Influenza Virus Reassortment Is Enhanced by Semi-infectious Particles but Can Be Suppressed by Defective Interfering Particles

A high particle to infectivity ratio is a feature common to many RNA viruses, with ~90–99% of particles unable to initiate a productive infection under low multiplicity conditions. A recent publication by Brooke et al. revealed that, for influenza A virus (IAV), a proportion of these seemingly non-infectious particles are in fact semi-infectious. Semi-infectious (SI) particles deliver an incomplete set of viral genes to the cell, and therefore cannot support a full cycle of replication unless complemented through co-infection. In addition to SI particles, IAV populations often contain defective-interfering (DI) particles, which actively interfere with production of infectious progeny. With the aim of understanding the significance to viral evolution of these incomplete particles, we tested the hypothesis that SI and DI particles promote diversification through reassortment. Our approach combined computational simulations with experimental determination of infection, co-infection and reassortment levels following co-inoculation of cultured cells with two distinct influenza A/Panama/2007/99 (H3N2)-based viruses. Computational results predicted enhanced reassortment at a given % infection or multiplicity of infection with increasing semi-infectious particle content. Comparison of experimental data to the model indicated that the likelihood that a given segment is missing varies among the segments and that most particles fail to deliver ≥1 segment. To verify the prediction that SI particles augment reassortment, we performed co-infections using viruses exposed to low dose UV. As expected, the introduction of semi-infectious particles with UV-induced lesions enhanced reassortment. In contrast to SI particles, inclusion of DI particles in modeled virus populations could not account for observed reassortment outcomes. DI particles were furthermore found experimentally to suppress detectable reassortment, relative to that seen with standard virus stocks, most likely by interfering with production of infectious progeny from co-infected cells. These data indicate that semi-infectious particles increase the rate of reassortment and may therefore accelerate adaptive evolution of IAV.     

THE FOURTEEN SPECIES OF ZIZIPHUS INCLUDING SARCOMPHALUS (RHAMNACEAE) INDIGENOUS TO THE WEST INDIES

Taxonomic treatment is presented for the 14 species of Ziziphus P. Mill. (Rhamnaceae: Dicotyledoneae) recognized in the West Indies, with key, synonymies, and statements of distribution. New combinations include Z. crenata (Sarcomphalus crenaius Urb.), Z. microdictya (S. microdictyus Urb. & Ekm.), Z. acutifolia (S. acutifolius Griseb.), Z. bidens (S. bidens Urb.), Z. obovata (S. obovatus Urb.), Z. havanensis var. bullata (S. bullatus Urb.), and Z. taylori (S. taylori Britt.). New names include Z. urbani (S. parvifolius Urb. & Ekm.) and Z. grisebachiana (S. divaricatus Griseb.). The available evidence of evolutionary relationships is assessed.     

Toxicity of Blastomyces dermatitidis

Following injections of the insoluble portion of disrupted yeast cells ofBlastomyces dermatitidis animals exhibited a biphasic pyrogenic response, a decrease in total serum proteins, and there was no release of interferon.