (1912), and by King and Jennings, under the direction of W. D. Hunter, of the Bureau of Entomology, and in cooperation with the Thompson-McFadden Pellagra Commission of the Department of Tropical Medicine of the New York Post-Graduate Medical School. An important series of experiments with monkeys has been undertaken by S. J. Hunter, of Kansas, but unfortunately we have as yet no satisfactory evidence that these animals are susceptible to the disease--a fact which renders the whole problem difficult.

The acc.u.mulated evidence is increasingly opposed to Sambon's hypothesis of the transmission of pellagra by _Simulium_. This has been so clearly manifested in the work of the Thompson-McFadden Commission that we quote here from the report by Jennings (1914):

"Our studies in 1912 convinced us that there was little evidence to support the incrimination of any species of _Simulium_ in South Carolina in the transmission of pellagra. Reviewing the group as a whole, we find that its species are essentially "wild" and lack those habits of intimate a.s.sociation with man which would be expected in the vector of such a disease as pellagra. Although these flies are excessively abundant in some parts of their range and are moderately so in Spartanburg County, man is merely an incidental host, and no disposition whatever to seek him out or to invade his domicile seems to be manifested. Critically considered, it is nearer the fact that usually man is attacked only when he invades their habitat."

"As our knowledge of pellagra acc.u.mulates, it is more and more evident that its origin is in some way closely a.s.sociated with the domicile. The possibility that an insect whose a.s.sociation with man and his immediate environment is, at the best, casual and desultory, can be active in the causation of the disease becomes increasingly remote."