Macrorhabdus ornithogaster is a yeast, which is found in many different avian species, especially in budgerigars. Macrorhabdiosis is also called megabacteriosis or going light syndrome. Infected animals may develop maldigestion and lose weight even though there is no change in appetite. Undigested seeds can be excreted with the faeces, sometimes there is also blood in the faeces. Choking and vomiting as well as a general weakness can also be found in macrorhabdiosis. Inapparent carriers are frequent. Transmission presumably occurs through billing and feeding as well as through contaminated feed and water.