Batrachochytrium dendrobatidis detected in Kihansi spray toads at a captive breeding facility (Kihansi, Tanzania)

Abstract

The chytrid fungus Batrachochytrium dendrobatidis (Bd) is the aetiological agent of amphibian chytridiomycosis, a disease associated with global amphibian population declines. In November 2012, mass mortalities of Kihansi spray toads Nectophrynoides asperginis were observed at the Kihansi captive breeding facility, located in the Udzungwa Mountains, Tanzania. Mortalities increased rapidly, and dead toads showed typical clinical signs of chytridiomycosis, including reddening of the skin that was especially evident on the toe pads. Treatment of toads with itraconazole rapidly reduced mortalities. Dead toads (n = 49) were collected and used to perform Bd-specific polymerase chain reaction and subsequent nucleotide sequencing. All toads collected at the facility were positive for Bd. The obtained Bd 5.8S rRNA gene and flanking internal transcribed spacer regions (ITS1 and ITS2) were not 100% identical to any other Bd sequences in GenBank, but closely resembled isolates from Ecuador, Japan, USA, Brazil, Korea, and South Africa. To our knowledge, this is the first study reporting molecular characteristics of Bd isolated from the Udzungwa Mountains. Strict biosecurity measures at the breeding facility and in Kihansi spray wetlands where toads have been reintroduced have been implemented. Further studies on Bd epidemiology in the Udzungwa Mountains are recommended in order to understand its origin, prevalence, and molecular characteristics in wild amphibian populations. This will be important for conservation of several endemic amphibian species in the Udzungwa Mountains, which are part of the Eastern Arc Mountains, a global biodiversity hotspot.

Disease driven extinction in the wild of the Kihansi spray toad,Nectophrynoides asperginis

“…Our results show that B. dendrobatidis is likely to persist in Kihansi Gorge in other amphibian species; it was detected even more recently in Phrynobatrachus mababiensis from below the gorge (Makange et al 2014). Sympatric amphibian species can act as reservoir hosts of B. dendrobatidis and transmit the pathogen to any repatriated spray toads.…”

“…In addition to the epidemic mortality seen in the wild, all of the spray toads in a single enclosure in the Wildlife Conservation Society's Bronx Zoo died from a chytridiomycosis outbreak following an incursion of B. dendrobatidis (McAloose et al 2008). The species' high susceptibility to chytridiomycosis was further demonstrated when 62% of the captive breeding facility population in Kihansi died of the disease in under seven weeks following incursion of B. dendrobatidis despite daily removal of carcases and antifungal treatment (Makange et al 2014).…”

Manipulating water for amphibian conservation

“…2006), chytridiomycosis ( Batrachochytrium dendrobatidis ) (Makange et al. 2014), and trophic shifts within the spray zone that reduced arthropod prey availability (Zilihona et al. 1998).…”

“…Failure of the interventions to stabilize the population was likely due to a combination of effects, including a reduction in the intensity and area of sprayed habitat, movement of safari ants (Dorylus sp.) into the drier areas (Channing et al 2006), chytridiomycosis (Batrachochytrium dendrobatidis) (Makange et al 2014), and trophic shifts within the spray zone that reduced arthropod prey availability (Zilihona et al 1998).…”

Amphibian chytrid fungus in Africa – realigning hypotheses and the research paradigm

“…A notable exception is the Kihansi Spray Toad Nectophrynoides asperginis that was driven to extinction in the wild in Tanzania during a rapid Bd epidemic wave (Weldon et al , ). The susceptibility of this species to lethal Bd infection has repeatedly been demonstrated in captive populations (McAloose et al , ; Makange et al , ). Although mass mortalities of the Lake Clawed Oku frog Xenopus longipes in Cameroon have been observed, Bd was ruled out as a causative factor (Doherty‐Bone et al , ).…”