Gastrointestinal parasites of the Polish primitive horses from the Biebrza National Park

The Polish primitive horses (Equus caballus) represent a breed of domestic horses that bear a strong resemblance to tarpans, their wild ancestors which had lived on the steppes of southeastern Europe and Asia (Western Siberia). The original breed was completely extinct by the end of the 19^th century. In the mid-twentieth century, primitive horses exhibiting tarpans’ exterior were found in small farms of eastern Poland and saved in the reserve as the Polish primitive horses, a subspecies of tarpans. Currently, there are four reserves in Poland in which these horses are being kept in natural conditions. The horses are perfectly adapted to the natu40 ral environment and climate where they live throughout the year. Polish primitive horses are kept in Biebrza National Park (BNP), situated in the valley of the Biebrza River in northeastern Poland since 2004. The habitat of horses embraces 200 hectares of forest, grassland and marsh places, currently occupied by two herds (10 and 11 horses each). For veterinary and zootechnical control, all free-ranging horses are captured in the reserve during November – December. No anthelmintic treatment has been applied to date to these horses.

Despite the fact that Polish primitive horses are well known for their strong disease resistance, parasitic infections may infl uence their health. Until now the investigations of parasitic fauna in Polish primitive horses were performed in the Popielno Forest Reserve in northeastern Poland (Slivinska et al., 2009) and the Roztocze National Park in southeastern Poland (Slivinska et al., 2013). There are no data available on the gastrointestinal parasite community of horses from the Biebrza National Park.

The aim of this study was to investigate the gastrointestinal parasite community structure in previously untreated Polish primitive horses in the Biebrza National Park, and compare these results with those previously obtained in free-ranging horses from two other natu ral reserves.

The results presented herein are the first in vivo comparative investigations of parasite communities in free-ranging and stabled horses in Poland. The effectiveness of intravital collection of intestinal helminthes was shown to provide data comparable with those based on postmortem methods (Osterman Lind et al., 2003; Kuzmina et al., 2005).

Only one infection (Strongyloides westeri) was not confirmed with diagnostic deworming but was defined by presence of eggs in faeces of three foals from one free-ranging herd and one foal from the stable. Despite a mean of 150 and 400 eggs per gram in faecal samples, no threadworm specimens were recovered after deworming. Possibly it was the result of low infection intensity or the worms may have been overlooked during examination for expelled parasites. These nematodes have a very thin cuticle and thus probably specimens passed out disintegrated. Moreover, they could have been digested during their transfer from the intestine to the rectum and passed in the faeces.

The present results are similar to those obtained in the earlier surveys in the Polish primitive horses living in the free-ranging conditions (Slivinska et al., 2009, 2013). A total of 37 gastro-intestinal parasite species were recorded in wild and stabled horses from the BNP in comparison with 35 such species in horses from the Roztocze National Park (Slivinska et al., 2013) and 28 species in wild yearlings from the Popielno Forest Reserve (Slivinska et al., 2009) – Table 3. Among a total of 25 cyathostome species recovered in the current study (from 19 to 24 in one group), five species (C. catinatum, C. minutus, C. longibursatus, C. nassatus and C. ashworthi) were of 100 % prevalence in three herds, while 14 species were 100 % prevalent in at least one group. We found the same 25 small strongyle species in horses from two wild herds as in the Roztocze National Park reserve (Slivinska et al., 2013). In the present study we examined horses that were not dewormed previously, which suggested that there might exist a rich parasite fauna. Kuzmina et al., (2008). The study aimed to evaluate the influence of anthelmintic treatments on strongylid community structure based on the hypothesis that regular anthelmintic treatments cause a reduction of species richness, diversity and concentration in strongylid communities. These parameters were significantly higher in cyathostome communities of horses from nontreated and occasionally treated horses than in regularly treated horses. The strongylid communities of wild equids or equids from natural reserves are characterized by multimodal distribution of species, with dominant, subdominant, background and rare species (Kuzmina et al., 2008). Some cyathostome species found dominant or subdominant in the wild Polish horses in the present study and in the previous surveys, have been recorded as background or rare/very rare species in brood horses in Poland. Cylicostephanus bidentatus, fairly prevalent in this study in horses from the reserve (30 % and 72.7 %), also was found in one horse from the stabled group (10 %). This cyathostome species recorded in 27.3 % of yearlings in the Popielno Forest Reserve, was the first occurrence in the horse in Poland (Slivinska et al., 2009). Cyathostome species, with 9.1 % prevalence, were rare in yearlings from Popielno (Poteriostomum imparidentatum and Parapoteriostomum mettami), while Poteriostomum ratzii and Petrovinema poculatum were not recorded in these horses. The present study showed these four species being subdominant or dominant (54.6 – 81.8 %) in horses from one free-ranging herd (Group II). For comparison, the prevalence of these species in working horses examined after slaughter in central Poland was 2 %, 8 %, 10 % and 20 % for P. ratzii, P. poculatum, P. mettami and P. imparidentatum, respectively (Gawor 1995). More recent survey in irregularly dewormed domestic horses from southern Poland (Kuzmina et al., 2011) revealed P. poculatum, P. mettami and P. imparidentatum, Regarding four cyathostome species, namely Cylicostephanus hybridus, Cylicocyclus radiatus, Poteriostomum ratzii and Gyalocephalus capitatus found in the group I and/or the group II (10 – 45.5 %) and also recorded in the wild horses from Roztocze Park, neither of them were revealed in stabled horses in the current study, and nor in such horses from Roztocze Park (Table 2 and 3). These horses occasionally were dewormed, which possibly eliminated the presence of these rare/background species. However, even under frequent anthelmintic treatments, dominant species are still present in the strongylid community (Kuzmina et al., 2008). The present findings that a few cyathostome species constitute the bulk among strongylids in the wild horses are similar to results of surveys conducted in various breeds of horses in different countries, i.e. Poland and Ukraine (Gawor 1995; Kuzmina et al., 2011), Spain (Meana et al., 2004), United States (Reinemeyer et al., 1984; Lyons et al., 1997), South Africa (Scialdo-Krecek et al., 1983) and Australia (Mfitilodze & Hutchinson 1990). In the present study, 9 cyathostome species found in horses from Group I, 14 species from Group II and 10 species from Group III were 90 – 100 % prevalent and comprised 92.5 – 96.9 % of the strongyle population representing 89.8 – 93.2 % of the total parasites recovered in each group.

In general, surveyed horses from BNP, Roztocze and Popielno with the high helminth diversity were associated with low intensity of infection. The mean number of cyathostome specimens in the current study was 1.0 – 170.2 and 1.0 – 134.7 and 1.3 – 166.1 in Roztocze and Popielno, respectively. Concerning large strongyle species, the mean number in the present study was 1.0 – 9.1 and 1.5 – 11.0 in Roztocze or 1.9 – 2.5 in Popielno (Slivinska et al., 2009, 2013).

We found the same six large strongyle species in two groups from the BNP reserve, similar to the wild horses from the Roztocze National Park. In the current study no large strongyle infection was found in the six foals examined. These results differ from the previous results found in 11 yearlings captured in the Popielno Reserve in which S. vulgaris and Triodontophorus serratus were found; the prevalence was 81.8 % and 90.9 %, respectively (Slivinska et al., 2009). These differences may be due to the younger foals’ age in the current study (6 – 10 months) when compared to those examined in the Popielno Reserve (12 – 14 months). On the whole, in wild horses from the recently examined reserves, Roztocze and Popielno, S. vulgaris and S. edentatus were highly prevalent, 57.1 % – 93.8 % and 81.3 % – 85.7 %, respectively. Two recent surveys in rarely dewormed horses from individual farms in southeastern Poland revealed these species had prevalences of 4 % for each species (Kuzmina et al., 2011) and 22.8 % and 18.3 %, respectively (Studzińska et al., 2012). Recent studies from different countries have shown that in well managed horse populations, S. vulgaris have become uncommon among equine parasites. Increased occurrence of this most pathogenic parasite infecting horses, has recently been associated with the widely recommended selective therapy approach for parasite control (Nielsen et al., 2012). Reduced treatment intensities, with the general approach to leave untreated horses with a low egg count value (selective therapy), potentially delays development of ivermectin and moxidectin resistance in cyathostomes and ascarids. This approach to leave horses with low egg counts (selective therapy) untreated, may be a possible reason of an increased prevalence of S. vulgaris in stud farms and training stables (Nielsen et al., 2012).

The present and previous surveys in the wild Polish primitive horses from the reserves in Poland, confirmed that these horses represent populations from the pretreatment era with parasite fauna not infl fenced by deworming practices. Large strongyle species richness with the high prevalence of S. vulgaris and S. edentatus, seems to be proof of this assumption.

The prevalence of pinworms (Oxyuris equi) in horses in three examined herds in the current study (60 – 100 %) was higher than in yearlings from the Popielno Forest Reserve (23.1 %) (Slivinska et al., 2009). No oxyurids were recovered in horses from the Roztocze National Park (Slivinska et al., 2013). The prevalence of Parascaris equorum in adult mares was 16.7 % – 30 % which is similar to that found in mares from Roztocze (15.4 % – 25.0 %). Habronema muscae specimens with 30 % prevalence were recorded in one group of wild horses which is similar to results from Roztocze and Popielno (55.2 % and 18.2 %, respectively). Ano46 plocephala perfoliata with prevalence of 90 %, was found in one wild herd. This was similar to a level found in Roztocze (72.2 %), meanwhile in Popielno, 24.2 % of yearlings were found infected with tapeworms. The prevalence of the botfl y larvae (Gasterophilus intestinalis) was 50 – 80 %, which is different from their occurrence in wild horses in Popielno (90.9 %) and Roztocze (41.4 %) (Slivinska et al., 2009, 2013).

Among the major parasitic pathogens in horses, cyathostomins, P. equorum, A. perfoliata and S. vulgaris are mentioned. Along with G. intestinalis having the potential for serious abdominal disorders, all these parasites were found at high prevalences in wild horses examined in the present study. Reliable detection and differentiation of these parasites is an important requirement for diagnostics in equine parasitology. Diagnostic deworming, used with collection and identification of expelled parasites to the species level, is laborious method. However, it provides detailed information on prevalence and intensity of gastro-intestinal parasite infection, including tapeworms whose eggs are specifically difficult to detect by fecal examination. The wild horses living freely in the reserve and not treated previously with anthelmintics, represent exceptional hosts for investigation of the horse primeval, indigenous parasite fauna. Performing comparative studies between differently managed and not managed herds of horses helps to address proper recommendations for control programs and predict the consequences of inadequate treatment strategies used.