MD is a lymphomatous and neuropathic disease of domestic birds caused by an alphaher-pesvirus. Fowls get infected by inhalation of infected dust from the poultry houses and the virus is shed from the feather follicle of infected birds. Chickens are the most important natural hosts for MD, which usually takes place at 12-30 weeks of age. Besides, MD is one of the most ubiquitous avian infections. It has been reported in chicken flocks worldwide. Every flock, except those maintained under strict pathogen-free conditions, is presumed to be infected. MD may cause important economic losses through a subclinical decrease in growth rate and egg production. Clinical signs observed include paralysis of the legs and wings and enlargement of peri-pheral nerves. Moreover, chickens may become persistently infected without developing clinical disease. According to the current situation, it is necessary to review and update this severe and widespread problem. To make it easier, the author, a prestigious specialist in this field, has developed a thorough assessment of this topic in a didactic and visual way. Many resour-ces (images, tables, graphs, etc.) have been included to facilitate the comprehension of this disease by the reader. This precise and straightforward information will help the vete-rinarians to know everything about this condition and tackle it properly.