Is Chytridiomycosis an Emerging Infectious Disease in Asia?

Abstract

The disease chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd), has caused dramatic amphibian population declines and extinctions in Australia, Central and North America, and Europe. Bd is associated with >200 species extinctions of amphibians, but not all species that become infected are susceptible to the disease. Specifically, Bd has rapidly emerged in some areas of the world, such as in Australia, USA, and throughout Central and South America, causing population and species collapse. The mechanism behind the rapid global emergence of the disease is poorly understood, in part due to an incomplete picture of the global distribution of Bd. At present, there is a considerable amount of geographic bias in survey effort for Bd, with Asia being the most neglected continent. To date, Bd surveys have been published for few Asian countries, and infected amphibians have been reported only from Indonesia, South Korea, China and Japan. Thus far, there have been no substantiated reports of enigmatic or suspected disease-caused population declines of the kind that has been attributed to Bd in other areas. In order to gain a more detailed picture of the distribution of Bd in Asia, we undertook a widespread, opportunistic survey of over 3,000 amphibians for Bd throughout Asia and adjoining Papua New Guinea. Survey sites spanned 15 countries, approximately 36° latitude, 111° longitude, and over 2000 m in elevation. Bd prevalence was very low throughout our survey area (2.35% overall) and infected animals were not clumped as would be expected in epizootic events. This suggests that Bd is either newly emerging in Asia, endemic at low prevalence, or that some other ecological factor is preventing Bd from fully invading Asian amphibians. The current observed pattern in Asia differs from that in many other parts of the world.

First survey for the amphibian chytrid fungus Batrachochytrium dendrobatidis in Connecticut (USA) finds widespread prevalence

“…In another region similarly persisting with Bd and asymptomatic individuals, the average Bd prevalence was high (0.83 of post-metamorphic individuals), and the average Bd load ranged between 4 and 3861 zoospores (mean = 514; Puschendorf et al 2011). These studies report both a greater infection prevalence and higher average zoospore load than that found in CT. Of other surveys for Bd done elsewhere in the world (95% CI range reported here, except where noted), , and 0.02−0.03 of all sampled individuals were found to be Bd-positive in Gabon, Peninsular Malaysia, Panama (El Cope), southeastern Brazil, and among 15 Asian countries, respectively (Lips et al 2006, Bell et al 2011, Savage et al 2011, Swei et al 2011, Gründler et al 2012). While our reported prevalence does not mirror the upper limit measured during a dieoff in Panama (Lips et al 2006) or levels measured at other persistent regions (California, Briggs et al 2010;Australia, Puschendorf et al 2011), a prevalence of 0.28 is moderate and within previously detected ranges.…”

Filling a gap in the distribution of Batrachochytrium dendrobatidis: evidence in amphibians from northern China

“…Moreover, recognizing species or populations susceptible to chytridiomycosis is essential to inform amphibian conservation management (Bletz et al 2015). Thus, central and northern Asia remain as the greatest gaps in the knowledge of the global distribution of Bd (Swei et al 2011, Olson & Ronnenberg. 2014.…”

“…1). All 8 positive individuals were collected from 2 sites in the Irtysh River Basin, extending by nearly 500 km the northern known distribution of Bd in Asia (Swei et al 2011). The Irtysh River flows from the Altai Mountains on the Mongolian−Chinese border, northwest to Ka zakh stan, and extends far north across Russia.…”

“…Bd infects at least 695 species of amphibians (anurans, salamanders, and caecilians) from all continents where they exist and has been implicated in the enigmatic disappearance of many frog species in Australia, Europe, and North, Central, and South America (Berger et al 1998, Lips et al 2006, Walker et al 2008, Vredenburg et al 2010, Cheng et al 2011, Soto-Azat et al 2013, Olson & Ronnenberg 2014. However, negative impacts at the population level on other regions where Bd exists, such as Asia and Africa, have not been recorded (Kusrini et al 2008, Goka et al 2009, Yang et al 2009, Bai et al 2010, Soto-Azat et al 2010, Savage et al 2011, Swei et al 2011. One possible explanation is that Bd is endemic in some areas but novel in others (Rosenblum et al 2013).…”

“…In Asia, Bd has been described infecting wild and captive amphibians from many countries, including China, Japan, South Korea, Indonesia, Malaysia, Laos, Philippines, Sri Lanka, Kyrgyzstan, Vietnam, and India (Kusrini et al 2008, Une et al 2008, Goka et al 2009, Yang et al 2009, Bai et al 2010, Savage et al 2011, Swei et al 2011, Bataille et al 2013, Dahanukar et al 2013, Zhu et al 2014a). Nevertheless, extensive areas of central, northern, and western mainland Asia still lack information on the presence and impacts of Bd (Olson et al 2013, Olson & Ronnenberg 2014.…”