Patterns of infection, origins, and transmission of ranaviruses among the ectothermic vertebrates of Asia

Abstract

Ranaviral infections, a malady of ectothermic vertebrates, are becoming frequent, severe, and widespread, causing mortality among both wild and cultured species, raising odds of species extinctions and economic losses. This increase in infection is possibly due to the broad host range of ranaviruses and the transmission of these pathogens through regional and international trade in Asia, where outbreaks have been increasingly reported over the past decade. Here, we focus attention on the origins, means of transmission, and patterns of spread of this infection within the region. Infections have been recorded in both cultured and wild populations in at least nine countries/administrative regions, together with mass die‐offs in some regions. Despite the imminent seriousness of the disease in Asia, surveillance efforts are still incipient. Some of the viral strains within Asia may transmit across host–taxon barriers, posing a significant risk to native species. Factors such as rising temperatures due to global climate change seem to exacerbate ranaviral activity, as most known outbreaks have been recorded during summer; however, data are still inadequate to verify this pattern for Asia. Import risk analysis, using protocols such as Pandora+, pre‐border pathogen screening, and effective biosecurity measures, can be used to mitigate introduction of ranaviruses to uninfected areas and curb transmission within Asia. Comprehensive surveillance using molecular diagnostic tools for ranavirus species and variants will help in understanding the prevalence and disease burden in the region. This is an important step toward conserving native biodiversity and safeguarding the aquaculture industry.

Prevalence of Ranavirus Infection in Three Anuran Species across South Korea

“…Among Asian countries, China has had the highest number of published studies, with 153 registered publications in the Web of Science database between 2010 and 2019 [ 10 ]. In addition to China, cases of ranavirus infection or mass die-offs due to ranavirus infection have been reported in eight Asian countries and regions, including Taiwan, Hong Kong, Japan, Korea, Thailand, Singapore, Malaysia, and India [ 16 ]. To date, ranavirus infection or mass mortality reports have been made for five amphibian species in South Korea, including larval Rana huanrenensis [ 17 ], adult R. uenoi [ 18 ], adult Kaloula borealis [ 19 ], larval P. chosenicus [ 12 ], and larval D. japonicus [ 19 ].…”

Climatic niche evolution of infectious diseases driving amphibian declines

“…Biodiversity hotspots and high-elevation areas with high amphibian diversity are especially vulnerable 47,48 . There is mounting evidence that species popular for frog aquaculture, such as the American bullfrog ( Lithobates catesbeianus ) and the Pig frog (L. grylio ) imported from North America to Asia, may have acted as reservoir hosts for ranavirus strains 49 . SPI outbreaks are causing mass mortalities of tadpoles across the United States since the pathogen was first detected in 1999 18 and are likely distributed throughout much of the Nearctic region 18 .…”

First Report of Endemic Frog Virus 3 (FV3)-like Ranaviruses in the Korean Clawed Salamander (Onychodactylus koreanus) in Asia

“…Ranavirus infection is one of the wellknown causes of the global decline of the amphibian population [2,[4][5][6]. Outbreaks of ranaviruses in amphibians have occurred worldwide, including in the United States of America (USA), Canada, Republic of Korea (ROK), Japan, China, and many countries (such as the United Kingdom (UK), Germany, France, Brazil, and Chile) in Europe and South America [7,8]. The World Organization for Animal Health (OIE) has designated ranaviruses as notifiable diseases in amphibians [9].…”