Study On Etiology And Pathogenesis Of Facial Eczema Outbreak In Grazing Sheep

Grazing sheep facial eczema is a severe disease that afflicts large populations of grazing sheep inspecific area of pasture. The clinical symptoms of the disease are characterized as acute facialinflammatory edema, exudation and necrosis of skin. This disease has been epidemic for many years in thegrazing sheep in the Shihezi Purple Mud Spring Sheep Breeding Farm, Xinjiang, which is located in thelow land of Artemisia Desert Grassland in northern slope of Tian Mountains, Every year, the duration fromMay to August is the season of high incidence of the disease, which results in a large number of sheepdeath, and led to serious economic losses to the farmers. The grassland area of the incidence has beendefined as "grazing prohibition" or "high risk" grassland. Though the disease has been occurred for manyyear in the area, its causes, influence factors and pathogenesis is still unknown. Therefore, the objectives ofthe study are (1) to investigate the epidemiologic factors related to outbreak of the disease, includinggeographical location, grass species and distribution, sheep breeds and age, season and climate factors,clinical and anatomical characteristics;(2) to look into the relationship between fungi species and theoccurrence of the disease by analyzing poisonous plants, light sensitive forage, soil samples, sheep oraland gastrointestinal contents;(3) to unravel etiopathogensis of the disease by comparative studies on serumliver enzyme activity and liver histopathology between sheeps infected naturally and artificially by usingmycotoxins, and on changes of inflammatory cytokine level between sheep and mouse infected withmycotoxins. The results are as follows:1Epidemiological survey: the incidence area is located in the lower mountain area, middle part of thenorthern slope of Tian Mountains Piedmont. The area is slant piedmont plain, and the geographicalposition is N44.016～44.022, E85.792～85.800with altitude925～1039m. It belongs to the typicaltemperate arid continental climate, the annual natural precipitation is180～220mm, and the annual meantemperature is8.5℃. This area is the most important spring and autumn grassland of the local farms. Theincidence of facial eczema only occurs in the shade, low-lying land and sheltered specific grassland. Thisarea is conducive to fungal growth and settlement due to appropriate rainfall, surface temperature andhumidity during the period from May to August, The incidence of the disease more likely occurs in young(less than6months old) fine wool sheep with the incidence rate20～50%. The incidence is characterizedas inflammatory edema in facial and submandibular.2. Clinical pathological examination: the autopsy showed yellowish white patchy necrosis in liversurface, nodular cirrhosis, fibrosis and congestion of the liver, bile duct necrosis, fatty degeneration.Glutamyl transpeptidase (GGT) activity in serum of diseased sheeps was94.93～260.78U/L, which wassignificantly higher than those in healthy sheep16.47～61.59U/L. Alanine aminotransferase (ALT) andtotal bilirubin (TBIL) were significantly higher in the diseased sheeps than those in the healthy sheep (P <0.01). The glutamic oxaloacetic transaminase (AST) activity between diseased and healthy sheeps,however, were not significant (P>0.05). The results showed that the incidence of liver damage is closely related to facial eczema.3. Isolation and identification of pathogenic fungi: A variety of fungi species were identified in thegrasses, soil and content of digestive tract of the illed sheep in the incidence area. Among the fungi species,the isolation rate of the4strains including pithomyces chartarum, Alternaria sp., Fusarium and Aspergilluswas higher than other genera of fungi, while pithomyces chartarum separation rate is the highest. Thedenatured gradient gel electrophoresis (DGGE) analysis indicated that abundance and saturation ofAlternaria sp., pithomyces chartarum spp., Fusarium, Aspergillus, Penicillium were higher in the incidenceregional while pithomyces chartarum fungi showed the highest abundance and saturation. The results wereconsistent with the above isolation and culture studies, and indicated that there was a strong correlationbetween fungi specises and that facial eczema in sheep in the area.4. Animal models infected with mycotoxins: The intensity LD50of mycotoxin toxicity of the fungispecises isolated from in the high incidence area was Niger> pithomyces chartarum> Fusarium, Alternariaalternate. The cytokines including IL-6, IL-12and TNF-α in serum in test group of mice were higherthan those in the control group. The difference was significant (P <0.05). The GGT activity was60.73～190.19U/L in the test group in sheep serum, which was significantly higher than26.17～60.29U/L in thecontrol group. The ALT and TBIL were significantly higher in the tested group than those in control group(P <0.01), but AST activities was not significantly difference between the test group and the control group(P>0.05). The sheeps which were given a variety of mycotoxins by perfusion didn’t exhibit typical facialeczema. the Pathoanatomy and histological analysis of the sheep with higher serum coenzyme activity intest group showed eblargement of the liver, patchy necrosis, section fibrosis cirrhosis, liver congention,liver cells and bile duct necrosis, severe fatty degeneration. The pathological changes were similar tonaturely happened incidence. The results show that mycotoxins of the isolated fungi specises were a majorcause of liver injury and the pathogenesis of inflammatory swelling of facial eczema.The study identified the etiology, contributory factors and Pathogenesis of the grazing sheep facialeczema in the area of Artemisia Desert Grassland in the northern slope of the Tianshan Mountains. Theresults provided a strong foundation for the successful and effective control of the disease.