Defective interfering particles (DIP) have frequently been advanced to explain the persistence of virus in vitro. However, DIP involvement in the establishment of respiratory syncytial virus (RSV) persistence in cell lines has not been documented. We report establishment of RSV persistence in human epithelial larynx (HEp-2) and lung (H358) cell lines by infection with RSV enriched with DIP. Viral persistence in HEp-2 and H358 has been stably maintained for >3 years without apparent cytopathic effect or periodic crises. Persistent cultures resisted superinfection with the original virus and no cyclic variations in infectious virus and DIP yields were observed. During passages, low levels of infectious RSV and defined species of DIP were produced. Moreover, 80–90% of the cells exhibited viral antigen. Persistence in H358 cells was established with a buoyant density band containing DIP and infectious virus obtained from a H358 persistently infected culture. Thus, DIP are required for establishment of RSV persistence cultures in human epithelial cell lines; however, DIP per se are not able to establish persistence.

Genetic variability among Taenia solium isolates was studied in 160 cysticerci from 6 pigs, 4 from Mexico, 1 from Honduras, and 1 from Tanzania. Random amplified polymorphic DNA (RAPD) analysis performed with 4 commercial primers showed 88% polymorphic loci and an average heterozygosity of 0.077; however, several alleles were fixed within each isolate. Linkage disequilibrium analysis indicated that 3 of the 6 isolates had a random association of alleles, whereas the other 3 had a clonal structure. These results suggest the existence of local lineages in T. solium, with events of genetic recombination within them