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 rôle 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.
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 précis. We can only touch briefly upon the entomological phases of the problems presented.