Facial Eczema - The Disease

The Problem

The fungus Pithomyces chartarum which causes facial eczema in stock, is found through the world, but is only a problem when producing high spore numbers. The fungus commonly occurs and thrives in locations of warm ground temperatures coinciding with high humidity and moisture. The degree of severity and regularity of facial eczema outbreaks depends on the weather, the location of the farm and on grazing management. The problem has become more widespread in recent years because higher stocking rates necessitate closer grazing of pastures. This causes the animals to ingest greater numbers of the toxic fungal spores, which are prolific on litter around the base of the pasture. Weather conditions have also been very conducive to extremely high levels of spores in the pasture.

Some pasture species are consistently safer than others. Clovers, chicory, plantain, kikuyu, paspalum and tall fescue are all safer than ryegrass dominant pasture. Ryegrass is one of the most hazardous grasses, especially if it has been burnt off in a dry summer and then receives showers in the autumn.

The Fungus

Pithomyces chartarum

The fungus is a saprophytic mould which lives on any dead litter lying at the base of pastures. This mould is present in pastures all year round but only becomes a problem at certain times when high ground temperatures coincide with high humidity and moisture. Under these conditions the mould grows rapidly producing many new hyphae which produce clusters of fruiting bodies called spores. The spores, when released, are spread by wind throughout the pasture.

The spores then germinate forming another fungus mould, which again produces spores and so the cycle continues. When the spores are formed a toxin called sporidesmin is produced and stored within the spore. The toxic sporidesmin is susceptible to ultra violet light breakdown, therefore freshly produced spores contain more toxin than the older spores. When grazing animals ingest spores of the fungus, it is the sporidesmin which is responsible for the symptoms known as facial eczema. The climatic conditions which favour the maximum production of spores are warm days and two to four nights with grass minimum temperatures above 12oC in conjunction with heavy dews or light rain.

Sudden drops in temperature will result in lower spore numbers. Heavy rain destroys many spores due to osmotic pressures, resulting in lower spore numbers, but is usually followed by rapid increases, particularly so if followed by warm temperatures.

Recognition of Pithomyces chartarum Spores (microscopic)

Pithomyces chartarum spores are of characteristic appearance, brown, barrel shaped, somewhat roughened, and several celled with cell divisions running both horizontally and vertically. Very young spores may have a greenish tinge and old ones may lose some of their colour. Roughness is not always apparent. The cells of old spores may be collapsed and the whole spore difficult to recognise. These old spores will have lost their toxin.

Symptoms

Although cattle, sheep, deer and goats are all susceptible to facial eczema there is some variance in species susceptibility. Fallow deer and sheep are most susceptible, followed by dairy cattle, beef cattle and red deer. Goats are least susceptible. Susceptibility also varies within species and within individual herds. Resistance to facial eczema in sheep is inherited and breeding resistant animals is now well advanced.

The grazing animal ingests spores from the pasture. In the gut, the toxin is absorbed from the spores into the bloodstream and then transported to the liver. Here the toxin causes inflammation of the bile duct which eventually closes, not allowing bile to be excreted into the small intestine. The bile then seeps back into the liver and bloodstream. The damaged liver cannot rid the body of wastes and a breakdown product of chlorophyll accumulates in the tissues. This results in the animal becoming photosensitive, and it tends to seek shade away from direct sunlight. If exposed to sunlight this results in immediate and severe inflammation of the skin on exposed non pigmented parts of the body. From the time the animal ingests toxic levels of spores to the appearance of the first symptoms is usually about ten days.

In cows the first signs are a drop in milk production immediately after grazing toxic pasture. Later cows become restless at milking time, seek shade and lick their udders as photosensitisation develops. Skin lesions appear on unpigmented skin, especially the escutcheon, inside the hind legs, the udder and teats, and the coronets.

Although these are the first outward signs a farmer sees in stock, considerable liver damage will have already occurred. With all types of animals those severely affected may die. Some animals which may not show outward signs of facial eczema may die during pregnancy, lactation or other periods of stress in the following winter or spring as a result of the disease. The liver has the ability to regenerate healthy tissue and providing management allows rest and a nutritious food supply, affected animals may recover.

Facial Eczema Prevention and Treatment

Weekly Spore Counts