Protein composition of unusual tobacco mosaic virus strains

Amino acid analyses have been made of the proteins of single-lesion isolates of five strains of tobacco mosaic virus (TMV) differentiated by Lycopersicon hosts. These hosts differed in their genetical control of resistance to TMV, and the virus strains had therefore survived specific selection pressures. Two of the five strains differed in their amino acid composition from type TMV and from all other tomato strains of TMV previously examined. Symptoms induced by the five strains in four tomato lines and in Nicotiana tabacum cvs White Burley and Kawala are described.     

VIRUSES OF COWPEA, VIGNA UNGUICULATA L. (WALP.), IN NIGERIA

The cowpea strain of tobacco mosaic virus was isolated from a range of leguminous hosts at Ibadan, but was rare in cultivated crops. Systemic symptoms in species infected experimentally are described.
A new virus of cowpea was also found in Nigeria. The physical properties (thermal inactivation point 56° C., dilution end-point 1/50,000 and longevity in vitro 4 days at 25° C.) differ from those for cowpea viruses reported elsewhere and the name cowpea yellow mosaic virus is proposed. This virus produces local lesions in French bean ( Phaseolus vulgaris L.) and local and systemic lesions in Bengal bean ( Mucuna aterrima Holland), but does not infect other leguminous hosts. The virus was purified and an antiserum prepared against it.
Both viruses are transmitted by a beetle ( Ootheca mutabilis Sahlb.) which loses infectivity within 48 hr. of leaving plants infected with either or both viruses.     

La Crosse virus: replication in vertebrate and invertebrate hosts

La Crosse virus is maintained in a cycle involving mosquitoes and small mammals. Vertebrate cell infection is generally cytolytic; vector cell infection results in persistent infection. Features of La Crosse virus replication that may permit the virus to traffic between vector and vertebrate hosts and condition different infection outcomes are described.     

Flaviviruses

Family Flaviviridae genus flavivirus contains numerous pathogenic viruses such as Japanese encephalitis virus, dengue virus, West Nile virus, etc, which cause public health problems in the world. Since many mammals and birds can act as amplifying hosts and reservoir hosts in nature and those viruses are transmitted by haematophagous mosquitoes or ticks, those viruses could not be eradicated from the nature. In the recent few decades, the viral replication mechanism and the ultrastructure of viral proteins as well as the viral immune evasion mechanism have been elucidated extensively, leading to develop novel types of antivirals and vaccines. In this review, the flavivirus nature and epidemiology, replication mechanism, immune response and immune evasion, and antivirals and vaccines against flaviviruses were described.     

Effect of a nuclear polyhedrosis virus on the relationship between Trichoplusia ni (Lepidoptera: Noctuidae) and the parasite, Hyposoter exiguae (hymenoptera: Ichneumonidae)

The effect of a nuclear polyhedrosis virus on the relationship between Trichoplusia ni and the parasite, Hyposoter exiguae, was investigated to determine if the virus could invade and multiply in the tissues of the parasites, if parasites which emerged from virus-infected T. ni larvae had normal emergence, fecundity, and longevity, and if the parasite could serve as a vector for the virus. Light microscopy revealed particles which appeared to be polyhedra within the lumen of the midgut of parasite larvae from virus-infected hosts. Transmission electron microscopy confirmed the presence of polyhedra and free virions within the midgut of the larvae. Polyhedra or free virions were never found within any parasite tissues. Parasite larvae within hosts exposed to virus before parasitization perished when their hosts died of virus infection. Parasite larvae in hosts exposed to virus after parasitization completed their development before their hosts died of virus infection. The proportion of parasites which survived increased as the time between host parasitization and host virus exposure increased. Parasite larvae which developed in hosts exposed to the virus soon after parasitization spent significantly less time in their hosts than did parasites which developed in noninfected hosts. There was no significant difference in time spent in the pupal stage, percent adult emergence, adult longevity with and without food and water, and fecundity of parasites which developed in virus-infected hosts and those which developed in noninfected hosts. Female parasites laid as many eggs in virus-infected hosts as they did in noninfected hosts. Sixty percent of the female parasites which oviposited in virus-infected hosts vectored infective doses of virus to an average of 6% of the healthy hosts subsequently exposed to them. None of the healthy host larvae exposed to male parasites which had been exposed to virus-infected host larvae became infected with the virus. Forty percent of the female parasites which developed in virus-infected hosts transmitted infective doses of the virus to an average of 65% of the healthy host larvae exposed to them. Ninety percent of the male parasites which developed in virus-infected hosts transferred infective doses of the virus to an average of 21% of the healthy host larvae exposed to them.     

Future virus problems?

Of seventeen viruses that infect British grasses several have been reported only recently; others that occur in Europe have hosts and vectors in Britain and could become a problem. Ryegrass bacilliform virus and ryegrass spherical virus are described and maize dwarf mosaic virus, maize rough dwarf virus and brome mosaic virus are considered as possible pathogens.     

颗粒体病毒、微红绒茧蜂、菜青虫相互关系的初步研究

近几年来,利用颗粒体病毒防治菜粉蝶(Pieris rapae以下称菜青虫)幼虫的工作,在我国已取得了较好的进展(梁东瑞等,1979;河北省菜青虫颗粒体病毒研究协作组,1981)。病毒杀虫剂与化学杀虫剂的显著区别之一,是前者具有选择性,不直接杀伤天敌昆虫。为了明确颗粒体病毒防治菜青虫对寄生蜂种群的影响,以便进一步了解病毒治虫在保持生态平衡上的意义,我们对颗粒体病毒、微红绒茧蜂(Apanteles rubecula)、菜青虫的相互关系作了一些实验室研究,现报道初步结果如后。     

Ecological dynamics of emerging bat virus spillover

Viruses that originate in bats may be the most notorious emerging zoonoses that spill over from wildlife into domestic animals and humans. Understanding how these infections filter through ecological systems to cause disease in humans is of profound importance to public health. Transmission of viruses from bats to humans requires a hierarchy of enabling conditions that connect the distribution of reservoir hosts, viral infection within these hosts, and exposure and susceptibility of recipient hosts. For many emerging bat viruses, spillover also requires viral shedding from bats, and survival of the virus in the environment. Focusing on Hendra virus, but also addressing Nipah virus, Ebola virus, Marburg virus and coronaviruses, we delineate this cross-species spillover dynamic from the within-host processes that drive virus excretion to land-use changes that increase interaction among species. We describe how land-use changes may affect co-occurrence and contact between bats and recipient hosts. Two hypotheses may explain temporal and spatial pulses of virus shedding in bat populations: episodic shedding from persistently infected bats or transient epidemics that occur as virus is transmitted among bat populations. Management of livestock also may affect the probability of exposure and disease. Interventions to decrease the probability of virus spillover can be implemented at multiple levels from targeting the reservoir host to managing recipient host exposure and susceptibility.     

Parasitoid-mediated transmission of an iridescent virus

We examined the interaction between an invertebrate iridescent virus (IIV) isolated from Spodoptera frugiperda (J.E. Smith) and the solitary ichneumonid endoparasitoid Eiphosoma vitticolle Cresson. In choice tests, parasitoids examined and stung significantly more virus infected than healthy larvae, apparently due to a lack of defense reaction in virus infected hosts. Parasitoid-mediated virus transmission was observed in 100% of the female parasitoids that stung a virus infected host in the laboratory. Each female parasitoid transmitted the virus to an average (+/-SE) of 3.7+/-0.3 larvae immediately after stinging an infected larva. Caged field experiments supported this result; virus transmission to healthy larvae only occurred in cages containing infected hosts (as inoculum) and parasitoids (as vectors). The virus was highly detrimental to parasitoid development because of premature host death and lethal infection of the developing endoparasitoid. Female parasitoids that emerged from virus infected hosts did not transmit the virus to healthy hosts. We suggest that the polyphagous habits of many noctuid parasitoids combined with the catholic host range of most IIVs may represent a mechanism for the transmission of IIVs between different host species in the field.     

Effect of deer density on tick infestation of rodents and the hazard of tick-borne encephalitis. II: population and infection models

Tick-borne encephalitis is an emerging vector-borne zoonotic disease reported in several European and Asiatic countries with complex transmission routes that involve various vertebrate host species other than a tick vector. Understanding and quantifying the contribution of the different hosts involved in the TBE virus cycle is crucial in estimating the threshold conditions for virus emergence and spread. Some hosts, such as rodents, act both as feeding hosts for ticks and reservoirs of the infection. Other species, such as deer, provide important sources of blood for feeding ticks but they do not support TBE virus transmission, acting instead as dead-end (i.e., incompetent) hosts. Here, we introduce an eco-epidemiological model to explore the dynamics of tick populations and TBE virus infection in relation to the density of two key hosts. In particular, our aim is to validate and interpret in a robust theoretical framework the empirical findings regarding the effect of deer density on tick infestation on rodents and thus TBE virus occurrence from selected European foci. Model results show hump-shaped relationships between deer density and both feeding ticks on rodents and the basic reproduction number for TBE virus. This suggests that deer may act as tick amplifiers, but may also divert tick bites from competent hosts, thus diluting pathogen transmission. However, our model shows that the mechanism responsible for the dilution effect is more complex than the simple reduction of tick burden on competent hosts. Indeed, while the number of feeding ticks on rodents may increase with deer density, the proportion of blood meals on competent compared with incompetent hosts may decrease, triggering a decline in infection. As a consequence, using simply the number of ticks per rodent as a predictor of TBE transmission potential could be misleading if competent hosts share habitats with incompetent hosts.     

核型多角体病毒与侧沟茧蜂对斜纹夜蛾幼虫的协同作用

研究了斜纹夜蛾幼虫体内的斜纹夜蛾侧沟茧蜂存活率、发育历期、寄主感染病毒时间、病毒浓度之间的关系,并测定了斜纹夜蛾侧沟茧蜂的传毒效率．结果表明,病毒对寄主体内寄生蜂历期无明显影响,寄生在幼虫体内的寄生蜂能在寄主病死前完成发育,存活比例因寄主感染病毒的时间和浓度而异．斜纹夜蛾被寄生后接种病毒(SINPV),距离寄生时间越长,饲毒浓度越低,寄生蜂完成发育的比例越大,但饲毒时间是主要影响因素．从感病幼虫体内发育成的侧沟茧蜂或曾经在感病寄主上产过卵的寄生蜂,以及通过人工方式使产卵器被病毒污染的寄生蜂,均能携带一定数量的病毒．通过产卵活动,侧沟茧蜂成蜂能在寄主幼虫个体间传递病毒．当寄生蜂在感病的寄主幼虫上产卵带毒后,平均可传递病毒给2．14头幼虫;发育于感病幼虫体内的寄生蜂,平均可传递病毒给2．45头幼虫．通过用病毒液浸茧或用混有病毒的蜂蜜饲喂成蜂等方式使产卵器污染病毒的寄生蜂,传毒效率随饲毒浓度增加而提高,平均可传递病毒1．45头和0．94头幼虫     

Partial molecular characterization of two simian immunodeficiency viruses (SIV) from African colobids: SIVwrc from Western red colobus (Piliocolobus badius) and SIVolc from olive colobus (Procolobus verus)

In order to study primate lentivirus evolution in the Colobinae subfamily, in which only one simian immunodeficiency virus (SIV) has been described to date, we screened additional species from the three different genera of African colobus monkeys for SIV infection. Blood was obtained from 13 West African colobids, and HIV cross-reactive antibodies were observed in 5 of 10 Piliocolobus badius, 1 of 2 Procolobus verus, and 0 of 1 Colobus polykomos specimens. Phylogenetic analyses of partial pol sequences revealed that the new SIVs were more closely related to each other than to the other SIVs and especially did not cluster with the previously described SIVcol from Colobus guereza. This study presents evidence that the three genera of African colobus monkeys are naturally infected with an SIV and indicates also that there was no coevolution between virus and hosts at the level of the Colobinae subfamily.     

Transmission dynamics of a zoonotic pathogen within and between wildlife host species

The transmission dynamics of the cowpox virus infection have been quantified in two mixed populations of bank voles (Clethrionomys glareolus) and wood mice (Apodemus sylvaticus), through analyses of detailed time-series of the numbers of susceptible, infectious and newly infected individuals. The cowpox virus is a zoonosis which circulates in these rodent hosts and has been shown to have an adverse effect on reproductive output. The transmission dynamics within species is best described as frequency dependent rather than density dependent, contrary to the 'mass action' assumption of most previous studies, both theoretical and empirical. Estimation of a transmission coefficient for each species in each population also allows annual and seasonal variations in transmission dynamics to be investigated through an analysis of regression residuals. Transmission between host species is found to be negligible despite their close cohabitation. The consequences of this for the combining ability of hosts as zoonotic reservoirs, and for apparent competition between hosts, are discussed.     

The detection of apple chlorotic leafspot virus by a modified procedure of enzyme-linked immunosorbent assay (ELISA)

The technique of enzyme-linked immunosorbent assay (ELISA) was modified to enable detection of apple chlorotic leafspot virus (CLSV) both in herbaceous hosts and in several naturally infected fruiting and ornamental woody host species. Some of the characteristics of the modified method as used with different virus-host combinations are described.     

Purification and composition of the proteins from Sindbis virus grown in chick and BHK cells.

Procedures are described for the purification of the Sindbis virus structural proteins. The amino acid and carbohydrate compositions of the purified proteins are presented for virus grown in BHK-21/13 and chicken embryo cells. Glycoprotein E1 from virus grown in BHK cells is deficient in a mannose-rich glycopeptide found on that glycoprotein when virus is grown in chicken embryo cells. The complex glactose-containing glycopeptides appear similar for virus grown in both hosts. However, when virus is grown in BHK cells, both glycoproteins are enriched in those glycopeptides containing more sialic acid. Since the two viral glycoproteins are difficult to separate cleanly during purification, it is suggested that there may be strong, but noncovalent, interactions between glycoproteins E1 and E2. It is also suggested that there may be an interaction between glycoprotein E2 and a component of the nucleocapsid.     

Move Over,Bacteria! Viruses Make Their Mark as Mutualistic Microbial Symbionts

Viruses are being redefined as more than just pathogens. They are also critical symbiotic partners in the health of their hosts. In some cases, viruses have fused with their hosts in symbiogenetic relationships. Mutualistic interactions are found in plant, insect, and mammalian viruses, as well as with eukaryotic and prokaryotic microbes, and some interactions involve multiple players of the holobiont. With increased virus discovery, more mutualistic interactions are being described and more will undoubtedly be discovered.     

Pseudorabies virus EP0 protein counteracts an interferon-induced antiviral state in a species-specific manner

Pseudorabies virus (PRV), an alphaherpesvirus related to herpes simplex virus type 1 and varicella-zoster virus, infects a broad host range of mammals. A striking characteristic of PRV infection is the different symptoms and outcomes of infection in natural and nonnatural hosts. Adult pigs, the natural hosts of PRV, survive infection with only mild respiratory symptoms, while nonnatural hosts, including rodents and cattle, invariably die after exhibiting neurological symptoms. Here, we show that the PRV EP0 protein is necessary to overcome an interferon-mediated antiviral response in primary cells from the natural host of PRV but is not necessary in nonnatural-host cells.     

Peanut Chlorotic Ringspot Virus (PCRV), a Newly Discovered Virus Infecting Peanut (Arachis hypogaea L.)

A virus causing wide chlorotic ringspot (PCRV) associated with chlorotic line pattern and motthng on an Erictoides hybrid growing in USDA-OSU greenhouses, Stillwater, Oklahoma, was discovered. The virus was isolated and characterized and found to differ in symptomology, host range and serological properties from all the previously described viruses infecting peanut, particularly those reported in the United States to be the most important ones, peanut mottle virus, peanut stripe virus, and tomato spotted wilt virus. The virus was transmitted by both mechanical inoctilation and grafting to fourteen peanut cultivars causing identical symptoms to those originally observed on the Erictoides hybrid. In addition to peanut, the virus systemically infected Pisum sativum L. ‘Little marvel’ causing mainly mosaic and Lupinus albus L. ‘Tiftwhite’ producing severe malformation and remarkable reduction in leaflet area. The virus did not infect many other plant species of which cowpea ‘California blackeye’ (Vigna unguiculata L.) and at least five cultivars of soybean (Glydne max L.) are known to be susceptible hosts to peanut mottle virus. Phaseolus vulgaris L. ‘Topcrop’ and Chenopodium amaranticohr Coste & Reyn were found to be two useful local lesion assay and diagnostic hosts for PCRV. The virus elicited necrotic local lesions on the first and chlorotic ringspots on the second. PCRV had a dilution end point between 10^?5 and 10^?6, thermal inactivation point between 55°C and 60°C, and longevity in vitro up to 6 days but not 7 days. Virus particles viewed hy electron microscopy and the negative stain uranyl aceute were flexuous filamentous particles ranging in length from 750–850 nm. In both indiren PAS-ELISA and Ouchterlony double immunodiffusion test, PCRV was serologically related to a PMV isolate from Oklahoma (PMV-OK.) but not to bean yellow mosaic virus, peanut stripe virus, potato virus Y, watermelon mosaic virus 1, watermelon mosaic virus 2, wheat streak mosaic virus, and zucchini yellow mosaic virus.     

Detection of lettuce necrotic yellows virus by an enzyme-linked immunosorbent assay in plant hosts and the insect vector

An enzyme-linked immunosorbent assay (ELISA) system for the rapid detection of the plant rhabdovirus, lettuce necrotic yellows virus (LNYV) in plant hosts and individual aphid vector is described. The method has been shown to be reliable and sensitive, and to have a number of advantages over the conventional methods of detecting LNYV in plants and insects by infectivity tests.