Connie Adriaensen

Recent introduction of a chytrid fungus endangers Western Palearctic salamanders

A new, yet old, threat to amphibians Globally, populations of amphibians have been severely affected by a disease caused by the fungus Batrachochytrium dendrobatidis. Recently, some European salamander populations were decimated by the emergence of a new, related chytrid fungus, B. salamandrivorans. Martel et al. screened amphibians across continents. This newly emerging threat seems to have originated in Asia and traveled to Europe with salamanders transported as part of the pet trade. Asian salamanders have evolved resistance to the pathogen, but salamanders from other parts of the world are highly susceptible. Science, this issue p. 630 A new fungal disease from Asia threatens salamanders in Europe, the Middle East, and North Africa. Emerging infectious diseases are reducing biodiversity on a global scale. Recently, the emergence of the chytrid fungus Batrachochytrium salamandrivorans resulted in rapid declines in populations of European fire salamanders. Here, we screened more than 5000 amphibians from across four continents and combined experimental assessment of pathogenicity with phylogenetic methods to estimate the threat that this infection poses to amphibian diversity. Results show that B. salamandrivorans is restricted to, but highly pathogenic for, salamanders and newts (Urodela). The pathogen likely originated and remained in coexistence with a clade of salamander hosts for millions of years in Asia. As a result of globalization and lack of biosecurity, it has recently been introduced into naïve European amphibian populations, where it is currently causing biodiversity loss.

Drivers of salamander extirpation mediated by Batrachochytrium salamandrivorans

The recent arrival of Batrachochytrium salamandrivorans in Europe was followed by rapid expansion of its geographical distribution and host range, confirming the unprecedented threat that this chytrid fungus poses to western Palaearctic amphibians. Mitigating this hazard requires a thorough understanding of the pathogen’s disease ecology that is driving the extinction process. Here, we monitored infection, disease and host population dynamics in a Belgian fire salamander (Salamandra salamandra) population for two years immediately after the first signs of infection. We show that arrival of this chytrid is associated with rapid population collapse without any sign of recovery, largely due to lack of increased resistance in the surviving salamanders and a demographic shift that prevents compensation for mortality. The pathogen adopts a dual transmission strategy, with environmentally resistant non-motile spores in addition to the motile spores identified in its sister species B. dendrobatidis. The fungus retains its virulence not only in water and soil, but also in anurans and less susceptible urodelan species that function as infection reservoirs. The combined characteristics of the disease ecology suggest that further expansion of this fungus will behave as a ‘perfect storm’ that is able to rapidly extirpate highly susceptible salamander populations across Europe.

Resistance to Chytridiomycosis in European Plethodontid Salamanders of the Genus Speleomantes

North America and the neotropics harbor nearly all species of plethodontid salamanders. In contrast, this family of caudate amphibians is represented in Europe and Asia by two genera, Speleomantes and Karsenia, which are confined to small geographic ranges. Compared to neotropical and North American plethodontids, mortality attributed to chytridiomycosis caused by Batrachochytrium dendrobatidis (Bd) has not been reported for European plethodontids, despite the established presence of Bd in their geographic distribution. We determined the extent to which Bd is present in populations of all eight species of European Speleomantes and show that Bd was undetectable in 921 skin swabs. We then compared the susceptibility of one of these species, Speleomantes strinatii, to experimental infection with a highly virulent isolate of Bd (BdGPL), and compared this to the susceptible species Alytes muletensis. Whereas the inoculated A. muletensis developed increasing Bd-loads over a 4-week period, none of five exposed S. strinatii were colonized by Bd beyond 2 weeks post inoculation. Finally, we determined the extent to which skin secretions of Speleomantes species are capable of killing Bd. Skin secretions of seven Speleomantes species showed pronounced killing activity against Bd over 24 hours. In conclusion, the absence of Bd in Speleomantes combined with resistance to experimental chytridiomycosis and highly efficient skin defenses indicate that the genus Speleomantes is a taxon unlikely to decline due to Bd.

A live Salmonella enterica serovar Enteritidis vaccine allows serological differentiation between vaccinated and infected animals.

ABSTRACT Three precisely defined deletion mutants of Salmonella enterica serovar Enteritidis were constructed, a guanine auxotrophic ΔguaB mutant, a nonflagellated ΔfliC mutant, and an auxotrophic and nonflagellated ΔguaB ΔfliC double mutant. All three mutants were less invasive than the wild-type strain in primary chicken cecal epithelial cells and the human epithelial cell line T84 and less efficiently internalized in the chicken macrophage cell line HD11. The ΔfliC mutant was pathogenic in orally infected BALB/c mice, while the ΔguaB mutant was attenuated and conferred protection against a challenge with the pathogenic parent strain. The ΔguaB ΔfliC double mutant was totally asymptomatic and conferred better protection than the ΔguaB mutant. This indicates that the major flagellar protein flagellin is not required for efficient vaccination of BALB/c mice against Salmonella infection. The ΔguaB ΔfliC mutant was also safe for vaccination of 1-day-old chickens. After two immunizations, it induced statistically significant protection against infection of the internal organs of the birds by a virulent S. enterica serovar Enteritidis challenge strain but not against intestinal colonization. These data demonstrate that nonflagellated attenuated Salmonella mutants can be used as marker vaccines.

The Absence of Zoonotic Agents in Invasive Bullfrogs (Lithobates catesbeianus) in Belgium and The Netherlands

Exotic invasive bullfrogs (Lithobates catesbeianus) are considered to exert a considerable negative impact on native amphibian communities. This can be due to competition and predation, but they are also a notorious source of the infectious diseases chytridiomycosis and ranavirosis, affecting amphibian populations globally. Little is known regarding their carriage of other microbial agents that might be transferred to humans or other animals. In this study we determined the occurrence of the amphibian pathogens Ranavirus and Batrachochytrium dendrobatidis and of the zoonotic agents Coxiella burnetii, Neospora caninum, Leptospira sp., Toxoplasma gondii, Mycoplasma sp., Campylobacter sp., Salmonella sp. and extended-spectrum beta-lactamase producing Escherichia coli in 164 bullfrogs from three populations in Belgium and The Netherlands. Although B. dendrobatidis was present at a high prevalence of 63%, mean infection loads were low with an average of 10.9 genomic equivalents (SD 35.5), confirming the role of bullfrogs as B. dendrobatidis carriers, but questioning their role as primary reservoirs for B. dendrobatidis transmission to native amphibian communities. All tested samples were negative for the other infectious agents examined. These results suggest a limited role of bullfrogs as carrier of these pathogens.

Racing pigeons: a reservoir for nitro-imidazole–resistant Trichomonas gallinae

Abstract:  Trichomonas gallinae, the cause of avian trichomonosis, is most commonly found in the order Columbiformes. Racing pigeons are often treated preventively with nitro-imidazoles, which could result in the emergence of resistant isolates, and these isolates can be a threat to wildlife when exchanges occur. The sequence type of 16 T. gallinae isolates obtained from racing pigeons and 15 isolates from wild pigeons was determined based on the ITS1/5.8S rRNA/ITS2 region sequence. In addition, the resistance profiles of these isolates against 5 different nitro-imidazoles (metronidazole, dimetridazole, ronidazole, tinidazole, and carnidazole) were determined. Two different Trichomonas sequence types were isolated. Sequence type A isolates were recovered from racing and wild pigeons, in contrast to sequence type B, which was only isolated from wild pigeons. Isolates with sequence type B were all susceptible to the tested nitro-imidazoles, except for tinidazole resistance in 3 isolates. Resistance to the nitro-imidazoles was observed more frequently in isolates obtained from racing pigeons than from wild pigeons, with most isolates belonging to sequence type A. A higher percentage of the sequence type A isolated from racing pigeons, in comparison with those isolated from the wild pigeons, were resistant to the nitro-imidazoles and displayed higher mean lethal concentration (MLC) values. Two isolates belonging to sequence type A, 1 recovered from a racing pigeon and 1 from a wild pigeon, displayed a similar resistance pattern, suggesting a potential exchange of resistant isolates between racing pigeons and wild pigeons.

Persistent Goose Hemorrhagic Polyomavirus Infection on a Belgian Goose Farm

SUMMARY Goose hemorrhagic polyomavirus (GHPV) is the causative agent of hemorrhagic nephritis enteritis of geese (HNEG), one of the major diseases of domestic geese in Europe. This case report describes a persistent outbreak of a GHPV infection on a Belgian goose farm. Clinical symptoms, necropsy lesions, and histopathologic lesions observed were compatible with previous reports of HNEG outbreaks. PCR analysis confirmed the diagnosis of GHPV. To our knowledge, this is the first report of an outbreak of a GHPV infection on a Belgian goose farm. This is evidence that GHPV is not only present in countries known for extensive waterfowl production, but disease outbreaks also occur in countries with less extensive goose production.

Co-occurrence of Mycoplasma Species and Pigeon Herpesvirus-1 Infectionin Racing Pigeons (Columba livia)

Abstract Oropharyngeal swab samples were collected from 438 live racing pigeons (Columba livia), with and without signs of respiratory disease, that were housed in 220 lofts in 3 provinces in the western part of the Netherlands. Polymerase chain reaction (PCR) was used to identify Mycoplasma species and pigeon herpesvirus-1 (PHV-1) from the samples. In 8.6% of the pigeon lofts tested, signs of respiratory disease were present in pigeons at sampling, and in 30.9% of the sampled pigeon lofts, respiratory signs were observed in pigeons during the 6-month period immediately before sampling. A total of 39.8% of tested pigeons (54.5% of tested lofts) were positive for Mycoplasma species, and 30.6% of tested pigeons (48.6% of tested lofts) were positive for PHV-1. In 15.8% of the tested pigeons (26.8% of tested pigeon lofts), coinfection by Mycoplasma species and PHV-1 was identified. The number of pigeon lofts having pigeons coinfected by Mycoplasma species and PHV-1 was higher than that where only one of the infections was identified. Neither the presence of Mycoplasma species, PHV-1, nor the co-occurrence of both infections was significantly associated with signs of respiratory disease.

Chironomidae bloodworms larvae as aquatic amphibian food

Different species of chironomids larvae (Diptera: Chironomidae) so-called bloodworms are widely distributed in the sediments of all types of freshwater habitats and considered as an important food source for amphibians. In our study, three species of Chironomidae (Baeotendipes noctivagus, Benthalia dissidens, and Chironomus riparius) were identified in 23 samples of larvae from Belgium, Poland, Russia, and Ukraine provided by a distributor in Belgium. We evaluated the suitability of these samples as amphibian food based on four different aspects: the likelihood of amphibian pathogens spreading, risk of heavy metal accumulation in amphibians, nutritive value, and risk of spreading of zoonotic bacteria (Salmonella, Campylobacter, and ESBL producing Enterobacteriaceae). We found neither zoonotic bacteria nor the amphibian pathogens Ranavirus and Batrachochytrium dendrobatidis in these samples. Our data showed that among the five heavy metals tested (Hg, Cu, Cd, Pb, and Zn), the excess level of Pb in two samples and low content of Zn in four samples implicated potential risk of Pb accumulation and Zn inadequacy. Proximate nutritional analysis revealed that, chironomidae larvae are consistently high in protein but more variable in lipid content. Accordingly, variations in the lipid: protein ratio can affect the amount and pathway of energy supply to the amphibians. Our study indicated although environmentally-collected chironomids larvae may not be vectors of specific pathogens, they can be associated with nutritional imbalances and may also result in Pb bioaccumulation and Zn inadequacy in amphibians. Chironomidae larvae may thus not be recommended as single diet item for amphibians.