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The antiviral effect of the combination acyclovir (ACV) and ribavirin (R) on herpes simplex virus type 1 (HSV-1) in diploid cell culture of human embryonal skin and muscle fibroblasts and the virus of pseudorabies in secondary culture of chicken embryonal fibroblasts is studied. The antiviral activity is studied under the checker-board combinations of twofold dilutions of the two substances on the basis of inhibition of the virus cytopathic effect in microplates. The viruses are applied at 100 CCID50, per 0.1 cm3 in each well. Dose isobologrammes are made which point out to the synergistic type of interaction of the substances in the combination in relation to the two viruses. The concentrations with maximal synergistic effect in relation to HSV-1-1.1 for ACV and 41 mu for R respectively, and in relation to the virus of pseudorabies of 3.3 and 9.2 M respectively, are established.

Strains of the swine transmissive gastroenteritis (TGE) virus were isolated for the first time in Bulgaria in 1972. The dynamics was followed up of some strains' propagation in primary cell cultures of kidney tissue and subcultures of the thyroid of pigs. The intracellular virus reached highest titers at the 24--48th hour in the kidney cells, and at the 24--36th hour in the thyroid cells, while the extracellular virus was subjected to inactivation by the 2nd hour after infecting the cultures, by the 4--6th h its titer dropped up to 50 per cent of its initial value, and by the 24th h it was completely inactivated. The viability of the virus was tested after freeze-drying and after it had been stored at 4degreesC and--20degreesC. It was found that chloroform fully inactivates the virus at 4degreesC for 24 hours. The same results were obtained with the use of sodium desoxycholate. The strains isolated in this country form plaques, and with some strains the plaques are of a varying size. Halogenic desoxyuridines (IUDR, BUDR), as well as 8-azoridine do not suppress the multiplication of the tested TGE strains even in high concentrations. Inhibitory effect has 5-bromurazyl which in given concentrations affects the titer of the virus and the size of the plaques formed. Two Bulgarian and two reference strains have lowered their plaque-forming titer by 2 log after being treated with rifamycin-B or rifampicin.

Ultrastructural studies were carried out on the morphology and morphogenesis of the Aujeszky's disease avirulent immunogenic mutant strain MK 35 and the virulent parental strain 2. It was found that MK 35 had a delayed cycle of replication, lasting about 10 hours as against the virulent strain 2. It also induced specific cytomorphology of the infected cells as well as the synthesis of a predominantly virus antigen in the form of empty viral capsids of tubular shape. THe culturing of the virulent strain in cell cultures in the presence of the antimetabolite 5-brom-desoxiuridine led to the synthesis of a limited amount of mature viral particles. Characteristic proved, the production, although in small amounts, of empty viral capsids. This process was observed after the 24th hour of infection of the cell cultures.

In order to master a new method for the production of a F. M. D. vaccine the authors have studied the reproduction dynamics of BHK21C13 cells in the conditions of a suspension culture. The culturing of the cells has been carried out under laboratory conditions, investigating also the concurrent changes in the pH value along with the cell dynamics. The nutrient medium used and the conditions of cultivation has made it possible to study the properties and obtain a qualitative cell suspension. The cells obtained have shown equally good growth in a monolayer medium and in a suspension, and are appropriate for the reproduction of the F. M. D. virus.

A study was carried out on the re-distribution of cell receptors with regard to Concavalin A, depending on two factors: the virulence of the strain the different time of the infection. It was proved that the difference in the virulence of the strains, with the use of a low multitude in the early hours after the infection, was not determined though agglutination with Koh A. The changes on the surface of the cells infected with the virus of Newcastle disease (NDV) occurred in the early hours after the infection and before the appearance of a cytopathic effect.

Attempts were made to modify the hemadsorption method used in the demonstration of the African swine fever virus. Use was made of fourteen strains of the virus with known hemadsorption properties and infectious titers, which were replicated in leukocyte cultures of swine blood, in three variants: (a) at direct infection of the cultures without changing the medium; (b) at infecting with changing the medium and adding erythrocytes to the new medium; and (c) infecting the cultures with changing the medium and adding 0.2 cm3 2 per cent erythrocyte suspension to each test tube at the 16th hour following infection. It was shown that in its third variant the hemadsorption method yielded most clearly expressed results, and all suspective fields were eliminated, the result being recorded as early as the second hour after the addition of erythrocytes, i.e., at the 18th hour following the infecting of cultures. With the third modification of the method no phagocytosis of the present erythrocytes effected by the emerging macrophages, which is common for the other two variants, could take place.

Theophylline is said to produce an inhibiting effect on the replication of the Newcastle disease virus in chick embryo fibroblast cultures when used in conc. of 1 mM. When the cultures are treated with theophylline 24 hours prior to their infection or following one-hour adsorption the virus titer is lowered in the process of replication by about 2 lg as against the titer when the virus is replicated in theophylline-free cultures. The inhibiting effect consists in blocking or arresting the production of mature virions.

Described is a respiratory enzootic in calves aged 30 to 90 days. Two cytopathic strains of the bovine respiratory syncytial virus were isolated from diseased calves in a cell culture of lamb thyroid. Clinical observations and the results of virologic and serologic investigations have revealed that mixed infections of the respiratory syncytial virus and the mucosa disease virus take part in the etiology of the respiratory enzootic described.

Experiments were carried out for the purification and concentration of the foot-and-mouth disease virus. For the purpose the virus suspensions were treated with chloroform and 8 per cent polyethylene glycol. The precipitated virus was eluated with phosphate buffer (of pH 7.6) up to 1:100 of the initial volume. The concentrated virus was subjected to gradient ultracentrifugation on gradient of CsCl. The fractions obtained were investigated through radial immunodiffusion reaction with early sera, containing IgM antibodies. The fractions that formed circles of precipitation were studied under electron microscope at negative contrasting. It was found that the fractions taken from between the CsCl layer of 1.42 g/cm3 density and the underlying CsCl layer of 1.50 g/cm3 density, which produced precipitation circles in the radial immunodiffusion test, contained purified virions of intact structure in concentration of 10(9).

Cytological and cytochemical studies were carried out of cell cultures of chick embryo fibroblasts infected with the vaccinal mutant strain MK 35 (4.8 X 10(7) PFU) of the Pseudorabies virus. It was found that the first cytologic changes in the infected cultures presented definite focal character. In the first hours of infection several rounded cells were included only, while later on an increasing number of cells were involved, and the foci grew in size. The cytoplasma of the infected cells contained inclusions which were small, spherical, basophilic, and Foelgen positive; six hours later the cytoplasmatic inclusions became larger, oval, acidophilic, surrounded by a brighter area, and were Fölgen-negative. Parallel to the cytologic changes in the infected cell cultures there set in metabolic disturbances and changes in the enzymatic activity. The infected cells showed enhanced lactate dehydrogenase, diphosphopyridin-nucleotide diaphorase, thiamine pyrophosphatase, and alkaline phosphatase activity and suppressed succinate dehydrogenase and acid phosphatase activity. These studies were said to reveal new biologic properties of the vaccinal mutant virus.

Adenoviruses isolated from pigs (RO-KL; SA3; RO; and R10) and the prototypic strain Compton 25R, belonging to the 1st serologic group, are responsible for the formation of intranuclear bodies of the Cowdry-A type, while the virus Ad5 strain (isolated from humans) cause the formation of another variant of nuclear inclusions of the Cowdry-B type known as Central mass. All virus strains propagate in primary cell cultures of pig kidney and calf and rabbit kidney, calf testis, and in the stable cell line PK-15, showing negligible variations. Resistance and stability experiments have demonstrated that the investigated strains posses physico-chemical and morphologic properties that are characteristic of the adenoviruses. The virus strain isolated in Bulgaria, and the strains isolated in Hungary can be classified in the IVth serologic group of swine adenoviruses. The study of serum samples taken in different regions of Bulgaria and Hungary in order to establish adenovirus antibodies have revealed that in about 20.5 per cent of the swine sera in Hungary, and in 19 per cent, on an average, of the sera taken in Bulgaria there are adenovirus antibodies.

Studied were the opportunities for employing the method of counter immunoelectrophoresis (CIE) to differentiate F. M. D. viruses of different origin, comparing the results obtained with those reached through the immunodiffusion test (IDT). It was found that CIE could be used successfully for the serotyping of F. M. D. viruses, the method being as precise as IDT, however, the results are recorded at the 90th minute, while IDT requires at least 24 hours to read the results.

Different variants were tested of the immunoperoxidase method for the demonstration of the mucous disease-virus diarrhoea agent in infected cells with the use of a specific conjugated antiserum. It was found that the virus could be specifically demonstrated in infected cell cultures. The test proved rapid and readily applicable.

Studied was the effect of actidione on the propagation of the Aujeszky's disease virus (strains 2,7,10--virulent,, and strain MK--avirulent virus mutant). It was found that at a concentration of 2 microng/cm3 actidione discontinues the reproduction of the most virulent strain 2 when the antibiotic was added immediately after the adsorption of the virus on the cells. The decrease in the virulence of the virus strain was associated with the decrease in the concentration of the antibiotic needed for the inhibition of its propagation. Thus, the reproduction of the more slightly virulent strain 10 was fully inhibited at actidione concentration of 0.75 microng/cm3, while that of the avirulent strain MK was discontinued at 0.4 microng/cm3. The preliminary cultivation of the cells with 1 microng/cm3 actidione for 24 hours and the adsorption of the virus on the cells jointly with actidione showed no effect on the vitality of the virus particles.

Attempts were made to culture the swine parvovirus under laboratory conditions. A reference strain and a field isolate were used along with steady cell lines of pig kidney PK-15, IBAS-2, and SPEV as well as primary and secondary cell cultures of pig kidney. It was found that the steady cell lines were slightly sensitive or totally unsusceptible to the swine parvovirus. The could serve for its isolation from pathologic material and culturing in laboratory conditions. Both the primary and the secondary cell cultures proved strongly susceptible to the virus, and they could be used for the isolation of filed strains as well as for the laboratory maintenance of the virus. The strains used produced no clearly distinguishable cytopathic effects in the inoculated cell cultures. The morphologic changes that set in following inoculation with higher amounts of the virus could be seen under the light microscope and could be evaluated through cytologic investigations (the presence of intranuclear inclusion bodies). The virus could be most readily demonstrated in the infected cell cultures via the hemagglutination test.

Experiments were carried out to inactivate F.M.D. viruses with the use of binary ethylene-imine. It was found that inactivation was optimal when the agent was used at the rate of 0.003 M for 18 hours at 26 degrees C. Its neutralization in the virus suspension was carried out with 3 mM sodium thiosulfate. The inactivated F.M.D. viruses retained their complement-fixing and immunogenic properties. Discussed are the advantages of using binary ethyleneimine as an inactivating agent as against other agents of the asiridine order.

The study on the effect of rifampicin on the reproduction of Aujeszky's disease virus (strains 2, 5, 7, 10, 12, and 17, which are virulent, and strain MK, which is an avirulent virus mutant) in cell cultures revealed that the formation of plaques is inhibited, though to a slighter extent, at a concentration of the inhibiting agent of 100 mug/ml, the value of their titer lowering by one logarithm. All virus strains have proved equally susceptible to the effect of rifampicin. During the virus multiplication in the presence of rifampicin the diameter of the plaques formed decreases from 2.8 to 0.5 mm, and with the avirulent strain MK it decreases up to 0.2 mm. They have rose tint in contrast to the plaques formed by strain 2, which are colourless. Rifampicin has no effect on virus reproduction when the cells are cultivated 24 hours prior to adding the antibiotic or when the virus adsorption on the cells takes place simultaneously with rifampicin. At lower rates the latter does not alter the reproduction process of the virus, however, at doses higher than 10 mug/ml it becomes toxic for the cells. Rifampicin inhibits the multiplication of the virus if it is added to the infected cell cultures up to the 12th hour following the adsorption of the virus. When 25-diacetyl-rifampicin is added to the nutrient medium the number of the plaques formed decreases but no change in their diameter occurs. However, with the avirulent MK strain both the number of plaques and their size decreases. Rifampicin B and rifampicin SV have no effect on the reproduction of Aujeszky's disease virus.

It was established that the complement binding reaction (CBR) is a suitable and very fast method for horse rhino-pneumonitis diagnostics. Cell cultural virus produced in cell cultures of pig kidneys was used as antigen. The antigen lots tested have no anticomplementary properties. Highest complement binding activity was evident in the non-diluted antigen, which discovered specific antibodies in immune serums. The CBR specificity was tested by the aid of homologous and heterologous serums and antigens. The titers of complement binding antibodies in the serums of 255 horses recovered from the disease varied from 1:10 to 1:320, and in some cases even to 1:640. The blood samples investigated were from studs having rhinopneumonitis proven by clinical observations, by virus neutralizing reaction and by virus isolation. In almost all animals under study neutralizing and complement binding antibodies were established simultaneously.

Experiments were carried out to establish whether the glucose antimetabolite, 2-desoxi-d-glucose (DDG), effected the proteolytic breakdown of the envelope proteins of NDV and if there was any effect on there antigenic properties. It was found that it inhibited the glucose action on the NDV envelope proteins, the hemagglutinin-neuraminidase (HN), and the F-protein so that their biologic properties were not manifested, and the production of infectious virus was blocked. In the presence of DDG the virus-infected were shown to contain the virus envelope proteins, the membrane protein, and the nucleocapsid both through electrophoresis in 10 percent polyacrylamide gel and through the agar gel immunodiffusion test (with the use of specific rabbit anti-HN, anti-F protein, and anti-M protein sera). The antigenic properties of the two glycoproteins of the NDV envelope did not change under the action of the DDG inhibitor as seen by the precipitation lines of the control variants (cells infected with the virus but not treated with the antimetabolite), which were identical with those obtained with the test variants (cells treated with DDG).

Attempts were made to work out a method for measuring the amount of the 140 S antigen in virus suspensions. Early postinfection sera were obtained from guinea pigs against the productional strains of the foot-and-mouth disease virus which were used in the radial immunodiffusion test. The investigated virus suspensions were concentrated 50 to 200 times and were placed in a CsCl gradient for gradient centrifugation. The 140 S antigen fractions obtained were titrated in a radial immunodiffusion test. The size of the resulting precipitation circles were defined for the individual dilutions of the antigen, and the method of least squares was employed to establish the standard straight lines for each of the investigated productional strains of the FMD virus. The new method makes it possible to fix the content of the 140 S antigen in productional series of the FMD virus intended for vaccine production.

Experiments were carried out to use polyethylene-glycol (PEG)--6000 in the isolation of the IBR virus from field material. The sedimentation with PEG proved easy, fast and selective. Large amounts of field material suspension could be treated which made it possible to attain volume concentration of such suspensions and to raise the relative concentration of the virus in them. Thus the virus could be isolated more quickly and in a more dependable way, avoiding the toxic effect of some of the initial materials on the cell culture.

Series of attempts were made to adapt the Phylaxia vaccinal strain (Hungary) to various cell cultures in vitro. The work with twenty-one successive passages of the virus in a culture of lamb testis resulted in the production of an adapted strain that could produce a characteristic cytopathic effect at the 24th--48th hour of the infection, reaching a titer of 10(4.5) ID/cm3. Cytologic and electron-microscope investigations confirmed the fact that this cell strain belonged to the Parapoxvirus genus. The experimental infection of 4-5-month-old lambs showed that the virus strain retained its capacity to cause typical clinical signs of infectious ectyma. It could be used in the production of a cell-cultural vaccine.

By applying the direct immunofluorescent method, a study was carried out on the appearance and accumulation of adenoviral antigen in cattle, in infected cellular cultures from the testes of calves and in epithelial cell obtained by smearing with nasal mucosa and conjunctiva of experimentally infected and spontaneously taken ill with adenoviral infection calves. A specific conjugate was obtained by the writers of the present study. In the cultures from calf testes, the earliest viral antigen was proved 36 hours after the infection in the form of a finely granulated nuclear fluorescence with a yellow-green colour. The highest quantity of fluorescent cells was observed after 72 hours. A specific nuclear fluorescence was observed as early as on the sixth day after the infection in the nasal mucosa of experimentally infected calves. An adenoviral antigen was detected on the tenth day in 30% of the cells, and in separate fields of vision the number of fluorescent cells predominated over the negative ones. During the next days the intensity of the nuclear fluorescence diminished, whereas in the cells obtained by smearing on the eighteenth and twenty fourth days of the infection of calves, it was no longer observed. No adenoviral antigen was proved in the first preparations produced from spontaneously ill calves. Such was proved after a second taking of nasal and conjunctival samples six days later. A conclusion was drawn that the immunofluorescent direct method allows the identification of an adenoviral antigen in cells of the epithelium of the upper respiratory routes during the first days of calves infected with adenoviruses.

The serial cultivation of a virulent strain of the virus of transmissive gastroenteritis in the presence of the antimetabolite 5-bromurazil has led after a definite number of passages to the production of a virus mutant of new biologic properties. It was established that the mutant is resistant to the antimetabolite, and it retains its infectious titer. It is avirulent to newborn and growing pigs, and confers solid immunity in the vaccinated animals which do not become virus carriers. It is stable with regard to its newly-obtained biologic properties.

Experiments were carried out to find the optimal conditions for the replication of BHK 21 C 13 cells in one 1 roller glassware with the use of a nutrient medium containing products of the enzymatic breakdown of white of egg. Studied was the sensitivity of these cells to the type C strain 'Hungary' of the foot-and-mouth disease virus. Two series of F. M. D. vaccines were produced, which proved to be sterile and innocuous for guinea pigs. Immunogenicity trials with regard to these animals revealed that the VD50 (vaccinal dose) values ranged from 0.12 to 0.26 cm3.

A number of physicochemical and immunoelectrophoretic investigations as well as tests were carried out for the standardization of an antigen for immunodiffusion prepared from an IBR virus. The antigen showed strict specificity and maximum activity at a concentration forming a 7.5-8.0 mm diffusion disc in a radical immunodiffusion. It is made up of two antigenic components and shows a pronounced lability. The antigen reacts more intensely with immunoglobulins of the IgM type but is also active with regard to IgG. The antigen makes positive all serums with virus neutralizing antibodies having a titre of 1:16 and above. It is susceptible to standardization and shows stability as regards preservation in a lyophilized state.

Investigations on the resistance of Aujeszky's disease virus to gamma irradiation from a 60Co source were performed. The resistance of the virus was tested in vitro in a fluid medium of 50% Henk's balanced saline solution, 50% Eagle's medium MEM and a supplement of 10% normal calf serum as well as its resistance on artificially virus infected pig skin and greasy wool of sheep. It is established that virus inactivation in the fluid medium occurs following 1.6 Mrad gamma irradiation. The irradiated with lower than 1.6 Mrad gamma doses live virus particles form smaller than and with irregular oval shape and dentated plates as compared to the non-irradiated control virus. 1.5 Mrad gamma rays are needed to inactivate the virus on pig skin and greasy wheep's wool. The presence of lanoline in greasy sheep's wool, due to the alkaline pH (9--13) it produces, has an effect on the vitality of the virus both in the control and in the experimental samples.

Specific high-titre bovine conjugated antisera were obtained against respiratory syncytial virus. Use was made of the reference strain Nomi and the local isolate Antonovo/448. The conjugates produced were shown to have equal qualities to those of the Belgian conjugate used for comparison. The anti-Antonovo/448 conjugated serum was used in the direct immunofluorescent method to demonstrate a respiratory syncytial virus antigen in organs of animals with acute respiratory diseases as well as to control the replication of the virus in cell cultures. An infection with a respiratory syncytial virus was demonstrated with the employment of the same test in 16 per cent of a total of 119 samples taken from diseased animals. In the inoculation of the diploid cell culture of lamb thyroid gland with strains of the virus a specific antigen was established at the forty-eighth to the seventy-second hour following infection.

The location of the rotaviral precipitating antigen and the possibility for its production from cattle rotaviral strains adapted on cell cultures of calf kidney were investigated. Highest titer antigen was produced by concentration with ammonium sulfate simultaneously from the maintaining medium and from the cell monolayer. Comparative studies on the antigenic and physico-chemical properties of the cell-cultural and the faeces rotaviral precipitating antigen were made. The identity of both antigens was proven by the immunodiffuse reaction and by their resistance to ether and tripsine. A considerably higher temperature sensitivity was established of the cell-cultural precipitating antigen as compared to that from faeces. The precipitating antigen was used for confirming the presence of antirotaviral antibodies in the serums of cattle, man and sheep.

In a passive hemagglutination reaction (micromethod for detecting IBP antibodies) were used 4 types of cellularly cultivated, group specific antigens from a cattle adenovirus, serotype 1. The most appropriate for the reaction proved to be the antigen obtained by a complete destruction of the infected cells and deduction of the soluble viral hexen components. The production of th antibodies does not require a special equipment. A high-titre antigen is obtained, which can be well loaded passively on tanninized sheep erythrocytes. A much higher sensitivity of passive hemagglutination reaction was obtained in comparison with virus neutralizing reaction and immunodiffusion reaction. Therefore, for mass serological investigations if serums from calves suffering from bronchial pneumonia, a much larger quantity of seroreagents are detected, which remain undetected if immunodiffusion reaction is applied. Prospects are discussed for the implementation of this micromethod for mass serological investigations in detecting the dissemination of adenoviral infections with cattle.

Experiments were carried out to isolate type 'B' of the chicken Herpes virus on a farm for stock layers with a low level of losses due to Marek's disease. Seven virus isolates were obtained from 3-4-month-old White Leghorn poults via direct kidney cell cultures. One of them, named strain C-80, was studied in chick embryo fibroblast cultures, and egg cultures (Büllow's test) as well as biochemically, serologically, and through the electron microscope. Results made it reasonable to identify it as a chicken Herpes virus type 'B'. In vivo experiments with strain C-80 inoculated in day-old chicks at the rate of 15 x 10(3) PFU showed that it did not cause gross and microlesions in the nervous system and the parenchymal organs in the course of 18 weeks of observation. The immunogenic properties of strain C-80 were studied in 2250 day-old White Plymouth Rock chicks inoculated at the rate of 1360 PFU, kept in an infected environment together with as many as 4500 control birds immunized three times with a vaccine (obtained from a turkey Herpes virus) at 1500 PFU. Twenty-four weeks later the losses due to Marek's disease were 3.4 per cent in the test group, and 7.2 per cent in the control one. It is believed that strain C-80 is appropriate for the production of a vaccine against Marek's diseases--Rispens type. Further studies are being performed on the antigenic composition and the immunogenic properties as well as series of in vivo passages with regard to reversibility.

High-titer, specific serum against porcine parvovirus was obtained via hyperimmunization of rabbits, with the use of a Bulgarian isolate that had been partially purified after a known, modified technique. A specific, high-titer conjugate was produced for the immunofluorescence diagnosis of porcine parvoviruses. The microscopic observation of the lamellae of cell cultures, treated with the conjugate, revealed the presence of a specific, typically granulated perinuclear (mostly unilaterally) and, in some cases nuclear fluorescence--at negative reaction in the control preparations. Immunofluorescent light was also established in cell cultures infected with the virus at highest dilution. It showed that immunofluorescence microscopy could be employed to demonstrate even the lowest amounts of the virus.

Studied was tentatively the occurrence of a respiratory syncytial virus infection on some farms with records of the disease. Investigations were carried out on the base of the complement-fixation test (CFT) specially worked out and on the specific complement-fixing antigen obtained from a bovine respiratory syncytial virus (BRSV). Tested were several methods for the production of a complement-fixing antigen. Most appropriate proved the one obtained by the extraction of an infected cell monolayer in glycerine buffer saline. It was stated that CFT was a proper test for the rapid herd diagnosis of BRSV infection. The study of double serum samples from 240 calves involved in 40 enzootics revealed that CFT could successfully be employed in 18 per cent of the cases of respiratory infections in calves in as many as 17 enzootics. However, the etiologic part played by the virus was dominating in some of these enzootics only. In the remaining ones the participation of the virus was either partial or sporadic.

Studied was the capacity of the soluble virus-specific glycoproteins of the virulent A-2 strain and its IUDR-resistant MK-25 mutant to induce the production of virus-neutralizing antibodies. It was found that both the purified virions and soluble glycoproteins of strain A-2 and those of strain MK-25 induced the release of virus-neutralizing antibodies in the injected rabbits. Use was made of affinity chromatography on Con-A-Sepharose to isolate the glycosylated virus-specific proteins. The quality of the soluble virus-specific glycoproteins to trigger the production of virus-neutralizing antibodies made it reasonable to believe that the virus glycoproteins are structural ones.

Comparative studies were carried out of the antiviral efficacy of 11 substances on the replication of Herpes simplex virus type 1 (strain DA), including compounds with selective antiherpes action--bromovinyldeoxyuridine, virazole, phosphonoformic acid, acycloguanosine, citarabine, vidarabine, iododeoxyuridine, and some nonspecific viral inhibitors with antiherpes effect as distamycin A, tunicamycin and deoxyglucose. The antiherpes activity of the substances was tested in two cell systems: cell strain of human embryonic skin-muscle fibroblasts and a cell line of green monkey kidneys. The dose-response curves and the 50% effective dose were defined for each compound by using a microtissue plate test system. Differences in the values of the 50% effective doses of iododeoxyuridine, phosphonoformic acid and distamycin A for the two types of cultures were found out. Bromovinyldeoxyuridine exhibited the highest antiherpes activity in both types of cells, and it was comparatively more active than citarabine, acycloguanosine or iododeoxyuridine, followed by vidarabine and virazole. The results obtained emphasized the necessity of specifying the experimental conditions for comparative studies.

Investigations were carried out to establish the possibility of using a micromethod of the complement-fixation test to determine the complement-fixing properties of productional series of the foot-and-mouth disease virus. It was found that the micromethod referred to is an economically profitable and practically simple one. It is readily applicable requiring no particular apparatuses and equipment, is specific, and can successfully be used instead of the routinely employed CFT method. The micromethod suggested is economical, requiring minimal amounts (0.025 cu.c7) of the components taking part.

Several methods were employed to obtain lymphocyte cultures from blood samples taken from normal cattle and from cattle affected with enzootic leukosis. Biologic and virologic experiments revealed that the cultures from diseased cattle contained an oncogenic leukosis virus, while those obtained from healthy animals were exempt from such virus. Electron microscopy was applied to study the morphologic aspects of the bovine leukosis virus with a total of 18 lymphocyte cultures. The viral particles noted were shown to have typical configuration and size of type C oncogenic viruses as described in the literature--possessing a central dense nucleotide and double membranes. Seen were also various stages in the development of the virus. Mature virus particles were likewise observed in a stable cell line FLK (percent of the virus) as well as in ultrathin cross sections of the spleen of leukosis-affected animals.

The virologic investigation of clinical and pathological material from calves affected with a respiratory disease at the age of 30 days to 10 months on 16 infected stock-breeding farms led to the isolation of two virus strains (D-117 and Ch-216) on primary cell cultures of fetal calf kidney from the nasal discharge of two 8-month-old calves. By their cytopathic changes, physico-chemical properties and the presence of a group-specific antigen they were said to belong to the adenovirus family. The results of the cross virus-neutralization test pointed to the assumption that they had to be referred to the bovine adenovirus type 1. Discussed is the problem concerning the participation and the importance of individual types of adenoviruses in the acute respiratory enzootics of grown-up calves.

Explored was the possibility of inhibiting the replication of the virus of the transmissive gastroenteritis by means of actidione. It was found that in certain concentrations the antibiotic completely inhibited the replication of this virus. In individual strains the process of replication was not influenced by the various concentrations applied. It was demonstrated that when the antibiotic was added to the infected cell cultures during individual phases its varying concentrations influenced the virus replication. When actidione was added to the cells at the time of virus adsorption it did not inhibit the synthesis of the virus. Similar were the results when the cells were cultivated 24 hours with specified concentrations of actidione prior to their infection with the virus.