The Influence of Relative Humidity on the Aerosol Stability of Different Strains of Foot-and-Mouth Disease Virus Suspended in Saliva

Abstract

Comparisons were made of the aerosol stabilities of eight strains of foot-and-mouth disease (FMD) virus suspended in bovine salivary fluid. The strains used were O₁ bfs 1860, O₁ pacheco, O₁ lombardy, O₂ brescia, A₅ eystrup (tübingen), A₂₂iraq 24/64, Cnoville and Clebanon 3/69. The strains were compared as aerosol clouds 1 sec. old at different relative humidities and during storage for up to 60 min. at 70% and 55% relative humidity (RH). In aerosol clouds 1 sec. old all virus strains showed maximum survival of infectivity at 60% RH and above. Below 60% RH, infectivity was reduced and little infectivity was detected below 20% RH. At low RH the aerosol survival of the A strains was about 10-fold higher than that for the O and C strains. The strains differed significantly in stability during storage of aerosols at 70% or 55% RH. Decay rates ranged from 1.1 log./hr (O₁ pacheco) to 3.2 log./hr (O₁ bfs 1860) at 70% RH and from 2.1 log./hr (O₁ pacheco) to 3.3 log./hr (A₂₂ iraq) at 55% RH. At 55% RH the infectivity recoveries of some strains were too low for decay rates to be determined.