Challenging successive mosquito generations with a densonucleosis virus yields progressive survival improvement but persistent, innocuous infections.
Research on cultivated shrimp suggests that they have the capability to tolerate viral pathogens in a highly specific manner by mechanisms currently unknown. The phenomenon is difficult to study in detail because they have a generation time of 1-2yr and lack continuous cell lines. Thus, we developed a mosquito-densovirus model to examine whether similar phenomena occur in insects. Serial challenge of five generations with a stock densovirus (AThDNV) resulted in progressive survival increases from 15% to 58%. Prevalence of AThDNV infection in surviving mosquito larvae (confirmed by PCR, histology, in situ hybridization and transmission electron microscopy) was relatively high (e.g. 36% in F2) but they grew normally to establish each succeeding generation. At the end of five generations, comparison of deduced amino acid sequences from genome fragments revealed a significantly higher (p=0.02) estimated prevalence of defective targets in the survivor virus population (29.7%+/-10.0 SD) than in the stored viral population (3.3%+/-5.8 SD). The results paralleled those reported for serially passaged C6/36 mosquito cell cultures infected with a densovirus. There, reduced infection rates are ascribed to the production of defective interfering particles (DIP). Thus, it is possible that the presence of prior AThDNV infections with a high level of DIP contributed to improved survival in our challenged F4 mosquito population. If so, it suggests that persistent viral infections in arthropods may serve in a specific, adaptive manner to reduce the incidence and severity of disease.
Roekring
Songsak
S
Centex Shrimp, Faculty of Science, Mahidol University, 272 Rama VI Road, Phayathai Rajdhevee, Bangkok 10400, Thailand.
Flegel
Timothy W
TW
Malasit
Prida
P
Kittayapong
Pattamaporn
P
D000330:Aedes / Q000821:virology*; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D004266:DNA Virus Infections / Q000503:physiopathology*; D019223:Densovirinae / Q000235:genetics / Q000502:physiology*; D005260:Female; D008297:Male; D008969:Molecular Sequence Data