Pathological findings in South American camelids presented at a farm animal clinic in Northern Germany (2005-2021).

To expand the knowledge about common diseases in llamas and alpacas in Germany, a screening of the cases of South American camelids presented at the Clinic for Swine and Small Ruminants of the University of Veterinary Medicine Hannover, Germany from 2005 to the end of November 2021 was performed. A retrospective evaluation of necropsy reports from this period was conducted. Overall, necropsy reports were evaluated from 187 alpacas, 35 llamas and one vicuña (n = 223). A total of 50.2% of the dissected animals were thin or cachectic. Pathological alterations of the gastrointestinal tract were the most common findings (44.8%). In addition, liver changes were recorded, most frequently in adult animals. In contrast, diseases of the respiratory tract and the nervous system were found more frequently in juvenile animals. This study provides an overview of common pathologies in South American camelids in Germany and thus may help to recognise different disease symptoms at an early stage.

[Diaphragmatic hernia in a female alpaca (Vicugna pacos)]. / Zwerchfellhernie bei einer Alpakastute (Vicugna pacos).

A 3-year-old pregnant female alpaca was noticed due to increased lying and decreased feed intake after shearing. Twelve days after shearing, she aborted an almost completely developed cria. After another two days, the alpaca was recumbent and subsequently died during transport to the clinic. A dissection of the carcass revealed a diaphragmatic hernia. Diaphragmatic hernias have been described in many different species, diagnosis can be made by radiography or ultrasound. Depending on the extent, surgical therapy may be successful.

Neurotropic Highly Pathogenic Avian Influenza A(H5N1) Virus in Red Foxes, Northern Germany.

In a 1-year survey of wild terrestrial predators in northern Germany, we found that 5 of 110 foxes were infected with contemporary avian influenza A(H5N1) viruses, forming a temporal cluster during January‒March 2023. Encephalitis and strong cerebral virus replication but only sporadic mammalian-adaptive viral polymerase basic 2 protein E627K mutations were seen.

Severe anaemia secondary to a perforated gastric ulcer in a male alpaca.

BACKGROUND: Anaemia is a common condition in alpacas and attributable to a variety of causes. Severe anaemia with a packed cell volume (PCV) less than 10% is frequently diagnosed, usually due to blood loss resulting from haemonchosis. Many South American camelids (SACs) also suffer from gastric ulcers, which are often associated with anaemia in other species. However, in alpacas and llamas, gastric ulcers usually do not lead to anaemia due to blood loss according to the current literature. There are no detailed clinical and laboratory data on this condition in the scientific literature so far. CASE PRESENTATION: We report on the case of a nine-year-old male alpaca that was presented to the clinic with suspected forestomach acidosis. The animal showed clinical signs of colic, hypothermia, tachypnea, tachycardia, pale mucous membranes, and died shortly after admission to the clinic. Laboratory diagnosis revealed a markedly decreased haematocrit (0.13 l/l), leucopaenia with band neutrophils, azotaemia, hypocalcaemia, hyperphosphataemia and vitamin D deficiency. Post-mortem examination revealed multiple ulcers in the first and third compartment with perforation of one ulcer in the first compartment, resulting in intraluminal blood loss and purulent peritonitis. CONCLUSIONS: To the authors' knowledge, this is the first detailed description of clinical and laboratory data of severe anaemia due to a perforated gastric ulcer in a SAC. Although the current literature suggests that severe blood loss due to gastric ulcers does not occur in SACs, this condition should be considered as a possible differential diagnosis in anaemic animals. Clinical indicators can be colic and pale mucous membranes.

Case report: Urolithiasis, nephrolithiasis and a urinary bladder malformation in a seven-month-old alpaca cria.

Urolithiasis is a common condition in male small ruminants where predisposing factors have been identified. Occasionally, urolithiasis is diagnosed in South American camelids (SACs). However, nephrolithiasis is rarely diagnosed in ruminants. To our knowledge, this is the first report focusing on a combined appearance of nephrolithiasis and urolithiasis in an alpaca cria. A 7-month-old alpaca cria suffering from impaired urinary flow was presented for examination. On admission, the alpaca had a wet prepuce and showed a standing posture with a wide-based stance. Ultrasonographic examination of the abdomen showed a distended bladder. Clinical chemistry revealed azotemia and hypophosphatemia. After the first examination, repeated urination was observed. Conservative therapy using antibiotics, anti-inflammatory and spasmolytic drugs was started with the suspected diagnosis of urinary calculus. During the first 24 h, plasma concentrations of creatinine and urea decreased, but increased again during the following days. During the second day after admission, urination was not observed for 16 h while the concentration of urea and creatinine further increased. Therefore, the animal was euthanized due to financial concerns of the owner. Necropsy revealed that calculi were located in the left kidney as well as in the urethra. In addition, the animal exhibited uroperitoneum. The urinary bladder was intact, moderately distended with urine and showed a malformation, which was covered with a translucent mucosal membrane. Histologic examination revealed that this malformation was a bladder diverticulum. The extent to which the unilateral nephroliths affected the general condition and renal function of the animal is unclear, since the uroliths also cause azotemia, and abdominal pain. Further studies are needed for a better understanding of obstructive urinary disease in SACs.

Neuropathologic and molecular aspects of a canine distemper epizootic in red foxes in Germany.

In the last fifteen years, an epidemic of canine distemper virus (CDV) with marked neurotropism has occurred in Europe after a longer period of endemic transmission. Many wildlife species have been infected, with red foxes (Vulpes vulpes) being particularly affected. Given that this species is assumed to mediate cross-species CDV infections to domestic and wild animals, tissue samples from foxes with confirmed CDV infection in North-Western Germany were investigated to better understand the neurotropic aspects of the disease. This analysis included histopathology, virus distribution and cell tropism, phenotyping of inflammatory responses and determination of the genotype of the viruses based on the phylogeny of the hemagglutinin (H) gene. The predominant lesion type is gliosis in both gray and white matter areas associated with an accumulation of Iba1+ macrophages/microglia and upregulation of major histocompatibility complex class II molecules in the brain, while sequestration of CD3+ T and Pax5+ B cell in CDV-infected foxes is limited. Demyelination is found in few foxes, characterized by reduced myelin staining with loss of CNPase+ oligodendrocytes in the cerebellar white matter and brainstem. In addition, axonal damage, characterized by ß-amyloid precursor protein expression, is found mainly in these brain regions. In situ hybridization reveals a primary infection of the cerebral and cerebellar gray matter and brain stem. Iba1+ cells and NeuN+ neurons represent the main CDV targets. Sequencing of the CDV H open reading frame from fox tissues reveals that the virus strains belongs to three different sub-lineages of the Europe-1/South America-1 genotype, suggesting independent transmission lines.

Gastric Ulcers in Alpacas- Clinical, Laboratory, and Pathological Findings.

Gastric ulcers are a common finding in post-mortem examinations of South American camelids (SAC), but diagnosis in living animals is often difficult. The aim of this study was to provide an overview of the incidence of gastric ulcers in alpacas, common concomitant diseases, and clinical as well as laboratory findings to facilitate diagnosis for veterinarians. For this purpose, a total of 187 necropsy reports of alpacas were evaluated, including clinical and laboratory findings on the living animal. A total of 23.5% of the animals (n = 44) were found to have gastric ulcers, nine were perforated. Compartment 3 was most frequently affected by gastric ulcers. No sex predilection could be detected, but animals 1 year of age and older were more frequently affected by gastric ulcers than animals under 1 year of age. Alpacas with gastric ulcers were presented to the clinic due to different non-specific symptoms. In alpacas with gastric ulcers, significantly more organs or organ systems besides the stomach revealed clinical findings than in animals without gastric ulcers. Of the 44 animals with gastric ulcers, a total of 21 alpacas (47.7%) had a poor nutritional status, but cachexia was not significantly more frequent in animals with gastric ulcers than in other dissected animals without ulcers. Hematologic investigations revealed a significantly lower white blood count and significantly lower segmented neutrophils than in deceased animals without ulcers. Compared to animals discharged after treatment, alpacas that died with gastric ulcers had significantly higher levels of band neutrophils and fewer eosinophils and basophils. Occult blood in feces was found in three of 12 animals with gastric ulcers examined for occult blood. In summary, gastric ulcers are a common problem in SAC, which is difficult to diagnose clinically or by laboratory investigations. As these are often chronic processes involving other organ systems, regular monitoring of the animals' nutritional status and early detection of disease symptoms may help to prevent gastric ulcers.

Impact of Coxiella burnetii vaccination on humoral immune response, vaginal shedding, and lamb mortality in naturally pre-infected sheep.

Introduction: Sheep are considered to be one of the main reservoirs for Coxiella burnetii, a gram-negative bacterium with high zoonotic potential. Infected sheep shed tremendous amounts of the pathogen through birth products which caused human Q fever epidemics in several countries. Information about the impact of an inactivated C. burnetii Phase I vaccine on humoral immune response, vaginal shedding, and lamb mortality in naturally pre-infected sheep is scarce. Methods: Two identically managed and naturally C. burnetii-infected sheep flocks were examined for two lambing seasons (2019 and 2020). One flock (VAC) received a primary vaccination against Q fever before mating and the second flock served as control (CTR). In each flock, one cohort of 100 ewes was included in follow-up investigations. Serum samples at eight different sampling dates were analyzed by C. burnetii phase-specific ELISAs to differentiate between the IgG Phase I and II responses. Vaginal swabs were collected within three days after parturition and examined by a C. burnetii real-time PCR (IS1111). Lamb losses were recorded to calculate lamb mortality parameters. Results: After primary vaccination, almost all animals from cohort VAC showed a high IgG Phase I response up until the end of the study period. In cohort CTR, the seropositivity rate varied from 35.1% to 66.3%, and the Phase I and Phase II pattern showed an undulating trend with higher IgG Phase II activity during both lambing seasons. The number of vaginal shedders was significantly reduced in cohort VAC compared to cohort CTR during the lambing season in 2019 (p < 0.0167). There was no significant difference of vaginal shedders in 2020. The total lamb losses were low in both cohorts during the two investigated lambing seasons (VAC 2019: 6.8%, 2020: 3.2%; CTR 2019: 1.4%, 2020: 2.7%). Discussion: Neither the C. burnetii vaccine nor the C. burnetii infection seem to have an impact on lamb mortality. Taken together, the inactivated C. burnetii Phase I vaccine induced a strong IgG Phase I antibody response in naturally pre-infected sheep. It might also reduce vaginal shedding in the short term but seems to have little beneficial impact on lamb mortality.

Congenital Myofibroblastic Skin Tumours in a Newborn Piglet Resembling the Multicentric Form of Infantile Myofibromatosis.

A 2-day-old female piglet was submitted with multiple congenital, nodular skin masses located on the head, neck, trunk and legs. Histopathological examination revealed the presence of nodular, cutaneous tumours with a biphasic growth pattern and comprising a population of undifferentiated, oval or slightly polygonal, frequently perivascularly located cells and a population of spindle-shaped, fibroblast-like cells arranged in bundles. Multifocally, tumour cells infiltrated subcutaneous adipose and muscular tissue. Immunohistochemically, the undifferentiated tumour cells expressed vimentin and calponin, whereas the spindle-shaped tumour cells were positive for vimentin, α-smooth muscle actin and calponin. Based on these findings, the diagnosis was myofibroblastic tumours closely resembling the multicentric form of human infantile myofibromatosis.

Calcinosis in Alpaca Crias (Vicugna pacos) Due to Vitamin D Intoxication-Clinical, Laboratory and Pathological Findings with a Focus on Kidney Function.

Alpacas kept in Central Europe are often deficient in vitamin D3, which is supplemented orally or by injection by the owners or veterinarians. Vitamin D3 can be specified in two different units (IU and µg), which differ by a factor of 40. By mixing up these units, an overdosage can be induced. In this study, three alpaca crias were examined after vitamin D3 intoxication, with particular reference to kidney function. All three animals developed non-specific clinical alterations 1-2 weeks after a vitamin D3 overdose of approximately 40 times. Plasma of the animals revealed several alterations. The main findings were severe azotemia, hypercalcemia and hyperphosphatemia, 15 days after treatment. Kidney function analysis (endogenous creatinine clearance) in two of the crias revealed severe glomerular damage. All crias died despite intensive treatment within 23 days after vitamin D3 treatment. Necropsy revealed calcification in different organs, mainly the kidneys, lungs and liver. Since nine other crias in the same group were treated with comparable doses of vitamin D3 and no clinical signs were observed in these animals, it is concluded that individual animals show different levels of sensitivity to vitamin D3.

A Case of Concurrent Molybdenosis, Secondary Copper, Cobalt and Selenium Deficiency in a Small Sheep Herd in Northern Germany.

To the author's knowledge this paper describes the first proven report of a combined primary molybdenosis, secondary copper (Cu) deficiency, Ovine White Liver Disease-Cobalt (Co) deficiency, and selenium (Se) deficiency in a small pedigree herd of White Horned Heath sheep in Germany (8 ewes, 2 rams, 3 yearling ewes, 17 lambs) for decades. Clinical signs associated with these mineral deficiencies in a group of pastured ram lambs included emaciation, conjunctivitis, anaemia, growth retardation, discolouration of the wool and photodermatitis. Morbidities and mortalities arose in 4-6-month-old lambs despite intensive veterinary treatment in the summer of 2014 and 2015 (n = 13, 23% died). Se (3/5), Cu (4/7), and Co (3/3) deficiencies in combination with elevated values for Molybdenum (Mo, 2/2) were found. Hamburg is a large industrial city and an input of heavy metals from surrounding industries and coal-fired power stations in combination with a sandy, non-fertilised soil and monoculture grass species might offer a potential explanation for the severity of mineral deficiencies observed in this herd.

Swine Conjunctivitis Associated with a Novel Mycoplasma Species Closely Related to Mycoplasma hyorhinis.

Conjunctivitis in swine is a common finding, usually considered to be a secondary symptom of respiratory or viral systemic disease, or a result of irritation by dust or ammonia, or of local infections with Mycoplasma (M.) hyorhinis or chlamydia. In three unrelated swine farms in Germany with a high prevalence of conjunctivitis, a novel mycoplasma species, tentatively named Mycoplasma sp. 1654_15, was isolated from conjunctival swabs taken from affected pigs. Although 16S rRNA gene sequences shared highest nucleotide similarities with M. hyorhinis, matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry, partial rpoB sequencing, and comparative whole genome analyses indicated the identification of a novel species within genus Mycoplasma. Noticeable differences between Mycoplasma sp. 1654_15 and M. hyorhinis were the lack of a vlp locus and the presence of a myo-inositol pathway in the genome of strain 1654_15. Since myo-inositol might be used as an alternative energy source by this pathogen on the conjunctival surface, robust colonization by outcompeting other bacteria could be the consequence. In summary, abundant isolation of Mycoplasma sp. 1654_15 from the conjunctiva of affected pigs, its close relationship to M. hyorhinis, and identification of a panel of coding sequences (CDSs) potentially associated with virulence and pathogenicity suggested a local eye disease caused by a so far unknown, highly specialized mycoplasma species.

Relation between Intensity of Biocide Practice and Residues of Anticoagulant Rodenticides in Red Foxes (Vulpes vulpes).

Anticoagulant rodenticides (ARs) are commonly used to control rodent infestations for biocidal and plant protection purposes. This can lead to AR exposure of non-target small mammals and their predators, which is known from several regions of the world. However, drivers of exposure variation are usually not known. To identify environmental drivers of AR exposure in non-targets we analyzed 331 liver samples of red foxes (Vulpes vulpes) for residues of eight ARs and used local parameters (percentage of urban area and livestock density) to test for associations to residue occurrence. 59.8% of samples collected across Germany contained at least one rodenticide, in 20.2% of cases at levels at which biological effects are suspected. Second generation anticoagulants (mainly brodifacoum and bromadiolone) occurred more often than first generation anticoagulants. Local livestock density and the percentage of urban area were good indicators for AR residue occurrence. There was a positive association between pooled ARs and brodifacoum occurrence with livestock density as well as of pooled ARs, brodifacoum and difenacoum occurrence with the percentage of urban area on administrative district level. Pig holding drove associations of livestock density to AR residue occurrence in foxes. Therefore, risk mitigation strategies should focus on areas of high pig density and on highly urbanized areas to minimize non-target risk.

HMGA1 and HMGA2 expression and comparative analyses of HMGA2, Lin28 and let-7 miRNAs in oral squamous cell carcinoma.

BACKGROUND: Humans and dogs are affected by squamous cell carcinomas of the oral cavity (OSCC) in a considerably high frequency. The high mobility group A2 (HMGA2) protein was found to be highly expressed in human OSCC and its expression was suggested to act as a useful predictive and prognostic tool in clinical management of oral carcinomas. Herein the expression of HMGA2 and its sister gene HMGA1 were analysed within human and canine OSCC samples. Additionally, the HMGA negatively regulating miRNAs of the let-7 family as well as the let-7 regulating gene Lin28 were also comparatively analysed. Deregulations of either one of these members could affect the progression of human and canine OSCC. METHODS: Expression levels of HMGA1, HMGA2, Lin28, let-7a and mir-98 were analysed via relative qPCR in primary human and canine OSCC, thereof derived cell lines and non-neoplastic samples. Additionally, comparative HMGA2 protein expression was analysed by immunohistochemistry. RESULTS: In both species, a significant up-regulation of the HMGA2 gene was found within the neoplastic samples while HMGA1 expression did not show significant deregulations. Comparative analyses showed down-regulation of mir-98 in human samples and up-regulation of let-7a and mir-98 in canine neoplastic samples. HMGA2 immunostainings showed higher intensities within the invasive front of the tumours than in the centre of the tumour in both species. CONCLUSIONS: HMGA2 could potentially serve as tumour marker in both species while HMGA1 might play a minor role in OSCC progression. Comparative studies indicate an inverse correlation of HMGA2 and mir-98 expression in human samples whereas in dogs no such characteristic could be found.

[Metastasizing epitheliotropic T-cell lymphoma (Mycosis fungoides) in two guinea pigs (Cavia porcellus)]. / Metastasierendes epitheliotropes T-Zell- Lymphom (Mycosis fungoides) bei zwei Meerschweinchen (Cavia porcellus).

Two guinea pigs (Cavia porcellus) were presented with a clinical history of a chronic, unresponsive skin disorder with scaling, itching and alopecia. After clinical differential diagnoses (e. g. ectoparasitosis, dermatomycosis, endocrinopathy or allergy) had been ruled out, a skin biopsy revealed an epitheliotropic lymphoma (Mycosis fungoides). The pathohistological examination of the skin showed focal intraepidermal accumulations of tumorous lymphocytes also known as pautrier microabscesses. A full necropsy displayed also metastases in lymph nodes, and additionally tumor cells within skeletal muscle, heart, lung, liver and kidney in one animal. Immunohistochemically, neoplastic cells were characterized by an expression of the T-cell receptor CD3. Generally epitheliotropic T-cell lymphomas are rare neoplasms of unknown cause and reports in guinea pigs are scarce. The most frequent neoplasms of the skin in this species are lipomas and trichofolliculomas. Initially a neoplasm was not suspected in both cases presented here. An epitheliotropic T-cell lymphoma should be considered as differential diagnosis in any case of unresponsive or recurrent scaling, itching and erythematous skin changes with alopecia, especially if the skin disorder is accompanied by weight loss and a poor general condition. In such cases the epitheliotropic T-cell lymphoma is easily diagnosed by using cutaneous biopsy samples. With those cutaneous biopsy samples the definitive diagnosis of an epitheliotropic lymphomas was made in both cases.

Long-term survival of Mycoplasma bovis in necrotic lesions and in phagocytic cells as demonstrated by transmission and immunogold electron microscopy in lung tissue from experimentally infected calves.

In the lungs of cattle infected with Mycoplasma bovis persistence of the agent for several weeks after infection has been demonstrated by different methods, e.g. isolation of the organism, immunohistochemistry for antigens, and in situ hybridization. The presence of macrophages and neutrophils with cytoplasmic M. bovis antigen suggests that phagocytosis occurs in vivo. It is, however, unknown whether this intracellular immunolabeling detected residual antigen after phagocytosis of M. bovis or surviving organisms in macrophages that use the intracellular survival as a strategy for evasion of the immune response. The aim of this electron microscopic investigation was to study the distribution of M. bovis within caseonecrotic lung lesions and to examine the phagocytes for intracellular presence of the agent. In lung tissue sections from 9 experimentally infected calves originating from two different infection experiments large numbers of mycoplasmas were detected by transmission electron microscopy and by immunogold electron microscopy using M. bovis-specific polyclonal antibodies. M. bovis were found throughout caseonecrotic foci and within the lumen of bronchi containing exudate. The majority of mycoplasmas were located extracellularly within necrotic lung lesions and around neutrophilic granulocytes and macrophages, while fewer organisms were found within the cytoplasm of phagocytes. The results of this study show that there is long-time survival of numerous intact M. bovis in necrotic lung lesions even though large numbers of neutrophils and macrophages are present. These findings show that the phagocytes are not able to eliminate M. bovis from the lungs from necrotic and inflamed lung tissue and indicate that persistence of the agent is possibly due to its capacity to avoid phagocytosis.

Presumptive primary central nervous system T cell lymphoma in a deer (Capreolus capreolus).

This report describes the morphological and immunohistochemical findings in an approximately 7-year old wild European roe deer (Capreolus capreolus) with an infiltrative primary central nervous system T cell lymphoma. The roebuck had lost its timidity and was shot by a hunter. It was submitted for necropsy to exclude rabies. Gross examination revealed besides a verminous pneumonia no abnormal findings. Histologically, there was a highly cellular, not well demarcated, unencapsulated, and infiltrative neoplasm within basal parts of the brain. Tumour cells were round, up to 15 µm in diameter and loosely arranged in sheets with a multifocally predominant perivascular infiltration. Immunohistochemically, tumour cells were positive for CD3 antigen. Whilst secondary lymphomas of the central nervous system emerge by metastatic seeding of tumour cells, primary lymphomas originate within the neuroparenchyma. This is the first report of a primary central nervous system lymphoma in an European roe deer.

Quantitative PCR and immunohistochemical analyses of HMGB1 and RAGE expression in canine disseminated histiocytic sarcoma (malignant histiocytosis).

BACKGROUND: Disorders of histiocytic origin affecting humans and dogs share various similarities. Canine disseminated histiocytic sarcoma (DHS) (formerly known as malignant histiocytosis) is an aggressive neoplasm of interstitial dendritic cells (DCs). The receptor for glycation end products (RAGE) and the high mobility group box1 protein (HMGB1) have been shown to be required for the maturation and migration of DCs. Thus, deregulation of the expression of these genes could have a major effect on the progression of histiocytic disorders. MATERIALS AND METHODS: Neoplastic canine DHS samples and non-neoplastic control samples were analysed immunohistochemically and via real-time PCR. RESULTS: Significant down-regulation of RAGE in the lung tumour samples and down-regulation of HMGB1 in the lung, lymph node and spleen tumour samples were detected compared to their non-neoplastic counterparts. CONCLUSION: RAGE and HMGB1 expression down-regulation in canine DHS points to a role in the progression of histiocytic disorders.

Structural and functional changes of neuronal and glial components of the feline enteric nervous system in cats with chronic inflammatory and non-inflammatory diseases of the gastrointestinal tract.

Immunohistochemical examinations of the enteric nervous system (ENS) were performed on biopsies of healthy cats and compared to findings in cats suffering from inflammatory bowel disease or intestinal lymphoma. In lymphocytic-plasmacytic enterocolitis all affected samples had significant reductions in glial fibrillary acidic protein and vasoactive intestinal peptide (VIP) and mostly of neuron-specific enolase (NSE) possibly reflecting alterations in enteric glial cells and neurons. In cases with eosinophilic gastroenterocolitis significantly reduced phosphorylated neurofilament (PN) expression was present suggesting a disturbance in neuronal cytoskeleton, whereas cats with fibrosing enteropathy had reduced expression of NSE, non-phosphorylated neurofilaments (NPN), PN and VIP, possibly reflecting neuronal disturbances. In cases with intestinal lymphoma only the reduction in PN and the increase in NPN were obvious suggesting direct damage or interference of neoplastic cells with enteric neurons. In conclusion, structural and functional alterations of the ENS may contribute to clinically evident signs of vomiting and/or diarrhea.

Phenotypical characterization, distribution and quantification of different mast cell subtypes in transmural biopsies from the gastrointestinal tract of cats with inflammatory bowel disease.

In this study subtypes, distribution and number of mast cells were investigated within mucosa and submucosa of the gastrointestinal tract of 24 cats with inflammatory bowel disease (IBD) in comparison to 11 control cats. Paraffin sections of formalin-fixed transmural gastrointestinal biopsies from stomach, duodenum, jejunum, ileum and colon were examined. Mast cells were phenotyped and quantified based on their chymase and tryptase content, by applying a combined enzyme-histochemical and immunohistochemical double-labeling technique and on their heparin content by a metachromatic staining method (kresylecht-violet, MC(KEV)). Mast cells containing both chymase and tryptase were not found in any of the samples examined. Furthermore, in the stomach neither chymase (MC(C)) nor tryptase (MC(T)) bearing mast cells were detected. In cats with lymphocytic-plasmacytic enteritis or enterocolitis elevated numbers of MC(T) or MC(C) were identified in comparison to controls mainly located in the inflamed segments. The highest quantity of MC(C) was found in cats with eosinophilic gastroenterocolitis or enterocolitis in comparison to other IBD forms, but only minor numbers of MC(T) were detected in these cases. In cats with fibrosing enteropathy (FE) a decrease of MC(C) and mast cells containing heparin was detected in affected segments, while increased numbers of MC(T) were detected in all locations. The elevation in the number of MC(T) was higher in unaffected areas than in fibrotic regions. Regarding all IBD cases higher counts of MC(C) were found especially in the inflamed locations, whereas in unaffected segments increased numbers of MC(T) were detected. The clear predominance of MC(C) and MC(T) within the mucosa and of MC(KEV) within the submucosa of all cats examined possibly represents differences of the cytokine milieu within the intestinal layers. In FE, mast cells are possibly pivotal for the containment of the inflammatory process because of their antiinflammatory properties. The results of this study indicate that mast cells and their mediators are involved in the pathogenesis of different IBD forms in cats.