Clinical signs and symptoms of infection

The effects from N. apis infections on honey bee colonies have been extensively documented (Fries, 1993). This disease is characterized (in acute forms) by the trembling of honey bee workers or dead bees around the hive. Bees may also exhibit a dilated abdomen and brown faecal marks on the comb and the front of the hives are often found. Further, heavily infected colonies have a decrease in brood production and slow colony growth, particularly in spring (Bailey, 1955; OIE, 2008). Although N. apis is correlated with winter mortality of infected colonies, the disease also appears without causing losses of infected colonies (Bailey, 1955).

Colony level symptoms produced by N. ceranae infections have been described to be different from N. apis symptoms (Higes et al., 2008; 2009). A gradual  depopulation of adult bees, higher autumn / winter colony mortality, and finally the queen surrounded by only young bees have been observed in southern Europe (Higes et al., 2006; 2008; 2009), whereas such severe symptoms or effects have not been described from more temperate climates (Gisder et al., 2010a) nor from South (Invernizzi et al., 2009) or North (Williams et al., 2011; Guzman-Novoa et al., 2010) America. Possibly, differences in honey bee subspecies, foraging conditions, agricultural practices, differences in hive management practices, or other abiotic or biotic factors may contribute to the variation in symptoms described for N. ceranae infections in different regions of the world. Further research efforts using standardized methodologies are most certainly warranted.