Host contribution to parasite persistence is consistent between parasites and over time, but varies spatially

Abstract

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Long-Term Monitoring of Amphibian Populations of a National Park in Northern Spain Reveals Negative Persisting Effects of Ranavirus, but Not Batrachochytrium dendrobatidis

“…One possibility is that Bd and Rv (which were first detected in 2005) caused declines in the most susceptible species before systematic monitoring of populations began (monitoring started in 2007). The common midwife toad, A. obstetricans , is known to be important in the persistence and spread of both Bd and Rv in amphibian communities ( 23 , 30 ). If their populations were reduced significantly before 2007, their role in the transmission of Bd infection to other species could have been greatly reduced, and hence the impact of Bd on sympatric species could have significantly reduced, which is consistent with the lack of strong association between the presence of Bd and mass mortalities or population decline.…”

“…In recent years, when no moribund Alytes tadpoles were present in the water, adult I. alpestris exhibited less severe and less frequent signs of ranavirosis (J. Bosch, personal observations) despite Rv infection being persistent in the species. Over-wintering larvae are known to be an important host for many infectious pathogens, including Bd and Rv ( 23 , 39 – 41 ), and so perhaps with a reduction in their abundance other species can benefit from more breaks in the chain of initial transmission and subsequent re-infections.…”

“…Our results are similar to those obtained in other, similar communities in the Iberian Peninsula (e.g., the species exhibiting the highest prevalence levels and susceptibility to decline), but vary in others (the importance of the pathogens in question). The effects of both pathogens can be highly context-dependent, with declines perhaps being driven by interactions with other important factors including climate ( 11 , 42 ); ozone levels ( 43 ); and microbiome ( 44 , 45 ) of hosts; and the specific ecological context in which the host community lives ( 23 ). All of these factors are likely to interact with pathogens as a driver of population-level effects and warrant careful attention both alone and in combination with each other.…”

“…Bd was also found to be present in PNPE shortly after the first mortality incidents associated with ranavirus, although no evidence of chytridiomycosis emergence has been observed ( 10 ). Two of the most common species in the park, the common midwife toad ( Alytes obstetricans ) and the alpine newt ( Ichthyosaura alpestris ), can act as drivers of persistence and spread of infection within the community ( 23 ). However, although both pathogens are present and life stages of some species harbor infection at high levels, the long-term effects on the host populations remain unclear.…”

Public Health Policy Pillars for the Sustainable Elimination of Zoonotic Schistosomiasis

“…The identification of locationspecific dominant animal reservoirs and their transmission contributions to humans, along with model calibration to local data are evidently crucial (27,28). Quantifying each host's contribution to transmission enables the identification of maintenance and essential hosts, and the predicted impacts of control strategies targeting these hosts (29,30,31). It has been shown that human-only treatment is insufficient to achieve EPHP because transmission is maintained by untreated reservoirs.…”