PREVALENCE OF THE GIANT LIVER FLUKE (Fascioloides magna, Bassi, 1875) IN RED DEER (Cervus elaphus) IN THE REGION OF FLOODPLAIN FORESTS OF NORTHERN SERBIA

This is the first study offering insights into the prevalence of giant liver fluke in the population of red deer in the territory of Serbia. Giang liver fluke (Fascioloides magna, Bassi, 1875) is the most important liver parasite among wild ruminants in Europe, especially in the region of floodplain forests along the upper watercourse of Danube river. The main objective of this research was establishing the prevalence of giant liver fluke in the region of floodplain forests of northern Serbia. In the observed regions (hunting grounds), the population prevalence rates ranged from 0 to 80% with an average prevalence in positive herds being 70.6%. The total population of red deer, from the observed hunting grounds, exposed to the giant liver fluke includes 47.9% of red deer population in Serbia, which is 0.7% of the total hunting area of Serbia. Giant liver fluke is present in north-western regions of Serbia in a narrow area of floodplain forests along the watercourse of Danube and Sava rivers next to the border with Croatia. The red deers populating the wetland basin of “Gornje Podunavlje” migrate freely through the tri-border area of Hungary, Croatia and Serbia making a consistent epizootical unit. Moreover, the game migrates freely between Croatia and Serbia in the area of Posavina forests along the river Sava. All data obtained in this research are essential for further activities aimed at preventing the spread of this parasite within red deer population and thus decreasing consequent damages and losses.

Ključne reči: američki metilj, evropski jelen, prevalencija, Dunav, Sava  (Erhardová, 1961). The organism is highly invasive species, which is mainly due to the wide spectrum of potential definitive and intermediate hosts, its pronounced ability to adapt to new hosts, extensive spatial distribution and potential to colonize new territories  The parasite is originally native to North America, but has been introduced to Europe during import of North American deers. The first case recorded in Europe was in the wapiti stag (Cervus elaphus nelsoni) imported in 1865 from Wyoming (USA) into the Royal National Park La Mandria in northwestern Italy (Pybus, 2001

MATERIAL AND METHODS
The research was conducted in the period September 2017 -January 2018 in the territory of northern Serbia (Vojvodina region) encompassing total 3.275 ha in the provinces of Bačka, Srem and Banat. In the province of Bačka, we observed the hunting areas: "Kozara", "Apatinski rit" and "Plavna", in the province of Srem "Bosutske šume", "Kućine" and "Karakuša", and in the province of Banat hunting ground "Deliblatska peščara" (Table 1.). The investigation sites are located along the watercourse of Danube and Sava rivers, mostly in floodplain forest habitats containing most dense red deer population. Observed red deer are grouped into three separate populations (Bačka, Srem, and Banat) based on territorial (regional) separation or degree of mutual contact (Figure 2.). The total area encompassed by the sampling was 60.396 ha with an estimated population of 3.275 deer game animals. A total of 79 samples of red deer liver was examined for the presence of the giant liver fluke (Fascioloides magna, Bassi, 1875). All animals encompassed by this research were shot during regular hunting. After shooting, the livers were collected, labeled and individually packet into the plastic bags and stored at 4 o C. Subsequently, parasitological and pathomorphological examination were performed. Parasitological and pathomorphological examination revealed the presence of parasites and the invasion rate and pathoanatomical liver changes were recorded. The obtained data were statistically analyzed using IBM SPSS Statistics 20 (IBM, Armonk, NY, USA), and for figure graphic processing we used software desktop QGIS 3.2.1 (OSGeo, USA) and CRS MGI 1901/Balkans zone 7, EPSG:3909. Figure 2. Location of the hunting ground (1. "Kozara", 2. "Apatinski rit", 3. " Plavna", 4. "Bosutske šume", 5. "Kućine", 6. "Karakuša", i 7. "Deliblatska peščara").

RESULTS
Total number of 79 livers from three distinct red deer populations was investigated as following: 25 livers from the hunting grounds in Bačka region, 26 livers from hunting grounds in Srem region and 28 livers from the hunting grounds in the Banat region revealing the overall prevalence of 45.6% (36/79) of positive animals. Among the red deer population on observed hunting grounds in the region of Bačka, the presence of parasite was confirmed in 80% (20/25) animals out of which 35% had 10≥ parasites in the liver, whereas the findings from hunting grounds in the region of Srem revealed parasite pres-ence in 61.5% (16/26) animals and 75% with 10≥ parasites in the liver. An average prevalence in populations with confirmed presence of giant liver fluke was 70.6% (36/51) animals, out of which 52.8% contained 10≥ parasites in the liver. On the observed hunting ground in the territory of Banat, the presence of giant liver fluke has not been confirmed in the population of red deer. All animals positive for the presence of giant liver fluke originated from floodplain forests along the upper watercourse of Danube and Sava rivers in Serbia. Giant liver fluke was identified in 36 livers. The observed pathoanatomical changes revealed presence of cysts filled with dark-coloured substance containing parasites, which in case of large number of individuals protrude above the liver surface and alter its outer appearance (Figure 3.). Liver parenchyma was marbled with dark pigmented stripes and spots in 63.9% (23/36) of cases, whereas perihepatitis was observed in 69.4% (25/36) livers.

DISCUSSION
First reports on the presence of giant liver fluke in Serbia date back to 2008. The parasite was indentified in fallow deer (Dama dama) originated from fenced hunting ground in South-Bačka District (Trailović et al., 2008(Trailović et al., , 2016. The data on the presence and/or distribution of giant liver fluke infection in red deer (Cervus elaphus) have not been available so far. Some available literature data on the presence of giant liver fluke among the red deer populations in neighboring countries such as Hungary and Croatia (Majoros and Sztojkov, 1994;Pybus, 2001;Marinculić et al., 2002;Janicki et al., 2005) suggested potential presence of the parasite in Serbia, especially in northwestern regions bordering Hungary and Croatia. In countries of the Danube River Basin, the programs for monitoring giant liver fluke in deer game have been implemented and are mainly based on the identification of parasites and/or their eggs in the faeces.
The prevalence of giant liver fluke recored in the observed population of red deer in the area of floodplain forests of northern Serbia ranged from 0 to 80.0% with an average prevalence in positive herds being 70.6% (61.5 -80.0%), which corresponds with the results in the countries of the Danube River Basin such as Slovakia, Austria, Hungary and Croatia, where prevalence rates sometimes exceeded 60% (Rajský et  In this research, we identified and defined the area in which the presence of giant liver fluke has been confirmed, that is, 46,495 ha of the total 60,396 ha that makes 0.7% and 2.4% of the total hunting ground surface in Serbia and Vojvodina, respectively, and with an average density of the investigated population being 5.6 animals / 100 ha. Total population exposed to the giant liver fluke infection includes 2,611 animals from observed hunting area of 46,495 ha, which makes 47.9% and 60.2% of red deer population in Serbia and Vojvodina Region, respectively.

CONCLUSION
The data on the prevalence of giant liver fluke within the observed hunting grounds in the area of floodplain forests of northern Serbia, provides important insights into the high rate of exposure and hazards to the population of red deer. Moreover, the broad transboundary epizootical area strongly suggest the necessity of continuous monitoring of distribution of giant liver fluke with an aim of preventing its spreading and preventing the damages and losses in the population of red deer in this area.