Thomas B. Waltzek

Genome Sequences of Three Koi Herpesvirus Isolates Representing the Expanding Distribution of an Emerging Disease Threatening Koi and Common Carp Worldwide

ABSTRACT Since the mid-1990s, lethal infections of koi herpesvirus (KHV) have been spreading, threatening the worldwide production of common carp and koi (both Cyprinus carpio). The complete genome sequences of three KHV strains from Japan, the United States, and Israel revealed a 295-kbp genome containing a 22-kbp terminal direct repeat. The finding that 15 KHV genes have clear homologs in the distantly related channel catfish virus (ictalurid herpesvirus 1) confirms the proposed place of KHV in the family Herpesviridae, specifically in the branch with fish and amphibian hosts. KHV thus has the largest genome reported to date for this family. The three strains were interpreted as having arisen from a wild-type parent encoding 156 unique protein-coding genes, 8 of which are duplicated in the terminal repeat. In each strain, four to seven genes from among a set of nine are fragmented by frameshifts likely to render the encoded proteins nonfunctional. Six of the affected genes encode predicted membrane glycoproteins. Frameshifts or other mutations close to the 3′ ends of coding sequences were identified in a further six genes. The conclusion that at least some of these mutations occurred in vivo prompts the hypothesis that loss of gene functions might be associated with emergence of the disease and provides a basis for further investigations into the molecular epidemiology of the virus.

Cetacean Morbillivirus: Current Knowledge and Future Directions

We review the molecular and epidemiological characteristics of cetacean morbillivirus (CeMV) and the diagnosis and pathogenesis of associated disease, with six different strains detected in cetaceans worldwide. CeMV has caused epidemics with high mortality in odontocetes in Europe, the USA and Australia. It represents a distinct species within the Morbillivirus genus. Although most CeMV strains are phylogenetically closely related, recent data indicate that morbilliviruses recovered from Indo-Pacific bottlenose dolphins (Tursiops aduncus), from Western Australia, and a Guiana dolphin (Sotalia guianensis), from Brazil, are divergent. The signaling lymphocyte activation molecule (SLAM) cell receptor for CeMV has been characterized in cetaceans. It shares higher amino acid identity with the ruminant SLAM than with the receptors of carnivores or humans, reflecting the evolutionary history of these mammalian taxa. In Delphinidae, three amino acid substitutions may result in a higher affinity for the virus. Infection is diagnosed by histology, immunohistochemistry, virus isolation, RT-PCR, and serology. Classical CeMV-associated lesions include bronchointerstitial pneumonia, encephalitis, syncytia, and lymphoid depletion associated with immunosuppression. Cetaceans that survive the acute disease may develop fatal secondary infections and chronic encephalitis. Endemically infected, gregarious odontocetes probably serve as reservoirs and vectors. Transmission likely occurs through the inhalation of aerosolized virus but mother to fetus transmission was also reported.

Do habitat shifts drive diversification in teleost fishes? An example from the pufferfishes (Tetraodontidae)

Habitat shifts are implicated as the cause of many vertebrate radiations, yet relatively few empirical studies quantify patterns of diversification following colonization of new habitats in fishes. The pufferfishes (family Tetraodon‐tidae) occur in several habitats, including coral reefs and freshwater, which are thought to provide ecological opportunity for adaptive radiation, and thus provide a unique system for testing the hypothesis that shifts to new habitats alter diversification rates. To test this hypothesis, we sequenced eight genes for 96 species of pufferfishes and closely related porcupine fishes, and added 19 species from sequences available in GenBank. We time‐calibrated the molecular phylogeny using three fossils, and performed several comparative analyses to test whether colonization of novel habitats led to shifts in the rate of speciation and body size evolution, central predictions of clades experiencing ecological adaptive radiation. Colonization of freshwater is associated with lower rates of cladogenesis in pufferfishes, although these lineages also exhibit accelerated rates of body size evolution. Increased rates of cladogenesis are associated with transitions to coral reefs, but reef lineages surprisingly exhibit significantly lower rates of body size evolution. These results suggest that ecological opportunity afforded by novel habitats may be limited for pufferfishes due to competition with other species, constraints relating to pufferfish life history and trophic ecology, and other factors.

Ranavirus: past, present and future

Emerging infectious diseases are a significant threat to global biodiversity. While historically overlooked, a group of iridoviruses in the genus Ranavirus has been responsible for die-offs in captive and wild amphibian, reptile and fish populations around the globe over the past two decades. In order to share contemporary information on ranaviruses and identify critical research directions, the First International Symposium on Ranaviruses was held in July 2011 in Minneapolis, MN, USA. Twenty-three scientists and veterinarians from nine countries examined the ecology and evolution of ranavirus–host interactions, potential reservoirs, transmission dynamics, as well as immunological and histopathological responses to infection. In addition, speakers discussed possible mechanisms for die-offs, and conservation strategies to control outbreaks.

Marine mammal zoonoses: a review of disease manifestations.

Marine mammals evoke strong public affection as well as considerable scientific interest. However, the resultant close contact with marine wildlife poses human health risks, including traumatic injury and zoonotic disease transmission. The majority of zoonotic marine mammal diseases result in localized skin infections in man that resolve spontaneously or with appropriate medical therapy. However, other marine mammal zoonoses, if left untreated, induce life‐threatening systemic diseases that could pose public health risks. As the number of zoonotic diseases rises, the diagnosis of and treatment for these emerging pathogens pose special challenges requiring the expertise of physicians, veterinarians and wildlife biologists. Here, we provide a comprehensive review of the bacterial, viral and fungal marine mammal zoonotic diseases that we hope will be utilized by public health professionals, physicians, veterinarians and wildlife biologists to better understand, diagnose and prevent marine mammal zoonotic diseases.

Metagenomic identification of a novel anellovirus in Pacific harbor seal (Phoca vitulina richardsii) lung samples and its detection in samples from multiple years.

To investigate viral pathogens potentially involved in a mortality event of 21 Pacific harbor seals (Phoca vitulina richardsii) in California in 2000, viral metagenomics was performed directly on lung samples from five individuals. Metagenomics revealed a novel seal anellovirus (SealAV), which clusters phylogenetically with anelloviruses from California sea lions and domestic cats. Using specific PCR, SealAV was identified in lung tissue from two of five animals involved in the 2000 mortality event, as well as one of 20 harbor seal samples examined post-mortem in 2008. The identification of SealAV in multiple years demonstrates that this virus is persistent in the harbor seal population. SealAV is the second anellovirus reported in the lungs of pinnipeds, suggesting that anellovirus infections may be common amongst marine mammals and that more research is needed to understand the roles of these viruses in marine mammal health and disease.

Distribution and Host Range of Ranaviruses

Ranaviruses are globally distributed pathogens in amphibian, fish, and reptile communities that appear to be emerging. Cases of ranavirus infection or disease have been confirmed in at least 105 amphibian species (18 families), 41 fish species (22 families), and 29 reptile species (12 families). Ranaviruses have been documented on all continents except Antarctica, and are frequently associated with mass die-offs. Host susceptibility differs among species, with some species harboring subclinical infections and likely serving as reservoirs for the virus, and other highly susceptible species amplifying the virus. Currently, there are six recognized species of ranavirus, and all are not equally pathogenic among hosts. Frog virus 3 (FV3) is the type species of the genus Ranavirus, and appears to be the most globally distributed species infecting ectothermic taxonomic across three vertebrate classes. International commerce involving subclinically infected ectothermic vertebrates undoubtedly has contributed to the global distribution and emergence of ranaviruses. Herein, we describe the global distributed species infecting ectothermic vertebrates across three taxonomic classes.

Transmission of Ranavirus between Ectothermic Vertebrate Hosts

Transmission is an essential process that contributes to the survival of pathogens. Ranaviruses are known to infect different classes of lower vertebrates including amphibians, fishes and reptiles. Differences in the likelihood of infection among ectothermic vertebrate hosts could explain the successful yearlong persistence of ranaviruses in aquatic environments. The goal of this study was to determine if transmission of a Frog Virus 3 (FV3)-like ranavirus was possible among three species from different ectothermic vertebrate classes: Cope’s gray treefrog (Hyla chrysoscelis) larvae, mosquito fish (Gambusia affinis), and red-eared slider (Trachemys scripta elegans). We housed individuals previously exposed to the FV3-like ranavirus with naïve (unexposed) individuals in containers divided by plastic mesh screen to permit water flow between subjects. Our results showed that infected gray treefrog larvae were capable of transmitting ranavirus to naïve larval conspecifics and turtles (60% and 30% infection, respectively), but not to fish. Also, infected turtles and fish transmitted ranavirus to 50% and 10% of the naïve gray treefrog larvae, respectively. Nearly all infected amphibians experienced mortality, whereas infected turtles and fish did not die. Our results demonstrate that ranavirus can be transmitted through water among ectothermic vertebrate classes, which has not been reported previously. Moreover, fish and reptiles might serve as reservoirs for ranavirus given their ability to live with subclinical infections. Subclinical infections of ranavirus in fish and aquatic turtles could contribute to the pathogen’s persistence, especially when highly susceptible hosts like amphibians are absent as a result of seasonal fluctuations in relative abundance.

Ranaviruses: not just for frogs.

Ranaviruses (family Iridoviridae) were discovered serendipitously during an attempt to generate frog kidney cell cultures for the propagation of Lucke herpesvirus, an oncogenic herpesvirus [1]. Unexpectedly, some cultures displayed spontaneous cytopathic effect suggestive of a viral infection. Frog virus (FV)-1 and -2 were recovered from normal kidneys, whereas FV3, isolated from a frog with renal carcinoma, became the focus of further study. A number of “intriguing” features, i.e., a highly methylated genome, ability to rapidly turn-off host macromolecular synthesis, a circularly permuted/terminally redundant genome, the use of both host- and virus-encoded RNA polymerases, and absence of polyadenylated mRNA [2], fueled early FV3 study and provided insight into a poorly characterized family of nuclear, cytoplasmic, large DNA-containing viruses. However, because ranaviruses were not pathogenic for humans or commercially important animals, were not, as originally thought, oncogenic, and did not appear to have adverse long-term impacts on wildlife, FV3 research remained a viral backwater. Recent years have seen renewed interest in ranaviruses and other iridoviruses because they have been increasingly linked to die-offs, often marked, among cultured and wild fish, amphibians, and reptiles. Here, we review ranavirus replication and gene function, then focus on their impact on cold-blooded vertebrates.

Isolation and characterization of H3N8 equine influenza A virus associated with the 2011 epizootic in Mongolia

Equine influenza virus (EIV) epizootics affect 2·1 million Mongolian horses approximately every 10 years and critically impact economy and nomadic livelihood of Mongolia.