Natural Host Range Research Articles

Natural host range, incidence on overwintering cotton and diversity of cotton leafroll dwarf virus in Georgia USA

In 2018–19, cotton leafroll dwarf virus (CLRDV) was reported from several cotton-producing states in the southern United States. An extensive survey was conducted in the spring, summer, and fall of 2019 to identify weeds and overwintering cotton as sources for primary inoculum for the next season crop. Foliage samples of 57 different weed species were collected from fields formerly planted to cotton and analyzed using RT-PCR with CLRDV specific primers. CLRDV was detected from 23 weed species belonging to 16 different botanical families. Overwintering cotton stalks (48%) and regrowth leaves (75%) both harbored CLRDV. A phylogenetic analysis conducted using nucleotide and amino acid sequences of complete ORF 0, ORF 3, and ORF 4 determined that the CLRDV from all weeds and overwintered cotton stalks from Georgia clustered with CLRDV isolates collected in the USA but differed from isolates reported from South America and Asia. Pairwise nucleotide and amino acid identity showed 91–100% sequence similarity for complete ORF3. For ORF4, pairwise identity among the nucleotide ranged from 92-100%, while amino acids ranged from 90.2-100% with isolates reported from the USA and South America, with the exception of three Asian CLRDV isolates and two weed isolates from Georgia. Similarly, CLRDV isolates from Georgia weeds shared 91.6–93% nucleotide and 88–90.8% amino acid for silencing suppressor compared to most of the isolates from North America and South America. The role of alternative hosts on disease incidence and spread has not been studied in cotton-producing countries where the disease is prevalent. This is the first comprehensive study that identifies weeds and overwintering cotton as a potential green bridge for the year-round survival of CLRDV.

Machine Learning Approach Effectively Predicts Binding Between SARS-CoV-2 Spike and ACE2 Across Mammalian Species - Worldwide, 2021.

IntroductionSevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a recently emergent coronavirus of natural origin and caused the coronavirus disease (COVID-19) pandemic. The study of its natural origin and host range is of particular importance for source tracing, monitoring of this virus, and prevention of recurrent infections. One major approach is to test the binding ability of the viral receptor gene ACE2 from various hosts to SARS-CoV-2 spike protein, but it is time-consuming and labor-intensive to cover a large collection of species.MethodsIn this paper, we applied state-of-the-art machine learning approaches and created a pipeline reaching >87% accuracy in predicting binding between different ACE2 and SARS-CoV-2 spike.ResultsWe further validated our prediction pipeline using 2 independent test sets involving >50 bat species and achieved >78% accuracy. A large-scale screening of 204 mammal species revealed 144 species (or 61%) were susceptible to SARS-CoV-2 infections, highlighting the importance of intensive monitoring and studies in mammalian species.DiscussionIn short, our study employed machine learning models to create an important tool for predicting potential hosts of SARS-CoV-2 and achieved the highest precision to our knowledge in experimental validation. This study also predicted that a wide range of mammals were capable of being infected by SARS-CoV-2.

Hop stunt viroid: A polyphagous pathogenic RNA that has shed light on viroid-host interactions.

Taxonomy Hop stunt viroid (HSVd) is the type species of the genus Hostuviroid (family Pospiviroidae). The other species of this genus is Dahlia latent viroid, which presents an identical central conserved region (CCR) but lacks other structural hallmarks present in Hop stunt viroid. HSVd replication occurs in the nucleus through an asymmetric rolling‐circle model as in the other members of the family Pospiviroidae, which also includes the genera Pospiviroid, Cocadviroid, Apscaviroid, and Coleoviroid.Physical properties Hop stunt viroid consists of a single‐stranded, circular RNA of 295–303 nucleotides depending on isolates and sequence variants. The most stable secondary structure is a rod‐like or quasi‐rod‐like conformation with two characteristic domains: a CCR and a terminal conserved hairpin similar to that of cocadviroids. HSVd lacks a terminal conserved region.Hosts and symptomsHSVd infects a very broad range of natural hosts and has been reported to be the causal agent of five different diseases (citrus cachexia, cucumber pale fruit, peach and plum apple apricot distortion, and hop stunt). It is distributed worldwide.TransmissionHSVd is transmitted mechanically and by seed.

Present Status and Future Management Strategies for Sugarcane Yellow Leaf Virus: A Major Constraint to the Global Sugarcane Production.

Sugarcane yellow leaf virus (SCYLV) is a distinct member of the Polerovirus genus of the Luteoviridae family. SCYLV is the major limitation to sugarcane production worldwide and presently occurring in most of the sugarcane growing countries. SCYLV having high genetic diversity within the species and presently ten genotypes are known to occur based on the complete genome sequence information. SCYLV is present in almost all the states of India where sugarcane is grown. Virion comprises of 180 coat protein units and are 24-29 nm in diameter. The genome of SCYLV is a monopartite and comprised of single-stranded (ss) positive-sense (+) linear RNA of about 6 kb in size. Virus genome consists of six open reading frames (ORFs) that are expressed by sub-genomic RNAs. The SCYLV is phloem-limited and transmitted by sugarcane aphid Melanaphis sacchari in a circulative and non-propagative manner. The other aphid species namely, Ceratovacuna lanigera, Rhopalosiphum rufiabdominalis, and R. maidis also been reported to transmit the virus. The virus is not transmitted mechanically, therefore, its transmission by M. sacchari has been studied in different countries. SCYLV has a limited natural host range and mainly infect sugarcane (Sachharum hybrid), grain sorghum (Sorghum bicolor), and Columbus grass (Sorghum almum). Recent insights in the protein-protein interactions of Polerovirus through protein interaction reporter (PIR) technology enable us to understand viral encoded proteins during virus replication, assembly, plant defence mechanism, short and long-distance travel of the virus. This review presents the recent understandings on virus biology, diagnosis, genetic diversity, virus-vector and host-virus interactions and conventional and next generation management approaches.

Pest categorisation of the non-EU phytoplasmas of tuber-forming Solanum spp.

Following a request from the European Commission, the EFSA Panel on Plant Health performed a pest categorisation of four phytoplasmas of tuber‐forming Solanum spp. known to occur only outside the EU or having a limited presence in the EU. The only tuber‐forming species of Solanum reported to be phytoplasma infected is S. tuberosum. This opinion covers ‘Candidatus Phytoplasma americanum’, ‘Ca. P. aurantifolia’‐related strains (GD32; St_JO_10, 14, 17; PPT‐SA; Rus‐343F; PPT‐GTO29, ‐GTO30, ‐SINTV; Potato Huayao Survey 2; Potato hair sprouts), ‘Ca. P. fragariae’‐related strains (YN‐169, YN‐10G) and ‘Ca. P. pruni’‐related strains (Clover yellow edge; Potato purple top AKpot7, MT117, AKpot6; PPT‐COAHP, ‐GTOP). Phytoplasmas can be detected by molecular methods and are efficiently transmitted by vegetative propagation. Phytoplasmas are also transmitted in a persistent and propagative manner by some insects belonging to families within Cicadomorpha, Fulgoromorpha and Sternorrhyncha (order Hemiptera). No transovarial, pollen or seed transmission has been reported. The reported natural host range of the phytoplasmas categorised here varies from restricted (‘Ca. P. americanum’, and ‘Ca. P. fragariae’‐related strains) to wide (‘Ca. P. aurantifolia’‐related strains and ‘Ca. P. pruni’‐related strains), thus increasing the possible entry pathways in the latter case. S. tuberosum is widely cultivated in the EU. All the categorised phytoplasmas can enter and spread through the trade of host plants for planting, and by vectors. Establishment of these phytoplasmas is not expected to be limited by EU environmental conditions. The introduction of these phytoplasmas in the EU would have an economic impact. There are measures to reduce the risk of entry, establishment, spread and impact. Uncertainties result from limited information on distribution, biology and epidemiology. All the phytoplasmas categorised here meet the criteria evaluated by EFSA to qualify as potential Union quarantine pests, and they do not meet all the criteria to qualify as potential regulated non‐quarantine pests, because they do not occur or are not known to be widespread in the EU.

Artichoke yellow ringspot virus as the causal agent of a new viral disease of lettuce: Epidemiology and molecular variability

AbstractIn 2015 and 2016, lettuce (Lactuca sativa) plants showing yellow ringspots and line patterns were observed in Argolida (Peloponnese, Greece). Symptoms resembled those caused by nepoviruses, especially artichoke yellow ringspot virus (AYRSV), an endemic virus in artichoke (Cynara scolymus) and onion (Allium cepa var. cepa) crops in this area. The aim of this work was to identify and characterize the viral agent associated with the observed disease. We carried out mechanical inoculations onto Nicotiana benthamiana and lettuce plants and also virus‐specific reverse transcription (RT)‐PCR. Results confirmed the presence of AYRSV in all lettuce plants with symptoms tested, and the natural and experimental host range of the virus was studied. The species Heliotropium europaeum, Solanum nigrum, Origanum vulgare, Lactuca seriola, and Sinapis arvensis, are recorded as hosts of AYRSV for the first time. Also, AYRSV was detected by RT‐PCR in seeds and in the produced seedlings of lettuce, N. benthamiana, N. glutinosa, N. tabacum, and S. nigrum. Sequencing of a partial fragment of the gene encoding the RNA‐dependent RNA polymerase was performed for 29 isolates of AYRSV originating from different hosts (lettuce, artichoke, onion, and arable weeds). Phylogenetic analysis of AYRSV isolates classified them in diverse clusters that exhibited no host grouping. All groups included isolates from cultivated and wild plant species. In this study, AYRSV was associated with a new lettuce disease for the first time, thus increasing the known natural host range of the virus.

Listeria monocytogenes Infection of Bat Pipistrellus nathusii Epithelial cells Depends on the Invasion Factors InlA and InlB.

L. monocytogenes is a widespread facultative intracellular pathogen. The range of natural hosts that supporting L. monocytogenes persistence in the environment has not been fully established yet. In this study, we were interested in the potential of L. monocytogenes to infect cells of bats, which are being increasingly recognized as a reservoir for microorganisms that are pathogenic to humans and domestic animals. A stable epithelial cell line was developed from the kidneys of Pipistrellus nathusii, a small bat widely distributed across Europe. The wild-type L. monocytogenes strain EGDe infected this cell line with an invasion efficiency of 0.0078 ± 0.0009%. Once it entered bat cells, L. monocytogenes doubled within about 70 min. When L. monocytogenes lacked either of the major invasion factors, InlA and InlB, invasion efficiency decreased by a factor of 10 and 25 respectively (p < 0.000001). The obtained results suggest that bat epithelial cells are susceptible to L. monocytogenes infection and that L. monocytogenes invasion of bat cells depends on the major invasion factors InlA and InlB. These results constitute the first report on in vitro studies of L. monocytogenes infection in bats.

Characterization of a DCL2-Insensitive Tomato Bushy Stunt Virus Isolate Infecting Arabidopsis thaliana

Tomato bushy stunt virus (TBSV), the type member of the genus Tombusvirus in the family Tombusviridae is one of the best studied plant viruses. The TBSV natural and experimental host range covers a wide spectrum of plants including agricultural crops, ornamentals, vegetables and Nicotiana benthamiana. However, Arabidopsis thaliana, the well-established model organism in plant biology, genetics and plant–microbe interactions is absent from the list of known TBSV host plant species. Most of our recent knowledge of the virus life cycle has emanated from studies in Saccharomyces cerevisiae, a surrogate host for TBSV that lacks crucial plant antiviral mechanisms such as RNA interference (RNAi). Here, we identified and characterized a TBSV isolate able to infect Arabidopsis with high efficiency. We demonstrated by confocal and 3D electron microscopy that in Arabidopsis TBSV-BS3Ng replicates in association with clustered peroxisomes in which numerous spherules are induced. A dsRNA-centered immunoprecipitation analysis allowed the identification of TBSV-associated host components including DRB2 and DRB4, which perfectly localized to replication sites, and NFD2 that accumulated in larger viral factories in which peroxisomes cluster. By challenging knock-out mutants for key RNAi factors, we showed that TBSV-BS3Ng undergoes a non-canonical RNAi defensive reaction. In fact, unlike other RNA viruses described, no 22nt TBSV-derived small RNA are detected in the absence of DCL4, indicating that this virus is DCL2-insensitive. The new Arabidopsis-TBSV-BS3Ng pathosystem should provide a valuable new model for dissecting plant–virus interactions in complement to Saccharomyces cerevisiae.

Possibility for reverse zoonotic transmission of SARS-CoV-2 to free-ranging wildlife: A case study of bats.

The COVID-19 pandemic highlights the substantial public health, economic, and societal consequences of virus spillover from a wildlife reservoir. Widespread human transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) also presents a new set of challenges when considering viral spillover from people to naïve wildlife and other animal populations. The establishment of new wildlife reservoirs for SARS-CoV-2 would further complicate public health control measures and could lead to wildlife health and conservation impacts. Given the likely bat origin of SARS-CoV-2 and related beta-coronaviruses (β-CoVs), free-ranging bats are a key group of concern for spillover from humans back to wildlife. Here, we review the diversity and natural host range of β-CoVs in bats and examine the risk of humans inadvertently infecting free-ranging bats with SARS-CoV-2. Our review of the global distribution and host range of β-CoV evolutionary lineages suggests that 40+ species of temperate-zone North American bats could be immunologically naïve and susceptible to infection by SARS-CoV-2. We highlight an urgent need to proactively connect the wellbeing of human and wildlife health during the current pandemic and to implement new tools to continue wildlife research while avoiding potentially severe health and conservation impacts of SARS-CoV-2 "spilling back" into free-ranging bat populations.

Ranking the host range of biological control agents with quantitative metrics of taxonomic specificity

The need to prevent negative impacts of importation biological control on native biodiversity has made evaluating the specificity (host range) of natural enemies a central issue for the application of biological control programs against pest organisms. Thus, when there are a number of candidate species being considered for introduction as biological control agents against a particular target pest, it is important to compare their relative host ranges. These comparisons are usually made informally using categorical terminology (e.g., generalist, specialist, oligophagous). However, relative differences in natural enemy host range are better expressed quantitatively, with both ecological (how many host species a natural enemy is capable of exploiting) and evolutionary (how the host species are related phylogenetically) components. We propose using two previously developed quantitative taxonomic and phylogenetic metrics (taxonomic host range – STD; phylogenetic species variability – PSV), in combination with the number of associated host species (host species richness), as heuristic tools to rank the relative host specificity of candidate biological control agents. We first show that although STD and PSV were developed independently, they are directly related mathematically and convey exactly the same information except on different numerical scales. We then apply the metrics to case studies regarding the host range of candidate biological control agents for: (i) an invasive whitefly in greenhouse crops, Aleurotrachelus trachoides (Hemiptera: Aleyrodidae), and (ii) an invasive pest of grapes, Lobesia botrana (Lepidoptera: Tortricidae). We also provide open source code to easily allow the calculation of these metrics for any natural enemy for which taxonomic host range information is available. Finally, we describe potential uses of these metrics in applied biological control as well as important caveats and limitations that require further theoretical work to address. We conclude that while these metrics should not be considered as absolute or infallible measurements of host range, their application should encourage biological control practitioners to explicitly consider the phylogenetic component of host range when ranking prospective candidate biological control agents.

Costus stripe mosaic virus, a tentative new member of the genus Potyvirus.

Morphological, biological, serological, and molecular tests underpin the description of costus stripe mosaic virus (CoSMV) as a new member of the genus Potyvirus, family Potyviridae. Found affecting the native ornamental Costus spiralis in Brazil, the pathogen showed a severely restricted natural and experimental host range. Excluding the poly(A) tail, the CoSMV genome contains a large open reading frame (ORF) of 9,446 nucleotides that encodes a polyprotein with 3,046 amino acids, which is potentially cleaved into ten products, and a small ORF (77 amino acids) knows as PIPO. Genome analysis demonstrated the highest CoSMV nucleotide sequence identity to onion yellow dwarf virus (51.79%). No evidence of recombination was detected in the CoSMV genome, and phylogenetic analysis revealed its basal position in a group formed by members of the genus Potyvirus, along with Cyrtanthus elatus virus A (Vallota speciosa virus) and canna yellow streak virus. CoSMV was not transmitted by aphids of the species Aphis solanella, Myzus persicae or Uroleucon sonchi, which could be due to mutations in the HC-Pro motifs required for aphid transmission. A divergence in the P1 protein cleavage site was found when compared to other members of the family Potyviridae. Based on its unique biological and molecular characteristics and the current species demarcation criteria, we propose CoSMV to be a new tentative member of the genus Potyvirus.

Lessons Learned from SARS-CoV and MERS-CoV: Preparation for SARS-CoV-2 induced COVID-19

Coronaviruses (CoVs) are the largest positive-sense RNA viruses with a wide range of natural hosts. To date, seven types of coronaviruses (HCoV-NL63; Human coronavirus NL63, HCoV-229E; Human coronavirus 229E, HCoV-OC43; Human coronavirus OC43, HCoV-HKU1; Human coronavirus HKU1, SARS-CoV; Severe acute respiratory syndrome-related coronavirus, MERS-Co; Middle East respiratory syndrome coronavirus, and SARS-CoV-2; Severe acute respiratory syndrome-related coronavirus) are known to cause disease in humans, and three of the CoVs (SARS-CoV, MERS-CoV, and SARS-CoV-2) cause severe, occasionally fatal, respiratory infections in humans. In November 2002, the case of severe acute respiratory syndrome (SARS), a new respiratory illness caused by SARS-CoV, was first reported in Guangdong Province, China. For the next several months, the SARS outbreak resulted in more than 8,000 cases of infection and 800 deaths. In June 2012, Middle East respiratory syndrome coronavirus (MERS-CoV) was first identified in Saudi Arabia with 2,373 reported viral infections and 823 associated deaths until February 2019. The outbreak of the MERS-CoV pandemic also occurred in South Korea in May 2015. In late December 2019, another novel coronavirus called SARS-CoV-2, genetically linked to SARS-CoV, emerged in Wuhan, Hubei Province of China that has spread worldwide. Outbreaks of coronavirus-infections are occurring frequently in the 21st century; therefore, it seems very likely that another pandemic of coronavirus can emerge anytime in the future. In this review, we outlined the biological characteristics of coronaviruses and summarized the status of vaccine development against SARS-CoV-2, SARS-CoV, and MERS-CoV in preparation for the unpredictable emergence of coronavirus pandemic.

What We Need to Consider During and After the SARS-CoV-2 Pandemic.

Even though extreme containment and mitigation strategies were implemented by numerous governments around the world to slow down the spread of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the number of critically ill patients and fatalities keeps rising. This crisis has highlighted the socioeconomic disparities of health care systems within and among countries. As new CoVID policies and responses are implemented to lessen the impact of the virus, it is imperative (1) to consider additional mitigation strategies critical for the development of effective countermeasures, (2) to promote long-term policies and strict regulations of the trade of wildlife and live animal markets, and (3) to advocate for necessary funding and investments in global health, specifically for the prevention of and response to natural and manmade pandemics. This document considers some of these challenges.

Coronavirus infections and immune responses.

Coronaviruses (CoVs) are by far the largest group of known positive‐sense RNA viruses having an extensive range of natural hosts. In the past few decades, newly evolved Coronaviruses have posed a global threat to public health. The immune response is essential to control and eliminate CoV infections, however, maladjusted immune responses may result in immunopathology and impaired pulmonary gas exchange. Gaining a deeper understanding of the interaction between Coronaviruses and the innate immune systems of the hosts may shed light on the development and persistence of inflammation in the lungs and hopefully can reduce the risk of lung inflammation caused by CoVs. In this review, we provide an update on CoV infections and relevant diseases, particularly the host defense against CoV‐induced inflammation of lung tissue, as well as the role of the innate immune system in the pathogenesis and clinical treatment.

Fringed Spiderflower (Cleome rutidosperma) Is a New Host for Purple Coneflower Witches’ Broom Phytoplasma, a 16SrII-V Subgroup Strain in Taiwan

Fringed spiderflower (Cleome rutidosperma) is an annual herbaceous plant that grows as a weed. Originally from tropical Africa, fringed spiderflower has been introduced and is becoming widely distributed at low altitudes in Taiwan. In June 2019, symptoms such as small leaves, witches’ broom, floral virescence, and phyllody were observed on fringed spiderflowers grown at the agricultural experiment station in Wufeng, Taichung City, Taiwan. These disease symptoms are similar to those associated with purple coneflower (Echinacea purpurea) witches’ broom disease caused by a 16SrII-A subgroup phytoplasma identified in the same area (Chang et al. 2015; Tseng et al. 2012). Leaf samples of spiderflowers exhibiting disease symptoms were collected for western blotting and PCR assays. Total proteins were extracted from plant samples and examined by western blotting using the polyclonal antibody raised against immunodominant membrane protein (Imp, accession no. KPN61379) of purple coneflower witches’ broom phytoplasma. A specific signal of expected size (19 kDa) for Imp was detected in the symptomatic leaf samples but not in healthy leaf samples. For PCR analysis, the total DNA of each sample was extracted using the Plant Genomic DNA Purification Kit (DP022, Genemark, Taiwan) and used as a template in nested PCR with the phytoplasma universal primer pairs P1/P7 followed by R16F2n/R16R2 (Lee et al. 1993). DNA extracted from leaves sampled on healthy plants were used as a negative control. An amplified DNA fragment of 1.2 kb specific for 16S ribosomal RNA (16S rRNA) obtained from symptomatic leaf samples was gel purified and sequenced. The nucleotide sequence was deposited into GenBank (accession no. MN213634). BLAST analysis revealed that MN213634 is identical to the nucleotide sequence of GenBank accession LKAC01000001.1 (complement [31093 to 32611]) of phytoplasma associated with purple coneflower witches’ broom disease. Using iPhyClassifier, the virtual restriction fragment length polymorphism pattern of the 16S rDNA fragment (accession no. MN213634) confirmed that the phytoplasma detected in symptomatic fringed spiderflower belongs to the 16SrII-V subgroup. Subsequent PCR and DNA sequencing assays further confirmed that the genes encoding the putative secreted proteins (accession nos. WP_054598519 and KPN61138) identified in purple coneflower witches’ broom phytoplasma were also found in samples of symptomatic fringed spiderflowers. Our findings revealed that the fringed spiderflower is a new weed plant host for purple coneflower witches’ broom phytoplasma. This result expands our knowledge of the natural host range of 16SrII-V subgroup strains.

Pest categorisation of the non-EU phytoplasmas of Cydonia Mill., Fragaria L., Malus Mill., Prunus L., Pyrus L., Ribes L., Rubus L. and Vitis L.

Following a request from the European Commission, the EFSA Panel on Plant Health performed a pest categorisation of nine phytoplasmas of Cydonia Mill., Fragaria L., Malus Mill., Prunus L., Pyrus L., Ribes L., Rubus L. and Vitis L. (hereafter “host plants”) known to occur only outside the EU or having a limited presence in the EU. This opinion covers the (i) reference strains of ‘Candidatus Phytoplasma australiense’, ‘Ca. P. fraxini’, ‘Ca. P. hispanicum’, ‘Ca. P. trifolii’, ‘Ca. P. ziziphi’, (ii) related strains infecting the host plants of ‘Ca. P. aurantifolia’, ‘Ca. P. pruni’, and ‘Ca. P. pyri’, and (iii) an unclassified phytoplasma causing Buckland valley grapevine yellows. Phytoplasmas can be detected by available methods and are efficiently transmitted by vegetative propagation, with plants for planting acting as a major entry pathway and a long‐distance spread mechanism. Phytoplasmas are also transmitted in a persistent and propagative manner by some insect families of the Fulgoromorpha, Cicadomorpha and Sternorrhyncha (order Hemiptera). No transovarial, pollen or seed transmission has been reported. The natural host range of the categorised phytoplasmas varies from one to more than 90 plant species, thus increasing the possible entry pathways. The host plants are widely cultivated in the EU. All the categorised phytoplasmas can enter and spread through the trade of host plants for planting, and by vectors. Establishment of these phytoplasmas is not expected to be limited by EU environmental conditions. The introduction of these phytoplasmas in the EU would have an economic impact. There are measures to reduce the risk of entry, establishment, spread and impact. Uncertainties result from limited information on distribution, biology and epidemiology. All the phytoplasmas categorised here meet the criteria evaluated by EFSA to qualify as potential Union quarantine pests, and they do not qualify as potential regulated non‐quarantine pests, because they are non‐EU phytoplasmas.

Natural host range and thrips transmission of capsicum chlorosis virus in Australia

The orthotospovirus, capscium chlorosis virus (CaCV) was shown to be common and widespread in the weed host Ageratum conyzoides in eastern coastal regions of Queensland, Australia with up to 92% of plants infected. This is the first report of A. conyzoides being an important host of CaCV in Australia. CaCV was also found as natural infections of Arachis hypogaea (peanut), Ananas comosus (pineapple), Sonchus oleraceus, Tagetes minuta and Emilia sonchifolia. This is the first report of CaCV infecting pineapple and being associated with severe disease symptoms. Thrips palmi, Frankliniella schultzei and Microcephalothrips abdominalis were shown to transmit CaCV while no transmission was achieved using F. occidentalis.

Development of Anncaliia algerae (Microsporidia) in Drosophila melanogaster

Representatives of the genus Anncaliia are known as natural parasites of dipteran and coleopteran insects, amphipod crustaceans, but also humans, primarily with immunodeficiency. Anncaliia algerae-caused fatal myositis is considered as an emergent infectious disease in humans. A. (=Nosema, Brachiola) algerae, the best studied species of the genus, demonstrates the broadest among microsporidia range of natural and experimental hosts, but it has never been propagated in Drosophila. We present ultrastructural analysis of development of A.algerae in visceral muscles and adipocytes of Drosophila melanogaster 2wk after per oral experimental infection. We observed typical to Anncaliia spp. features of ultrastructure and cell pathology including spore morphology, characteristic extensions of the plasma membrane, and presence of "ridges" and appendages of tubular material at proliferative stages. Anncaliia algerae development in D.melanogaster was particularly similar to one of A.algerae and A.(Brachiola) vesicularum in humans with acute myositis. Given D.melanogaster is currently the most established genetic model, with a fully sequenced genome and easily available transgenic forms and genomic markers, a novel host-parasite system might provide new genetic tools to investigate host-pathogen interactions of A.algerae, as well to test antimicrosporidia drugs.

Identification of natural weed hosts of Cucumber mosaic virus subgroup-I and the absence of seed transmission in weed hosts in Pakistan

ABSTRACT Every year in Pakistan the Cucumber mosaic virus (CMV) severely damages tomato crops, but little is known about the epidemiology of this disease. Tomato fields with a high incidence of CMV were tested to determine the range of potential natural alternative weed hosts of CMV. A total of 553 symptomatic leaf samples from 36 plant species representing 19 families were analysed for the presence of CMV subgroup-I and subgroup-II using triple antibody sandwich enzyme-linked immunosorbant assay (TAS-ELISA) and reverse transcription polymerase chain reaction (RT-PCR). CMV subgroup-I was detected for the first time in nine plant species: Chenopodium album, Calotropis procera, Heliotropium indicum, Cornopus didymus, Convolvulus arvensis, Melilotus indica, Galium aparine, Nicotiana plumbaginifolia and Withania somnifera. Back indexing with leaf extracts of naturally infected TAS-ELISA- and RT-PCR-positive plants of all of these weed species produced severe symptoms in tomato plants of the susceptible variety Nagina. Grow-out testing proved the absence of seed transmission of CMV subgroup-I in TAS-ELISA- and RT-PCR-positive weed species. This information is useful for reducing early CMV infection by eradicating these weed species, thereby reducing virus reservoirs and the vector aphid population. However, the TAS-ELISA and RT-PCR tests proved the absence of CMV subgroup-II in the tested samples.

Solving the species problem in viral taxonomy: recommendations on non-Latinized binomial species names and on abandoning attempts to assign metagenomic viral sequences to species taxa.

Properties useful for defining virus species are phenotypic properties of viruses that can be altered by a few mutations. Such properties include the natural host range, cell and tissue tropism, symptomatology, pathogenicity and mode of transmission. All these properties are not necessarily present in identical form in all the members of a species; therefore, a virus species is a polythetic class of viruses defined by a variable combination of several properties rather than by a single conserved property present in all the members of the species. This review will discuss current controversies about what virus species actually are as well as which names should be given to them. It will be emphasized that most species-defining properties are so-called relational properties that arise because viruses necessarily interact with biological partners such as vectors, hosts and immune systems. Although these relational properties are of utmost importance to laboratory and clinical virologists, they remain unknown if only the viral genome is available and the relational partners of the virus have not yet been identified. Since the International Committee on Taxonomy of Viruses (ICTV) in 2013 ratified a new definition of virus species, which no longer accepts that species are polythetic classes but instead are monophyletic groups, the implications of this new definition for viral taxonomy and nomenclature will be analyzed. In my private capacity, I also make the following recommendations regarding current debates on proposed new names for virus species as well as on the feasibility of assigning viral sequences found in metagenomic databases to individual species taxa in the current ICTV classification. 1) The ICTV should abandon the current rule that the names of virus species (for instance Measles virus) should differ from the virus name (measles virus) only by typography. 2) Non-Latinized binomial species names based on familiar virus and genus names should become the norm. This would obviate the need to create about 5000 hard-to-memorize Latinized species names. 3) Virus species are defined not by the intrinsic properties of virions and viral genomes but by the relational properties of viruses that arise from their interactions with host and vector partners. Since the hosts and vectors associated with nearly all viral sequences found in metagenomic databases are unknown, the phenotypic properties of the putative viruses also remain unknown, and these viral sequences cannot be allocated to established species in the ICTV classification.