Pathomorphological Findings and Infectious Diseases in Selected European Brown Hare (Lepus europaeus Pallas, 1778) Populations from Schleswig-Holstein, Germany

Abstract

In the northernmost German federal state Schleswig-Holstein, populations of European brown hares (Lepus europaeus Pallas, 1778) show diverse densities and varying courses over the years. To examine differences in pathomorphological findings and infectious diseases as possible reasons for varying population dynamics, we assessed 155 hunted hares from three locations in Schleswig-Holstein from 2016 to 2020. We investigated the association of location, year, age, and sex of animals to certain pathomorphological findings and infectious diseases. Frequent pathomorphological findings were intestinal parasites (63.9%), hepatitis (55.5%), nephritis (31.0%), steatitis (23.2%), enteritis (13.5%), and pneumonia (5.2%). Body condition differed significantly between locations, and the prevalence of pneumonia was significantly higher in females. Enteritis was not detected in 2019, when much more juveniles were sampled. Hepatitis and nephritis occurred significantly more often in 2016 and among adults. Additionally, more adults showed hepatitis with concurrent serotitre for European brown hare syndrome virus (EBHSV), while intestinal parasitosis as well as high excretion rates of coccidia were more common in juveniles. Sampled animals showed high infection rates with Eimeria spp. (96.1%), Trichostrongylus spp. (52.0%), Graphidium strigosum (41.2%), and a high seroprevalence (90.9%) for EBHSV, without severe symptoms. This study revealed a low prevalence of infectious pathogens, but a high prevalence of chronic inflammations of unknown origin in the tested brown hare populations. Overall, our results indicate a rather minor importance of infectious diseases for observed population dynamics of analysed hare populations in Schleswig-Holstein.

Keywords: EBHSV; Eimeria spp.; Graphidium strigosum; Lepus europaeus; Trichostrongylus spp.; hepatitis; nephritis; steatitis.

Figure 1

Development of population densities for L. europaeus in Schleswig-Holstein from 1995 to 2022 based on spotlight counts in spring with dynamic, but different population densities for whole Schleswig-Holstein and different natural regions (geest, downs, marshland) (adjusted from Wildtierkataster Schleswig-Holstein [12]).

Figure 2

Locations of the three sampled hunting grounds (triangles). From north to south: Tetenbüll, Elpersbüttel, Friedrichskoog.

Figure 3

Effect of (a) sampling year and (b) age category on the prevalence of hepatitis. Confidence bars show the 95% confidence intervals around the estimates obtained through logistic regression. The effect of sampling year is depicted for adults (a), and the effect of age category is depicted for a weighted average across the sampling year effects with weights proportional to the number of samples obtained in each year (b). Significant differences between sampling years and age categories are illustrated individually using square brackets including the p-value and show a significant decrease in prevalence from 2017 to 2019 and 2020 as well as a higher prevalence of hepatitis in adults.

Figure 4

Liver, L. europaeus; severe infiltration of lymphocytes, macrophages, and plasma cells within a portal triad (arrows = bile ducts) and the periportal liver tissue. HE, 200×.

Figure 5

Intestine, L. europaeus; intestinal protozoonosis with coccidial stages in enterocytes (arrows) and oocysts in crypt lumina (arrowhead). HE, 100×.

Figure 6

Effect of age and sex on the prevalence of parasites in the intestine. Confidence bars show the 95% confidence intervals around the estimates obtained through logistic regression. A significant difference was only detected within males between juveniles and adults and illustrated with a square bracket including the p-value.

Figure 7

Effect of (a) hunting ground and (b) sampling year on the prevalence of enteritis. Confidence bars show the 95% confidence intervals around the estimates obtained through logistic regression. A significant effect of sampling years on prevalence of enteritis was detected in likelihood ratio tests, but post-hoc analyses did not reveal between which years this difference was present. In 2019, no enteritis was diagnosed.

Figure 8

Intestine, L. europaeus; moderate lymphoplasmacytic and eosinophilic (arrowheads) enteritis. HE, 200×.

Figure 9

Retroperitoneal fat tissue, L. europaeus; severe granulomatous to necrotising steatitis with extensive necrosis (X) and adjacent infiltration of macrophages and multinucleated giant cells. HE, 100×.

Figure 10

Effect of sex on the prevalence of pneumonia. Confidence bars show the 95% confidence intervals around the estimates obtained through logistic regression. Significantly more females were diagnosed with pneumonia compared to males (p = 0.02).

Figure 11

Effect of (a) sampling year and (b) age category on the prevalence of nephritis. Confidence bars show the 95% confidence intervals around the estimates obtained through logistic regression. Significant effects were detected for sampling years (2019 > 2017) and age categories (adults > juveniles) and are highlighted with square brackets and p-values in the graphs.

Figure 12

Kidney, L. europaeus; multifocal mild to moderate lymphoplasmacytic (arrows) interstitial nephritis. HE, 200×.

Figure 13

Liver, L. europaeus; severe cysticercosis (T. pisiformis) with multifocal cysts in the serosa of the liver of an adult male hare from Friedrichskoog.

Figure 14

Liver, L. europaeus; multifocal bright and round spots in the liver parenchyma of an adult female hare from Elpersbüttel, infected with B. suis Biovar 2. The macroscopic alterations are suggestive of a granulomatous to necrotising hepatitis.