Handbook of Medical Entomology

by William A. Riley; O. A. Johannsen

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 Japan 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, diarrhœa, 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 passive 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 Söderkoping, 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.