No abstract

Isolates of FMDV from bovine carriers were compared with the original infecting viruses for changes in biological properties. Occasional marked differences existed between the original virus and succeeding isolates from the same animal. In 2 cattle which were carriers of type A virus and reinfected with type O virus, it was found that some isolates had the antigenic characteristics of both virus types.

No abstract

Foot-and-mouth disease virus, type A, strain 119, propagated in cultures of calf kidney cells and in the tongue epithelium of cattle was used. The process of freeze-drying was conducted in two cycles on unit volumes of 4 ml in Pyrex ampoules, averaging 150 ampoules per run, and was studied separately from the problems of storage. Ampoules containing freeze-dried virus were flame-sealed for either immediate study or storage at 4 C for later reference. Tissue-culture virus dried with various additives had a mean processing loss of 0.8 log LD 50 per ml for six different preparations. Virus freeze-dried in tissue suspension had a mean loss of 0.8 log LD 50 per ml for three different preparations. A second set of preparations was processed and specifically studied for storage quality at 4 C. The virus in 14 freeze-dried tissue-culture preparations had a mean loss of 0.75 log LD 50 per ml while stored at 4 C for 1 year. Virus in four freeze-dried tissue suspensions had a mean loss of 0.05 log LD 50 per ml held at 4 C for 1 year. None of the specific additives used for conservation of the virus during the freeze-drying process or during storage at 4 C contributed significantly to the stability of the virus preparations over and above that observed with the normal growth medium of the tissue culture or the ordinary diluents used in making suspensions of tissue virus.

No abstract