Assessment of transmission risk in WSSV-infected shrimp Litopenaeus vannamei upon cooking

White spot syndrome virus has been a threat to the global shrimp industry since it was discovered in Taiwan in 1992. Thus, shrimp-producing countries have launched regulations to prevent import of WSSV-infected commodity shrimp from endemic areas. Recently, cooked shrimp that is infected with WSSV tested positive by PCR. However, there is no study to determine the infectivity of WSSV in cooked shrimp that tested positive by PCR. In the present study, WSSV-infected shrimp were cooked at boiling temperature for different times including 0, 1, 3, 5, 10 and 30 min. Upon exposure to boiling temperature, WSSV-infected shrimp were fed to SPF shrimp (Litopenaeus vannamei). The result showed experimentally challenged shrimp from 0-min treatment (positive control) indeed got infected with WSSV. However, experimentally challenged shrimp that were fed tissues boiled at 1, 3, 5, 10 and 30 min were not infected with WSSV. Mortality data showed that only the positive control (0-min) treatment displayed high mortality, whereas no mortality was observed in any other treatment category. These findings suggest that cooking shrimp at boiling temperature for at least 1 min might prevent any potential spread of WSSV from endemic countries to other geographical areas where WSSV has not yet been reported.

The Molecular Epidemiology and Phylogeny of Torque Teno Virus (TTV) in Jordan

Torque teno virus (TTV) is the most common component of the human blood virobiota. Little is known, however, about the prevalence of TTV in humans and the most common farm domesticates in Jordan, or the history and modality of TTV transmission across species lines. We therefore tested sera from 396 Jordanians and 171 farm animals for the presence of TTV DNA using nested 5'-UTR-PCR. We then performed phylogenetic, ordination and evolutionary diversity analyses on detected DNA sequences. We detected a very high prevalence of TTV in Jordanians (~96%); much higher than in farm animal domesticates (~29% pooled over species). TTV prevalence in the human participants is not associated with geography, demography or physical attributes. Phylogenetic, ordination and evolutionary diversity analyses indicated that TTV is transmitted readily between humans across the geography of the country and between various species of animal domesticates. However, the majority of animal TTV isolates seem to derive from a single human-to-animal transmission event in the past, and current human-animal transmission in either direction is relatively rare. In conclusion, animal TTV in Jordan is historically derived from human variants; however, ongoing human-animal TTV exchange is minimal and zoonotic infection seems to be of limited importance.

Modelling Ranavirus Transmission in Populations of Common Frogs (Rana temporaria) in the United Kingdom

Ranaviruses began emerging in common frogs (Rana temporaria) in the United Kingdom in the late 1980s and early 1990s, causing severe disease and declines in the populations of these animals. Herein, we explored the transmission dynamics of the ranavirus(es) present in common frog populations, in the context of a simple susceptible-infected (SI) model, using parameters derived from the literature. We explored the effects of disease-induced population decline on the dynamics of the ranavirus. We then extended the model to consider the infection dynamics in populations exposed to both ulcerative and hemorrhagic forms of the ranaviral disease. The preliminary investigation indicated the important interactions between the forms. When the ulcerative form was present in a population and the hemorrhagic form was later introduced, the hemorrhagic form of the disease needed to be highly contagious, to persist. We highlighted the areas where further research and experimental evidence is needed and hope that these models would act as a guide for further research into the amphibian disease dynamics.

Searching for unknown transfusion-transmitted hepatitis viruses: a binational cohort study of 1.5 million transfused patients

BACKGROUND

Both hepatitis B and C viruses were transmitted through blood transfusion before implementation of donor screening. The existence of additional, yet unknown transfusion transmittable agents causing liver disease could have important public health implications.

METHODS

Analyses were based on the Scandinavian Donations and Transfusions (SCANDAT2) database. Cox regression models were used to estimate the hazard ratio (HR) of developing chronic liver disease in recipients of blood from donors who later developed any chronic liver disease compared to recipients who received blood transfusion from healthy donors. We also studied whether the risk of liver disease was increased in patients who received units from 'high-risk' donors, defined as donors who had a higher than expected occurrence of liver disease amongst their previous recipients. All analyses were stratified before and after 1992 to account for the effect of screening for hepatitis C virus.

RESULTS

A total of 1 482 922 transfused patients were included in the analyses. Analyses showed evidence of transfusion transmission of liver diseases before, but not after the implementation of hepatitis C virus screening in 1992, with HRs for any liver disease of 1.38 [95% confidence interval (CI), 1.30-1.46] and 0.99 (95% CI, 0.91-1.07), before and after 1992, respectively. Similarly, blood components from 'high-risk' donors conferred increased risks before, but not after 1992.

CONCLUSIONS

Our data provide no evidence for transfusion transmission of agents causing liver disease after the implementation of screening for hepatitis B and C, and suggest that if such transmission does occur, it is rare.

Assessing the Epidemic Potential of RNA and DNA Viruses

Many new and emerging RNA and DNA viruses are zoonotic or have zoonotic origins in an animal reservoir that is usually mammalian and sometimes avian. Not all zoonotic viruses are transmissible (directly or by an arthropod vector) between human hosts. Virus genome sequence data provide the best evidence of transmission. Of human transmissible virus, 37 species have so far been restricted to self-limiting outbreaks. These viruses are priorities for surveillance because relatively minor changes in their epidemiologies can potentially lead to major changes in the threat they pose to public health. On the basis of comparisons across all recognized human viruses, we consider the characteristics of these priority viruses and assess the likelihood that they will further emerge in human populations. We also assess the likelihood that a virus that can infect humans but is not capable of transmission (directly or by a vector) between human hosts can acquire that capability.

Quantitative risk assessment of WSSV transmission through partial harvesting and transport practices for shrimp aquaculture in Mexico

This quantitative risk assessment provided an analytical framework to estimate white spot syndrome virus (WSSV) transmission risks in the following different scenarios: (1) partial harvest from rearing ponds and (2) post-harvest transportation, assuming that the introduction of contaminated water with viral particles into shrimp culture ponds is the main source of viral transmission risk. Probabilities of infecting shrimp with waterborne WSSV were obtained by approaching the functional form that best fits (likelihood ratio test) published data on the dose-response relationship for WSSV orally inoculated through water into shrimp. Expert opinion defined the ranges for the following uncertain factors: (1) the concentrations of WSSV in the water spilled from the vehicles transporting the infected shrimp, (2) the total volume of these spills, and (3) the dilution into culture ponds. Multiple scenarios were analysed, starting with a viral load (VL) of 1×10²mL^-1 in the contaminated water spilled that reached the culture pond, whose probability of infection of an individual shrimp (P_i) was negligible (1.7×10^-7). Increasing the VL to 1×10^4.5mL^-1 and 1×10⁷mL^-1 yielded results into very low (P_i=5.3×10^-5) and high risk (P_i=1.6×10^-2) categories, respectively. Furthermore, different pond stocking density (SD) scenarios (20 and 30 post-larvae [PL]/m²) were evaluated, and the probability of infection of at least one out of the total number of shrimp exposed (P_N) was derived; for the scenarios with a low VL (1×10²mL^-1), the P_N remained at a negligible risk level (P_N, 2.4×10^-7 to 1.8×10^-6). For most of the scenarios with the moderate VL (1×10^4.5mL^-1), the P_N scaled up to a low risk category (P_N, 1.1×10^-4 to 5.6×10^-4), whereas for the scenarios with a high VL (1×10⁷mL^-1), the risk levels were high (P_N, 2.3×10^-2 to 3.5×10^-2) or very high (P_N, 1.1×10^-1 to 1.6×10^-1) depending on the volume of contaminated water spilled in the culture pond (VCWSCP, 4 or 20L). In the sensitivity analysis, for a SD of 30 PL/m², it was shown that starting with a VL of 1×10⁵mL^-1 and a VCWSCP of 12L, the P_N was moderate (1.05×10^-3). This was the threshold for greater risks, given the increase in either the VCWSCP or VL. These findings supported recommendations to prevent WSSV spread through more controlled transportation and partial harvesting practices.

Susceptibility of a number of Australian freshwater fishes to dwarf gourami iridovirus (Infectious spleen and kidney necrosis virus)

Megalocytiviruses cause high mortality diseases that have seriously impacted aquaculture, with the most frequent outbreaks occurring in East and South-East Asia. The international trade of juvenile fish for food and ornamental aquaculture has aided the spread of these viruses, which have spread to Europe and Australia and other regions. Australian freshwater fishes were examined for susceptibility to infection with the exotic megalocytivirus, dwarf gourami iridovirus (DGIV), which belongs to a group with the type species, Infectious spleen and kidney necrosis virus (ISKNV). Fish were held at 23 ± 1 °C and challenged by intraperitoneal (IP) injection or by cohabitation with Murray cod, Maccullochella peelii (Mitchell) infected with DGIV. A species was deemed to be susceptible to DGIV based on evidence of viral replication, as determined by qPCR, and megalocytic inclusion bodies observed histologically. Horizontal transmission occurred between infected Murray cod and golden perch, Macquaria ambigua (Richardson), Macquarie perch, Macquaria australasica (Cuvier) and Murray cod. This indicated that DGIV shed from infected fish held at 23 °C can survive in fresh water and subsequently infect these naïve fish. Further, DGIV administered IP was highly pathogenic to golden perch, Macquarie perch and Murray cod. Compared to these species, the susceptibility of southern pygmy perch, Nannoperca australis (Gunther) was lower. Freshwater catfish (dewfish), Tandanus tandanus (Mitchell), were not susceptible under the experimental conditions based on the absence of clinical disease, mortality and virus replication. This study showed the potential risks associated with naïve and DGIV-infected fish sharing a common water source.

Experimental Transmission and Induction of Ranaviral Disease in Western Ornate Box Turtles (Terrapene ornata ornata) and Red-Eared Sliders (Trachemys scripta elegans)

An experimental transmission study was designed to determine whether a causal relationship exists between a Ranavirus (BSTRV) isolated from a Burmese star tortoise that died and the lesions observed in that tortoise. A pilot study was performed with 3 box turtles ( Terrapene ornata ornata) and 3 red-eared sliders (RESs; Trachemys scripta elegans) to assess their suitability in a larger study. Based on the outcome of this study, RESs were selected, and 2 groups of 4 RESs received either an oral (PO) or intramuscular (IM) inoculum containing105 50% Tissue Culture Infecting Dose (TCID50) of a BSTRV-infected cell lysate. One turtle each was mock inoculated PO or IM with the same volume of uninfected cell lysate. Three of four IM-inoculated RESs developed clinical signs (nasal and ocular discharge [3 of 3], oral plaques [1 of 3], conjunctivitis and hyphema [1 of 3] and extreme lethargy [3 of 3]). A Ranavirus was isolated from kidney homogenates of 3 euthanatized turtles; DNA sequences of a portion of the major capsid protein gene were amplified by polymerase chain reaction. Consistent histologic lesions were observed only in IM-inoculated turtles and included fibrinoid vasculitis centered on splenic ellipsoids, multifocal hepatic necrosis, and multicentric fibrin thrombi in a variety of locations, including hepatic sinusoids, glomerular capillary loops, and pulmonary capillaries. Virions compatible with Ranavirus were observed within necrotic cells of the spleen of 1 IM-inoculated turtle using transmission electron microscopy. This study fulfills Koch's postulates, confirming a causal relationship between BSTRV and the clinical and histologic changes in chelonians infected with this virus.

Mosquitoes as a Potential Vector of Ranavirus Transmission in Terrestrial Turtles

Ranaviruses are significant pathogens of amphibians, reptiles, and fishes, contributing to mass mortality events worldwide. Despite an increasing focus on ranavirus ecology, our understanding of ranavirus transmission, especially among reptilian hosts, remains limited. For example, experimental evidence for oral transmission of the virus in chelonians is mixed. Consequently, vector-borne transmission has been hypothesized in terrestrial turtle species. To test this hypothesis, mosquitoes captured during a 2012/2013 ranavirus outbreak in box turtles from southwestern Indiana were pooled by genus and tested for ranavirus DNA using qPCR. Two of 30 pools tested positive for ranavirus. Additionally, an individual Aedes sp. mosquito observed engorging on a box turtle also tested positive for ranavirus. Although our approach does not rule out the possibility that the sequenced ranavirus was simply from virus in bloodmeal, it does suggests that mosquitoes may be involved in virus transmission as a mechanical or biological vector among ectothermic vertebrates. While additional studies are needed to elucidate the exact role of mosquitoes in ranavirus ecology, our study suggests that a greater focus on vector-borne transmission may be necessary to fully understand ranaviral disease dynamics in herpetofauna.

Isolation and characterization of a ranavirus from koi, Cyprinus carpio L., experiencing mass mortalities in India

We investigated mass mortalities of koi, Cyprinus carpio Linnaeus, 1758, experienced in South Indian fish farms by virus isolation, electron microscopy, PCR detection, sequencing of capsid protein gene and transmission studies. Samples of moribund koi brought to the laboratory suffered continuous mortality exhibiting swimming abnormalities, intermittent surfacing and skin darkening. Irido-like virus was isolated from the infected fish in the indigenous snakehead kidney cell line (SNKD2a). Icosahedral virus particles of 100 to 120 nm were observed in the infected cell cultures, budding from the cell membrane. Virus transmission and pathogenicity studies revealed that horizontal transmission occurred associated with mortality. PCR analysis of infected fish and cell cultures confirmed the presence of Ranavirus capsid protein sequences. Sequence analysis of the major capsid protein gene showed an identity of 99.9% to that of largemouth bass virus isolated from North America. Detection and successful isolation of this viral agent becomes the first record of isolation of a virus resembling Santee-Cooper Ranavirus from a koi and from India. We propose the name koi ranavirus to this agent.

Detection and characterization of viruses of the genus Megalocytivirus in ornamental fish imported into an Australian border quarantine premises: an emerging risk to national biosecurity

This report documents an emerging trend of identification of Megalocytivirus-like inclusions in a range of ornamental fish species intercepted during quarantine detention at the Australian border. From September 2012 to February 2013, 5 species of fish that had suffered mortality levels in excess of 25% whilst in the post-entry quarantine and had Megalocytivirus-like inclusion bodies in histological sections were examined by PCR. The fish had been imported from Singapore, Malaysia and Sri Lanka. Ninety-seven of 111 individual fish from affected tanks of fish tested were positive for the presence of Megalocytivirus by PCR. Sequence analysis of representative PCR products revealed an identical sequence of 621 bp in all cases which was identical to a previously characterized Megalocytivirus (Sabah/RAA1/2012 strain BMGIV48). Phylogenetic analysis of available Megalocytivirus major capsid protein (MCP) sequences confirmed the existence of 3 major clades of Megalocytivirus. The virus detected in this study was identified as a member of Genotype II. The broad host range and pathogenicity of megalocytiviruses, coupled to the documented spread of ornamental fish into the environment, render this a significant and emerging biosecurity threat to Australia.

Oysters as hot spots for mimivirus isolation

Viruses are ubiquitous organisms, but their role in the ecosystem and their prevalence are still poorly understood. Mimiviruses are extremely complex and large DNA viruses. Although metagenomic studies have suggested that members of the family Mimiviridae are abundant in oceans, there is a lack of information about the association of mimiviruses with marine organisms. In this work, we demonstrate by molecular and virological methods that oysters are excellent sources for mimiviruses isolation. Our data not only provide new information about the biology of these viruses but also raise questions regarding the role of oyster consumption as a putative source of mimivirus infection in humans.

Transmission of lymphocystis disease virus to cultured gilthead seabream, Sparus aurata L., larvae

The transmission of lymphocystis disease virus (LCDV) to gilthead seabream, Sparus aurata L., larvae was investigated using fertilized eggs from a farm with previous reports of lymphocystis disease. LCDV genome was detected by PCR-hybridization in blood samples from 17.5% of the asymptomatic gilthead seabream broodstock analysed. Using the same methodology, eggs spawned from these animals were LCDV positive, as well as larvae hatched from them. The presence of infective viral particles was confirmed by cytopathic effects development on SAF-1 cells. Whole-mount in situ hybridization (ISH) and immunohistochemistry (IHC) showed the presence of LCDV in the epidermis of larvae hatched from LCDV-positive eggs. When fertilized eggs were disinfected with iodine, no viral DNA was detected either in eggs (analysed by PCR-hybridization) or in larvae (PCR-hybridization and ISH). These results suggest the vertical transmission of LCDV, the virus being transmitted on the egg surface. Larvae hatched from disinfected eggs remain LCDV negative during the endotrophic phase, as showed by PCR-hybridization, ISH and IHC. After feeding on LCDV-positive rotifers, viral antigens were observed in the digestive tract, which suggests that viral entry could be achieved via the alimentary canal, and that rotifers can act as a vector in LCDV transmission to gilthead seabream larvae.

Do wild fish species contribute to the transmission of koi herpesvirus to carp in hatchery ponds?

The koi herpesvirus (KHV) has spread worldwide since its discovery in 1998 and causes disease and mortality in koi and common carp populations with a high impact on the carp production industry. Many investigations have been conducted to examine ways of distribution and to identify possible transmission vectors. The answers, however, raise many new questions. In the present study, different wild fish species taken from carp ponds with a history of KHV infection were examined for their susceptibility to the virus. In the tissue of these fish, the virus load was determined and it was tested whether a release of the virus could be induced by stress and the virus then could be transferred to naive carp. Wild fish were gathered from carp ponds during acute outbreaks of virus-induced mortality in summer and from ponds stocked with carp carrying a latent KHV infection. From these ponds, wild fish were collected during the harvesting process in autumn or spring when the ponds were drained. We found that regardless of season, temperature variation, age and infection status of the carp stock, wild fish from carp ponds and its outlets could be tested positive for the KHV genome using real-time PCR with a low prevalence and virus load. Furthermore, virus transfer to naive carp was observed after a period of cohabitation. Cyprinid and non-cyprinid wild fish can therefore be considered as an epidemiological risk for pond carp farms.

A DNA virus of Drosophila

Little is known about the viruses infecting most species. Even in groups as well-studied as Drosophila, only a handful of viruses have been well-characterized. A viral metagenomic approach was used to explore viral diversity in 83 wild-caught Drosophila innubila, a mushroom feeding member of the quinaria group. A single fly that was injected with, and died from, Drosophila C Virus (DCV) was added to the sample as a control. Two-thirds of reads in the infected sample had DCV as the best BLAST hit, suggesting that the protocol developed is highly sensitive. In addition to the DCV hits, several sequences had Oryctes rhinoceros Nudivirus, a double-stranded DNA virus, as a best BLAST hit. The virus associated with these sequences was termed Drosophila innubila Nudivirus (DiNV). PCR screens of natural populations showed that DiNV was both common and widespread taxonomically and geographically. Electron microscopy confirms the presence of virions in fly fecal material similar in structure to other described Nudiviruses. In 2 species, D. innubila and D. falleni, the virus is associated with a severe (∼80-90%) loss of fecundity and significantly decreased lifespan.

Pathogen host switching in commercial trade with management recommendations

Global wildlife trade exacerbates the spread of nonindigenous species. Pathogens also move with hosts through trade and often are released into naïve populations with unpredictable outcomes. Amphibians are moved commercially for pets, food, bait, and biomedicine, and are an excellent model for studying how wildlife trade relates to pathogen pollution. Ranaviruses are amphibian pathogens associated with annual population die-offs; multiple strains of tiger salamander ranaviruses move through the bait trade in the western United States. Ranaviruses infect amphibians, reptiles, and fish and are of additional concern because they can switch hosts. Tiger salamanders are used as live bait for freshwater fishing and are a potential source for ranaviruses switching hosts from amphibians to fish. We experimentally injected largemouth bass with a bait trade tiger salamander ranavirus. Largemouth bass became infected but exhibited no signs of disease or mortality. Amphibian bait ranaviruses have the potential to switch hosts to infect fish, but fish may act as dead-end hosts or nonsymptomatic carriers, potentially spreading infection as a result of trade.

Iridovirus infections in finfish - critical review with emphasis on ranaviruses

Viruses in three genera of the family Iridoviridae (iridoviruses) affect finfish. Ranaviruses and megalocytiviruses are recently emerged pathogens. Both cause severe systemic disease, occur globally and affect a diversity of hosts. In contrast, lymphocystiviruses cause superficial lesions and rarely cause economic loss. The ranavirus epizootic haematopoietic necrosis virus (EHNV) from Australia was the first iridovirus to cause epizootic mortality in finfish. Like other ranaviruses, it lacks host specificity. A distinct but closely related virus, European catfish virus, occurs in finfish in Europe, while very similar ranaviruses occur in amphibians in Europe, Asia, Australia, North America and South America. These viruses can be distinguished from one another by conserved differences in the sequence of the major capsid protein gene, which informs policies of the World Organisation for Animal Health to minimize transboundary spread of these agents. However, limited epidemiological information and variations in disease expression create difficulties for design of sampling strategies for surveillance. There is still uncertainty surrounding the taxonomy of some putative ranaviruses such as Singapore grouper iridovirus and Santee-Cooper ranavirus, both of which cause serious disease in fish, and confusion continues with diseases caused by megalocytiviruses. In this review, aspects of the agents and diseases caused by ranaviruses are contrasted with those due to megalocytiviruses to promote accurate diagnosis and characterization of the agents responsible. Ranavirus epizootics in amphibians are also discussed because of possible links with finfish and common anthropogenic mechanisms of spread. The source of the global epizootic of disease caused by systemic iridoviruses in finfish and amphibians is uncertain, but three possibilities are discussed: trade in food fish, trade in ornamental fish, reptiles and amphibians and emergence from unknown reservoir hosts associated with environmental change.

Analysis of the entire genomes of torque teno midi virus variants in chimpanzees: infrequent cross-species infection between humans and chimpanzees

Humans are frequently infected with three anelloviruses which have circular DNA genomes of 3.6-3.9 kb [Torque teno virus (TTV)], 2.8-2.9 kb [Torque teno mini virus (TTMV)] and 3.2 kb [a recently discovered anellovirus named Torque teno midi virus (TTMDV)]. Unexpectedly, human TTMDV DNA was not detectable in any of 74 chimpanzees tested, although all but one tested positive for both human TTV and TTMV DNA. Using universal primers for anelloviruses, novel variants of TTMDV that are phylogenetically clearly separate from human TTMDV were identified from chimpanzees, and over the entire genome, three chimpanzee TTMDV variants differed by 17.9-20.3 % from each other and by 40.4-43.6 % from all 18 reported human TTMDVs. A newly developed PCR assay that uses chimpanzee TTMDV-specific primers revealed the high prevalence of chimpanzee TTMDV in chimpanzees (63/74, 85 %) but low prevalence in humans (1/100). While variants of TTV and TTMV from chimpanzees and humans were phylogenetically interspersed, those of TTMDV were monophyletic for each species, with sequence diversity of <33 and <20 % within the 18 human and three chimpanzee TTMDV variants, respectively. Maximum within-group divergence values for TTV and TTMV were 51 and 57 %, respectively; both of these values were substantially greater than the maximum divergence among TTMDV variants (44 %), consistent with a later evolutionary emergence of TTMDV. However, substantiation of this hypothesis will require further analysis of genetic diversity using an expanded dataset of TTMDV variants in humans and chimpanzees. Similarly, the underlying mechanism of observed infrequent cross-species infection of TTMDV between humans and chimpanzees deserves further analysis.

Amphibian commerce as a likely source of pathogen pollution

The commercial trade of wildlife occurs on a global scale. In addition to removing animals from their native populations, this trade may lead to the release and subsequent introduction of nonindigenous species and the pathogens they carry. Emerging infectious diseases, such as chytridiomycosis caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd), and ranaviral disease have spread with global trade in amphibians and are linked to amphibian declines and die-offs worldwide, which suggests that the commercial trade in amphibians may be a source of pathogen pollution. We screened tiger salamanders involved in the bait trade in the western United States for both ranaviruses and Bd with polymerase chain reaction and used oral reports from bait shops and ranavirus DNA sequences from infected bait salamanders to determine how these animals and their pathogens are moved geographically by commerce. In addition, we conducted 2 surveys of anglers to determine how often tiger salamanders are used as bait and how often they are released into fishing waters by anglers, and organized bait-shop surveys to determine whether tiger salamanders are released back into the wild after being housed in bait shops. Ranaviruses were detected in the tiger salamander bait trade in Arizona, Colorado, and New Mexico, and Bd was detected in Arizona bait shops. Ranaviruses were spread geographically through the bait trade. All tiger salamanders in the bait trade were collected from the wild, and in general they moved east to west and north to south, bringing with them their multiple ranavirus strains. Finally, 26-73% of anglers used tiger salamanders as fishing bait, 26-67% of anglers released tiger salamanders bought as bait into fishing waters, and 4% of bait shops released tiger salamanders back into the wild after they were housed in shops with infected animals. The tiger salamander bait trade in the western United States is a useful model for understanding the consequences of the unregulated anthropogenic movement of amphibians and their pathogens through trade.

Transmission dynamics of the amphibian ranavirus Ambystoma tigrinum virus

Transmission is central to pathogen fitness and strongly influences the impact of pathogens on host populations. Particularly important to transmission dynamics is the distinction between direct transmission requiring close physical contact (e.g. bumping, fighting, or coughing) and indirect transmission from environmental sources such as contaminated substrates. We present data from 4 experiments addressing the form, routes, and timing of transmission of Ambystoma tigrinum virus (ATV) among tiger salamanders Ambystoma tigrinum nebulosum. Our data suggest that ATV is efficiently transmitted by direct interactions between live animals (bumping, biting and cannibalism) as well as by necrophagy and indirectly via water and fomites. Determining which form of transmission is most important in nature is essential for understanding transmission at the population level. Our experiments also revealed an important temporal aspect of infectiousness: larval salamanders become infectious soon after exposure to ATV and their propensity to infect others increases with time. These results begin to clarify the mechanisms and dynamics of ATV transmission and lead to key questions that need to be addressed in future research.

Phylogenetic concordance analysis shows an emerging pathogen is novel and endemic

Distinguishing whether pathogens are novel or endemic is critical for controlling emerging infectious diseases, an increasing threat to wildlife and human health. To test the endemic vs. novel pathogen hypothesis, we present a unique analysis of intraspecific host-pathogen phylogenetic concordance of tiger salamanders and an emerging Ranavirus throughout Western North America. There is significant non-concordance of host and virus gene trees, suggesting pathogen novelty. However, non-concordance has likely resulted from virus introductions by human movement of infected salamanders. When human-associated viral introductions are excluded, host and virus gene trees are identical, strongly supporting coevolution and endemism. A laboratory experiment showed an introduced virus strain is significantly more virulent than endemic strains, likely due to artificial selection for high virulence. Thus, our analysis of intraspecific phylogenetic concordance revealed that human introduction of viruses is the mechanism underlying tree non-concordance and possibly disease emergence via artificial selection.

SEN virus co-infection among HCV-RNA-positive mothers, risk of transmission to the offspring and outcome of child infection during a 1-year follow-up

SEN is a newly discovered blood-transmissible virus. Among its variants, SENV-D and -H are most often associated with non-A, -E hepatitis. Very little is known about the risk of vertical transmission of the virus. By using polymerase chain reaction with specific primers for SENV-D and -H, we investigated the prevalence of SENV-H and -D infection, the transmission rate of SENV infection and clinical features of SENV-infected children in 89 hepatitis C virus (HCV)-positive human immunodeficiency virus type 1-negative mothers. SENV infection was found in 36 (40%) mothers, and SENV-D was more frequent than SENV-H infection (34/36, 94%vs 5/36, 14%, P < 0.01). No difference in SENV infection rates was found between injection drug user (IDU) mothers (17/51, 33%) and mothers with no risk for bloodborne infection (19/38, 50%, P = ns). SENV-H infection was found only in IDU mothers and mothers with HCV genotype1b. Both SENV-D and -H can be transmitted to the offspring with an overall rate of 47%. Vertical transmission of HCV does not facilitate SENV infection of the offspring. Among 17 SENV-infected children, none was co-infected with HCV. Maternal HCV genotype or viral load does not interfere with mother-to-infant transmission of SENV. Persistence of SENV infection was demonstrated in 100% of infected children after 1-year follow-up, but none had clinical evidence of liver disease.