Introduction
Little is known about the helminth parasites of the European badger (Meles meles) in the Republic of Ireland (ROI), the western limit of its Eurasian distribution (Roper, Reference Roper2010). Sleeman and Kelly (Reference Sleeman and Kelly1997), in a review of parasites and diseases of Irish badgers, which focused on ectoparasites and tuberculosis (TB), stated that no attempt had yet been made to document the helminth parasite community of this important wildlife species. Subsequently, one study assessed the parasites of red foxes, pine martens and badgers in the ROI through the inspection of faeces (Stuart et al., Reference Stuart2013). Researchers found eggs from two nematode species in a sample of 50 roadkill badgers collected across Ireland and reported a prevalence of 40% for Uncinaria criniformis and 6% for Eucoleous aerophilus.
Since 1980, 16 studies have been published on helminth infections of the European badger. However, only five described the parasite community (Jones et al., Reference Jones, Neal and Harris1980; Magi et al., Reference Magi1999; Torres et al., Reference Torres, Miquel and Motjé2001; Millan et al., Reference Millan2004; Rosalino et al., Reference Rosalino, Torres and Santos-Reis2006). The remainder focused upon a single species of helminth (Priemer and Lux, Reference Priemer and Lux1994; Davidson et al., Reference Davidson, Handeland and Gjerde2006; Popiołek et al., Reference Popiołek, Jarnecki and Łuczyński2009; Gerrikagoitia et al., Reference Gerrikagoitia, Barral and Juste2010; Moskwa et al., Reference Moskwa2012; Ribas et al., Reference Ribas2012) or the incidental detection of infection during examination of a range of wild carnivore hosts (Loos-Frank and Zeyhle, Reference Loos-Frank and Zeyhle1982; Górski et al., Reference Górski, Zalewski and Lakomy2006; Magi et al., Reference Magi2009), where badger helminth infection was reported tangentially and sample sizes were small. Additionally, reporting of intensity of infection is very rare (n = 4 studies), despite agreement within the parasitological community that intensity of infection is a critical parameter for understanding the epidemiology and population biology of macroparasite infections (Anderson et al., Reference Anderson, Truscott and Hollingsworth2014; Poulin, Reference Poulin2019).
The aims of this study were therefore three-fold: (1) to describe the helminth community of European badgers in the ROI for the first time, (2) to report the prevalence, abundance, intensity and aggregation of each helminth infection detected, and (3) to explore the relationship between infection and factors such as host sex, region and season of sampling.
Materials and methods
Collection of study animals and diagnosis of helminth infection
In total, 289 badgers were examined for helminth parasites. Badgers were provided by the Irish Department of Agriculture, Food and the Marine (DAFM) and no animals were killed specifically for the purposes of this study. Badgers were transported from their site of culling to the post-mortem laboratory within 1–3 days and dissected on the day of arrival.
All organs were removed from the cadavers by an experienced veterinary surgeon (UF) and labelled with unique DAFM badger identification codes. Samples were chosen at random from western counties and eastern counties across one sample year: spring (March, April, May), summer (June, July, August), autumn (September, October, November) and winter (December, January, February). The influence of badger age on the parasite community could not be explored because very few yearling badgers were caught due to the capture method used by DAFM. Hearts, lungs, livers and gastrointestinal tracts were collected and frozen without preservative at −20°C until examination. Faecal samples were extruded from the rectum of gastrointestinal tracts and fixed in 10% formalin (Garcia and Bruckner, Reference Garcia and Bruckner2001).
Organs were dissected over 3–12 months and were defrosted overnight at 5°C and inspected within 8 hours. Hearts, lungs and GI tracts were examined as described in Byrne et al. (Reference Byrne2018). The lobes of the liver were separated and submerged into warm water, and the liver was then cut into 2 cm2 cubes and wrapped in a nylon/viscose cotton mesh fabric. The cubes were again submerged in warm water, with manual pressure being applied by opening and closing the fist in which the samples were held. This process was repeated three times for each sample. The fabric was then unwrapped and visually inspected for parasites, as were the cubes of liver. The bags in which the organs had been stored were turned inside out and submerged in water. The water was then passed through sieves of aperture 150 and 64 μm and scrutinized for parasites. Whenever they were found, helminth parasites were removed, identified (EH), counted and preserved in 70% ethanol.
A modified formol–ether concentration technique (Allen and Ridley, Reference Allen and Ridley1970) was used to detect helminth parasite eggs and larvae. Samples were processed blind, with two slides being examined for each individual badger, and the egg per gram count (e.p.g) and larvae per gram (l.p.g) were calculated for each sample.
Statistical analysis
All results were calculated from the recorded data, and using the statistical analysis software package, R Studio 1.0.153 for Mac (R Core Team, 2017). The prevalence, abundance, intensity and aggregation of each helminth species was calculated. Where available, these were analysed using worm burden data (Aelurostrongylus falciformis, Crenosoma spp., Uncinaria criniformis) or faecal egg/larval counts (Eucoleus aerophilus, Strongyloides spp., Species A, Unknown 1, 2). The mean species richness was calculated as a measure of the infracommunity (Loxton et al., Reference Loxton2016). Abundance and intensity were modelled using a modified negative binominal GLM (Loxton et al., Reference Loxton2016) from the MASS package in R (Venables and Ripley, Reference Venables, William and Ripley2002). Full factorial models incorporated measures of season (four levels: spring, summer, autumn, winter); region (two levels: east, west) and sex (two levels: female, male). The minimal sufficient model was derived by simplifying the model using the step procedure (see Loxton et al., Reference Loxton2016). The level of significance was set at P < 0.05.
Results
Of the 289 badgers examined, 83.2% (95% CI 78.2–87.1%) were positive for one or more helminth species. Overall, eight distinct helminth taxa were recovered from Irish badgers. Five species of adult worms were recovered via gross organ dissection, two of which were located in the lungs; 663 were Aelurostrongylus falciformis and 236 were Crenosoma melesi. The remaining three taxa were from the GI tract, of which a total of 6516 were Unicinaria criniformis and two were unidentifiable but morphologically distinct nematodes (Unknown 1 and Unknown 2). Species identification could not be confirmed due to the condition of specimens. No badgers were infected only with these nematodes; individuals infected with nematodes 1 and 2 were not incorporated into the helminth parasite community analysis (i.e. the calculation of species richness) due to the low prevalence recorded and lack of identification. Two helminths (one genus and one species) were identified from faeces: Eucoleus aerophilus (eggs) and Strongyloides spp. (larvae). In addition, a large number (n = 4640) of unknown larvae (Species A) were recorded but could not be identified, as no adult worms were recovered from 76 individuals. Seven badgers were infected by only Species A and these were incorporated into the species richness calculation.
The prevalence, abundance, intensity, range and aggregation of helminth infection based on adult worm burden or faecal egg/larval counts were calculated (table 1). The most prevalent and abundant helminth was U. criniformis, with 171 badgers (59.2%, 95% CI 53.25–64.88%) infected and an average abundance (± S.E.) of 22.5 (± 3.16). Of the helminths found in the lungs, A. falciformis was the most common, infecting 60 individual badgers, resulting in a prevalence of 20.7% (95% CI 16.2–25.9%). Despite having the lowest prevalence of 1.03% (95% CI 0.2–3.0%) C. melesi had the highest mean intensity (± S.E) (78.6 ± 125.8) compared to all other helminths. All species of helminth exhibited an aggregated distribution within the sampled host population. Uncinaria criniformis demonstrated the highest level of aggregation (S2/x̄ = 127.8), with 62% of the 6513 U. criniformis recovered from 28 individuals.
The prevalence (95% CI), mean abundance (± S.E.), range (minimum–maximum), intensity (± S.E.) and aggregation (S2/x̄) of helminth parasites in European badgers (Meles meles) in the Republic of Ireland.
The mean species richness was 1.73 (± S.E. 0.92). Species richness did not differ significantly between the sexes, the region of origin or season of culling. Overall, 110 individuals were infected with a single species of helminth and 131 (54.1%) badgers were co-infected with two or more helminth species. The highest level of co-infection was six.
The relationship between the prevalence, abundance and intensity of each helminth species and host sex, region and season of sampling was explored but none of these factors were found to statistically significantly influence the prevalence, abundance or intensity of any of the helminth species.
Discussion
This is the first characterization of the helminth parasite community of Irish badgers. Within our sample of 289 badgers, helminth infection was shown to be endemic within the Irish population, with 83.2% of all individuals positive for at least one species of helminth. All helminths described in our study are nematodes. The two most prevalent helminths described here, Uncinaria criniformis (59.2%) and Strongyloides spp. (28.2%), are both known to be transmitted directly (Rosalino et al., Reference Rosalino, Torres and Santos-Reis2006). This higher prevalence is to be expected as transmission is not reliant on an intermediate host (Anderson, Reference Anderson1980). Additionally, all helminths demonstrated an aggregated distribution throughout the host population (see table 1), resulting in some badgers harbouring significantly higher helminth burdens than others. Furthermore, over half of all U. criniformis infections (62%) were found in less than 8% of the population.
Our study represents the first records of C. melesi and Strongyloides spp. helminths in a badger host in the ROI. We found a high prevalence of Strongyloides spp. infection (28%), and given the numerous reports of Strongyloides westeri helminths parasitizing horses in the ROI (O'Meara and Mulcahy, Reference O'Meara and Mulcahy2002), further studies should be conducted to allow the identification of the Strongyloides spp. found in badger hosts, to determine whether these helminths overlap with those found in equine helminth communities.
One important caveat is that for three of the eight species reported here, population parameters were calculated using faecal egg and larval counts. This method of detection is known to have lower sensitivity for diagnosing helminth infection compared to adult worm burden in wild hosts (Gassó et al., Reference Gassó2015; Byrne et al., Reference Byrne2018). However, in a recent analysis, utilizing both adult worm burden data and egg/larval counts (Byrne et al., Reference Byrne2018), we were able to demonstrate that although coprological analysis was not a sensitive test for diagnosing helminth infection, where eggs or larvae were detected, the abundance of these eggs or larvae in the faeces was a suitable indicator of intensity of infection.
In conclusion, the helminth parasite community of European badgers (Meles meles) from the ROI is reported in this, the largest study to date of badger helminths conducted within their geographical range. In total, eight distinct helminth taxa were identified (one genus, four species and three unknown), all of which were nematodes. This is the first report of C. melesi in the ROI. Helminth infection was found to be endemic throughout the Irish community, irrespective of host sex, region of origin or season of sampling. Observations from this study can serve as a baseline for badger health surveillance as well as an important comparison for reports of helminth parasitism in badgers from other countries across the badger's range.
Supplementary material
To view supplementary material for this article, please visit https://doi.org/10.1017/S0022149X19000051
Author ORCIDs
R. L. Byrne, 0000-0001-5398-3125
A. Mooney, 0000-0002-2592-9786
M. Good, 0000-0002-4720-2940
N. Marples, 0000-0003-4693-2607
C.V. Holland, 0000-0002-0550-7287
Acknowledgements
We are grateful for the financial support (to RB) from the Department of Agriculture, Food and the Marine and the logistical support of the Irish Equine Centre for sample collection, notably Noel Buckley for his expertise. Special thanks are due to Alison Boyce for technical advice and Emy Constanti for assistance with dissections. The authors thank Professor Eric Morgan, Professor Grainne McCarthy and Dr Annetta Zintl of the UCD Veterinary Parasitology Department for invaluable guidance in the lungworm methodological procedure.
Conflict of interest
None.
