Disease hazard identification and assessment associated with wildlife population declines

Abstract

Summary Disease is increasingly being recognised as a risk factor in declining wildlife populations around the globe. However, there are limited protocols to assess disease risks in declining wildlife. Using epidemiological principles, we define a step‐by‐step framework to complete this complex and critical task. As an example, we assessed the potential role of diseases in relation to the decline of the woylie or brush‐tailed bettong (Bettongia penicillata ogilbyi) in Western Australia. Between 1999 and 2006, woylie populations declined by 90%. The wildlife disease risk assessment began with a list of all known or suspected diseases to which the woylie, a species of macropod, is susceptible. This list was assessed against the spatial, temporal and demographic characteristics of the decline. Diseases causing widespread and high mortalities or debilitation leading to predation received high scores. Based on this assessment, priority diseases or pathogens for investigation identified were haemoparasites, gastrointestinal helminths, Neospora caninum, Toxoplasmosis (Toxoplasma gondii), Encephalomyocarditis virus, Macropod Orbiviruses (Wallal virus and Warrego virus), Macropod Herpesviruses (Macropodid herpesvirus 1 and 2) and Salmonella spp.

Reduced growth in wild juvenile sockeye salmon Oncorhynchus nerka infected with sea lice

“…Pathogens are known to influence wildlife populations, especially when they interact with other stressors (Smith et al, 2009;Pacioni et al, 2015). Effects on biota resulting from the spread of pathogens are commonly associated with anthropogenic activities, such as through the introduction of non-native species (Dunn, 2009), climate change (Harvell et al, 2009;Maynard et al, 2015), and spill-over from domestic animal stocks (Daszak et al, 2000).…”

Disease Risk Analysis in sea turtles: A baseline study to inform conservation efforts

“…Postmortem examination provides the 84 most robust opportunity to identify diseases and their aetiology. Unfortunately, the difficulty of 85 retrieving carcasses in the wild, as well as postmortem changes, can complicate the process of 86 making a reliable diagnosis (6). In addition, the results of such studies would not aid in determining 87 the rate of morbidity versus mortality.…”

“…The list of hazards, compiled in the review of the literature, were presented to the groups of 226 specialists in sea turtle health. The "Paired Ranking Tool" was used to prioritise the top three 227 hazards from each group according to a conservation, surveillance and research perspective (6,11).…”

“…As mentioned by Jakob-Hoff et al (11): "This is a tool for a qualitative risk analysis that 231 assists groups to rank hazards based on their collective judgement." The criteria used to compare 232 the diseases were defined as: current knowledge of the pathogen in sea turtles, the likelihood of 233 exposure/susceptibility, the pathogenic potential, the severity for populations and the correlation 234 with climatic/anthropogenic events (6,11). Appropriate management interventions such as by-catch reduction, restrictions on commercial use 248 and trade, and creation of protected habitats can allow recovery of a depleted population (31,32).…”

“…It is worth mentioning that this is a feature 502 of all wildlife DRAs and the process enables information gaps to be identified and the level of 503 uncertainty made explicit. Such level of confidence by experts is referred to in Pacioni's ranking 504 criteria as "levels of knowledge" (6).…”