Sheep are an important part of the global agricultural economy by providing wool, meat, milk and other byproducts. Wool was historically one of the first textiles but synthetic fabrics became more popular in the late 20th century, causing wool prices to fall. Sheep meat and milk have long been staple proteins for human civilization. Parasitic nematodes like Dictyocaulus filaria cause economically important diseases in sheep by inhabiting the lungs and causing bronchitis, particularly in young sheep. D. filaria has a direct lifecycle involving eggs, larvae and infection through grazing.