Patricia E Lind

A Genetic Approach to Variation in Influenza Viruses: 4. Recombination of Characters Between the Influenza Virus A Strain NWS and Strains of Different Serological Subtypes

SUMMARY: Mice were inoculated intracerebrally with mixtures of the influenza virus strain NWS and the serologically distinct non-neurotropie strains MEL, OcI and SW. From mouse brains removed about the 5th or 6th day virus strains were obtained which, after at least two passages at limiting infective dilution, showed active encephalitogenic power with the serological character of the second strain of the original mixture. These are regarded as recombinants. The strains in general show in vitro characters close to those of the serologically similar ‘parent’. They have, however, diminished enzymie action on ovomucin and do not readily clute from red cells; in this they resemble the strain NWS. They are more readily converted to the indicator state than either of the original strains. The process by which these unusual types arise is discussed in the light of recent views that intracellular multiplication of bacterial viruses and of some animaal viruses takes place not by binary fission but by the breaking down of the infective unit into smaller particles which are the replicating units. It is concluded that the recombinants arise by recenstitution of infective particles from the pool of repticating units produced by double infection of a single cell by virus particles of both parent types.

Studies on filamentary forms of influenza virus with special reference to the use of dark-ground-microscopy.

In 1946, Mosley and Wyc]co//reported that electron micrographs of the influenza virus strain PR 8 showed a small proportion of short filaments amongst the spherical particles. Three years later Dawson and El]ord (1949) described the use of red cell ghosts to adsorb viruses of the influenza group (Myxovirus) as a preliminary to electron microscopy. They noted that fowl plague and influenza B viruses might show long filaments which appeared to be specifically adsorbed to the red cell membranes. A little later Chu, Dawson and El/ord (1949) made the importan t discovery tha t all recently isolated influenza A strains showed a high proportion of filaments. They provided cogent evidence tha t the filaments represented a form of the virus by showing a) that filaments were absorbed to and eluted from red cell membranes b) that heated virus did not elute but could be removed by antiserum and c) tha t clumping of filaments by immune serum could be demonstrated. Two other important findings by the same authors were a ) t h a t simple dark ground examination of infected fluid showed the filaments clearly and b) tha t fluids could be freed of filaments by filtration through membranes tha t wouid allow spherical forms to pass and that, if such a filtrate was used to initiate infection, the fluid subsequently obtained showed the proportion of filaments characteristic of the strain. Donald and Isaacs (1954) used quantitative methods to approach the problem of whether filaments were or were not infective. They found that the haemagglutinating power of a fluid from a fi lamentary strain was greater than that of a fluid from a wholly spherical strain on the basis