Demonstration of bovine respiratory syncytial virus RNA in peripheral blood leukocytes of naturally infected cattle

RNA of Bovine respiratory syncytial virus (BRSV) was found in peripheral leukocytes and nasal mucosa of infected cows by nested reverse transcription-polymerase chain reaction (nRT-PCR). We suppose that this finding obtained in the convalescent phase of infection indicates possible persistence of the virus in cells of the immune system.

Identification of spring viraemia of carp virus (SVCV) by combined RT-PCR and nested PCR

A combination of single-tube reverse transcription (RT)-PCR and nested PCR was used to identify spring viraemia of carp rhabdovirus (SVCV) in infected cell cultures and fish tissues. Two pairs of specific primers (external and internal) were selected from the glycoprotein gene sequence. A specific product of 470 bp was amplified from RNA derived from 34 SVCV isolates including the reference strain (Fijan), using RT-PCR with the external primers. The subsequent PCR using the internal primers yielded a specific product of 141 bp in all cases. No PCR product was obtained following attempts to amplify RNA derived from other fish viruses including pike fry rhabdovirus (PFRV), or from non-infected cells. The identity of the cDNA was confirmed by direct sequencing. PCR sensitivity in the cell-culture system was assessed as about 10(-1) TCID50 ml(-1). PCR was further used for the detection of SVCV in 14 clinical samples. Nested PCR allowed us to diagnose the infection in all clinical samples in which SVCV infection was demonstrated by electron microscopy and ELISA. PCR amplification of the SVCV glycoprotein (G) gene is a potential method for rapid diagnosis of spring viraemia of carp; however, it is necessary to verify the method in a higher number of clinical tissue samples. PCR can now be added to current confirmatory diagnostic methods, for determination of SVCV in cell culture. Sequencing of RT-PCR products performed for 7 SVCV isolates (4 Czech, 2 Hungarian, and 1 isolate of unknown origin) revealed a high degree of homogeneity of the G gene region with that of the previously sequenced Fijan strain. The highest nucleotide variability (97.4 to 98.1% nucleotide similarity) was found between the Hungarian and the other isolates. Knowledge of genetic differences among SVCV isolates will be useful in the development of diagnostic methods and elaboration of vaccination programmes.

Atypical Myxomatosis - Virus Isolation, Experimental Infection of Rabbits and Restriction Endonuclease Analysis of the Isolate

Atypical form of myxomatosis, which caused non-lethal and clinically mild disease in domestic rabbits 1 month after immunization with a commercially available vaccine MXT, is described. The isolated myxoma virus designated as Litovel 2 (Li-2) did not induce systemic disease following subcutaneous and intradermal applications in susceptible experimental rabbits but led to the immune response demonstrated by ELISA. No severe disease was induced in those Li-2 inoculated rabbits by challenge with the virulent strains Lausanne (Lu) or Sanar (SA), while the control animals showed nodular form of myxomatosis with lethal course of the illness. Restriction fragment length polymorphism (RFLP) of genomic DNA with KpnI and BamHI endonucleases was used for genetic characterization of the Li-2 isolate, the vaccine strain MXT and both virulent strains Lu and SA, respectively. In general, RFLP analysis has shown to be informative for inferring genetic relatedness between myxoma viruses. Based on restriction endonuclease DNA fragment size distribution, it was evident that the pathogenic strain SA is genetically related to the reference strain Lu and the isolate Li-2 is more related, but not identical, to the vaccination strain MXT.

Colorimetric detection of lagomorphs' calicivirus genomic sequences by polymerase chain reaction incorporating digoxigenin dUTP

A method of reverse transcription followed by polymerase chain reaction (RT-PCR) has been implemented for the demonstration of the rabbit haemorrhagic disease virus (RHDV) genome in organ suspensions, leukocytes and excretions of infected rabbits. RT-PCR has been tested with 10 RHDV strains isolated at various geographic sites and times using a pair of primers coming from the gene region coding for the capsid protein VP60. The same primers were effective in the amplification of 4 of 5 European brown hare syndrome (EBHS) virus isolates. Non-radioactive labelling of PCR products with digoxigenin during the amplification and a system of colorimetric assessment of hybridization reactions between a biotin-labelled RHDV capture probe and the chains of labelled amplicons (PCR ELISA) were used for specific analyses of nucleic acid synthesis. The sensitivity of the alternative procedure of analysis of the dig-labelled PCR products with PCR ELISA was two logs10 higher than that of conventional electrophoresis in agarose gel stained with ethidium bromide. The results of the hybridization reactions, carried out under various stringency conditions, have confirmed the presumption that the genomic similarity between the amplified and the probed areas of the capsid protein VP60 gene was not uniform within all the tested caliciviruses. A higher degree of heterogeneity was observed between the isolates of EBHSV and RHDV.

[Cell-mediated immunity in calves immunized against or infected with the bovine rhinotracheitis virus]

Simple and expeditious methods--leucocyte adherence inhibition LAI and leucocyte migration inhibition LMI--are described in the present paper; these methods enable to investigate cell-mediated immunity of animals. The two tests, along with serological and virological methods, were used to study changes in the immunity of calves after experimental infection by IBRV and after immunization by inactivated oil vaccine against IBRV. The results have indicated that the changes in cell-mediated immunity after experimental infection and vaccination of calves assumed courses independent of the changes in humoral reaction. Total cell-mediated immunity reaction started earlier in experimentally infected calves than in vaccinated ones. In some vaccinated calves a modified course of cellular immunity reactions was observed, characterized also by elimination of IBR virus on the nasal mucous membrane after challenge infection. The LAI and LMI test can be recommended for immunological monitoring in clinical laboratories and in research.

[The complex etiology of epidemic diseases in calves on large-capacity farms and their clinical and epizootic characteristics]

It is not easy to exactly diagnose the etiology of the mass infections of new-born calves on large farms where considerable losses are suffered. On the basis of the complex epizootological, clinical and laboratory examination in four large calf-rearing facilities, rotaviruses, coronaviruses, the infectious bovine rhinotracheitis (IBR) virus and the bovine viral diarrhoea (BVD) virus, and in some cases also the enteropathogenic E. coli, were found to be etiologically involved in the mass rise of diarrhoea, complicated by respiratory symptoms already during the first days after birth. The clinical picture of the disease, therapeutically difficult and reminding of "pneumoenteritis", has often been observed in stocks where, in addition to rotaviruses and coronaviruses in the faeces, the IBR or BVD viruses (sometimes both at the same time) were detected and identified in the respiratory and enteral tract. The serological examination of a higher number of animals in the stocks of calves under study confirmed the considerable rate of spreading of all the four viruses in the cattle population and, at the same time, demonstrated the very unfavourable immunological profile of the herds. The high percentage of animals low in antibody titres and the serologically negative animals constitute the infection-sensitive part of population in the affected herds. With the high culling rate and with the open herd turnover it is impossible to reach the required immunity through natural disinfection. Loss-free rearing of healthy calves will be achieved on the basis of a well-oriented vaccination programme with a good combination of inoculants.

[Phagocytic activity of blood leukocytes in calves from birth to 3 months of age]

Forty-three calves of various age from the day of birth to the age of three months were subjected to the 2-hydroxyethylmethacrylate (HEMA) particle phagocytosis test. Significant differences in the phagocytic activity of blood leucocytes were recorded, all depending on age. New-born calves had very low phagocytic activity: only 16.5% of the leucocytes were found to be phagocytic, the phagocytic index being 0.39. A rapid increase in phagocytic activity was recorded during the subsequent days. At the age of three days 43% of the leucocytes of the calves were phagocytic. A decrease in phagocytic activity was found on the sixth to seventh day, and another increase was recorded only from the age of three to four weeks of age. No such changes in the development of phagocytic activity were observed in the calves reared without colostrum administration. Low values were maintained for a longer time after birth without the typical increase on the third to fifth day. Phagocytic activity increased in the zero-colostrum calves experimentally infected with rotavirus.

[Test of phagocytic activity of blood leukocytes in calves]

The 2-hydroxyethylmethacrylate-particle (HEMA) phagocytosis method in whole blood was adapted to the evaluation of the phagocytic activity of the leucocytes of calves. Several test variants were compared and the best procedure was determined, based on the following principles: keeping the heparin concentration at 10 i. u. in 1 ml of blood at the maximum, using fresh samples, incubating at 37 degrees C for 0.5 to 1 hour, thoroughly agitating the sample after incubation, with possible addition of EDTA. The phagocytic activity of nine calves, 2.5 to 3 months old, was examined by the proposed procedure and 18.6% phagocytic leucocytes were found, the phagocytic index being 7.07%.