Chronic facial eczema in sheep: description of gross and histological changes in the liver and association with serum gamma-glutamyltransferase activity at the time of sporidesmin intoxication

Chronic pithomycotoxicosis associated with obstructive rhinopathy in sheep

Pithomycotoxicosis (facial eczema) is a seasonal hepatogenous photosensitization of sheep caused by the ingestion of sporidesmin contained in the spores of the fungus Pithomyces chartarum. We describe 4 cases of obstructive rhinopathy associated with chronic pithomycotoxicosis naturally occurring in the north of Spain. Sheep were 5 to 7 years old and Latxa breed. A detailed clinical study was conducted together with computerized tomography examination and completed by necropsy and histopathology. All sheep developed a permanent narrowing of the nasal lumen close to the nostrils causing inspiratory dyspnea and snoring. Computerized tomography demonstrated a significant increase of soft tissue in the rostral nasal cavity. Elevated gamma-glutamyl transferase, alanine aminotransferase, and lipase were noted on serum biochemistry. At necropsy, liver atrophy and fibrosis associated with chronic pithomycotoxicosis was identified in 3 of the sheep. All sheep had whitish elevations and rough surfaces on the alar folds and areas adjacent to the nasal surfaces. Histopathologic assessments, which included histochemical and immunohistochemical techniques, of the nasal lesions identified moderate to severe arteriosclerosis in 21.5% to 61.9% of the small arteries evaluated with surrounding fibrosis and edema. No changes associated with hypersensitivity reactions were found. These lesions were similar to the ones described in blood vessels of the liver in chronic pithomycotoxicosis and in our cases. The results of this study suggest a direct action of the sporidesmin on the rostral nasal cavity. Further studies are needed to analyze the impact of the sporidesmin on the sheep nasal mucosa.

Fungal Pathogens in Grasslands

Grasslands are major primary producers and function as major components of important watersheds. Although a concise definition of grasslands cannot be given using a physiognomic or structural approach, grasslands can be described as vegetation communities experiencing periodical droughts and with canopies dominated by grasses and grass-like plants. Grasslands have a cosmopolitan distribution except for the Antarctic region. Fungal interactions with grasses can be pathogenic or symbiotic. Herbivorous mammals, insects, other grassland animals, and fungal pathogens are known to play important roles in maintaining the biomass and biodiversity of grasslands. Although most pathogenicity studies on the members of Poaceae have been focused on economically important crops, the plant-fungal pathogenic interactions involved can extend to the full range of ecological circumstances that exist in nature. Hence, it is important to delineate the fungal pathogen communities and their interactions in man-made monoculture systems and highly diverse natural ecosystems. A better understanding of the key fungal players can be achieved by combining modern techniques such as next-generation sequencing (NGS) together with studies involving classic phytopathology, taxonomy, and phylogeny. It is of utmost importance to develop experimental designs that account for the ecological complexity of the relationships between grasses and fungi, both above and below ground. In grasslands, loss in species diversity increases interactions such as herbivory, mutualism, predation or infectious disease transmission. Host species density and the presence of heterospecific host species, also affect the disease dynamics in grasslands. Many studies have shown that lower species diversity increases the severity as well as the transmission rate of fungal diseases. Moreover, communities that were once highly diverse but have experienced decreased species richness and dominancy have also shown higher pathogenicity load due to the relaxed competition, although this effect is lower in natural communities. This review addresses the taxonomy, phylogeny, and ecology of grassland fungal pathogens and their interactions in grassland ecosystems.