Meteorological factors affecting seroconversion of Akabane disease in sentinel calves in the subtropical Okinawa Islands of Japan.

Akabane virus, the pathogen-causing Akabane disease, is an arthropod-borne virus (arbovirus) transmitted by the Culicoides biting midge. A nationwide serological surveillance program for bovine arboviral diseases, including Akabane disease, has been established in Japan to monitor the circulation of arboviruses by targeting sentinel calves. Okinawa, which is located in the southwestern-most region of Japan, is a high-risk area for incursion of arboviruses. The aim of the present study was to identify the meteorological factors related to farm-level seroconversion of Akabane virus by analyzing the serological surveillance data for sentinel calves collected in Okinawa between 2007 and 2015. Rainfall in winter, spring, and autumn was positively associated with seroconversion. Adequate rainfall seems to keep the soil in a suitably moist state for growth and survival of biting midges. Maximum temperature in winter was also positively associated with seroconversion in sentinel calves. The warmer temperatures in winter may provide conditions suitable for shortening the larval development cycle and increase production of adult midges. Our findings indicate that meteorological factors such as temperature and rainfall may be important factors that produce circumstances conducive to effective transmission of the virus between vectors and the host. The results of this study provide a better understanding of the circulation of arboviruses and offer suggestions for developing better surveillance and measures to prevent arboviral disease.

Four Myxobolus spp. (Myxosporea: Bivalvulida) from the gill lamellae of common carp (Cyprinus carpio) and Japanese silver crucian carp (Carassius langsdorfii) in the western part of Japan, with the description of three new species (M. tanakai n. sp., M. paratoyamai n. sp., and M. ginbuna n. sp.).

Approximately three dozen Myxobolus spp. (Myxozoa: Myxosporea: Bivalvulida) have been described to parasitize the gills of carp of the genera Cyprinus and Carassius. Hitherto, these fish were often introduced to temperate waters worldwide as food and ornamental fish from Asia, their place of origin. The present study examined the myxosporean infection of seven common carp (Cyprinus carpio) and seven Japanese silver crucian carp (Carassius langsdorfii) collected from the Fushinogawa River around the university in Yamaguchi City, Japan, during the period April 2015 to October 2016. In total, four Myxobolus spp. were detected in the gill lamellae of Cy. carpio and Ca. langsdorfii, i.e., two species in each species of fish. The four species were characterized morphologically and genetically based on the 18S ribosomal RNA gene (rDNA). A new species, Myxobolus tanakai n. sp., from four individuals of Cy. carpio had an elongated pyriform spore (15.4-18.6 µm by 6.3-8.4 µm), resembling the spore shape of Myxobolus koi from Cy. carpio or Carassius auratus in Japan, China, and the USA, but bigger than it (13.2-15.6 µm by 6.6-7.8 µm). The new species formed a clade with M. koi but was distinct from any of the isolates of this species (nucleotide identities less than 98.6%). The second new species, Myxobolus paratoyamai n. sp., from a single Cy. carpio with its one prominent and one rudimentary polar capsule closely resembled the spore morphology of Myxobolus toyamai from Cy. carpio or Carassius gibelio in Japan, China, and the USA. However, the isolate formed a clade with Myxobolus longisporus from Cy. rubrofuscus in China rather than with M. toyamai isolates (nucleotide identities less than 97.9% with known species). Another new species, Myxobolus ginbuna n. sp., from two individuals of Ca. langsdorfii had similar-shaped spores to Myxobolus wulii, but the dimensions were smaller (11.7-13.9 µm by 8.5-9.8 µm vs. 17.6-18.5 µm by 8.9-10.0 µm). This new species formed a clade with M. wulii but was distinct from any of the M. wulii isolates from Ca. gibelio in China (nucleotide identities less than 99.1%). An additional species, Myxobolus pyramidis, from six individuals of Ca. langsdorfii was morphologically and genetically similar to the previous record from Ca. gibelio in China (99.6% nucleotide identity of the 18S rDNA). Two of these six individuals were mix-infected with M. ginbuna n. sp. This is a new host and geographical distribution record for M. pyramidis.

Three Unicapsula species (Myxosporea: Trilosporidae) of Asian marine fishes, including the description of Unicapsula setoensis n. sp. in the yellowfin goby (Acanthogobius flavimanus) from the Inland Sea of Japan.

The myxosporean genus Unicapsula (Multivalvulida: Trilosporidae) is defined as having a spore with three unequal shell valves and polar capsules, of which one is prominent and the two other polar capsules are rudimentary. Genetic characterization of members of the genus, currently 11 nominal species, is, at present, unsatisfactory yet when comparing to the closely related genus Kudoa (Multivalvulida: Kudoidae). In the present study, we characterized long ribosomal RNA gene (rDNA) sequences of three Unicapsula spp., namely Unicapsula pyramidata, Unicapsula seriolae, and a novel myxosporean species, Unicapsula setoensis n. sp., from Asian fishes. Elongated plasmodia of U. pyramidata were found in the trunk muscle of Japanese threadfin breams, Nemipterus japonicus, fished off northern Vietnam in the South China Sea. Semitriangular spores, 5.5-6.4 µm in length and 5.6-9.6 µm in width, consisted of three shell valves with two caudal appendages, 7.2-7.4 µm in length. One prominent polar capsule, 2.0-2.4 µm in diameter, was located in the apical shell valve and two rudimentary polar capsules, 0.4-0.5 µm in diameter, in each caudal shell valve. Elongated plasmodia of U. seriolae were found in the trunk muscle of a greater yellowtail, Seriola dumerili, aquacultured in Japan. Semispherical spores, 5.9-7.4 µm in length and 6.3-7.4 µm in width, also consisted of three shell valves and one prominent polar capsule, 3.4-3.8 µm in diameter, with two rudimentary polar capsules, 0.7-1.0 µm in diameter. Plasmodia of U. setoensis n. sp. were found in the trunk muscle of yellowfin gobies, Acanthogobius flavimanus, fished off Hofu, Yamaguchi Prefecture, in the Inland Sea of Japan. Semispherical spores, 5.6-6.9 µm in diameter, displayed three shell valves and one prominent and two rudimentary polar capsules. The former functional polar capsule was 1.9-2.5 µm in diameter and extruded a 9.4-13.8-µm-long polar filament. Nearly the whole length of the 18S rDNA and more than 2,200 bp of the 28S rDNA of the three Unicapsula spp. were sequenced along with nucleotide sequences of the 5.8S rDNA and internal transcribed spacer-1 and spacer-2 of U. pyramidata and U. setoensis n. sp. Molecular genetic analyses supported the morphological species differentiation of U. pyramidata and U. seriolae, and the distinctness of U. setoensis n. sp. from hitherto known species.

Complete Genome Sequence of a Genotype 3 Atypical Porcine Pestivirus Strain (OKN/2021) from Okinawa Prefecture, Japan.

We report the complete genome sequence of atypical porcine pestivirus (APPV) OKN/2021, which was sampled in the Okinawa Prefecture, Japan. The sequence bears the closest resemblance to another previously detected Japanese genotype 3 APPV sequence. This genome sequencing will help researchers in Japan learn more about the virus epidemiology and evolutionary characteristics.