Przewalski’s horses (
In 1992 the first two reintroduction projects were launched in Mongolia, to restore a population of Przewalski’s horse within their native area. At present, 12 large breeding and reintroduction centers for Przewalski’s horses have been established in Europe (France, Hungary, Ukraine) and in Asia (China, Mongolia, Uzbekistan, Kazakhstan, Russia) (Zimmermann, 2004; Bakirova & Zharkikh, 2016). In 1998 – 1999 the first captive bred wild horses (n=21) were introduced to the Chernobyl Exclusion Zone (CEZ) from the Askania Nova Biosphere Reserve in Ukraine. The purpose of this introduction was breeding of this unique equid species as well as to re-wild the area through grazing by wild horses.
Currently there are about 130 Przewalski
However, over the last decade, no data regarding gastrointestinal parasites within the population of wild Przewalski
Parasitological studies of wild Przewalski’s horses kept in zoos, semi-reserves and natural reserves have been previously reported (Dvojnos, 1975; Dvojnos & Kharchenko, 1994; Epe et al., 2001; Elias et al., 2002; Slivinska et al., 2006; Zvegintsova et al., 2008; Painer et al., 2011; Liu et al., 2016; Kuzmina et al., 2009, 2017). Most of these studies were performed with coprological methods which determined the presence or absence of certain groups of intestinal parasites and estimated the intensity of infection by Fecal Egg Counts (FECs). A few publications have reported information on species composition and structure of intestinal parasites population (Dvojnos & Kharchenko, 1994; Slivinska & Dvojnos, 2006; Kuzmina et al., 2009, 2017). Nematodes from the family Strongylidae are the most prevalent and pathogenic group of intestinal parasites of wild and domestic horses worldwide (Dvojnos & Kharchenko, 1994; Love et al., 1999; Lichtenfels et al., 2008). Coprological examination of intestinal helminths of wild horses is the only ante-mortem method available to study parasites of free-roaming Przewalski’s horses in the CEZ (Zvegintsova et al., 2008) as well as wild horses worldwide (Rubenstein & Hohmann, 1989; Debaffe et al., 2016; Cain et al., 2018; Harvey et al., 2019).
Previously, differences in strongyle faecal egg counts between adults wild Przewalski
The aim of this study was to investigate the difference in Fecal Egg Counts (FECs) with regard to group size, age, sex and body condition of wild free-roaming Przewalski
The CEZ is located c. 200 km N of Kiev, Ukraine (51.3°N; 30.005°E), 123 m above sea level. This zone covers an area of 2,600 km2 and falls entirely within the Polesie Lowland, Russian Plain. The climate in the CEZ is humid, with relatively mild winters and warm summers. The mean annual temperature is 5 – 7°C, with a mean temperature in July of 18°C (max. 32°C), and in January of -6°C (min. -25°C). The annual precipitation ranges from 550 to 750 mm. The snow cover lasts on average c. 50 days per year. The mean depth of the snow cover is 12 – 13 cm (Barjachtar et al.(ed), Chernobyl disaster 1996).
The CEZ is surrounded by metal fencing two meters high. Approximately c. 50 peasants also are still living in the CEZ; only few other persons have constant access to this area. Before the nuclear disaster, the CEZ consisted of farmlands with patchy areas of forest. Currently, ca. 60 % of the area is covered with forests, 50 % of which is pine forest and the remaining consists of abandoned arable grounds, meadows, pastures and human settlements.
Faecal samples from wild Przewalski
During this time the location of feces deposition was determined for each horse. After the group moved to graze to other sites of the meadow, samples of feces were collected and the GPS location was recorded for each collection (Fig. 1). During each survey, samples of fresh feces that were found on roads or other open places, were also collected. The samples were cooled in a portable refrigerator, transported to a laboratory and stored in a refrigerator at 3°C for 2 – 6 days, until analyzed. 72 fecal samples were performed according to the spring season (13 in 2014, 14 in 2015, 15 in 2016 and 30 in 2017, respectively) and 46 fecal samples were performed according to the autumn season (38 in 2015 and 8 in 2018, respectively). In total, 118 fecal samples were examined from April 2014 to September 2018. Although we were able to distinguish horses during collection of samples during one year, we were not able to check weather samples were collected from the same horse during the following years.
Fecal egg counts (FECs) were performed using the McMaster technique, with a sensitivity of 25 Eggs Per Gram feces (EPG) (Herd, 1992). Mean FEC (average number of EPG per infected animal) and prevalence (percentage of animals infected) were calculated for each horse individually, and assigned to either ‘harems’ or ‘bachelor groups’. Fresh feces that were opportunistically found on roads or other open places were assigned as ‘unknown groups’. A total of 118 horses from 21 groups (14 harems; 4 bachelor groups; 3 unknown groups) were examined.
For further analysis, we used samples that were positive for strongylids egg counts, which was the most common species observed. We excluded 8 samples where other species of parasites were more common (over 50 eggs EPG) since different parasite species can influence the FECs of other parasitic species (Paterson & Lello, 2003). To investigate the differences in strongylid parasitic infection, we used a generalized linear model with egg counts of strongylids as a response variable. The sex, age of each known horse, season (spring and autumn) and the year of the sample collection were fixed factors; the group size was a covariate. In this model we used a Tweedie distribution with log link after comparison with the Poisson and a negative binomial distribution model using the Akaike information criterion (AIC) and the Bayesian information criterion (BIC). The model with Tweedie distribution showed lower values of both information criteria (AIC and BIC). Selection of the models was performed with backward elimination procedure basing on the AIC values. The model was constructed with SPSS software (version 24.0, IBM Corporation, Armonk, NY).
Nematode (Strongylidae,
Egg counts of the gastrointestinal parasites of wild Przewalski’s horses in the Chernobyl Exclusion Zone between April 2014 to September 2018. (EPG – eggs per gram of feces; EI – prevalence of infections; FEC – mean fecal egg counts, SD – standard deviation)
Year | Group type (n = number of horses) | No. of feces samples | Strongylidae | Parascaris spp |
Habronematidae | Anoplocephalidae | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
EI, % | FEC, EPG | ±SD | EI, % | FEC, EPG | ±SD | EI, % | FEC, EPG | ±SD | EI, % | FEC, EPG | ±SD | |||
2014 | Harem (5) | 5 | 100 | 470 | 258.2 | - | - | - | 60 | 41.7 | 29.9 | |||
Harem (8) | 8 | 100 | 925 | 512.3 | - | - | - | - | - | - | - | - | - | |
2015 | Harem (15) | 3 | 100 | 158.3 | 52 | - | - | - | - | - | - | |||
Harem (4) | 3 | 66.7 | 25 | 14.4 | - | - | - | - | - | - | ||||
Harem (5) | 2 | 100 | 37.5 | 17.7 | - | - | - | - | - | - | ||||
Harem (7) | 6 | 100 | 125 | 52.4 | - | - | - | - | - | - | ||||
Harem (11) | 3 | 66.7 | 187.5 | 175 | - | - | - | - | - | - | ||||
Bachelors (8) | 8 | 100 | 33.4 | 166.9 | - | - | 12.5 | 25 | 25 | 25 | 11.6 | |||
Unknown | 27 | 88.9 | 117.1 | 142.1 | 11.1 | 191.7 | 76.2 | - | - | 7.4 | 25 | 6.7 | ||
2016 | Harem (12) | 7 | 100 | 660.7 | 677.4 | - | - | - | - | - | - | |||
Harem (3) | 3 | 100 | 300 | 201 | - | - | - | - | - | - | ||||
Bachelors (5) | 4 | 100 | 487.5 | 512.6 | 25 | 25 | - | - | - | - | ||||
Unknown | 1 | 100 | 250 | - | - | - | - | - | - | |||||
2017 | Harem (8) | 4 | 100 | 718.8 | 451 | - | - | - | - | - | - | |||
Harem (14) | 11 | 100 | 788.6 | 377.9 | - | - | - | - | 9.1 | 25 | ||||
Harem (3) | 3 | 100 | 250 | 106.1 | 33.3 | 25 | - | - | 66.6 | 25 | ||||
Bachelors (11) | 11 | 100 | 479.5 | 237.4 | 18.2 | 112.5 | 123.7 | - | - | 9.1 | 25 | |||
Unknown | 1 | 100 | 600 | - | - | - | - | - | - | |||||
2018 | Harem (3) | 2 | 100 | 250 | 70.7 | - | - | - | - | - | - | - | - | - |
Harem (9) | 2 | 100 | 112.5 | 17.7 | 50 | 25 | - | - | - | - | - | - | - | |
Bachelors (6) | 4 | 100 | 193.8 | 104.8 | 25 | 25 | - | - | - | - | - | - | - |
The prevalence of parascarides infection was also recorded and ranged from 11.1 – 50 %. The mean FEC of
In additional, a few cestode eggs were detected in some groups of horses (7.4 – 66.6 %; 25 – 41.7
Externally observable clinical signs of parasitosis among these wild horses were not noted in any individual. All horses were in good clinical condition, with ‘regular’ body condition score and typical coat condition.
The best model for egg counts of strongylids in feces of Przewalski’s horses included the season, age and group size; and was highly statistically significant (Table 2). The model selection procedure excluded the variable “sex”, “year” and all interactions. Horses presented a significantly higher parasitic infection level during spring than autumn (p=0.000). During Spring, feces contained over three times a higher number of strongylids eggs than during autumn (mean= 624.5 and 219.6, respectively) – Fig. 2. Group size was positively correlated to strongylid FECs. The bigger the group size, the higher the strongylid FECs (p=0.045). Age was not statistically significant in this model.
Effects season, age and group size on the egg counts of strongylids in feces of Przewalski’s horses (
Source | Wald |
||
---|---|---|---|
Intercept* | 961.1 | 1 | 0.000 |
Season* | 52.58 | 1 | 0.000 |
Group size* | 4.03 | 1 | 0.045 |
Age | 1.65 | 2 | 0.439 |
The dominant helminth group (both in terms of prevalence and FEC) was Strongylidae. Domination by strongylids in the intestinal helminthic fauna of horses of the Chernobyl population has been previously reported (Slivinska, 2004; Slivinska et al., 2006; Zvegintsova et al., 2008). Other potentially important gastrointestinal parasites (
Strongylids are prevalent in horses of different breeds and throughout different regions of the world, despite huge climatic differences (Ogbourne, 1976; Anderson & Hasslinger, 1982; Reinemeyer et al., 1984; Krecek et al., 1989; Bucknell et al., 1995; Silva et al., 1999; Gawor, 1995; Lind et al., 2003; Kuzmina et al., 2005).
Wild horses of the CEZ were documented to have variable strongylid FECs, which depended on the season of sample collection and horses
Mean total egg emissions differ significantly depends of season according to our research. Four times higher values of strongylid FECs were in spring than in autumn (555.2
Group size was positively correlated to strongylid FECs. The results confirm previous studies, where the larger the group the higher the FEC (Rubenstein & Hohmann, 1989; Harvey et al., 2019). We hypothesize that this could be a result of parasite transmission between individuals within group, which is observed in areas where animals aggregate (Reinemeyer & Nielsen, 2018). Moreover, transmission may be higher than stated in other studies, because we have found a lack of influence of sex and age on strongylid FECs. In general, sex and age is indicated to influence the infection level in horses (Côté & Poulin, 1995; Bucknell et al., 1995; Romaniuk et al., 2004; Fikru et al., 2005; Francisco et al., 2009; Kornas et al., 2010). Significant differences in gastrointestinal parasite communities associated with sex were observed for intestinal strongylids: mares had significantly higher numbers of strongylids as compared to stallions (Slivinska et al., 2016). Moreover, significant differences with infection of intestinal parasites associated with age were observed for Strongylidae and
Results obtained in this study broaden the knowledge of parasite communities in free-roaming wild horses in the Chernobyl Exclusion Zone. This paper also documents factors that could influence the parasitic infections in wild horses under natural conditions.
Results obtained in this study broaden the knowledge of parasite communities in free-roaming wild Przewalski
Results presented in this study gives an overview of the situation over the years in protected animals inhabiting a peculiar niche, where the material is difficult to access and there are not many sources of knowledge regarding the health and parasitological status of these animals.
Results obtained in this study broaden the knowledge of parasite communities in free-roaming wild horses in the Chernobyl Exclusion Zone. This paper also documents factors that could influence the parasitic infecstations in wild horses underin natural conditions.