Influence of management and biological factors on parasitic invasions in the wild – Spread of the blood-sucking nematode Ashworthius sidemi in European bison ( Bison bonasus )

Abstract

The full course of new parasite introductions in wild animals is difficult to accurately trace. We documented and analysed the invasive blood-sucking nematode Ashworthius sidemi (Trichostrongylidae) introduction and spread in European bison (Bison bonasus) from the initial phase of its progression. In the Polish part of the Białowieża Primeval Forest (BPF) the parasite was first found in 2000. From 2002 to 2015, 165 culled bison were investigated. The prevalence and intensity of A. sidemi Schulz, 1933 infection increased over the following years, reaching 100% of investigated bison four years after introduction and a maximal median intensity of 8200 nematodes per animal in the winter of 2008/2009. Afterwards, a significant decline of median infection intensity was observed to the minimum value of 410 nematodes per animal. Between 2011 and 2014 prevalence varied from 89 to 100%. Among the factors analysed, the number of years since introduction, herd size, age and sex proved to significantly influence infection intensity. A higher infection intensity was recorded in sub-adults compared to juveniles and adults. Males had significantly lower infection intensity than females, but this was the case for adults only. The highest infection intensities were recorded in the biggest bison herds, where the winter supplementary feeding of bison is intense. Moreover, the longer the parasite was present in the host population, the more important herd size became as a factor. Our study indicates that it is not solely biological factors that determine the spread of a newly detected parasite in wildlife, but that management practices can also have a strong influence. This is especially important in endangered species under intensive human care as the management practices may pose a threat to the species.

Increased Parasitic Load in Captive-Released European Bison (Bison bonasus) has Important Implications for Reintroduction Programs

“…Bison get infected usually directly by ingestion of contaminated food (Dróżdż et al 1998). Previous studies have shown the influence of herd size and winter bison aggregation on A. sidemi and coccidia infection (Kołodziej-Sobocińska et al 2016a; Pyziel et al 2011; Radwan et al 2010) as well as on the seasonal pattern of parasite egg excretion (Kołodziej-Sobocińska et al 2016c). …”

“…Among the 88 parasite species discovered in European bison (Dróżdż et al 1998; Karbowiak 2014a, b), the blood-sucking nematode Ashworthius sidemi is probably the most pathogenic. This parasite is specific to Asian deer species, especially sika deer ( Cervus nippon ) (Dróżdż et al 1998) and was first found in bison from Białowieża Forest (BF) in 2000 (Kołodziej-Sobocińska et al 2016a). Adult nematodes are located in abomasa of bison and other ruminants; eggs are shed with faeces.…”

“…Moreover, host susceptibility to disease may be influenced by population density which might increase pathogen transmission and social stress, innate resistance and the ability to mount an immune response (Radwan et al 2010; Wakelin 1978). For example, the increased contact rate between bison in winter due to large aggregations arising from supplementary feeding in fixed locations promotes parasite transmission (Karbowiak et al 2014b; Kołodziej-Sobocińska et al 2016a; Pyziel et al 2011; Radwan et al 2010). The five bison released from captivity stayed in the places where supplementary feeding was intense, which further increased the number of parasites transmitted to these immunologically naïve individuals.…”

“…However, treatment of animals prior to release may not be beneficial, because it may reduce their levels of immunity to disease (Faria et al 2010; Viggers et al 1993). This is especially important if such pathogens are present in wild populations, as is the case of blood-sucking nematode A. sidemi in the bison population in BF (Dróżdż et al 1998; Kołodziej-Sobocińska et al 2016a, c); regularly dewormed captive bison have no chance to acquire immunity against A. sidemi or other parasites that they come into contact with upon release. Moreover, release into the wild probably stresses bison, which could make them more susceptible to infection (Dickens et al 2010).…”

Winter supplementary feeding influences forest soil seed banks and vegetation

“…increasing transmission of parasites in the fed population (Kołodziej‐Sobocińska et al. ), limiting plant growth in the vicinity of feeding sites (van Beest et al. ) or causing degradation of habitats (Putman & Staines ).…”