How sensitive and specific is the visual diagnosis of sarcoptic mange in free-ranging Iberian ibexes?

Abstract

Background Sarcoptic mange is a broadly distributed parasitic disease caused by Sarcoptes scabiei that affects wild mammals from all over the world, including the Iberian ibex ( Capra pyrenaica ). Selective culling of the scabietic individuals is the main management measure for disease control in Iberian ibex populations. Although visual identification of mange-compatible lesions is the reference method to decide the target individual, both false negative and positive cases are common in the wild. The aim of this work is to determine the sensitivity (SE), and the specificity (SP) of selective culling after evaluating 403 ibexes hunted in the Sierra Nevada Nature Space for sarcoptic mange control between 2002 and 2015. Methods A combination of skin scrapings and potassium hidroxide (KOH) skin digestion was used for sarcoptic mange diagnosis. Generalized linear models (GLM) were used to assess the effects of sex, age (juveniles and adults) and period of the year (wet and dry periods) on the SE and SP of the visual diagnosis method. Results The SE obtained for the visual determination of scabietic ibexes was 87.14%, whereas the SP was 60.71%. According to our model selection, SE of the visual diagnosis was explained by the additive effects of age and the period of the year. In fact, SE was lower in juveniles (64.76%) than in adults (94.26%) and during the dry period (73.44%) as compared to the wet period (92.09%). On the other hand, SP was best explained by the GLM including the additive effects of sex and the period of the year. The visual diagnosis of sarcoptic mange resulted less specific in females (22.73%) than in males (74.19%) and during the wet (55.22%) than in the dry period (82.35%). Conclusions Maximizing SE and SP is essential to achieving a high rate of removal of affected individuals from the environment without eliminating potentially resistant individuals. Selective culling must be conservative during the wet period and with females due to the lower SP. Conversely, visual diagnosis of scabietic juveniles and during the dry period has to be improved, due to the lower SE.

Sarcoptic mange outbreak decimates South American wild camelid populations in San Guillermo National Park, Argentina

“…We used the same transects but only evaluated individuals within 200 m from the transect after several trials in which we established that this was the most conservative distance at which we could confidently identify infected animals with the available telescope [42]. Notwithstanding, because incipient infections are undetectable without laboratory diagnosis which require diagnostic specimens, our visual estimates represent the minimum infected proportion [43].…”

Biology and management of sarcoptic mange in wild Caprinae populations

“…lice infestation or dermatophilosis) or conditions such as moulting. While the sensitivity of visual diagnosis high (87%), the specificity is low (61%; Valldeperes et al 2019), and both sensitivity and specificity are affected by factors such as age, sex, and time of year. Due to these limitations, the combination of visual diagnosis with the detection of mites and their eggs in skin scrapings or in skin digested with potassium hydroxide is considered the gold standard method (Valldeperes et al 2019).…”

Infectious diseases surveillance of the Iberian ibex (Capra pyrenaica victoriae) in Western Spain: health and conservation implications

“…Importantly, ticks collected from sympatric Red deer near the study area have been recently demonstrated to harbor pathogens such as Coxiella burnetii, Babesia ovis, Borrelia burgdorferi and the Crimean-Congo Hemorrhagic Fever virus (Estrada-Peña et al 2012). Despite no cases of infestation by Sarcoptes scabiei mites were detected, a serological analysis to discard possible contact with the parasite would have been desirable; currently no standardized assay for wild ruminants is available (Valldeperes et al 2019).…”