Assessing Fifty Years of General Health Surveillance of Roe Deer in Switzerland: A Retrospective Analysis of Necropsy Reports

Abstract

General wildlife health surveillance is a valuable source of information on the causes of mortality, disease susceptibility and pathology of the investigated hosts and it is considered to be an essential component of early warning systems. However, the representativeness of data from such surveillance programs is known to be limited by numerous biases. The roe deer (Capreolus capreolus capreolus) is the most abundant ungulate and a major game species all over Europe. Yet, internationally available literature on roe deer pathology is scarce. The aims of this study were (1) to provide an overview of the causes of mortality or morbidity observed in roe deer in Switzerland and to assess potential changes in the disease pattern over time; and (2) to evaluate the value and limitations of a long term dataset originating from general wildlife health surveillance. We compiled 1571 necropsy reports of free ranging roe deer examined at the Centre for Fish and Wildlife Health in Switzerland from 1958 to 2014. Descriptive data analysis was performed considering animal metadata, submitter, pathologist in charge, laboratory methods, morphological diagnoses and etiologies. Recurrent causes of mortality and disease pictures included pneumonia, diarrhea, meningoencephalitis, actinomycosis, blunt trauma, predation, neoplasms and anomalies. By contrast, other diagnoses such as fatal parasitic gastritis, suspected alimentary intoxication and reproductive disorders appeared only in earlier time periods. Diseases potentially relevant for other animals or humans such as caseous lymphadenitis (or pseudotuberculosis), salmonellosis, paratuberculosis and listeriosis were sporadically observed. The disease pattern in roe deer from Switzerland was largely in accordance with previous reports. The observed fluctuations were consistent with methodical and/or personnel changes and varying disease awareness. Nevertheless, despite such limitations, the compiled data provide a valuable baseline. To facilitate comparison among studies, we recommend systematically archiving all case documents and fixed tissues and to perform data analyses more regularly and in a harmonized way.

Fig 1. Map of Switzerland depicting the cantonal origin of the submitted roe deer.

Shades of grey illustrate the number of roe deer per 10 years and 100km² of cantonal surface. Abbreviations: AG = Aargau, AI = Appenzell Innerrhoden, AR = Appenzell Ausserrhoden, BE = Bern, BL = Basel-Landschaft, BS = Basel-Stadt, FR = Fribourg, GE = Geneva, GL = Glarus, GR = Graubünden, JU = Jura, LU = Luzern, NE = Neuchâtel, NW = Nidwalden, OW = Obwalden, SG = St. Gallen, SH = Schaffhausen, SO = Solothurn, SZ = Schwyz, TG = Thurgau, TI = Ticino, UR = Uri, VD, Vaud, VS = Valais, ZG = Zug, ZH = Zurich. FIWI = Centre for Fish and Wildlife Health (white triangle).

Fig 2. Number of submitted roe deer per canton and year.

Slightly more than half of the cases were submitted by official game wardens (n = 893) followed by voluntary gamekeepers (n = 259). Considerably fewer cases were delivered by the police (n = 68), hunters (n = 57), private veterinarians or veterinary authorities (n = 48), and cantonal hunting authorities (n = 37). Overall, cantons with official game wardens submitted more animals (78%; n = 1227) than cantons without game wardens (20%; n = 313).

Fig 3. Performed parasitic, bacteriological and histological investigations over time.

Fig 4. Selected gross pathology findings in free-ranging roe deer from Switzerland.

(A) Skull, actinomycosis-like lesions of bacterial origin. A severe proliferative and destructive process is affecting the lateral aspect of the skull. Inset: The right mandibular region is severely expanded by a proliferative inflammatory process similar to that shown in the main figure (both cases were from 2013). (B) Spleen, lymphoma. There is diffuse and severe splenomegaly with multiple nodules expanding within the parenchyma and elevating the capsule. Additional similar lesions were also observed in liver, bone marrow and lymph nodes (1994). (C) Skull, osteomyelitis secondary to traumatic injury. A transverse fracture is associated with a granular appearance of the bone consistent with remodeling secondary to osteo-myelitis. Obvious bone loss and rarefaction is seen in cross section (inset) (1958). (D) Mesenteric lymph nodes, paratuberculosis. The mesenteric lymph nodes are severely enlarged (lymph-adenomegaly), up to 2–4 x 1.5–1 x 2–2.5 cm (2011). (E) Lung, tarsal and metatarsal bones, pyogranulo-matous fungal pneumonia and hypertrophic osteopathy. A large pyogranuloma is expanding, compressing and replacing the lung parenchyma. The cortical bone of the frontal aspect of the metatarsus is diffusely and markedly thickened by a bony proliferation (2010). (F) Inguinal hernia. A large mass covered by normal skin is bulging in the region of the left inguinal space (diameter 46cm). The mass contained small intestine loops and part of the caecum (2011).

Fig 5. Selected microscopic pathology findings in free-ranging roe deer from Switzerland.

(A) Mesenteric lymph node, paratuberculosis. There are large clusters of macrophages scattered in the lymph node parenchyma. Hematoxylin and eosin. Cells contain large numbers of intracytoplamatic acid fast bacteria (Inset). Ziehl Neelsen. (B) Brain, malignant catarrhal fever. Multifocal hemorrhages often associated with variably extensive clear spaces (edema) and hypereosinophilic neurons with glassy appearence (necrotic neurons) are present in the neuropil. There is multifocal fibrinoid vascular necrosis with weak mononuclear cuffing. Prominent syncytial cells are seen in the affected vessels (Inset). Hematoxylin and eosin. (C) Liver, lymphoma. Multifocal to coalescent sheets of neoplastic cells are infiltrating the liver parenchyma. The neoplastic lymphoid cells have large basophilic nuclei with small amounts of cytoplasm and show occasional mitoses (inset). Hematoxylin and eosin. (D) Lung, acute capture myopathy. The lumen of a bronchiole is completely obscured by large amounts of mucous. The wall of the bronchus is diffusely infiltrated by often degranulating globular leukocytes, associated with hyperemic vessels surrounded by clear spaces (edema) (Inset). Hematoxylin and eosin. (E) Lung, severe lungworm infestation. The alveolar spaces are diffusely replaced by embryonated nematode eggs. Eggs contain either morulas with a variable number of cells or variably developed larvae. (F) Metatarsal bone, hypertrophic osteopathy. A thick layer of proliferating bone is expanding radially from the cortical bone. Hematoxylin and eosin.

Fig 6. Submitted roe deer with documented gastrointestinal nematodes over time.

Percentages correspond to the number of cases with reported gastrointestinal nematodes in relation to the total number of investigated carcasses, independently of the investigation methods (necropsy, washouts, coprology, mucosal scraping). Grey bars: total of gastrointestinal nematodes. Red line: small gastric worms. Blue line: Chabertia ovina.

Fig 7. Selected categories of main diagnoses in percentage of total submitted cases per year.

(A) Parasitic. (B) Bacterial. (C) Traumatic. (D) Undetermined. Dashed horizontal black lines indicate total number of submitted cases. Vertical dotted lines separate time periods with different main pathologists.