No abstract

Alphaviruses are enveloped RNA viruses that contain several human pathogens. Due to intrinsic heterogeneity of alphavirus particles, a high resolution structure of the virion is currently lacking. Here we provide a 3.5 Å cryo-EM structure of Sindbis virus, using block based reconstruction method that overcomes the heterogeneity problem. Our structural analysis identifies a number of conserved residues that play pivotal roles in the virus life cycle. We identify a hydrophobic pocket in the subdomain D of E2 protein that is stabilized by an unknown pocket factor near the viral membrane. Residues in the pocket are conserved in different alphaviruses. The pocket strengthens the interactions of the E1/E2 heterodimer and may facilitate virus assembly. Our study provides structural insights into alphaviruses that may inform the design of drugs and vaccines.

Hepatitis E virus (HEV) is an important human pathogen. Due to the lack of a cell culture system and a practical animal model for HEV, little is known about its pathogenesis and replication. The discovery of a strain of HEV in chickens, designated avian HEV, prompted us to evaluate chickens as a model for the study of HEV. Eighty-five 60-week-old specific-pathogen-free chickens were randomly divided into three groups. Group 1 chickens (n ‫؍‬ 28) were each inoculated with 5 ؋ 10 4.5 50% chicken infectious doses of avian HEV by the oronasal route, group 2 chickens (n ‫؍‬ 29) were each inoculated with the same dose by the intravenous (i.v.) route, and group 3 chickens (n ‫؍‬ 28) were not inoculated and were used as controls. Two chickens from each group were necropsied at 1, 3, 5, 7, 10, 13, 16, 20, 24, 28, 35, and 42 days postinoculation (dpi), and the remaining chickens were necropsied at 56 dpi. Serum, fecal, and various tissue samples, including liver and spleen samples, were collected at each necropsy for pathological and virological testing. By 21 dpi, all oronasally and i.v. inoculated chickens had seroconverted. Fecal virus shedding was detected variably from 1 to 20 dpi for the i.v. group and from 10 to 56 dpi for the oronasal group. Avian HEV RNA was detected in serum, bile, and liver samples from both i.v. and oronasally inoculated chickens. Gross liver lesions, characterized by subcapsular hemorrhages or enlargement of the right intermediate lobe, were observed in 7 of 28 oronasally and 7 of 29 i.v. inoculated chickens. Microscopic liver lesions were mainly lymphocytic periphlebitis and phlebitis. The lesion scores were higher for oronasal (P ‫؍‬ 0.0008) and i.v. (P ‫؍‬ 0.0029) group birds than for control birds. Slight elevations of the plasma liver enzyme lactate dehydrogenase were observed in infected chickens. The results indicated that chickens are a useful model for studying HEV replication and pathogenesis. This is the first report of HEV transmission via its natural route in a homologous animal model. Hepatitis E virus (HEV), the causative agent of hepatitis E, is responsible for the majority of enterically transmitted cases of non-A and non-B hepatitis (2,34,35). HEV is a singlestranded, positive-sense, nonenveloped RNA virus with a genome of about 7.2 kb (34). The genome contains three open reading frames (ORFs) and short 5Ј and 3Ј untranslated regions. ORF1, the largest of the three ORFs, encodes nonstructural proteins, and ORF2 encodes the putative capsid protein.The small ORF3, which partially overlaps ORF1 and ORF2, encodes a cytoskeleton-associated phosphoprotein (34,35). Hepatitis E is epidemic and endemic in many developing countries.