**6. Emerging, re-emerging, and vector-borne pathogens infecting European bison**

The twenty-first century brings new challenges of the protection of animal health, including free living. Social and economic changes, globalization, intensification of intra- and intercontinental trade and travels, and environment and climate change contributed to the observed increase in the risk of emergence and re-emergence of pathogens [66]. The last few years have brought an increase in the importance of new pathogens, completely unknown before or not present in a given geographical latitude [67, 68], which may also have a significant impact on the health of an endangered species such as the European bison. It is related to processes related to human activity or changes in the environment but also to the development of science, improvement of disease diagnostics, and the introduction of new cognitive techniques, such as metagenomics and next-generation sequencing (NGS). Due to the habitat and the maintenance of a part of the European bison population in captivity, they are exposed to pathogens from both wild and domestic animals. Along with climate change, infections caused by pathogens transmitted by vectors such as arthropods (ticks, biting midges, mosquitoes) are more and more frequently reported in our part of Europe. In 2007, the first cases of infection with bluetongue virus (BTV) serotype 8 (BTV-8) causing significant mortality in European bison at an enclosure in Hardehausen occurred. The virus is transmitted by the blood-sucking midges of the family of *Culicoides* spp. (**Figure 7a, b**). BTV infections have never been detected as far north of Europe. During the epizootics more than 30% of European bison kept in Hardehausen died, and the surviving animals received a vaccine containing homologous inactivated BTV-8 [69]. BTV-8 epizootics did not reach Poland; however another strain, BTV-14, was detected almost simultaneously in cattle and in European bison at the northeast of Poland, near the Belarusian and Lithuanian borders [11, 70].

The source remains puzzling, particularily since the virus was highly homologous to South African BTV-14 reference strains used in vaccines, which were never used in Europe. However, closely related BTV-14 was detected in Russia almost at the same time. Therefore, combining this with the dynamics of geographical spread of BTV-14 in Poland, use of some illegal vaccine containing or contaminated with this BTV strain was suggested [71]. Serosurveillance of BTV in European bison showed that the infections occurred only in the eastern populations [11]. Interestingly, despite that the discovered BTV-14 has been described as attenuated strain causing only subclinical infection in cattle, significant association between health status of European bison and the presence of specific antibodies was observed [11]. The exposure rate to BTV in selectively eliminated and fallen animals in respect to healthy ones was clear; however multivariable analysis has not confirmed the health status as a risk factor. Notwithstanding, the most important consequences of the occurring of BT are the culling of diseases or suspected animals and restrictions on the movement of animals, since the disease is notifiable disease listed by the World Organization. Control or eradication of BTV in protected wild species such as European bison is rather doomed, especially that the environment provides more susceptible species such as cervids and favorable conditions for midge reproduction and survival [72, 73]. BTV epidemiological situation remains under continuous supervision (unpublished data). Additionally, the occurrence of epizootic hemorrhagic disease virus (EHDV) infections transmitted by *Culicoides* spp. in European bison in Poland was also ruled out [11]. However, since some diseases of wildlife considered so far as absent in certain geographic areas such as African swine fever in wild boar or chronic wasting disease (CWD) in cervids become endemic in Europe, the threat of EHD in the future should also be considered real [9].

After the bluetongue epizootics (BTV) in 2007 [67], a new pathogen named Schmallenberg virus (SBV) was identified in Europe in 2011 [74], which spread very quickly across the continent. The first SBV infection in cattle in Poland was found in 2012, and in the same year, virus transmission to the ruminants of free-living ruminants in the Białowieża Forest, including European bison, was observed [75]. The first case of acute SBV infection in wild animals was actually confirmed in a fallen elk calf rescued by the animal keepers of the Białowieża National Park [76, 77]. This was the first report on the identification of the SBV virus in a free-living animal that began an international discussion on the importance of free-living animals as a reservoir of this new virus [77]. It proceeded the subsequent surveillance of European bison and other

#### **Figure 7.**

*BTV, EHDV, and SBV insect vectors: biting midges of Culicoides obsoletus species—(a) freshly blood-fed and (b) gravid (containing a mature egg batch in the abdomen). Ultraviolet (UV) light trap (CDC 1212, John W. Hock Company, USA) for Culicoides spp. midges collection set at the Show Reserve in Białowieża National Park (c) (photo: Ł. Mazurek). The midges are active at night; therefore the trap was set on from dusk till dawn once a week during the vector activity season (April-October). UV light attracts the insects, which were trapped and fell down into the jar containing water with detergent [73].*

**159**

**7. Conclusions**

*Infectious Disease Monitoring of European Bison (*Bison bonasus*)*

wild ruminants at Białowieża Forest, what allowed to determined that the transmission of SBV occurred during 2012 *Culicoides* activity season [76]. Further studies concentrated on the epidemiology of SBV in European bison and the environment (other susceptible species, vector) [11, 73, 78]. SBV seroprevalence in European bison in all studies was significantly much higher than observed in the cervids sampled simultaneously at the same locations. It is not, however, due to the higher susceptibility of the European bison to SBV infection, rather than higher exposure to midge biting. Similar differences were reported between cattle and small ruminants. Most probably, higher exposure in larger ruminants is associated with their higher production of carbon dioxide, one of the strongest attractants of many arthropods including *Culicoides* spp. [79, 80]. SBV *in utero* infections may lead to congenital malformations of newborns, stillbirths, or abortions. Limited access to the material of aborted fetus in the wild European bison did not allow to draw many conclusions [73]; however

some losses in reproduction rate may be expected as observed in cattle.

infections including BTV in the sylvatic habitat of European bison.

European health remains unexplored.

able, and therefore the studies are being continued.

Since the transmission of arthropod-borne pathogens involves environmental factors, entomological and virological studies of the midges near European bison were performed between 2014 and 2015 [73]. Using specially designed ultraviolet (UV) light traps (**Figure 7c**) placed near European bison resting places at Białowieża National Park abundance, species composition and virus exposure were tested. The wood midges of *Culicoides achrayi* species were the most abundant with almost 280 thousand (over 50% of the whole midge number collected) individual midges of the species trapped over the 2-year period [73]. The presence of SBV was confirmed in some midges trapped in 2015. The work except its originality provided very needed data to study all *Culicoides*-borne

Further studies suggest that European bison may be an important reservoir of tick-borne Lyme disease, since *Borrelia burgdorferi* was detected in blood of several animals in Białowieża [81]. Earlier, the presence of specific antibodies to *B. burgdorferi* was confirmed in European bison in the same area in the 1990s [82]. Other documented in European bison investigations of the infections transmitted by ticks include tick-borne encephalitis (TBE), tularemia, and anaplasmosis. While TBE virus was detected in the ticks collected from European bison [83], no antibodies supported the hypothesis that the species is an important reservoir of the virus [84]. European bison probably have little importance in the transmission of another zoonotic pathogen, *Francisella tularensis*, since none of the 251 individuals from eight Polish populations had antibodies against the bacteria according to Krzysiak et al. [46]. However, it is different when *Anaplasma phagocytophilum* responsible for human granulocytic ehrlichiosis (HGE) is considered. This tick-transmitted bacterium was found in a blood of over 66% of European bison in Białowieża Forest [85]. The pathogen was also confirmed to be present in the ticks collected from the animals [86]. However, whether any of the detailed tick-borne pathogens influences

The last emerging disease with high epizootic potential we would like to discuss shortly is hepatitis E. The pigs including wild boar are the main reservoirs of hepatitis E virus (HEV); however, cases of virus to humans through cervid meat have been also reported. In a recent study, none of the European bison had antibodies against HEV [87]; however, the sensitivity of the methods to ruminants is debat-

European bison survived to the present times, only thanks to human care and protection. Because Europe, unlike the Americas, was significantly more

*DOI: http://dx.doi.org/10.5772/intechopen.84290*

#### *Infectious Disease Monitoring of European Bison (*Bison bonasus*) DOI: http://dx.doi.org/10.5772/intechopen.84290*

*Wildlife Population Monitoring*

also be considered real [9].

The source remains puzzling, particularily since the virus was highly homologous to South African BTV-14 reference strains used in vaccines, which were never used in Europe. However, closely related BTV-14 was detected in Russia almost at the same time. Therefore, combining this with the dynamics of geographical spread of BTV-14 in Poland, use of some illegal vaccine containing or contaminated with this BTV strain was suggested [71]. Serosurveillance of BTV in European bison showed that the infections occurred only in the eastern populations [11]. Interestingly, despite that the discovered BTV-14 has been described as attenuated strain causing only subclinical infection in cattle, significant association between health status of European bison and the presence of specific antibodies was observed [11]. The exposure rate to BTV in selectively eliminated and fallen animals in respect to healthy ones was clear; however multivariable analysis has not confirmed the health status as a risk factor. Notwithstanding, the most important consequences of the occurring of BT are the culling of diseases or suspected animals and restrictions on the movement of animals, since the disease is notifiable disease listed by the World Organization. Control or eradication of BTV in protected wild species such as European bison is rather doomed, especially that the environment provides more susceptible species such as cervids and favorable conditions for midge reproduction and survival [72, 73]. BTV epidemiological situation remains under continuous supervision (unpublished data). Additionally, the occurrence of epizootic hemorrhagic disease virus (EHDV) infections transmitted by *Culicoides* spp. in European bison in Poland was also ruled out [11]. However, since some diseases of wildlife considered so far as absent in certain geographic areas such as African swine fever in wild boar or chronic wasting disease (CWD) in cervids become endemic in Europe, the threat of EHD in the future should

After the bluetongue epizootics (BTV) in 2007 [67], a new pathogen named Schmallenberg virus (SBV) was identified in Europe in 2011 [74], which spread very quickly across the continent. The first SBV infection in cattle in Poland was found in 2012, and in the same year, virus transmission to the ruminants of free-living ruminants in the Białowieża Forest, including European bison, was observed [75]. The first case of acute SBV infection in wild animals was actually confirmed in a fallen elk calf rescued by the animal keepers of the Białowieża National Park [76, 77]. This was the first report on the identification of the SBV virus in a free-living animal that began an international discussion on the importance of free-living animals as a reservoir of this new virus [77]. It proceeded the subsequent surveillance of European bison and other

*BTV, EHDV, and SBV insect vectors: biting midges of Culicoides obsoletus species—(a) freshly blood-fed and (b) gravid (containing a mature egg batch in the abdomen). Ultraviolet (UV) light trap (CDC 1212, John W. Hock Company, USA) for Culicoides spp. midges collection set at the Show Reserve in Białowieża National Park (c) (photo: Ł. Mazurek). The midges are active at night; therefore the trap was set on from dusk till dawn once a week during the vector activity season (April-October). UV light attracts the insects, which were trapped* 

*and fell down into the jar containing water with detergent [73].*

**158**

**Figure 7.**

wild ruminants at Białowieża Forest, what allowed to determined that the transmission of SBV occurred during 2012 *Culicoides* activity season [76]. Further studies concentrated on the epidemiology of SBV in European bison and the environment (other susceptible species, vector) [11, 73, 78]. SBV seroprevalence in European bison in all studies was significantly much higher than observed in the cervids sampled simultaneously at the same locations. It is not, however, due to the higher susceptibility of the European bison to SBV infection, rather than higher exposure to midge biting. Similar differences were reported between cattle and small ruminants. Most probably, higher exposure in larger ruminants is associated with their higher production of carbon dioxide, one of the strongest attractants of many arthropods including *Culicoides* spp. [79, 80]. SBV *in utero* infections may lead to congenital malformations of newborns, stillbirths, or abortions. Limited access to the material of aborted fetus in the wild European bison did not allow to draw many conclusions [73]; however some losses in reproduction rate may be expected as observed in cattle.

Since the transmission of arthropod-borne pathogens involves environmental factors, entomological and virological studies of the midges near European bison were performed between 2014 and 2015 [73]. Using specially designed ultraviolet (UV) light traps (**Figure 7c**) placed near European bison resting places at Białowieża National Park abundance, species composition and virus exposure were tested. The wood midges of *Culicoides achrayi* species were the most abundant with almost 280 thousand (over 50% of the whole midge number collected) individual midges of the species trapped over the 2-year period [73]. The presence of SBV was confirmed in some midges trapped in 2015. The work except its originality provided very needed data to study all *Culicoides*-borne infections including BTV in the sylvatic habitat of European bison.

Further studies suggest that European bison may be an important reservoir of tick-borne Lyme disease, since *Borrelia burgdorferi* was detected in blood of several animals in Białowieża [81]. Earlier, the presence of specific antibodies to *B. burgdorferi* was confirmed in European bison in the same area in the 1990s [82]. Other documented in European bison investigations of the infections transmitted by ticks include tick-borne encephalitis (TBE), tularemia, and anaplasmosis. While TBE virus was detected in the ticks collected from European bison [83], no antibodies supported the hypothesis that the species is an important reservoir of the virus [84]. European bison probably have little importance in the transmission of another zoonotic pathogen, *Francisella tularensis*, since none of the 251 individuals from eight Polish populations had antibodies against the bacteria according to Krzysiak et al. [46]. However, it is different when *Anaplasma phagocytophilum* responsible for human granulocytic ehrlichiosis (HGE) is considered. This tick-transmitted bacterium was found in a blood of over 66% of European bison in Białowieża Forest [85]. The pathogen was also confirmed to be present in the ticks collected from the animals [86]. However, whether any of the detailed tick-borne pathogens influences European health remains unexplored.

The last emerging disease with high epizootic potential we would like to discuss shortly is hepatitis E. The pigs including wild boar are the main reservoirs of hepatitis E virus (HEV); however, cases of virus to humans through cervid meat have been also reported. In a recent study, none of the European bison had antibodies against HEV [87]; however, the sensitivity of the methods to ruminants is debatable, and therefore the studies are being continued.
