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Enzyme immunoassay (EIA) for detection of antibodies to measles virus designed in the Moscow Research Institute of Viral Preparations has proved highly sensitive (98%) and specific (100%) as tested in 492 vaccinated children. Comparison of EIA and haemagglutination inhibition (HI) test allowed to determine the cut-off value of the optical density to be equal to 0.1. The serum dilution 1:10 was found appropriate for the screening.

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Several antispecies peroxidase conjugates from human and rabbit immunoglobulins G (IgG) and a conjugate from IgG fraction of hyperimmune rabbit serum against the membranes of herpes simplex virus type 1 (HSV-1) infected cells have been prepared and characterized. The conjugates when tested in enzyme immunoassay for detection of antiherpetic antibodies in human and hyperimmune rabbit sera, as well as for detection of HSV-1 antigen in infected Vero cells appeared active and highly specific. Comparison with the peroxidase conjugates from antiherpetic IgGs prepared by means of ion- exchange and affinity chromatography has shown similar activities.

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Enzyme-linked immunosorbent assays (ELISA) for detection of antibodies to herpes simplex virus type 1 (HSV-1) have been performed by using different immunosorbents prepared by passive adsorption of four HSV-1 antigen preparations to the wells of polystyrene microtitre plates in order to compare the the sensitivity, specificity and reproducibility of the tests. The following antigen preparations have been used: virus-infected native Vero cells and their lysates, membrane glycoproteins and virus nucleocapsid proteins. The optimal conditions have been established for each assay system: the concentrations of adsorbed antigen and the "threshold" values of the optical density. For each antigen tested except of the nucleocapsid (NC) proteins, comparable antibody titres were found in the sera of 6 patients with different forms of herpes infections and in 86 healthy subjects. In the sera of 6 herpetic patients the antibody titres were higher against NC antigen than against other antigen preparations.

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The experience with ELISA technique utilized at serological screening for orthopoxviruses in the Republic of Ivory Coast revealed factors reducing the sensitivity and the specificity of the test. It was found out that routine controls such as "positive" and "negative" sera as well as the accepted reading of the results by two-fold or higher increase of OD values as compared to the "negative" control may be not sufficient. A significantly enhanced sensitivity and specificity of reaction was achieved by simultaneous examination of each serum under study with a control antigen. Selection of optimal dilutions of each test component followed by spectrophotometric assay and calculation of results according to the given formula contributed to the same aim. As a result of these improvements the rate of antibody detection among revaccinees was enhanced from 19 to 78.8% and the titres of ELISA and virus neutralization tests correlated in 88% of cases.

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Monkeypox virus cloning and isolation of the so-called 'white' clones from white pocks which this virus forms on the chorioallantoic membrane (CAM) were carried out. The isolated clones were stable and differed considerably from the parental strain. By their properties, they were identical to whitepox viruses formerly isolated from wildlife monkeys and rodents in Equatorial Africa. Besides stable 'white' clones, a number of virus cultures in the process of cloning were obtained which differed in quantitative content of virions, forming on CAM white pocks and pocks with hemorrhages. It appeared that the properties of the viral population as a whole (reaction type on rabbit skin, hemagglutination activity, etc.) depended on the rate of virions produced with different characteristics.

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A new poxvirus was isolated in 1974 from the kidney of a wild big gerbil (Rhombomys opimus) caught in Turkmenia, where these gerbils are wide-spread. The virus resembles cowpox virus and is markedly different from the virus of infectious ectromelia, the best-known poxvirus of rodents. The new virus is apparently identical to other poxvirus isolates made from white rats and Felidae in the Moscow Zoo. Experimental inoculation of the natural hosts--big gerbils and yellow susliks (Citellus fulvus)--produced a severe infection with a high mortality rate. Trnasmission of virus to uninoculated cage mates was shown to occur. Virus persisted in convalescent animals and was present in urine 3 weeks after inoculation and in kidney and testis for at least 5 weeks after inoculation. The role of rodents as natural hosts of poxviruses is discussed.

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An outbreak of pox disease in Carnivora of the family Felidae occurred in the Moscow Zoo. Two forms of the disease were found: (1) fatal, fulminant pulmonary without skin lesions and (2) dermal with rash. The severity of the dermal form varied from subclinical to lethal. The pulmonary form was characterized by pneumonia and exudative pleuritis, and large concentrations of virus were observed in the lungs and exudate. In addition to Carnivora of the family Felidae, two giant anteaters had a severe form of the disease (dermal with hemorrhages) and died. The agent of the outbreak appeared to be very closely related to cowpox virus; however, pocks developed at a lower temperature than do those that result from infection with cowpox virus. Strains isolated from sick animals were identical to the virus previously isolated from an outbreak of pox among elephants and okapi. The most probable sources of infection were rats that were fed to some of the animals. During the outbreak, a female attendant at the zoo became infected.

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A two-step gel precipitation reaction with antiserum to vaccinia virus, based on sequential addition of two test viruses was elaborated for differentiation of closely related orthopoxviruses. The appearance of an additional precipitation line indicated differences in the antigenic structure of the viruses compared. Differences in the antigenic structure of vaccinia, variola and monkey pox viruses as well as the antigenic identity with cow pox virus of poxviruses isolated from carnivora, elephants and okapi were established.

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The results of application of the fluorescent antibodies method (MFA) with the diagnostic purpose of detecting pox antigen in specimens from smallpox patients are presented. The method was found highly effective for the examination of material taken directly from the patients (smears) in the early stages of disease (maculo-papular and vesicular). The results of examination of smears from pustular fluid and scabs were not reliable in 44% of cases due to the presence of nonspecific fluorescence of tissue fragments and leukocytes. The technique of preliminary accumulation of the virus in a sensitive cell culture made the MFA suitable for the examination of material taken at any stage of disease. Results of the assessment of sensitivity of MFA in comparison with other methods of rapid diagnosis of smallpox are presented.

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