Letter to the editors

Relationship between virus particle size and filterability through gradocol membranes

To celebrate the sixtieth anniversary of Virology a survey is made of the plant viruses, virologists and their institutions, and tools and technology described in the first decade of plant virus publications in Virology. This was a period when plant viruses increasingly became tools of discovery as epistemic objects and plant virology became a discipline discrete from plant pathology and other life sciences.

Poliovirus 1, with and without radioactive label, has been used to evaluate membrane filters for several purposes in virology. Filters of several polymers will pass virus and retain larger particles. Cellulose nitrate can adsorb virus for concentration purposes. Polycarbonate does not adsorb virus and is well suited to particle sizing.

Nine cytopathic bovine rotavirus strains were isolated in MA-104 cell cultures from fecal specimens of dairy calves suffering from diarrhea. Isolation of the virus was accomplished from three outbreaks which occurred on dairy farms located in Central and Southern Italy.

Fecal suspensions were treated with a high concentration (1000 μg/ml) of trypsin, and inoculated into MA-104 cell cultures grown out in Eagle's minimum essential medium (MEM) containing 5 μg/ml of the enzyme. Cytopathic effects (CPE), characterized by intracytoplasmic inclusion bodies of different sizes and shapes, were observed on the 1st passage with five of the strains and on the 2nd (2 strains) or the 3rd (2 strains) passage for the others.

The presence of trypsin and the use of MA-104 cells appeared to be essential for the occurrence of CPE, inasmuch as no CPE was detected when trypsin was omitted in the MA-104 cell system. Replication failed to occur when primary bovine embryo kidney cell cultures with or without trypsin were used.

Electron microscopy revealed the presence of particles with a typical rotavirus morphology.

In MA-104 cells, the titre of virus reached its maximum 48 hr after inoculation.

Small, clear-cut plaques were produced by the isolates in MA-104 cells under the overlay of MEM containing carboxymethylecellulose, trypsin and DEAE-dextran.

The nine rotavirus strains were antigenically related, whereas the relationship to either the Nebraska or the Compton rotaviruses was quite weak.

Neuf souches de rotavirus cytopathogènes de bovin ont été isolés sur cellules MA-104 de fèces provenant de veaux atteints de diarrhée. L'isolement du virus a été realisé de trois foyers d'infection qui ont eu lieu dans des effectifs laitiers situés dans le Centre-Sud de l'Italie. Les suspensions fécales ont été traitées avec une concentration elevée (1000 μg/ml) de trypsine et inoculées sur cellules MA-104 en présence de Eagle minimum essential medium (MEM) contenant 5 μg/ml de l'enzyme. L'effet cytopathogène (CPE), caracterisé par la présence des inclusions cytoplasmatiques de dimensions et formes differentes, a été observe au premier passage avec 5 souches, au second avec 2 souches et au troisième passage avec les dernières 2 souches. La présence de la trypsine et l'emploi de cellules MA-104 sont essentiels pour l'obtention de CPE. En effet, l'omission de la trypsine dans les cultures de la souche cellulaire MA-104 ou dans l'emploi de cellules primaires de rein d'embryon de bovin contenant ou non de trypsine, a pour conséquence l'absence d'effet cytopathogène. L'étude au microscope electronique a demontré la présence d'une morphologie typique de rotavirus. Le titre du virus atteint son maximum sur les cellules MA-104 48 hr après l'inoculation. Le virus sur les cellules MA-104, en présence du milieu constitué par MEM contenant carboxymethylcellulose, trypsine et DEAE-dextrane, produit de petites plaques bien délimitées. Les souches de rotavirus isolées sont corrélées entre elles du point de vue antigénique. Cette correlation, d'autre part, est très réduite à l'égard des souches Nebraska et Compton de rotavirus.

Using the early production of a placetal lesion as a criterion of infection with Border disease some physical properties of the causal agent have been demonstrated. It appears to be a small particle, in the region of 27 n.m. in size, with an ether soluble envelope and it is inactivated by heating to 60°C. for 90 minutes.

Electron microscopic observations were made on 42 poults and 26 turkey embryos in various stages of infection with transmissible enteritis infection. Primary lesions included damaged microvilli and mitochondria and a disruption of mucin production. Lesions were similar in both poults and embryos indicating that the presence of secondary bacteria had no specific structural effect. Enveloped virus-like particles were observed in the intestinal epithelium of infected poults and embryos. These particles fulfill all known criteria for the agent of transmissible enteritis. Their morphogenesis is described. It is suggested that the turkey embryo may serve as an inexpensive and readily available model for the study of mucin production during infection, and other general phenomena associated with injury.