Table 1

Calculation of ID50 for MHV68 intranasal inoculation of 129S1/SVImJ miceb

Virus dilution (PFU)No. of infected test units (mice)aCumulative infected (A)Cumulative uninfected (B)Ratio of A/(A + B)% infected
10010/1017017/17100.00
106/10747/1163.64
11/101131/147.14
  • a Infection was determined by plaque assay of the lungs harvested at 8 days after inoculation.

  • b Proportionate distance = [(% positive above 50%) − 50%]/[(% positive above 50%) − (% positive below 50%)]; proportionate distance = (63.64 − 50)/(63.64 − 7.14) = 0.24. Log ID50 = (log dilution above 50%) + (proportionate distance × log dilution factor) = 1 + (0.24 × −1) = 0.76; ID50 = 100.76 = 5.75 PFU.