THE INCIDENCE OF NEUTRALIZING ANTIBODIES FOR SWINE INFLUENZA VIRUS IN THE SERA OF HUMAN BEINGS OF DIFFERENT AGES

Sera from a very high proportion of the human adults and new-born infants studied neutralized swine influenza virus; sera from children below the age of 12 years seldom exerted such an effect. The results of neutralization experiments with human sera and the virus of swine influenza have been compared with the outcome of similar tests with the virus of human influenza, and it seems evident that the presence of antibodies neutralizing swine influenza virus cannot be deemed the result of repeated exposures to the current human type of virus. From the known history of swine influenza and the similarity of its etiologic virus to that obtained from man it seems likely that the virus of swine influenza is the surviving prototype of the agent primarily responsible for the great human pandemic of 1918, as Laidlaw has already suggested. The presence in human sera of antibodies neutralizing swine influenza virus is believed to indicate a previous immunizing exposure to, or infection with, an influenza virus of the 1918 type

IMMUNIZATION OF RABBITS TO INFECTIOUS PAPILLOMATOSIS

Two intraperitoneal injections of either infectious or non-infectious rabbit papilloma suspensions actively immunize rabbits against papillomatosis. The capacity of the non-infectious suspensions to immunize is considered as evidence that they contain papilloma virus even though none can be demonstrated by the usual infection test

THE LEECH AS A POTENTIAL VIRUS RESERVOIR

Leeches, fed on swine infected with hog cholera, contained virus for as long as 87 days after their infective blood meals. In three instances, infected leeches apparently transmitted hog cholera virus to susceptible swine in the process of normal feeding. Myxoma virus persisted in leeches for as long as 154 days after the ingestion of a blood meal from rabbits with myxomatosis. Leeches fed consecutively, first on swine with hog cholera, and later on rabbits with myxomatosis, acquired both viruses. In such dually infected leeches, the hog cholera virus persisted for as long as 122 days and the myxoma virus for as long as 110 days, the longest periods tested. Leeches fed consecutively, first on rabbits with myxomatosis, and later on swine with hog cholera, acquired only the myxoma virus. Hog cholera virus could not be demonstrated in such dually fed leeches. Myxoma and hog cholera viruses appeared to be present in about equivalent amounts in the anterior and posterior thirds of the bodies of infected leeches. Myxoma and hog cholera viruses were present in the bloody gut contents of infected leeches but were not demonstrable in the body tissues of these leeches. It seems from the findings presented that leeches are not biological carriers of either myxoma or hog cholera virus but instead carry these two agents mechanically in their gastrointestinal tracts. In doing this, they appear to protect the viruses from various deleterious chemical and physical influences to which they would have been exposed in the open. It is speculated that leeches could play a role in nature in perpetuating the blood-borne viruses of certain diseases in which close association with bodies of fresh water is of epidemiological importance

THE SWINE LUNGWORM AS A RESERVOIR AND INTERMEDIATE HOST FOR HOG CHOLERA VIRUS : I. THE PROVOCATION OF MASKED HOG CHOLERA VIRUS IN LUNGWORM-INFESTED SWINE BY ASCARIS LARVAE

Evidence that the swine lungworm can serve as reservoir and intermediate host for the hog cholera virus has been presented. The virus, however, is ordinarily carried in a masked form and must be provoked to pathogenicity by some stress before it can cause apparent disease. In the present experiments, ascaris larvae supplied the provocation needed to induce hog cholera in swine carrying lungworms infected with masked hog cholera virus. Provocation of the masked virus by ascaris larvae was seasonal in that it was effective only during a period embracing the first 5 months of the year

AN ANTIVIRAL SUBSTANCE FROM PENICILLIUM FUNICULOSUM : VI. PREVENTION OF THE ESTABLISHMENT OF PASSIVE IMMUNITY TO SEMLIKI FOREST VIRUS INFECTION IN MICE BY HELENINE

1. Helenine prevents the establishment in mice of passive viral immunity by anti-Semliki serum of swine, rabbit, or guinea pig origin. 2. A period of 12 days must elapse, between the antiviral serum administration and challenge with virus, for prevention of the establishment of passive immunity to become apparent. This period is believed to correspond to that in which injected antibody persists in circulation in the injected host. 3. Helenine is effective in preventing the establishment of passive viral immunity by heterologous antiviral sera when it is administered any time during a period of 6 days, extending from 4 days before to 2 days after injection of the antiviral serum. 4. Helenine does not prevent the establishment of passive viral immunity by antiviral sera of mouse origin (homologous). 5. Evidence is presented to indicate that the phenomenon of the prevention of the establishment of passive viral immunity by heterologous antiviral sera is not effected directly, but rather is mediated through some substance that helenine induces the injected host to elaborate. 6. The capacity to prevent the establishment of passive viral immunity could not be exhausted by repeated preceding injections of helenine at 2- or 3-day intervals. 7. Evidence is presented to indicate that the helenine-induced material does not act upon antiviral antibody per se but rather on heterologous foreign protein that happens to be labeled as Semliki Forest virus antibody. This helenine-induced material, whatever its nature, appears to enhance the capacity of the injected host to recognize and dispose of foreign protein. 8. Statolon, a material that like helenine is a known inducer of interferon, is, like helenine, also capable of preventing the establishment of passive viral immunity by heterologous antiviral sera. 9. Experiments designed to determine whether the induced material responsible for the antipassive immunity effect of helenine is interferon have yielded inconclusive answers thus far

STUDIES ON IMMUNITY TO SWINE INFLUENZA

Of the two etiological components of swine influenza, only the filtrable virus possessed immunizing properties. H. influenzae suis, while essential to the production of the disease, played only a secondary and contributory rôle and, alone, conferred no immunity. Serum of swine convalescent from the filtrate disease neutralized the swine influenza etiological complex of organism and virus. Intramuscularly administered swine influenza virus was incapable of inducing illness but did render hogs immune to swine influenza. It is suggested that a specific relationship, as regards infectivity, exists between the swine influenza virus and the tissues of the respiratory tract

THE SWINE LUNGWORM AS A RESERVOIR AND INTERMEDIATE HOST FOR SWINE INFLUENZA VIRUS : IV. THE DEMONSTRATION OF MASKED SWINE INFLUENZA VIRUS IN LUNGWORM LARVAE AND SWINE UNDER NATURAL CONDITIONS

1. The presence of masked swine influenza virus has been demonstrated in lungworm larvae from earthworms dug on Midwestern farms. 2. Swine influenza virus infections were provoked in 2 of 3 swine obtained from an Iowa farm during an interepizootic period. 3. The evidence presented has been interpreted as indicating that the swine lungworm is the reservoir and intermediate host for swine influenza virus in the field. 4. A concept of the epidemiology of swine influenza in which the causative virus is represented as being maintained and disseminated in a masked form by its lungworm intermediate host has been presented

THE QUANTITY OF CHOLESTEROL IN THE BLOOD SERUM OF THE GUINEA PIG AS AN INHERITED CHARACTER; ITS RELATION TO NATURAL RESISTANCE TO TUBERCULOSIS, AND TO TUBERCULOSIS INFECTION

1. Infection with tubercle bacilli of bovine type produced no alteration in the serum cholesterol content in guinea pigs. 2. Certain controlled variations in diet produced no changes in the serum cholesterol content in guinea pigs. 3. Inbred families of guinea pigs known to manifest differing resistances to tuberculosis gave differing serum cholesterol values, but no direct relationship between the two sets of phenomena could be established. 4. It seems probable that in the guinea pig the cholesterol content of the blood serum is influenced by inherited factors

THE SWINE LUNGWORM AS A RESERVOIR AND INTERMEDIATE HOST FOR SWINE INFLUENZA VIRUS : III. FACTORS INFLUENCING TRANSMISSION OF THE VIRUS AND THE PROVOCATION OF INFLUENZA

1. During a 3 year study of the lungworm as intermediate host for the swine influenza virus 98 transmission experiments, using 216 swine, have been conducted. Of these, 50 gave negative results. In the remaining 48, transmission of swine influenza virus by way of the lungworm was demonstrated in one or more animals of each experiment. Irregularities in the results would appear to be due not so much to lack of transmission of masked virus by the lungworms as to failure to evoke its pathogenic capabilities. 2. The stimulus of choice that was most successful in the provocation of swine influenza consisted of multiple intramuscular injections of H. influenzae suis. In several experiments pigs developed swine influenza virus infections 9 to 17 days after infestation with infected lungworms in the absence of any known provocative stress. In these instances an immune response of the swine to the lungworms themselves is suspected of having furnished the provocation. 3. During May, June, July, and August, swine prepared by the ingestion of lungworms carrying virus were absolutely refractory to the provocation of influenza, and they were relatively refractory in September and October. The masked virus was activated most readily during the first 4 months of the year. 4. In a single experiment we succeeded in demonstrating by direct means the presence of swine influenza virus in the neighborhood of lungworms at the base of the lung at a time when the virus was not demonstrable anywhere else in the respiratory tract. 5. Masked swine influenza virus was found to be present in lungworm ova obtained either from the respiratory tracts or the feces of infected swine. 6. In a number of instances, masked swine influenza virus has been found to persist for over a year in lungworm larvae within the earthworm intermediate hosts, and in one case its presence was demonstrated after 32 months. 7. Two varieties of a single species of earthworm, namely, Allolobophora caliginosa f. typica (Savigny) and A. caliginosa f. trapezoides (Dugès), have been found separately capable of serving as intermediate hosts for virus-infected lungworms. 8. Lungworm ova, obtained from convalescent swine which are no longer carrying swine influenza virus in infectious form in their respiratory tracts, contain masked virus

IMMUNIZATION EXPERIMENTS WITH SWINE INFLUENZA VIRUS

1. Swine influenza virus obtained from the lungs of infected ferrets or mice, when administered intramuscularly or subcutaneously, immunizes swine to swine influenza. 2. Ferrets, which have received subcutaneous injections of swine influenza virus obtained from the lungs of infected ferrets, are immune to intranasal infection with this virus. Similar injections with virus from the lungs of infected mice or swine do not immunize. 3. Mice can be immunized to intranasal infection with swine influenza virus by the subcutaneous injection of virus obtained from the lungs of infected mice, but not by similar injection with virus from the lungs of infected ferrets or swine. Repeated injections induce greater immunity than a single one. 4. Intraperitoneal inoculation of both mice and ferrets with swine influenza virus immunizes them to intranasal infection and it appears to make little or no difference whether the virus used as vaccine is obtained from the lungs of infected mice, ferrets, or swine. 5. Field experiments in which swine influenza followed the intramuscular administration of virus are cited as examples of the hazard involved in the use of this means of immunization in a densely crowded susceptible population