**5. Current major epidemic threats and monitoring of European bison**

When considering the problems of infectious and invasive diseases, three aspects (the so-called epidemiological triangle: animal-environment-pathogen) should be considered. The epizootic and epidemiological situation is a resultant of the interactions between the natural environment of the free-living animals, other wild reservoir species and farm animals at the wildlife-lifestock interface. An important environmental component will also be access to competent vectors of a given microorganism. In the case of environmental impact, it is also necessary to take into account people who are susceptible to zoonoses, can themselves be a source of infections, or can be a mechanical vector of infectious and invasive agents transmitted to animals, becoming endemic in sylvatic environment [39]. Those aspects meet in the One Health approach, which include wildlife as a key component of the ecosystem [9, 32, 40, 41]. Therefore, in the case of an epizootic, surveillance should be carried out in both domestic and non-domestic populations, both free-living and captive, and the potential role of humans (animal care takers, breeders, vets) as vectors should be taken into account. Climate, environment, socioeconomical changes create alterations also in the distribution of infectious diseases and remind us that animals and humans, environment, and pathogens are the elements of the same ecosystem.

In the last 20 years, the population size of European bison in Białowieża Forest and in the whole country increased more than twice (**Figure 2**). It generated an increasing epidemiological pressure connected to higher animal density, a need for expanding the habitat, and what further increases the frequency of contacts between wildlife, farm animals, and humans. The evident environmental changes may provoke also emergence and re-emergence of new pathogens, change the seasonality of wild species, and induce stress and therefore the immunosuppression leading to increased susceptibility to diseases.

Since the European bison population was on the verge of extinction at the beginning of the twentieth century, each individual was extremely valuable; therefore one of the main aspects of European bison restitution still remains veterinary health protection, especially in terms of the threat of infectious and invasive disease occurrence. The role of European bison veterinarians and keepers include the supervision, health monitoring, understanding disease characteristics, identification of disease risks, provision of information for control, prevention or treatment, and evaluation of the effectiveness of control and its adjustment. One of the effective tools to control the disease is selective elimination of diseased animals and limiting the population size to reduce its density [32]. The selection is made by a panel of experts in the field; however, it should be remembered that the approach presented here is based on veterinary health protection sometimes argued by epidemiologists [42]. In the case of protected species such European bison, enforcement of the veterinary regulations to protect the species by a sacrifice of few diseased individuals, which are reservoirs of the pathogens putting on risk the whole population, becomes often inconvenient decision against some environmentalist protests.

European bison monitoring in Poland consists of four elements: (1) passive surveillance, (2) active (targeted) monitoring, (3) sanitary control of transported animals, and (4) habitat monitoring (**Figure 5**) [43]. The first approach is based on one of the most suitable ways of health control, the postmortem examination as an element of mortality and morbidity investigations and sampling of the material for laboratory testing [6, 23, 44].

The most recent study involved the analysis of necropsy findings of over 230 fallen or selectively culled European bison from Białowieża Forest between 2008 and 2013 [6]. Changes in the male reproductive tract such as posthitis and balanoposthitis remained the most common pathological changes observed in European bison bulls; however, it should be kept in mind that those changes are the main reason for bull elimination (**Figure 6**). Moreover, the decrease in the proportion of males with prepuce and penis lesions of the whole Białowieża male population in regard to the last century was significant [1, 44].

The next most common problem included pneumonia (45% necropsied animals) and pulmonary emphysema (33%) [6], which were also reported in earlier studies [44]. Respiratory problems were associated with *Dictyocaulus viviparus* invasion of the lungs observed macroscopically; however, the characteristic picture of interstitial or catarrhal-purulent pneumonia suggested also involvement of some infectious agents, what was confirmed for *Pasteurella multocida* [16]. The study has shown that the liver fluke *Fasciola hepatica* still remained endemic in European bison in Białowieża [6]. The presence of the parasite is associated directly with the habitat of European bison in Białowieża [45]. The most frequent cause of death of European bison under the age of 6 months were body injuries caused by other European bison or less often as a result of other accidents. An important finding was that the frequency of pathological changes was higher in the selectively culled European bison than those that were found dead in the wild. This confirms the purposefulness of selection and elimination of diseased individuals as a tool to improve the health and welfare of the population of the species and allows to limit the number

**155**

**Figure 5.**

**Figure 6.**

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

*The four main elements of the European bison health monitoring scheme in Poland.*

of animals that constitute a potential reservoir of infectious and invasive diseases [32]. Additionally, unlike farm animals, European bison are protected animals and live to a mature age; the pathological changes characteristic of elderly individuals, such as kidney cysts, fatty liver, and cataracts may be observed [6]. However, their

*Percentage of European bison with individual pathological changes and parasitic invasions observed at* 

*postmortem examinations performed between 2008 and 2013 in Białowieża Forest [6].*

Another large serosurvey has revealed the possible involvement of some respiratory viruses in the pathogenesis of the frequent changes observed in the lungs or in the upper respiratory tract such as bovine adenovirus type 3 (BAdV-3), bovine parainfluenza type 3 (PIV-3), and bovine respiratory syncytial virus (BRSV) [46]. The high seroprevalences observed especially for BAdV-3 (60%) and PIV-3 (34%) were surprising, also because they have not been studied too intensively before [47]. Interestingly, the association between BAdV-3 and PIV-3 infections and health status of European bison were demonstrated, with significantly lowest seroprevalences in the apparently healthy animals. Whether the high BAdV-3 and PIV-3

frequency in the studied European bison did not exceed several percent.

*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*

#### **Figure 5.**

*Wildlife Population Monitoring*

susceptibility to diseases.

laboratory testing [6, 23, 44].

regard to the last century was significant [1, 44].

In the last 20 years, the population size of European bison in Białowieża Forest and in the whole country increased more than twice (**Figure 2**). It generated an increasing epidemiological pressure connected to higher animal density, a need for expanding the habitat, and what further increases the frequency of contacts between wildlife, farm animals, and humans. The evident environmental changes may provoke also emergence and re-emergence of new pathogens, change the seasonality of wild species, and induce stress and therefore the immunosuppression leading to increased

Since the European bison population was on the verge of extinction at the beginning of the twentieth century, each individual was extremely valuable; therefore one of the main aspects of European bison restitution still remains veterinary health protection, especially in terms of the threat of infectious and invasive disease occurrence. The role of European bison veterinarians and keepers include the supervision, health monitoring, understanding disease characteristics, identification of disease risks, provision of information for control, prevention or treatment, and evaluation of the effectiveness of control and its adjustment. One of the effective tools to control the disease is selective elimination of diseased animals and limiting the population size to reduce its density [32]. The selection is made by a panel of experts in the field; however, it should be remembered that the approach presented here is based on veterinary health protection sometimes argued by epidemiologists [42]. In the case of protected species such European bison, enforcement of the veterinary regulations to protect the species by a sacrifice of few diseased individuals, which are reservoirs of the pathogens putting on risk the whole population, becomes often inconvenient decision against some environmentalist protests. European bison monitoring in Poland consists of four elements: (1) passive surveillance, (2) active (targeted) monitoring, (3) sanitary control of transported animals, and (4) habitat monitoring (**Figure 5**) [43]. The first approach is based on one of the most suitable ways of health control, the postmortem examination as an element of mortality and morbidity investigations and sampling of the material for

The most recent study involved the analysis of necropsy findings of over 230 fallen or selectively culled European bison from Białowieża Forest between 2008 and 2013 [6]. Changes in the male reproductive tract such as posthitis and balanoposthitis remained the most common pathological changes observed in European bison bulls; however, it should be kept in mind that those changes are the main reason for bull elimination (**Figure 6**). Moreover, the decrease in the proportion of males with prepuce and penis lesions of the whole Białowieża male population in

The next most common problem included pneumonia (45% necropsied animals) and pulmonary emphysema (33%) [6], which were also reported in earlier studies [44]. Respiratory problems were associated with *Dictyocaulus viviparus* invasion of the lungs observed macroscopically; however, the characteristic picture of interstitial or catarrhal-purulent pneumonia suggested also involvement of some infectious agents, what was confirmed for *Pasteurella multocida* [16]. The study has shown that the liver fluke *Fasciola hepatica* still remained endemic in European bison in Białowieża [6]. The presence of the parasite is associated directly with the habitat of European bison in Białowieża [45]. The most frequent cause of death of European bison under the age of 6 months were body injuries caused by other European bison or less often as a result of other accidents. An important finding was that the frequency of pathological changes was higher in the selectively culled European bison than those that were found dead in the wild. This confirms the purposefulness of selection and elimination of diseased individuals as a tool to improve the health and welfare of the population of the species and allows to limit the number

**154**

*The four main elements of the European bison health monitoring scheme in Poland.*

**Figure 6.** *Percentage of European bison with individual pathological changes and parasitic invasions observed at postmortem examinations performed between 2008 and 2013 in Białowieża Forest [6].*

of animals that constitute a potential reservoir of infectious and invasive diseases [32]. Additionally, unlike farm animals, European bison are protected animals and live to a mature age; the pathological changes characteristic of elderly individuals, such as kidney cysts, fatty liver, and cataracts may be observed [6]. However, their frequency in the studied European bison did not exceed several percent.

Another large serosurvey has revealed the possible involvement of some respiratory viruses in the pathogenesis of the frequent changes observed in the lungs or in the upper respiratory tract such as bovine adenovirus type 3 (BAdV-3), bovine parainfluenza type 3 (PIV-3), and bovine respiratory syncytial virus (BRSV) [46]. The high seroprevalences observed especially for BAdV-3 (60%) and PIV-3 (34%) were surprising, also because they have not been studied too intensively before [47]. Interestingly, the association between BAdV-3 and PIV-3 infections and health status of European bison were demonstrated, with significantly lowest seroprevalences in the apparently healthy animals. Whether the high BAdV-3 and PIV-3

infection rates were due to the circulation inside the European bison population or it is connected to the transmission of those viruses from domestic ruminants remains unsolved. However, higher infection rates in the free-living European bison suggested that it might have been associated with a spillover from farm animals. The European bison kept in the enclosures were possibly protected from a direct contact with domestic species, not sharing grazing areas as observed in Białowieża [48, 49]. The studies on the characterization of the viral strains in European bison, what may explain the transmission source, are ongoing.

Moreover, other endemic in ruminants infectious agents were considered as potential threats to European bison. Those included pestiviruses with bovine viral diarrhea virus type 1 (BVDV-1) and alpha- and gammaherpesviruses (bovine herpesvirus type 1—BoHV-1, BoHV-4, and BoHV-6), endemic in Polish cattle herds [46]. While in farm animals those viruses are responsible for economic losses, they may prevent the reproduction of an endangered species and make the restitution program fail. However, very low seroprevalence to those viruses suggests certain resistance or only accidental exposure of European bison and hence little importance for European bison at present [15, 25, 46, 47]. On the other hand, low seroprevalence means that most European bison are naïve and fully susceptible to infections with BVDV-1 and BoHV-1, BoHV-4, and BoHV-6. The involvement of herpesviruses in the etiology of balanoposthitis was also disclosed [22].

Other respiratory agents, which could affect the clinical picture observed frequently postmortem in European bison such as *Mycoplasma* spp. and *Mycobacterium* spp., are probably of limited geographical importance [33, 46, 50, 51]. Infections with *Mycoplasma bovis* in few individuals suggest that the exposure was accidental and, however, might have added to some pathological changes of the respiratory tract observed in one case such as intrabronchial pneumonia and pleurisy [51]. In addition, *Mycoplasma bovigenitalium* was suggested to be involved in balanoposthitis under serological evidence; however, the bacteria have never been detected in the lesions of the male genital tract [50]. Moreover, the occurrence of *Mycoplasma ovipneumoniae* infections was never investigated; notwithstanding this direction is worth considering in the pathogenesis of respiratory disorders [52]. Bovine tuberculosis (bTB) remains one of the major infections putting on risk the whole population. *Mycobacterium* accompanies European bison since the dawn of time. Bacterial DNA has been discovered in the bison fossil dated 17,000 years before the present [53]. One of the major obstacles for tuberculosis control in wildlife is that the mycobacteria spread among different mammalian species and survive in numerous biotopes (soil, water, vegetation) becoming endemic in the wild ecosystem for a very long time. Additionally, the diagnostic test used for European bison is dedicated mostly to cattle; therefore, the sensitivity may vary. Sample quality is critical, and the use of several complementary diagnostic methods is necessary to confirm a bTB case in European bison [54]. Fortunately, the disease has not been observed in European bison from the world largest population in Białowieża for some decades now, probably owing to the elimination of the pathogen from cattle in Poland. The disease stroke, however, in a reserve in the European bison breeding center in Smardzewice [33, 46], what has led to stamping out of the whole herd in 2018. The outbreak as the previous one in Bieszczady mountains was connected to *Mycobacterium caprae* [31, 35]. Reports of tuberculosis in captive European bison caused by *M. bovis* in German and Brazilian zoos underline the need for control in the species being important bTB reservoir worldwide [55–57].

Further studies are concerned with pathogens, which may be depopulating through their influence on European bison reproduction, reducing already fragile number of the species under restitution. Low seroprevalences of *Brucella* spp., *Leptospira* spp., and *Toxoplasma gondii* observed in European bison in

**157**

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

eight main Polish populations sampled between 2011 and 2015 by Krzysiak et al. [46] suggest limited importance of those agents for the species conservation at present. It had been also confirmed by the results of some previous investigations [47, 58]. Only slightly higher *T. gondii* parasite seroprevalence was observed in European bison from Białowieża prior to the study of Krzysiak et al. [46, 59]. It was followed by the report of *T. gondii* isolation from an aborted at 4–5-monthold gestation of European bison fetus in Białowieża in 2014 [60]. Similar to *T. gondii*, European bison pose some potential as *Neospora caninum* and *Chlamydia*

Bovine leukemia virus (BLV) and *Mycobacterium avium subsp. paratuberculosis* (Johne's disease) infections, endemic in Polish cattle, are subject of official tests performed routinely in the movement of European bison inside the European Union. Only one case of subclinical BLV infection has been reported so far in the 1880s. Just as paratuberculosis [51], bovine leukemia does not pose a serious threat

Finally, it is worth mentioning European bison susceptibility to malignant catarrhal fever virus (MCFV) infection, which is comparable to cattle's. The reports of clinical picture of MCF in the species kept in zoos are quite old [62, 63]. MCF is considered more emerging and non-endemic in Poland; therefore, no current data exists. However, it was well documented that the exposure of American bison to sheep-associated MCFV is frequently fatal [64, 65]. In 2018, an outbreak of fatal MCF in European bison enclosure in Switzerland was consulted with European Bison Pedigree Book department at the Białowieża National Park; however no report was published officially (Baumgartner, personal communication).

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

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].

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

spp. reservoirs [58, 61].

**European bison**

to Polish European bison at present.

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

*Wildlife Population Monitoring*

explain the transmission source, are ongoing.

infection rates were due to the circulation inside the European bison population or it is connected to the transmission of those viruses from domestic ruminants remains unsolved. However, higher infection rates in the free-living European bison suggested that it might have been associated with a spillover from farm animals. The European bison kept in the enclosures were possibly protected from a direct contact with domestic species, not sharing grazing areas as observed in Białowieża [48, 49]. The studies on the characterization of the viral strains in European bison, what may

Moreover, other endemic in ruminants infectious agents were considered as potential threats to European bison. Those included pestiviruses with bovine viral diarrhea virus type 1 (BVDV-1) and alpha- and gammaherpesviruses (bovine herpesvirus type 1—BoHV-1, BoHV-4, and BoHV-6), endemic in Polish cattle herds [46]. While in farm animals those viruses are responsible for economic losses, they may prevent the reproduction of an endangered species and make the restitution program fail. However, very low seroprevalence to those viruses suggests certain resistance or only accidental exposure of European bison and hence little importance for European bison at present [15, 25, 46, 47]. On the other hand, low seroprevalence means that most European bison are naïve and fully susceptible to infections with BVDV-1 and BoHV-1, BoHV-4, and BoHV-6. The involvement of

herpesviruses in the etiology of balanoposthitis was also disclosed [22].

the species being important bTB reservoir worldwide [55–57].

Further studies are concerned with pathogens, which may be depopulating through their influence on European bison reproduction, reducing already fragile number of the species under restitution. Low seroprevalences of *Brucella* spp., *Leptospira* spp., and *Toxoplasma gondii* observed in European bison in

Other respiratory agents, which could affect the clinical picture observed frequently postmortem in European bison such as *Mycoplasma* spp. and *Mycobacterium* spp., are probably of limited geographical importance [33, 46, 50, 51]. Infections with *Mycoplasma bovis* in few individuals suggest that the exposure was accidental and, however, might have added to some pathological changes of the respiratory tract observed in one case such as intrabronchial pneumonia and pleurisy [51]. In addition, *Mycoplasma bovigenitalium* was suggested to be involved in balanoposthitis under serological evidence; however, the bacteria have never been detected in the lesions of the male genital tract [50]. Moreover, the occurrence of *Mycoplasma ovipneumoniae* infections was never investigated; notwithstanding this direction is worth considering in the pathogenesis of respiratory disorders [52]. Bovine tuberculosis (bTB) remains one of the major infections putting on risk the whole population. *Mycobacterium* accompanies European bison since the dawn of time. Bacterial DNA has been discovered in the bison fossil dated 17,000 years before the present [53]. One of the major obstacles for tuberculosis control in wildlife is that the mycobacteria spread among different mammalian species and survive in numerous biotopes (soil, water, vegetation) becoming endemic in the wild ecosystem for a very long time. Additionally, the diagnostic test used for European bison is dedicated mostly to cattle; therefore, the sensitivity may vary. Sample quality is critical, and the use of several complementary diagnostic methods is necessary to confirm a bTB case in European bison [54]. Fortunately, the disease has not been observed in European bison from the world largest population in Białowieża for some decades now, probably owing to the elimination of the pathogen from cattle in Poland. The disease stroke, however, in a reserve in the European bison breeding center in Smardzewice [33, 46], what has led to stamping out of the whole herd in 2018. The outbreak as the previous one in Bieszczady mountains was connected to *Mycobacterium caprae* [31, 35]. Reports of tuberculosis in captive European bison caused by *M. bovis* in German and Brazilian zoos underline the need for control in

**156**

eight main Polish populations sampled between 2011 and 2015 by Krzysiak et al. [46] suggest limited importance of those agents for the species conservation at present. It had been also confirmed by the results of some previous investigations [47, 58]. Only slightly higher *T. gondii* parasite seroprevalence was observed in European bison from Białowieża prior to the study of Krzysiak et al. [46, 59]. It was followed by the report of *T. gondii* isolation from an aborted at 4–5-monthold gestation of European bison fetus in Białowieża in 2014 [60]. Similar to *T. gondii*, European bison pose some potential as *Neospora caninum* and *Chlamydia* spp. reservoirs [58, 61].

Bovine leukemia virus (BLV) and *Mycobacterium avium subsp. paratuberculosis* (Johne's disease) infections, endemic in Polish cattle, are subject of official tests performed routinely in the movement of European bison inside the European Union. Only one case of subclinical BLV infection has been reported so far in the 1880s. Just as paratuberculosis [51], bovine leukemia does not pose a serious threat to Polish European bison at present.

Finally, it is worth mentioning European bison susceptibility to malignant catarrhal fever virus (MCFV) infection, which is comparable to cattle's. The reports of clinical picture of MCF in the species kept in zoos are quite old [62, 63]. MCF is considered more emerging and non-endemic in Poland; therefore, no current data exists. However, it was well documented that the exposure of American bison to sheep-associated MCFV is frequently fatal [64, 65]. In 2018, an outbreak of fatal MCF in European bison enclosure in Switzerland was consulted with European Bison Pedigree Book department at the Białowieża National Park; however no report was published officially (Baumgartner, personal communication).
