MECHANISM OF RECOVERY FROM VIRAL INFECTION

A probabilistic approach for the study of epidemiological dynamics of infectious diseases: Basic model and properties

The dynamics of epidemiological phenomena associated to infectious diseases have long been modelled taking different approaches. However, recent pandemic events exposed many areas of opportunity to improve the existing models. We develop a stochastic model based on the idea that transitions between epidemiological stages are alike sampling processes that may involve more than one subset of the population or may be mostly dependent on time intervals defined by pathological or clinical criteria. We apply the model to simulate epidemics, analyse the final distribution of the case fatality ratio, and define a basic reproductive number to determine the existence of a probabilistic phase transition for the dynamics. The resulting modelling scheme is robust, easy to implement, and can readily lend itself for extensions aimed at answering questions that emerge from close examination of data trends, such as those emerging from the COVID-19 pandemic, and other infectious diseases.

Comparative production of interferon by human fetal, neonatal, and maternal cells

Production of interferon was studied in fibroblasts cultured from human fetal, neonatal, and maternal tissue. Human fetal and maternal cells were paired to diminish genetic variability. Fetal cells displayed an increased response to two inducers of interferon, virus and synthetic double-stranded ribopolynucleotide. Fetal cells released 300-fold more interferon than maternal cells on exposure to poly rI:rC. This enhanced capacity for interferon production was consistent in cultures developed from fetal skin obtained between the 10th and 20th gestational week. The response was relatively stable, persisting in cells cultured for 18 generations (about 14 weeks). On infection with Newcastle disease virus, fetal cells produced, on the average, 4 to 6.5 times more interferon than maternal or neonatal cells. The virus was adsorbed with equal efficiency by each type of cell. Increased production is apparently independent of the rates of overall protein synthesis, since fetal and maternal cells have very similar rates of total protein synthesis.

Variation in interferon sensitivity and induction among strains of eastern equine encephalitis virus

Eastern equine encephalitis virus (EEEV) causes human encephalitis in North America (NA), but in South America (SA) it has rarely been associated with human disease, suggesting that SA strains are less virulent. To evaluate the hypothesis that this virulence difference is due to a greater ability of NA strains to evade innate immunity, we compared replication of NA and SA strains in Vero cells pretreated with interferon (IFN). Human IFN-alpha, -beta, and -gamma generally exhibited less effect on replication of NA than SA strains, supporting this hypothesis. In the murine model, no consistent difference in IFN induction was observed between NA and SA strains. After infection with most EEEV strains, higher viremia levels and shorter survival times were observed in mice deficient in IFN-alpha/beta receptors than in wild-type mice, suggesting that IFN-alpha/beta is important in controlling replication. In contrast, IFN-gamma receptor-deficient mice infected with NA and SA strains had similar viremia levels and mortality rates to those of wild-type mice, suggesting that IFN-gamma does not play a major role in murine protection. Mice pretreated with poly(I-C), a nonspecific IFN inducer, exhibited dose-dependent protection against fatal eastern equine encephalitis, further evidence that IFN is important in controlling disease. Overall, our in vivo results did not support the hypothesis that NA strains are more virulent in humans due to their greater ability to counteract the IFN response. However, further studies using a better model of human disease are needed to confirm the results of differential human IFN sensitivity obtained in our in vitro experiments.

Biological and clinical basis for molecular studies of interferons

The cytokine family of interferons (IFNs) has multiple functions, including antiviral, anti-tumor, and immunomodulatory effects and regulation of cell differentiation. The multiple functions of the IFN system are thought to be an innate defense against microbes and foreign substances. The IFN system consists first of cells that produce IFNs in response to viral infection or other foreign stimuli and second of cells that establish the antiviral state in response to IFNs. This process of innate immunity involves multiple signaling mechanisms and activation of various host genes. Viruses have evolved to develop mechanisms that circumvent this system. IFNs have also been used clinically in the treatment of viral diseases. Improved treatments will be possible with better understanding of the IFN system and its interactions with viral factors. In addition, IFNs have direct and indirect effects on tumor cell proliferation, effector leukocytes and on apoptosis and have been used in the treatment of some cancers. Improved knowledge of how IFNs affect tumors and the mechanism that lead to a lack of response to IFNs would help the development of better IFN treatments for malignancies.

Innate antiviral defenses in body fluids and tissues

Innate, non-specific, resistance mechanisms are important barriers to pathogens, particularly delaying virus multiplication at the onset of infections. These innate defense mechanisms include a series of mechanical barriers, pre-existing inhibitory molecules, and cellular responses with antimicrobial activity. The antiviral activities of these innate inhibitors reside in a variety of partly characterized substances. This review presents the innate antiviral inhibitors in cell cultures, urine, serum, the gastrointestinal tract, the nervous system, tissues of crustaceans, and saliva. Medical adaptation of the innate antiviral defense mechanisms may be useful for prevention and treatment of viral infections.

CIRCULATING INTERFERON IN MICE AFTER INTRAVENOUS INJECTION OF VIRUS

Circulating interferon was detectable in mouse serum within 1 hour after the intravenous injection of various types of virus and it reached maximum levels in about 4 hours. Rapidly produced interferon may play a role in the pathogenesis of viral infection and in viral interference.

Mitogen responses and interferon production after exposure of human macrophages to infectious and inactivated influenza viruses

Human macrophages were exposed to two influenza A viruses representing different subtypes. The donors were likely to have been exposed to one subtype (H3N2) but not to the other (H0N 1). Similar effects upon the macrophages were observed for both subtypes: macrophage enhancement of mitogen-stimulated lymphocyte transformation responses was depressed, and the macrophages produced interferon. In contrast, macrophages exposed to inactivated virus exhibited normal enhancement of lymphocyte transformation response, yet produced interferon, although in lower titers than did macrophages exposed to infectious virus.

Paralytic poliomyelitis in a child with agammaglobulinemia

This paper gives the clinical, immunological and virological data on a patient with agammaglobulinemia who developed paralytic poliomyelitis. The patient was a 3 year-old boy who had a typical B-cell defect without a T-cell defect. He had profound hypogammaglobulinemia and defective plasma cells and had repeated pyogenic infections which were controlled by gammaglobulin replacement therapy. At 3 years of age, he was admitted to our hospital with suspected meningitis. He had fewer, tremor and neck stiffness for 3 days and subsequently developed paralysis in his left arm and right leg. There was lymphocytosis in the cerebrospinal fluid. A non vaccine-like strain of poliovirus type 2 was isolated from the stool.

Interferon production in children with respiratory syncytial, influenza, and parainfluenza virus infections

To better understand the recovery process of infants with lower respiratory tract disease due to respiratory syncytial virus, the production of interferon by 129 children (ages 10 days to 24 months) with RSV infection was compared to that of 20 children with influenza (ages 1 to 36 months), and 37 children with parainfluenza virus infection (ages 4 to 66 months). Interferon assays of 285 nasal washes from children with RSV revealed that interferon production occurred in only 5 (4%) of the children. Significantly more children infected with infleunza virus, 55% (P less than 0.001), and parainfluenza virus, 30% (P less than 0.001), produced interferon. In addition, the quantity of interferon produced by children with RSV (geometric mean titer = 2) was significantly less than that of children with influenza (GMT = 26.8, P less than 0.001) and parainfluenza virus (GMT = 23.5, P less than 0.001). In the children infected with RSV, in constrast to those with influenza, interferon detection was not associated with diminished shedding of virus.

Three strains of influenza A virus (H3N2): interferon sensitivity in vitro and interferon production in volunteers

Three antigenic variants of the H3N2 subtype of wild-type influenza A virus (representing the years 1968, 1972, and 1974) were examined for their sensitivity to interferon and for their ability to induce local respiratory tract interferon in volunteers. In addition, the time of appearance of symptoms in infected volunteers was correlated with the patterns of virus shedding and interferon production. The sensitivity to interferon and the ability to stimulate nasopharyngeal interferon were similarly high for all three strains. Symptomatic illness, peak virus shedding, and peak interferon response all occurred within a 26-h period. These findings imply that interferon or its inducers theoretically could be protective if applied prophylactically, but would be less efficacious when used therapeutically.

The ability of blood plasma from drinking water vaccinated turkeys to protect against a lethal challenge of Pasteurella multocida

Turkeys were vaccinated against fowl cholera with the Clemson University avirulent Pasteurella multocida vaccine strain (C.U. strain), using the drinking water route. Plasma was harvested from these turkeys, which later withstood challenge with a highly virulent P-1059 strain of P. multocida. Baby chicks were injected between the thigh and abdominal cavity with the immune plasma and simultaneously, into the breast muscle, with the same highly virulent strain referred to in the foregoing. The results demonstrated that plasma from turkeys vaccinated by the drinking water route protected baby chicks against intramuscular challenge with a virulent strain of P. multocida and suggest that a favorable systemic immunologic response did occur. This is in contrast to the Minnesota M-2283 strain which, reportedly, produces a localized protection only, when used as a drinking water vaccine.

Viral interference and interferon

Viral interference is a phenomenon for which a cell infected by a virus becomes resistant toward a second outcoming infection by a superinfectant virus. Even though other mechanisms are known, it can be assumed that most cases of viral interference occurring in natural conditions are mediated by interferon, a low molecular weight protein produced by the infected cell in response to a stimulus provided by viral nucleic acid(s). The interferon produced by a cell can migrate to other cells not yet involved by the spreading infection, transmitting to them the antiviral-resistant state. Available evidence indicates that interferon acts by inducing the production of a second cellular protein, called antiviral protein, which is directly responsible for the antiviral state through some alterations of the cellular, virus-directed, proteosynthetic system. In addition to the antiviral activity, the interferon system can affect the growth of several nonviral organisms and that of tumour cells; rather controversial effects have been shown also on the immune responses; the mechanisms underlying these effects are still nuclear. However a relationship to the specific immune system is suggested also by the finding that interferon can be liberated by sensitized T-lymphocytes following antigenic stimulus. Activation of the interferon system can be operated in vitro and in vivo also by several non-viral substances of various nature, such as nucleic acids, polysaccharides, aromatic amines, etc. This fact, considering that interferon has been shown to play a critical role on the mechanisms of recovery from viral infections, may open new perspectives for their possible prophylactic and/or therapeutic use in viral diseases. This problem can be approached also by administering exogenous interferon. Encouraging preliminary results have so far been obtained either with interferon or its inducers. However, several problems of various nature have to be resolved before considering the actual use of interferon system as a wide range antiviral drug in natural viral diseases of man.

Effects of high ambient temperature on various stages of rabies virus infection in mice

Effects of high ambient temperatures on various stages of rabies virus infection have been studied. Ambient temperature increased within the tolerated range was found to have little effect upon body temperature of normal mice, but caused marked elevation of temperature during illness. Temperatures at onset of patent illness in mice were lower than normal. Increased body temperature in the higher thermic ambience during the incubation period was associated with decreased mortality and frequent abortive infections. Exposure to high ambient temperature late in the incubation period delayed onset of illness, decreased mortality, and increased frequency of abortive infections, but exposure to high ambient temperature after onset of patent illness did not affect the course of the disease.

Intrauterine virus infections and congenital heart disease

The etiologic basis for the vast majority of cases of congenital heart disease remains largely undefined. Viruses have been considered to be likely candidates since the recognition of the association between intrauterine rubella and congenital heart disease. Although the pathogenesis of cardiovascular defects is poorly understood, information gained from the study of congenital rubella syndrome suggests that mechanisms such as focal endothelial cell damage, resulting in obliteration of vascular supply, decreased growth rate, and shortened survival time of certain cells, and disturbed DNA replication in cells whose chromosomes were damaged secondary to the effects of virus replication may be operative in the production of defects in the developing fetus. In addition to rubella there is suggestive, but not conclusive, evidence that Coxsackie B3 and B4 virus infections during pregnancy can result in the birth of infants with a variety of types of congenital heart lesions and that intrauterine mumps virus infection may be etiologically related to the postnatal development of endocardial fibroelastosis (EFE). Although there are a number of other viruses that are potential etiologic agents of congenital heart disease, the current status of information is inadequate to allow even suggestive associations to be made. The most profitable areas for future investigation appear to be: (1) the epidemiology of congenital heart disease, (2) prospective studies of the association of maternal viral infection with abnormal offspring, (3) the in-depth virologic investigation of the infant with a cardiac defect, and (4) the development of experimental animal models of congenital heart disease. Successful control of virus-induced congenital heart disease will depend on the results of these investigations and the development of vaccines against the identified causative viruses and/or safe and effective antiviral chemotherapy for the woman in early gestation who is infected with a known teratogenic agent.

Interferon in nasal secretions and sera of calves after intranasal administration of avirulent infectious bovine rhinotracheitis virus: association of interferon in nasal secretions with early resistance to challenge with virulent virus

Calves which had received avirulent infectious bovine rhinotracheitis virus (AV-IBR) by intranasal (IN) administration developed detectable levels of interferon (IF) in nasal secretions as early as 40 hr later. Peak titers (1:640) of IF appeared in secretions 72 to 96 hr after administration of virus, and titers of 1:80 to 1:320 were maintained through the 8th day. Lower titers (1:5 to 1:10) of IF were detected in sera obtained on the 4th to 8th days after administration of virus. Peak titers of IF in respiratory tract secretions were accompanied by a 100- to > 1,000-fold reduction in the levels of AV-IBR present in the secretions. Serum antibody was not detected prior to the 8th day after administration of AV-IBR. Calves which received AV-IBR by the IN route 72 or 96 hr earlier were refractory to challenge with virulent infectious bovine rhinotracheitis virus (IBR), whereas calves receiving AV-IBR 18 or 40 hr earlier became clinically ill following challenge. The temporal association between appearance of IF in respiratory tract secretions and onset of protection against challenge suggests a cause and effect relationship. No IF was detected in either nasal secretions or sera of calves receiving modified IBR virus by intramuscular injection. Following subsequent IN challenge of these calves, IF was detected in nasal secretions as early as 24 hr postchallenge and was maintained at titers of 1:40 to 1:80 for approximately 4 days, even in the absence of virus recovery. Greater ease of local IF induction with IBR virus in calves previously sensitized with that virus is suggested.

Mechanisms of recovery from a generalized viral infection: mousepox. I. The effects of anti-thymocyte serum

Agglutination and immunofluorescence tests in vitro showed that the ATS used in these experiments cross-reacted with macrophages and RBC. However, ATS was not toxic in vivo, and small doses given subcutaneously depleted thymus-dependent areas of lymphoid tissues and selectively depressed blood lymphocyte counts without affecting other cell types in the blood. Furthermore, the function of littoral macrophages as indicated by the clearance of blood-borne virus and its subsequent behavior over a 48 hr period in the liver and spleen was not changed by ATS. Thus, the innate resistance of these vital target organs was not depressed. A similar regimen of subcutaneous ATS caused a highly significant increase in mortality from mousepox with an associated failure to control virus growth in the liver and spleen which was manifest by 6 days after infection. The interferon and neutralizing antibody responses were not impaired in ATS-treated mice, but the cell-mediated immune response was significantly suppressed. This evidence, and consideration of the timing of these host responses during the course of infection in relation to the control of virus growth in the liver and spleen, led to the conclusion that cell-mediated immunity probably contributed an essential acquired recovery mechanism. However, no evidence was obtained concerning the nature of this antiviral mechanism.

Immunosuppression and experimental virus infection of the nervous system

This chapter describes the current views of the pathogenesis of virus infections of the nervous system, with particular attention to certain aspects of virus-host interactions. Following invasion of the central nervous system, infection can follow a variety of patterns, as to number and distribution of neuronal and non-neuronal cells involved. There is a corresponding diversity in the pathological lesions of the central nervous system (CNS) produced by acute virus infection. Infection can be pictured as a race between virus and host defenses, where many factors, acting through different mechanisms, can influence the outcome. Outcome is always determined by multiple virus and host variables, although single variables can be independently studied under experimentally controlled conditions in the laboratory. The chapter demonstrates that in many virus-host combinations, the immune response plays an important role in recovery from primary infections. It mentions that an immunopathological process mediates the disease which follows certain CNS virus infections.

Factors modifying host resistance to viral infection. 3. Effect of whole body x-irradiation on experimental encephalomyocarditis virus infection in mice

The resistance of mice to encephalomyocarditis (EMC) virus was markedly decreased by prior exposure to whole body X-irradiation. In contrast to non-irradiated controls, the course of EMC virus infection in X-irradiated animals was characterized by (a) an enhanced mortality, (b) shortening of the incubation period, (c) higher levels of virus in the blood during the viremic phase and persistence of the viremia until death, (d) failure to develop detectable serum levels of neutralizing antibody, and (e) the earlier appearance and higher levels of virus in brain and heart tissue. The level of interferon in the serum during the course of infection was similar in both groups. The administration of relatively small quantities of anti-EMC virus neutralizing antibody to X-irradiated mice during the early phases of the infection with EMC virus restored their resistance to levels comparable to nonirradiated animals. An alteration of local organ defense mechanisms in the central nervous system could not be demonstrated. It is proposed that (a) the inability of the X-irradiated animal to elaborate specific neutralizing antibody was a critical determinant in their failure to clear the viremia, (b) this increase in the level and duration of the viremic phase resulted in the exposure of target organs to a greater inoculum of virus, and (c) the enhanced mortality observed in irradiated mice reflected this greater target organ involvement. The experimental model presented, therefore, suggests that the immunologic response is a critical determinant of host resistance during this primary systemic virus infection.

Depression of circulating interferon response in Balb-c mice after urethan treatment

Urethan, when given to female Balb/c mice, impaired the capacity of these animals to produce circulating interferon. The effect appeared rapidly after a single injection of either 1 or 1.5 milligrams of urethan per gram of body weight and was of short duration. The possibility that this inhibition of the production of interferon plays a role in the enhancement of viral leukemia by urethan should now be considered.

Leukocytes and interferon in the host response to viral infections. II. Enhanced interferon response of leukocytes from immune animals

Glasgow, Lowell A. (University of Rochester School of Medicine and Dentistry, Rochester, N.Y.). Leukocytes and interferon in the host response to viral infections. II. Enhanced interferon response of leukocytes from immune animals. J. Bacteriol. 91:2185-2191. 1966.-The production of interferon was studied under in vitro conditions in peritoneal leukocytes or macrophages from mice immunized with Chikungunya virus (CV). Cultures of leukocytes obtained from animals immune to CV produced 2- to 10-fold greater amounts of interferon when exposed to an inoculum of CV than similar cell preparations from nonimmune, control animals. The viral inhibitor produced in increased quantity by CV-immune leukocytes had the biological and biochemical properties of interferon. The enhanced interferon production was inhibited by actinomycin D. This response of immune leukocytes was specific, and was initiated only by CV; it was not observed in leukocytes from animals immunized against other viruses which were challenged with CV. The presence of neutralizing antibody could not be related to this response. The observed increase in interferon production was not dependent upon an enhanced virus uptake. The data are presented as a possible new dimension of the "immune response" and may suggest a mechanism for the phenomenon of "tissue immunity."