Persistence of Invertebrate iridescent virus 6 in soil

Soil represents an important reservoir for mostentomopathogenic viruses. Invertebrateiridescent viruses (IIVs) (Iridoviridae) arenon-occluded DNA viruses that infectagriculturally and medically important insectspecies, especially in damp or aquatichabitats. We used virus extraction and insectbioassay techniques to determine the effect ofsoil moisture and soil sterility on thepersistence of Invertebrate iridescentvirus 6 (IIV-6) in a soil over a 90 day periodin the laboratory. Loss of activity of IIV-6in dry soil (6.4% moisture, –1000 kPa matricpotential) was very rapid and was not studiedbeyond 24 h. Soil moisture did not affect therate of inactivation of virus in damp (17%moisture, –114 kPa matric potential) or wetsoil (37% moisture, –9.0 kPa matricpotential). In contrast, soil sterilizationsignificantly improved the persistence of IIV-6activity, both in damp and wet soil. Controlvirus suspensions retained 0.72–0.87% oforiginal activity after 90 days, which wassignificantly more than the activity retainedin soil. These figures represent half lives of4.9 days for IIV-6 in non-sterile soil, 6.3days in sterilized soil (data pooled formoisture treatments), and 12.9 days for thecontrol virus suspension. We conclude thatextra-host persistence in soil habitats may bean important aspect of the ecology of IIVs.