Submitted to: Journal of General Virology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/6/2004
Publication Date: 6/30/2004
Citation: Popham, H.J., Shelby, K., Brandt, S.L., Coudron, T.A. 2004. Potent virucidal activity against hzsnpv in larval heliothis virescens plasma. Journal of General Virology. 85(8):2255-2261. Interpretive Summary: A group of viruses that infect insects, known as baculoviruses, have great potential for the safe control of caterpillars that infest major crops. When a caterpillar eats just a few baculovirus particles, the caterpillar becomes sickened to a point that it can not eat. Within a few days it will die. Some information is known about how this infection attacks an insect but more information is needed before these viruses can begin to be used in place of chemical pesticides in the field. In this study, a method was developed to examine if there was anything in the caterpillars blood that would fight off infection. A factor was found that reduced viral infection by 64 times. This finding will impact scientists working on how an insect resists infection because it begins to explain, along with other studies in the field, why some infections are fatal while others are not and how viruses can become more useful as a control measure in the field.
Technical Abstract: Lepidopteran larvae are known to resist baculovirus infection by the selective apoptosis of infected midgut epithelial cells, and by the sloughing off of infected cells from the midgut. Once the infection breaches the midgut epithelial barrier and propagates from infective foci to the hemocoel however, there are few known mechanisms to account for the resistance and clearance of infection observed in some virus/host combinations. We tested the hypothesis that factors present in the plasma of infected pest larvae act to limit the spread of viruses from initial infective foci within the hemocoel. We have developed an in vitro bioassay in which Helicoverpa zea single nucleopolyhedrovirus (HzSNPV) was incubated with plasma collected from uninfected Heliothis virescens larvae. Surviving HzSNPV were then titered on HzAM-1 cells. In vitro incubation with diluted larval H. virescens plasma exhibited a virucidal effect against HzSNPV, reducing TCID50/ml by more than 64-fold (4.3±3.6x10**5 to 6.7±0.6x10**3). The antiviral activity was heat-inactivated but retained when the plasma was frozen at -85C and was inhibited by proteinase K, a battery of protease inhibitors, and PTU. This is the first demonstration of a constitutive humoral mechanism that has an antiviral effect in insects.