Recombinants between attenuated and virulent strains of poliovirus type 1: derivation and characterization of recombinants with centrally located crossover points.

Recombinants with a centrally located crossover point were selected from crosses between poliovirus type 1 strains and intertypic (type 3/type 1) recombinants. Two such recombinants were characterized in some detail. In one of them (v1/a1-6), the 5' half of the genome was derived from a virulent type 1 strain, while the 3' half came from an attenuated type 1 strain.

Construction and properties of intertypic poliovirus recombinants: first approximation mapping of the major determinants of neurovirulence.

An attempt was made to map, in a general way, the region of the poliovirus genome that is responsible for the neurovirulent and attenuated phenotypes of different virus strains. A set of four recombinants was investigated, one described previously (E. A.

Morphometric method for evaluating the neurovirulence of live poliomyelitis vaccine.

A method for measuring morphological changes caused by residual neurovirulence in live poliomyelitis vaccine is described. The entire area of 16 standard parts of the central nervous system is measured directly under the microscope using a morphometric eyepiece grid. The method can be used to supplement the conventional system of scoring morphological lesions.

Morphological methods of Kilham virus detection.

Morphological investigations on organs from Kilham virus (KV)-infected Syrian hamsters revealed acute glomerulonephritis with a clear-cut haemorrhagic syndrome. No pathological changes were found in internal organs from KV-infected rats.