INTRODUCTION
The effects exerted by predators in ecosystems can have profound consequences for species of conservation importance, but also for human and animal health. The red fox (Vulpes vulpes; hereafter ‘fox’) is the most widely distributed wild terrestrial carnivore in the world with the species range of approximately 70 million km2 (Macdonald and Reynolds, Reference Macdonald and Reynolds2008) due to its high ecological plasticity. Foxes influence other species primarily in two ways: via predation and through transmission of pathogens. Considering these and the relatively high numbers, fox can be regarded as one of the most influential mesopredators in the Holarctic. Together with other mesopredators such as the raccoon dog (Nyctereutes procyonoides) they are highly effective vectors of multiple zoonotic diseases, including rabies, alveolar echinococcosis and sarcoptic mange, posing significant risk for humans and domesticated animals (Smith et al. Reference Smith, Gangadharan, Taylor, Laurenson, Bradshaw, Hide, Hughes, Dinkel, Romig and Craig2003; Deplazes et al. Reference Deplazes, Hegglin, Gloor and Romig2004; Letkova et al. Reference Letkova, Lazar, Čurlik, Goldova, Kočišova, Košuthova and Mojžišova2006; Kauhala and Kowalczyk, Reference Kauhala and Kowalczyk2011; Süld et al. Reference Süld, Valdmann, Laurimaa, Soe, Davison and Saarma2014; Laurimaa et al. Reference Laurimaa, Davison, Plumer, Süld, Oja, Moks, Keis, Hindrikson, Kinkar, Laurimäe, Abner, Remm, Anijalg and Saarma2015a , Reference Laurimaa, Süld, Moks, Valdmann, Umhang, Knapp and Saarma b ).
The parasite fauna of the fox has been of considerable scientific interest in Europe, largely because the species harbours zoonotic parasites (Smith et al. Reference Smith, Gangadharan, Taylor, Laurenson, Bradshaw, Hide, Hughes, Dinkel, Romig and Craig2003; Letkova et al. Reference Letkova, Lazar, Čurlik, Goldova, Kočišova, Košuthova and Mojžišova2006). However, informing the general public of potential risks related to foxes is becoming more and more important since fox density appears to have increased in many countries of Europe partly as a consequence of highly successful vaccination of wildlife against rabies (Vos, Reference Vos1995; Gloor et al. Reference Gloor, Bontadina, Hegglin, Deplazes and Breitenmoser2001). Moreover, foxes are colonizing urban areas in Europe and around the world with increasing pace (Harris and Rayner Reference Harris and Rayner1986; Gloor et al. Reference Gloor, Bontadina, Hegglin, Deplazes and Breitenmoser2001; Bateman and Fleming, Reference Bateman and Fleming2012), bringing zoonotic pathogens to the immediate neighbourhood of humans and their companion animals (Deplazes et al. Reference Deplazes, Hegglin, Gloor and Romig2004; Davidson et al. Reference Davidson, Romig, Jenkins, Tryland and Robertson2012; Laurimaa et al. Reference Laurimaa, Davison, Plumer, Süld, Oja, Moks, Keis, Hindrikson, Kinkar, Laurimäe, Abner, Remm, Anijalg and Saarma2015a ; Umhang et al. Reference Umhang, Forin-Wiart, Hormaz, Caillot, Boucher, Poulle and Franck2015). The same trend has also been observed among Estonian foxes that have over the last decade colonized urban areas in Estonia (Plumer et al. Reference Plumer, Davison and Saarma2014).
The parasite fauna of Estonian red foxes was investigated about a decade ago, when a pilot study based on examination of 17 animals revealed 16 endoparasite taxa, including the small fox tapeworm Echinococcus multilocularis (Moks et al. Reference Moks, Saarma and Valdmann2005; Moks, Reference Moks2008). This tapeworm is probably the most studied parasite of foxes in Europe (Conraths and Deplazes, Reference Conraths and Deplazes2015; Knapp et al. Reference Knapp, Gottstein, Saarma and Millon2015; Vuitton et al. Reference Vuitton, Demonmerot, Knapp, Richou, Grenouillet, Chauchet, Vuitton, Bresson-Hadni and Millon2015), including the Baltic States (Marcinkute et al. Reference Marcinkute, Šarkunas, Moks, Saarma, Jokelainen, Bagrade, Laivacuma, Strupas, Sokolovas and Deplazes2015), as it can cause a potentially fatal disease in humans (Eckert et al. Reference Eckert, Gemmell, Meslin and Pawlowski2001). Considering the relatively small number of animals examined by Moks (Reference Moks2008), it is important to evaluate the fox parasite fauna in Estonia by including significantly larger set of samples. Moreover, as approximately a decade has passed since the last study by Moks et al. (Reference Moks, Saarma and Valdmann2005), it would be of considerable interest to evaluate the changes in the prevalence of E. multilocularis.
MATERIALS AND METHODS
Sample collection
In total, 111 red fox carcasses provided by hunters were examined for internal parasites. Legally hunted red foxes were collected during the hunting seasons 2010/11 and 2011/12. All the animals originated from the mainland of Estonia (eight counties; Fig. 1).
Fig. 1. Map of red fox carcasses collected in Estonia. The number of carcasses examined is given in parenthesis; Em – the number Echinococcus multilocularis positive animals.
Sex, sampling region and time were recorded for each animal. All animals collected with fur (n = 99) were examined for sores and patches of thick crusty skin as clinical signs of sarcoptic mange. After weighing the carcasses, internal organs were removed and kept at −80°C for at least 5 days before parasitological examination for safety precautions (Eckert et al. Reference Eckert, Gemmell, Meslin and Pawlowski2001), since highly dangerous tapeworms E. multilocularis (Moks et al. Reference Moks, Saarma and Valdmann2005; Laurimaa et al. Reference Laurimaa, Davison, Plumer, Süld, Oja, Moks, Keis, Hindrikson, Kinkar, Laurimäe, Abner, Remm, Anijalg and Saarma2015a , Reference Laurimaa, Süld, Moks, Valdmann, Umhang, Knapp and Saarma b ) and E. granulosus (Moks et al. Reference Moks, Jõgisalu, Saarma, Talvik, Järvis and Valdmann2006, Reference Moks, Jõgisalu, Valdmann and Saarma2008; Laurimaa et al. Reference Laurimaa, Davison, Süld, Plumer, Oja, Moks, Keis, Hindrikson, Kinkar, Laurimäe, Abner, Remm, Anijalg and Saarma2015c ) have been found in Estonia. Lungs, gall bladder and urinary bladder were studied using established washing and sieving techniques for helminth detection (Parre, Reference Parre1985). Briefly, the respective organ was cut open and the lumen was washed with tap water through 200 µm mesh sieve to reveal helminth infection. The small and large intestines were separated and examined by sedimentation and counting technique (Hofer et al. Reference Hofer, Gloor, Müller, Mathis, Hegglin and Deplazes2000). Up to 200 specimens were counted per helminth species, since continuing to very large numbers (often thousands) would have been too laborious. Parasites were stored in 95% ethanol.
Parasite identification
Trematodes, cestodes and nematodes were identified according to their morphology after Kozlov (Reference Kozlov1977). Cestodes from genera Echinococcus and Mesocestoides were further identified after Abuladze (Reference Abuladze1964) and Hrčkova et al. (Reference Hrčkova, Miterpakova, O'Connor, Šnabel and Olson2011), respectively.
As the scoleces of tapeworms from the genus Taenia were deformed and lacking some of the features required for morphological identification (e.g. hooks and gravid proglottids), these samples were submitted to genetic identification. PCR-based genetic identification of Taenia species was conducted as described in Laurimaa et al. (Reference Laurimaa, Süld, Davison, Moks, Valdmann and Saarma2016). Essentially, DNA was extracted using the High Pure PCR Template Preparation Kit (Roche) according to the manufacturer's instructions and primers CesCox1F and CesCox2R were used to amplify a fragment of cox1 gene of mitochondrial DNA with total length of 506 base pairs. PCR was performed using a touchdown protocol described in Laurimaa et al. (Reference Laurimaa, Süld, Davison, Moks, Valdmann and Saarma2016). Eventually, samples were purified and sequenced using the same primers as used in the primary PCR.
Statistical analyses
For statistical analysis, collected animals were divided between two seasons: autumn (September–November) and winter (December–March). We used nonparametric Mann–Whitney U test to analyse variation in the number of helminth species between animal gender, the two seasons and sarcoptic mange, and to measure if male foxes weighed more than females. The same analysis was used to determine whether sarcoptic mange or animal gender influenced the overall intensity of helminth infection. Intensity of parasitic infection in each fox was determined as a sum of the number of observed parasite specimens from different species (varying between 1 and 784). However, as the upper limit in counting the parasite specimens from one species was set to 200, this should be considered as relative intensity.
A multivariable analysis was used to study the abundance of different parasite species in red foxes with respect to gender, sampling season (autumn/winter), and infection with scabies. Initially, the mathematical distribution (Poisson or negative binomial) that produced the best description of the abundance data was determined for the most abundant parasite taxa. Parasite species found in < 20 foxes were excluded from the analysis due to low variability. The final analyses using negative binomial generalized linear model examined the factors gender, season and scabies as fixed effects. Multivariable analyses were performed using package ‘MASS’ (Venables and Ripley, Reference Venables and Ripley2002) in software R (R Development Core Team, 2014). In addition, chi-square was calculated to compare parasite infection between the sexes.
To assess the co-occurrence of different parasite species, we calculated the C-score (Stone and Roberts, Reference Stone and Roberts1990) for all pairs of parasite species as described in Süld et al. (Reference Süld, Valdmann, Laurimaa, Soe, Davison and Saarma2014). Essentially, we generated 999 random matrices with fixed row and column occurrence (e.g. if parasite A has a prevalence of 20% in the raw data, this level of prevalence will remain the same in all randomized datasets) and recalculated all pairwise C-scores for each matrix. Observed C-scores were standardized and the significance of effect was estimated from the number of randomized C-scores more extreme than the observed value. The co-occurrence analysis was carried out using package ‘vegan’ (Oksanen et al. Reference Oksanen, Blanchet, Kindt, Legendre, Minchin, O'Hara, Simpson, Solymos, Stevens and Wagner2015) in software R.
RESULTS
Red fox parasite fauna in Estonia
Due to decomposition or hunting damage some samples were excluded. In total, 108 small intestine, 105 lung and 106 urinary bladder samples were examined. Gall bladders were examined for 15 animals, though parasites detected in this organ were not included to statistical analyses due to the small sample size.
We identified 16 helminth species: nine nematode species, three trematode species, four cestode species and one additional cestode taxon that was determined at the genus level (Table 1). Examined red foxes were highly infected with Pearsonema plica (91·5%), Alaria alata (90·7%), Eucoleus aerophilus (87·6%), Uncinaria stenocephala (84·3%) and Mesocestoides spp. (77·8%). Infection with other helminth species was lower (Table 1). In autumn, foxes had on average more helminth species than in winter (mean number of species 7·7 vs 6·3; Mann–Whitney U test: z = −2·36; P = 0·02). However, the number of helminth species varied more in winter period. To support the occurrence of higher parasite abundance in autumn, factor winter was associated with lower infection risk with U. stenocephala and Toxocara canis in the multivariable analysis (Table 2). We detected zoonotic tapeworm E. multilocularis infection in 31·5% (n = 34) of the animals and ectoparasitic Sarcoptes scabiei infection in 21·2% (n = 21) of the animals. Two Mesocestoides species (M. litteratus and M. lineatus) were present in foxes, but we were not able to determine the species in most of the cases due to the absence of mature proglottids. Although two morphotypes of Taenia species could be differentiated on the basis of scolex morphology, the genetic identification revealed the presence of only T. polyacantha.
Table 1. Prevalence of helminth species in Estonian red foxes
Asterisks (*) mark the species/taxa of zoonotic potential.
a Note that the upper limit in counting was 200 and therefore the numbers are indicative.
b Single specimens identified genetically as Taenia polyacantha, see also Laurimaa et al. Reference Laurimaa, Süld, Davison, Moks, Valdmann and Saarma2016.
Table 2. Risk factors for parasite infection in Estonian red foxes
IRR, incidence rate ratio.
Significant factors are shown in bold typeface.
All the analysed animals were infected. Average parasite species richness was 6·37 species (95% CI 5·99–6·75). Considering animals whose all organs were examined (intestines, lungs and urinary bladder; n = 98), majority of red foxes (75·5%) were infected with five to eight species (Table 3). Scabied animals were infected with an average of 7·33 (95% CI 6·32–8·35) parasite species. The highest number of different parasites in the internal organs of a single fox was 12.
Table 3. The number of endoparasite taxa in red foxes (n = 98). Taenia and Mesocestoides species were included as one species, respectively. Gall bladder parasites were omitted
Numbers in superscript mark the number of animals infected with sarcoptic mange.
Scabies
Considering animals whose all organs were examined (intestines, lungs and urinary bladder; n = 98) we found that scabied animals were parasitized with significantly higher number of parasite specimens (mean number of specimens 468 vs 259; Mann–Whitney U test: z = −3·61; P < 0·01). However, no statistically significant difference was found for the number of helminth species between scabied and healthy foxes (Mann–Whitney U test: z = −1·87; P = 0·06). The multivariable analysis showed no significant interactions between risk factors, but detected sarcoptic mange as a significant factor in estimating infection risk with three nematode species: U. stenocephala, T. canis and E. aerophilus (Table 2). Positive regression parameters indicate increased risk of infection with a certain parasite species due to the presence of analysed risk factor (e.g. male for U. stenocephala), while the negative regression parameters indicate that the opposite factors (e.g. autumn and presence of scabies for U. stenocephala) are associated with increased risk of infection. The incidence rate ratio (IRR in Table 2) provides the estimated rate ratio of parasite abundance in the presence or absence of a specific risk factor when all other variables are constant [e.g. male fox sampled in winter with no signs of scabies would have 0·11 times the abundance rate of T. canis compared with that of a scabied male fox sampled in winter (a 89% decrease)].
Variation between males and females
The analysed males weighed significantly more than females (Mann–Whitney U test: z = 4·33; P < 0·01). Mean weights were 5·26 and 4·52 kg for males and females, respectively. There was no significant relationship between gender and both the number of helminth species and infection intensity [Mann–Whitney U test: (1) z = 1·25; P = 0·21; (2) z = 1·34; P = 0·18]. Neither did the multivariable analysis detect gender as significant factor estimating parasite infection intensity (Table 2). However, the chi-square test (χ 2) detected significant effects in parasite species infection between the sexes: infection with nematode Molineus patens occurred more often in females (2·3 vs 15·1%; χ 2 = 4·56; P = 0·03), and T. canis infection was more prevalent in males (44·2 vs 17·0%; χ 2 = 8·50; P < 0·01).
Co-occurrence analysis
The co-occurrence analysis between different parasite species did not reveal any significant relationships (Supplementary Table S1).
DISCUSSION
Parasite fauna of the red fox in Estonia
The foxes examined in this study were highly parasitized: all examined animals were infected (100% infection rate). Similar results, with all the animals being infected, have previously been reported in Germany (Schöffel et al. Reference Schöffel, Schein, Wittstadt and Hentsche1991) and Ukraine (Zvegintsova et al. Reference Zvegintsova, Dumenko and Varodi2007).
We identified 16 endoparasite species and one additional cestode taxon at the genus level (Table 1). Although based on a rather limited number of fox samples (n = 17) Moks (Reference Moks2008) reported a similar number of endoparasite taxa (n = 16) from the same internal organs. However, there are some differences in the species composition between these two studies. We found four nematode species that have previously not been identified in Estonian foxes: T. leonina, M. patens, A. vasorum and A. putorii. In contrast, while only a single cestode species from genus Taenia, namely T. polyacantha, was identified (genetically) in this study, Moks (Reference Moks2008) reported three species (T. polyacantha, T. pisiformis and T. serialis). There were two other parasites recorded by Moks (Reference Moks2008) but not found in this study: Spirocerca lupi and an unidentified acanthocephalan. Taking into account the results of these two studies, Estonian red foxes seem to harbour a minimum of 21 helminth species, which is very similar with the results from a Danish study (n = 21; Saeed et al. Reference Saeed, Maddox-Hyttel, Monrad and Kapel2006), but less than found in Iberia (n = 34; Segovia et al. Reference Segovia, Torres and Miquel2004) and Belarus (n = 32; Shimalov and Shimalov, Reference Shimalov and Shimalov2003).
Despite the smaller number of animals examined from the autumn period (n = 11) than from winter (n = 87), we found that foxes sampled in autumn harboured on average more helminth species (mean number of helminths 7·7 vs 6·3). This finding is supported by the fact that the availability of different food categories is higher in autumn: all the crops ripen during that period, amphibians are in move to find hibernating places and the abundance of small rodents is the highest. Thus, all these food categories represent potential sources of different helminth infections.
Variation between males and females
Sexual dimorphism, with males being larger than females, has previously been reported in red foxes by Cavallini (Reference Cavallini1995) and Heptner and Naumov (Reference Heptner and Naumov1998). In this study, we also found that males weighed significantly more than females. Although we did not detect any significant relationship between the animal sex and the number of helminth species, male foxes harboured on average more T. canis, whereas M. patens occurred more often in females. The difference in the infection between the sexes could be associated with different food habits: while the females consumed more rodents, the remains of larger mammals were more prevalent in the stomach of male foxes in Estonia (E. Soe, personal communication).
Co-occurrence analyses
In principle, a parasite species could facilitate or prevent the infection of another parasite species. However, we did not detect any significant competitive or facilitative interaction (Supplementary Table S1) regardless that four of the most prevalent parasite species (A. alata, U. stenocephala, E. aerophilus and P. plica) frequently appeared together in one host. It is important to note, however, that as the analysis determines whether the level of co-occurrence is higher or lower than what would be expected at random, abundant species will also occur with high co-occurrence at random.
Since the parasite fauna of an animal is intimately related to its feeding habits (most parasites must be ingested in order to infect the host organism), and as the fox diet has been studied in the same animals as used in this study (Soe et al. unpublished observation), it was also possible to assess the co-occurrence of parasite species and food categories. For this analysis identifiable material obtained from stomachs of hunted foxes was sorted into six food categories: (1) Birds, (2) Fish, (3) Invertebrates, (4) Plants (fruit and cereal), (5) Ungulates (wild boar, roe deer carrion) and (6) Small mammals (rodents). However, the co-occurrence analysis between parasite species and food categories did not reveal any significant relationships (not shown), although we expected to find some, e.g. between ‘Small mammals’ and E. multilocularis, as this parasite is assimilated by consuming the mentioned food category. One of the reasons for not detecting any significant effects could be that the stomach content analysis reflects animal's food consumption during a short time period (basically the last meal). Significantly larger sample size could potentially help to overcome this limitation.
Red fox as a vector for zoonotic parasites in Estonia
Of the 17 endoparasite taxa recorded in this study, ten are of zoonotic importance (Table 1), capable of causing serious health problems to humans, but also to domesticated animals. Echinococcus multilocularis, a tapeworm causing potentially fatal disease – alveolar echinococcosis – in humans (Eckert et al. Reference Eckert, Gemmell, Meslin and Pawlowski2001; Vuitton et al. Reference Vuitton, Demonmerot, Knapp, Richou, Grenouillet, Chauchet, Vuitton, Bresson-Hadni and Millon2015), is probably the most important zoonotic agent found in this study. Typical transmission cycle of E. multilocularis in Europe is wildlife-based, involving red foxes as predominant definitive host and small rodents as intermediate host. In addition to red foxes, several other canid species, e.g. the arctic fox (Vulpes lagopus), raccoon dog, golden jackal (Canis aureus) and grey wolf (Canis lupus), can act as definitive hosts for E. multilocularis in Europe (Eckert et al. Reference Eckert, Gemmell, Meslin and Pawlowski2001; Fuglei et al. Reference Fuglei, Stien, Yoccoz, Ims, Eide, Prestrud, Deplazes and Oksanen2008; Szell et al. Reference Szell, Marucci, Pozio and Sreter2013; Marcinkute et al. Reference Marcinkute, Šarkunas, Moks, Saarma, Jokelainen, Bagrade, Laivacuma, Strupas, Sokolovas and Deplazes2015). Humans are considered as accidental hosts for this parasite and they can be infected by ingesting parasite eggs via direct contact with a definitive host or through contact with contaminated water, soil or food (Eckert et al. Reference Eckert, Gemmell, Meslin and Pawlowski2001). Upon infection, the parasite causes tumour-like cysts in internal organs of humans, mainly in the liver, but can also spread to other distant organs.
During a previous pilot study of Estonian red foxes about a decade ago, E. multilocularis was found in 29·4% (5/17) of red foxes (Moks et al. Reference Moks, Saarma and Valdmann2005). As only a small number of carcasses were examined in that study, we aimed to specify the abundance of E. multilocularis by involving considerably higher number of fox samples. Nonetheless, we found a rather similar share of infected animals (31·5%), confirming the relatively high infection rate of E. multilocularis among Estonian red foxes. Even higher prevalence rates have been reported for foxes in Lithuania (58·7%; Bružinskaite-Schmidhalter et al. Reference Bružinskaite-Schmidhalter, Šarkunas, Malakauskas, Mathis, Torgerson and Deplazes2012) and in Kyrgyzstan (63·6%; Ziadinov et al. Reference Ziadinov, Deplazes, Mathis, Mutunova, Abdykerimov, Nurgaziev and Torgerson2010). The highest number of E. multilocularis specimens counted earlier in Estonian red fox was 927 (Moks et al. Reference Moks, Saarma and Valdmann2005). Although we stopped parasite counting at 200 in this study, two samples likely included more than 1000 specimens. Moks et al. (Reference Moks, Saarma and Valdmann2005) identified E. multilocularis-positive foxes from all three counties examined (Hiiu, Põlva, Tartu), whereas the infected animals from this study originated from six counties (Harju, Pärnu, Põlva, Rapla, Tartu and Valga; Fig. 1). However, the parasite is likely to exist all over the country and only due to low sample size the infection was not found in animals from counties Järva (n = 1) and Viljandi (n = 2). Estonia has the lowest human echinococcosis rate of the three Baltic States (Marcinkute et al. Reference Marcinkute, Šarkunas, Moks, Saarma, Jokelainen, Bagrade, Laivacuma, Strupas, Sokolovas and Deplazes2015): altogether 13 cases of unspecified echinococcosis have officially been registered in Estonia since 1986. However, considering the rapid increase in fox numbers during 2006–2010 (Plumer et al. Reference Plumer, Davison and Saarma2014), the number of human cases could grow in coming years as the incubation period for E. multilocularis is usually 5–15 years.
One of the reasons why the proportion of infected foxes has remained high could be related to supplementary feeding sites. While these sites are intended for wild boars (Sus scrofa), they are also known to attract many non-target species, e.g. rodents, red foxes and raccoon dogs (Oja, Reference Oja2011). Rodents, as the intermediate host species for E. multilocularis, can easily become infected with the tapeworm by eating contaminated substances at the supplementary feeding sites. Rodents, however, constitute a large share of red foxes diet in Estonia (Süld et al. Reference Süld, Valdmann, Laurimaa, Soe, Davison and Saarma2014). Supplementary feeding sites therefore represent potential hot-spots for the spread of E. multilocularis and other zoonotic pathogens in Estonian wildlife.
While susceptible to E. multilocularis, the red fox seems ‘immune’ to another species of this genus, namely the Echinococcus granulosus, although the parasite can infect the red fox in nature (Jenkins and Craig, Reference Jenkins and Craig1992; Segovia et al. Reference Segovia, Torres and Miquel2004; Keidans et al. Reference Keidans, Kruklite and Keidane2005). Moreover, no significant difference in growth, segmentation or maturation of the parasite has been detected between dogs and foxes (Thompson, Reference Thompson1983). Echinococcus granulosus has been recorded in Estonia in other canid species, such as the grey wolf (Moks et al. Reference Moks, Jõgisalu, Saarma, Talvik, Järvis and Valdmann2006) and domestic dog (Laurimaa et al. Reference Laurimaa, Davison, Süld, Plumer, Oja, Moks, Keis, Hindrikson, Kinkar, Laurimäe, Abner, Remm, Anijalg and Saarma2015c ), but never in foxes. Both moose (Alces alces; Moks et al. Reference Moks, Jõgisalu, Valdmann and Saarma2008) and roe deer (Capreolus capreolus; Marcinkute et al. Reference Marcinkute, Šarkunas, Moks, Saarma, Jokelainen, Bagrade, Laivacuma, Strupas, Sokolovas and Deplazes2015) have been reported as intermediate host species for the parasite in Estonia, but foxes apparently do not consume internal organs of these ungulate carcasses available in nature. On the other hand, the susceptibility to infection could depend on the genotype of E. granulosus: while the infection in foxes has been proven with genotype G1 (Thompson, Reference Thompson1983; Jenkins and Craig, Reference Jenkins and Craig1992), this genotype has in Estonia been reported only in few dogs (Laurimaa et al. Reference Laurimaa, Davison, Süld, Plumer, Oja, Moks, Keis, Hindrikson, Kinkar, Laurimäe, Abner, Remm, Anijalg and Saarma2015c ), whereas the most abundant genotypes in the country appear to be G8 and G10 (Moks et al. Reference Moks, Jõgisalu, Valdmann and Saarma2008; Marcinkute et al. Reference Marcinkute, Šarkunas, Moks, Saarma, Jokelainen, Bagrade, Laivacuma, Strupas, Sokolovas and Deplazes2015). As G1 is evolutionarily highly divergent from G8 and G10 (Saarma et al. Reference Saarma, Jõgisalu, Moks, Varcasia, Lavikainen, Oksanen, Simsek, Andresiuk, Denegri, Gonzalez, Ferrer, Garate, Rinaldi and Maravilla2009; Knapp et al. Reference Knapp, Nakao, Yanagida, Okamoto, Saarma, Lavikainen and Ito2011), it could result in variations in infectivity between different E. granulosus genotypes.
Shortly after the oral vaccination campaign against rabies was imposed to Estonian wildlife in 2005, the number of foxes started to increase rapidly (Veeroja and Männil, Reference Veeroja and Männil2015). With eradicating rabies from Estonia (Pärtel, Reference Pärtel2013), one of the most important factors regulating the fox population size was lost. However, after the harsh winter of 2010/2011 sarcoptic mange started to spread extensively and the estimated number of foxes has since been continuously decreasing (Veeroja and Männil, Reference Veeroja and Männil2015). Sarcoptic mange has been reported to be the main cause in reducing population densities of red foxes and raccoon dogs in Estonia (Süld et al. Reference Süld, Valdmann, Laurimaa, Soe, Davison and Saarma2014, Laurimaa et al. Reference Laurimaa, Süld, Davison, Moks, Valdmann and Saarma2016) and elsewhere in Europe (Kauhala and Kowalczyk, Reference Kauhala and Kowalczyk2011). Scabies (mange) is a contagious disease that can infect domestic animals, notably dogs and the disease has been reported from urban foxes in Estonia (Plumer et al. Reference Plumer, Davison and Saarma2014). Animal scabies can also occasionally infect humans, causing severe itching as it burrows into the skin, but this infection is usually short-lived (Arlian, Reference Arlian1989; Heukelbach and Feldmeier, Reference Heukelbach and Feldmeier2006). Although the prevalence of sarcoptic mange in Estonian foxes is 21·2%, the actual proportion of infected animals could be lower. It could be suggested that the skinned animals (n = 12) provided by the hunters were also scabies-free, since the hunters only collect the skin of healthy animals (fur of wild fox is inexpensive and the costs of hunting and tannery are high).
Animals infected with scabies are frequently undernourished (Newman et al. Reference Newman, Baker and Harris2002), and are therefore constantly in search of food, encountering potentially a wider range of different parasites than healthy animals. As the animals examined in this study were from the period when mange became widespread in Estonia (2010–2012), comparison of parasite fauna in scabied and healthy animals was of considerable interest. In this study, we showed that although there was no statistically significant difference in the number of helminth species between scabied and healthy foxes (P = 0·06), the infected foxes appeared to harbour more helminth species (mean numbers 7·33 and 6·18, respectively). Scabied animals were also parasitized with higher number of parasite specimens. In addition, we found that parasite infection was more intense among scabied animals in case of three nematode species: U. stenocephala, T. canis and E. aerophilus (Table 2). Uncinaria stenocephala and T. canis are typical geohelminths and animals could have got the infection by simply cleaning their fur, which is already in bad condition due to the sarcoptic mange. It is not clear why such relation was found with E. aerophilus. This nematode is located in respiratory organs of the definitive host, suggesting that there might be an association with scabies and lung parasites. It is likely that infection with this species occurred more frequently in scabied animals because earthworms, the intermediate hosts for E. aerophilus, are relatively easy to catch.
Although the most prevalent parasite species identified in this study P. plica (91·5%) is not considered as zoonotic, the three other species (A. alata, E. aerophilus, U. stenocephala) with both high prevalence rate and mean intensity (Table 1) can be considered as parasites with high zoonotic potential. Clinical symptoms of the lung worm E. aerophilus are mainly pulmonary (Laloševic et al. Reference Laloševic, Laloševic, Klem, Stanojev-Jovanovic and Pozio2008). The nematode is mostly transmitted with earthworms, but humans can probably be infected directly by ingesting the parasite eggs with inadequately washed vegetables. Uncinaria stenocephala and A. alata can occasionally infect humans and cause severe diseases that are characterized by migrating larvae (Tamminga et al. Reference Tamminga, Bierman and de Vries2009; Wasiluk, Reference Wasiluk2009). Infectivity to humans and the observed high prevalence rates in Estonia make E. aerophilus, U. stenocephala and A. alata together with E. multilocularis the pathogens representing a considerable public health risk. Lithuania is the only country, where P. plica, A. alata, E. aerophilus and E. multilocularis are even more abundant among red foxes than in Estonia (Bružinskaite-Schmidhalter et al. Reference Bružinskaite-Schmidhalter, Šarkunas, Malakauskas, Mathis, Torgerson and Deplazes2012; Marcinkute et al. Reference Marcinkute, Šarkunas, Moks, Saarma, Jokelainen, Bagrade, Laivacuma, Strupas, Sokolovas and Deplazes2015), making the Baltic region hyperendemic for these four parasite species.
SUPPLEMENTARY MATERIAL
The supplementary material for this article can be found at http://dx.doi.org/10.1017/S0031182016001013.
ACKNOWLEDGEMENTS
We wish to thank John Davison and Ragne Oja for their generous help.
FINANCIAL SUPPORT
U.S., E.M. and H.V. were supported by Institutional Research Funding (IUT20-32) from the Estonian Ministry of Education and Research; and the European Union through the European Regional Development Fund (Centre of Excellence FIBIR); L.L. and E.S. were supported by the Estonian Doctoral School of Ecology and Environmental Sciences.
