Significance of the heterogeneity of respiratory syncytial viral populations in the development of the epidemic process

The manifestations of the epidemic process in respiratory syncytial (RS) virus infection induced by the strains of the infective agent, differing in their capacity for reproduction at 39 degrees and 37 degrees C and in their sensitivity to antibodies, were compared. The observation of children in a group (about 80 children simultaneously) with the systematic serological and virological examination of sick and healthy children was the main method in this investigation. The circulation of RS viruses with greater capacity for reproduction at 39 degrees and 37 degrees C and lesser sensitivity to antibodies, i.e. viruses with greater virulence, was accompanied by the increased intensity of manifestations of the epidemic process. An increase in the heterogeneity of RS virus populations isolated at the same period of observation was accompanied by the intensification of the epidemic process, which was manifested by increased morbidity rate and a higher level of contamination in children, an increase in the incidence of outbreaks and in the frequency of RS virus reinfection.     

Identification and characterization of the virus causing rabbit hemorrhagic disease.

Liver tissue from animals that died of rabbit hemorrhagic disease (RHD) was used to identify the causative agent. After extraction of liver homogenates and sucrose density gradient ultracentrifugation, distinct bands were obtained. The respective gradient fractions reacted positively in an enzyme-linked immunosorbent assay as well as in hemagglutination assays and were infective for rabbits. These fractions contained virions which had a diameter of 40 nm and resembled morphologically those of the family Caliciviridae. By immunoblotting, a major structural protein with a molecular weight of 60,000 was identified. Highly pure RNA of about 8 kilobases was isolated from virions. Labeled cDNA synthesized from virion RNA detected two RNAs of 8 and 2 kilobases in Northern (RNA) blots of liver RNA from animals infected with RHD virus. Finally, isolated virion RNA injected into the liver of rabbits produced a disease with clinical symptoms and pathological findings typical of RHD. We conclude that a calicivirus represents the causative agent of RHD.     

Vaccinia Virus Replication and Cytopathic Effect in Cultures of Phytohemagglutinin-treated Human Peripheral Blood Leukocytes

Titers of vaccinia virus consistently increased in cultures of washed phytohemagglutinin-treated, peripheral blood leukocytes of a vaccinated adult. Concomitantly, a gradual rise occurred in the numbers of infected leukocytes, as determined by the infective center assay. Increase in viral titer was accompanied by cell injury, decline in cell numbers, and decreased acid production. Leukocytes not pretreated with phytohemagglutinin appeared to form infective centers after exposure to the vaccinia agent, but they did not replicate infectious virus. For viral replication, the continuous presence of phytohemagglutinin was required.     

The particle morphology and some other properties of chloris striate mosaic virus

The causal agent of Chloris striate mosaic disease appears to be a virus with polyhedral particles 18 nm in diameter usually occurring as paired structures about 18 times 30 nm in negatively stained preparations. These particles were detected in the nuclei of infected plants forming characteristic inclusions in all cells except those of the epidermis. Such particles were not detected in thin sections of viruliferous leaf hopper vectors (Nesoclutha pallida). Purified virus preparations were shown to be highly infective when assayed by feeding vector leaf hoppers through membranes and confining them on indicator plants. In particle morphology, chloris striate mosaic virus (CSMV) differs from other viruses of Gramineae in Australia but resembles maize streak virus isolated in Africa, which however is serologically unrelated.     

Efficacy of chemical disinfectants against snakehead rhabdovirus

The susceptibility of snakehead rhabdovirus to treatment at 20°C with 5 commercially available disinfectants was examined. No reduction in virus infectivity occurred following exposure to 5 ppm malachite green for 6 hours. Treatment of infective cell culture fluids with 2% formalin resulted in > 99.9% reduction in virus titre within 5 minutes and complete inactivation within 30 minutes, but a negligible loss in infectivity after exposure to 0.025% formalin for 1 hour. Suspensions of virus in distilled water were completely inactivated within 5 minutes by 12.5 ppm chlorine, 50 ppm iodine, or a 1:2000 dilution of a peroxygen disinfectant. In the presence of serum in infective cell culture fluids, however, > 50 ppm chlorine was required to inactivate the agent and no measurable reduction in infectivity was observed following treatment with 500 ppm iodine for 30 minutes.     

Aspects of the cross transmission to Galleria mellonella of a Baculovirus from the alfalfa looper, Autographa californica

The nuclear polyhedrosis virus originally isolated from the alfalfa looper, Autographa californica, was successfully transmitted to the greater wax moth, Galleria mellonella. Both the many polyhedra per nucleus (MP) and the few polyhedra per nucleus (FP) plaque variants of this virus were found to be infective when injected intracoelomically. When polyhedra of each plaque variant were fed to G. mellonella larvae, a difference in response was observed; the MP plaque variant was estimated to be 30 times more infective than the FP variant.     

STUDIES ON DANDELION YELLOW MOSAIC AND OTHER VIRUS DISEASES OF LETTUCE

The symptoms caused by dandelion yellow mosaic virus on cultivated lettuce, Lactuca serriola and L. virosa , are described and compared with those caused by lettuce mosaic virus. Lettuce is much more susceptible than dandelion to the yellow mosaic virus; no infections of dandelion were obtained by mechanical inoculation and only three by aphides, whereas infection of lettuce is regularly obtained by aphides and by inoculation provided an abrasive is used. Myzus ornatus, M. ascalonicus and Aulacorthum solani transmitted dandelion yellow mosaic virus but not lettuce mosaic virus, whereas Myzus persicae transmitted the latter but not the former. Nasonovia ribicola , the common lettuce aphis, transmitted neither. Aphides became infective only after feeding periods of some hours on the diseased plants and ceased to be infective within an hour of the infective feeding. Their efficiency as vectors was not increased by a preliminary starving period, as happens with Myzus persicae and lettuce mosaic virus. Lettuce mosaic virus was found in most samples of commercial seed, which explains its prevalence; no evidence was found for the seed-transmission of dandelion mosaic virus and it is doubtful if it occurs, for infected lettuce are so severely affected that they rarely set seed.
Cucumber mosaic virus was isolated from naturally infected lettuce.     

Leucocyte migration inhibition test as an index of immunological response to measles virus. IV. Blood, spleen, lymph nodes and peritoneal exudate cell reaction.

The migration inhibition test of leucocytes isolated both from the peripheral blood, spleen and lymph nodes as well as peritoneal exudate cells of guinea pigs, immunized with the various doses of measles virus was determined. For in vitro testing of cellular immunity to measles virus, viral antigens could be used in both infective and inactivated form.     

Are Animal Tumor Viruses Always Virus-Like?

Three tumors initiated by well characterized viruses, but in which virus is not detectable by ordinary virological techniques, are discussed. The question of the possible state of the virus within these seemingly non-infectious tumors is considered, largely from the standpoint of findings with the rabbit papilloma virus. This agent in its natural host, the cottontail rabbit, is infective, can be seen as virus bodies with the electron microscope, and can be visualized with fluorescent antibody only in the upper keratinizing cells of individual papillomas. At the growing bases of such papillomas, where neoplasia is in active progress, no infective virus is demonstrable and viral bodies cannot be visualized by either the electron microscope or fluorescent antibody. A hypothesis is presented that rabbit papilloma virus exists in cottontail papillomas in two forms—one, the complete mature virus, composed of nucleic acid and protein, and the other, immature virus, composed of naked viral nucleic acid without its protein coating. The function of the mature papilloma virus is to initiate tumor formation,—that of the immature virus, to maintain neoplasia. In the non-infective domestic rabbit papilloma, the viral nucleic acid and protein fail to combine to form mature infective virus and, as in the cottontail papilloma, neoplasia is maintained by the activity of the viral nucleic acid alone.     

Cultivation of Tuleniy virus (strain Murman) in vitro.

In vitro culturability of Murman strain of Tuleniy flavivirus isolated recently in the northern regions of the USSR was studied. Stable PS pig kidney line was found suitable as a primary sensitive cell substrate for the isolation, proliferation and serial propagation of the virus. The pronounced pathogenicity of the virus to PS cells permits the testing of its infective activity comparable with i.c. titrations on mice, VNT in vitro and the plaquing technique. PS line is suitable for the demonstration and identification of the virus antigen and/or for the study of reproduction of the virus on cellular level using the technique of immunofluorescence.     

Crimean-Congo hemorrhagic fever in Rostov Province: the epidemiological characteristics of an outbreak

The results of the epidemiological analysis of the outbreak of hemorrhagic fever which was caused by Crimean-Congo hemorrhagic fever virus and occurred during the period of July 3-19, 1999, in the Oblivskaya district of Rostov Province are presented. The specific epidemiological features of the outbreak have been determined. The possible versions of the appearance of the focus of infection and the role of Ixodes ticks in the circulation of the infective agent are discussed.     

A Virus from Epidemic Vomiting Disease

An illness consisting of vomiting, fever, and mild diarrhoea after a short incubation period was observed in a boarding school and reproduced in volunteers who received filtered extracts of faeces from a typical case. The main discriminatory diagnostic feature of the illness in volunteers was vomiting. The faeces contained no pathogenic bacteria nor any virus that could be detected in tissue cultures and there was no evidence that an infective agent could be grown in organ cultures of human intestine. The agent was shown to be ether stable and passed a 50-nm filter. Laboratory studies on another agent of uncertain significance and obtained in other epidemics are briefly described.     

Comparative Studies on Large- and Small-Plaque-Forming Clones of Newcastle Disease Virus (Miyadera Strain)

The Miyadera strain of Newcastle disease virus (NDV) consisted predominantly of virus particles forming small plaques on monolayers of chick embryo fibroblasts (CEF), and contained small amounts of virus particles forming large plaques. These large- and small-plaque-forming clones of this virus (NDV-L and NDV-S) were isolated. The small size of the NDV-S plaques did not appear to be due to an agar inhibitor. NDV-L produced a much higher yield of infective virus particles in CEF and they were released more completely from the infected cells than were those produced by NDV-S. The yield of infective virus of NDV-L per cell from cultures of CEF was comparable to the yield from the allantoic cells. The infectivity/hemagglutinin ratio for NDV-L from CEF was as high as the ratio for virus from the allantoic cells, but the ratio for NDV-S from CEF was lower. NDV-S demonstrated an autointerference phenomenon in CEF when infected at high multiplicities, but NDV-L did not. Contrary to virus multiplication, NDV-S exhibited a more rapid and marked cytopathic effect on monolayers of CEF than NDV-L. In the allantoic cavity of eggs NDV-S produced slightly higher virus yields than NDV-L. No correlation existed between plaque size of the two viruses and the capacity to induce interferon synthesis or the susceptibility to the action of interferon. The properties of both distinctive plaque isolates were stable on egg passage.     

Evaluation of the probability of the infection of medical personnel with Crimean-Congo hemorrhagic fever virus in cases of introduction of the infective agent to a non-endemic territory of Russia

The data on the secondary cases of infection with Crimean-Congo hemorrhagic fever (CHF) virus during the period of 1960 - 2002 have been analyzed and the probability of the infection of medical personnel with this virus has been evaluated. The data obtained in this study may be used in the development of the mathematical model of CHF epidemics (outbreaks), taking into account not only the transmission of the infective agent, but also hospital infection, as well as for calculating the number medical personnel, necessary for the liquidation of CHF epidemics (outbreaks).     

Erysipeloid as an occupational disease of workers in shoe enterprises

An outbreak of erysipeloid among the workers of a shoe factory is described. The spread of infection occurred due to contact with infected raw materials, which was confirmed by the isolation of Erysipelotrix rhusiopathiae from washings made from chrome and Russia leather supplied by different tanneries, as well as from casein glue. The raw materials could be additionally infected by rodents, in particular by common voles; the above-mentioned infective agent had been repeatedly isolated from these animals on the territory of this region. Leather was also infected in the process of soaking: the infective agent was isolated from the water of soaking baths. For the first time the routes of the spread of erysipeloid infection among shoe factory workers were bacteriologically confirmed. The recommended complex of sanitary, medical and antiepidemic measures led to the liquidation of the outbreak and thus proved to be effective. The authors draw the attention of epidemiologists, sanitary inspectors, occupational pathologists and heads of medical centers at shoe factories to the necessity of preventing the spread of occupational erysipeloid infection among the workers, as well as to the necessity for dermatologists, surgeons and infectionists, most frequently dealing with erysipeloid patients, to be correctly oriented in respect to this infection.     

Agricultural animals as a source of yersiniosis

The role of agricultural animals as the sources of infection was studied. 8 Yersinia strains were isolated from 83 samples taken from cattle. Yersinia were isolated from feces, udder washings and milk. In the examination of 63 samples obtained from sheep the infective agent was isolated from feces in 6 cases. 6 Yersinia strains were isolated from 92 fecal samples taken from pigs. Y. enterocolitica were isolated from sick animals. The isolated strains were classified with serovars 03, 058, 08 and 09. In the foci of animal infection thus revealed antibodies to various Yersinia strains were detected in the blood sera of the animal-tending personnel, which indicates the professional character of the spread of this infection among humans. The infection is probably transferred by the contact and alimentary routes.     

Growth characteristics and intraspecies host specificity of a large virus infecting the dinoflagellate Heterocapsa circularisquama

The growth characteristics and intraspecies host specificity of Heterocapsa circularisquama virus (HcV), a large icosahedral virus specifically infecting the bivalve-killing dinoflagellate H. circularisquama, were examined. Exponentially growing host cells were more sensitive to HcV than those in the stationary phase, and host cells were more susceptible to HcV infection in the culture when a higher percent of the culture was replaced with fresh medium each day, suggesting an intimate relationship between virus sensitivity and the physiological condition of the host cells. HcV was infective over a wide range of temperatures, 15 to 30 degrees C, and the latent period and burst size were estimated at 40 to 56 h and 1,800 to 2,440 infective particles, respectively. Transmission electron microscopy revealed that capsid formation began within 16 h postinfection, and mature virus particles appeared within 24 h postinfection at 20 degrees C. Compared to Heterosigma akashiwo virus, HcV was more widely infectious to H. circularisquama strains that had been independently isolated in the western part of Japan, and only 5.3% of the host-virus combinations (53 host and 10 viral strains) showed resistance to viral infection. The present results are helpful in understanding the ecology of algal host-virus systems in nature.     

Viruses of Entamoeba histolytica III. Properties of the Polyhedral Virus of the HB-301 Strain

Some biological characteristics and bioassay of a polyhedral virus isolated from normal-appearing strain HB-301 of Entamoeba histolytica are described. The virus produced lysis of susceptible strains of E. histolytica, yet it caused no cytopathological effect in the host strain, HB-301. The virus and host amoeba existed in an equilibrium; approximately 10(4) mean infective dose units of virus were produced per million HB-301 amoebae. Superinfection and antiviral antiserum treatment failed to disturb this equilibrium permanently. The mechanism of viral persistence in strain HB-301 amoebae remains to be determined. Purification of the virus was attempted. Ninety-nine percent of the viral infectivity was associated with a low-speed pellet which consisted of complexes of virus and cellular membranes. Various treatments of this low-speed pellet failed to release virus. Biologically active, membrane-free virus of low titer was prepared by differential centrifugation of supernatant solutions and employed in electron microscopy and other studies.     

Characterization of virulent and avirulent A/chicken/Pennsylvania/83 influenza A viruses: potential role of defective interfering RNAs in nature.

In April 1983, an influenza virus of low virulence appeared in chickens in Pennsylvania. Subsequently, in October 1983, the virus became virulent and caused high mortality in poultry. The causative agent has been identified as an influenza virus of the H5N2 serotype. The hemagglutinin is antigenically closely related to tern/South Africa/61 (H5N3) and the neuraminidase is similar to that from human H2N2 strains (e.g., A/Japan/305/57) and from some avian influenza virus strains (e.g., A/turkey/Mass/66 [H6N2]). Comparison of the genome RNAs of chicken/Penn with other influenza virus isolates by RNA-RNA hybridization indicated that all of the genes of this virus were closely related to those of various other influenza virus isolates from wild birds. Chickens infected with the virulent strain shed high concentrations of virus in their feces (10(7) 50% egg infective dose per g), and the virus was isolated from the albumin and yolk of eggs layed just before death. Virus was also isolated from house flies in chicken houses. Serological and virological studies showed that humans are not susceptible to infection with the virus, but can serve as short-term mechanical carriers. Analysis of the RNA of the viruses isolated in April and October by gel migration and RNA-RNA hybridization suggested that these strains were very closely related. Oligonucleotide mapping of the individual genes of virulent and avirulent strains showed a limited number of changes in the genome RNAs, but no consistent differences between the virulent and avirulent strains that could be correlated with pathogenicity were found. Polyacrylamide gel analysis of the early (avirulent) isolates demonstrated the presence of low-molecular-weight RNA bands which is indicative of defective-interfering particles. These RNAs were not present in the virulent isolates. Experimental infection of chickens with mixtures of the avirulent and virulent strains demonstrated that the avirulent virus interferes with the pathogenicity of the virulent virus. The results suggest that the original avirulent virus was probably derived from influenza viruses from wild birds and that the virulent strain was derived from the avirulent strain by selective adaptation rather than by recombination or the introduction of a new virus into the population. This adaptation may have involved the loss of defective RNAs, as well as mutations, and thus provides a possible model for a role of defective-interfering particles in nature.     

Influenza C: the immunological aspects of the problem

The use of the complex of methods for the characterization of cell-mediated and humoral immunity to influenza C virus has made it possible to establish that with the increase of the age of children and, simultaneously, with the increase of the number of persons found to be seropositive to influenza C the asymptomatic forms of this infection occur more frequently. Practically all examined adults selected by random choice have proved to be immune to this infective agent. The results of this investigation indicate that influenza C virus constantly circulates among the population.