Viral Diseases
Sacbrood
Viruses are pieces of genetic material that parasitize a host cell, making the cell produce more viruses. No vaccines or medications are available for any of the honey bee viruses; however, new RNA Silencing technology may soon provide a means to reverse virus symptoms in Sacbrood and other bee viruses. Until then, good sanitation practices are the key to prevention. Comb replacement and requeening are the best practical responses to a virus infection.
Beekeepers rarely consider sacbrood a serious threat, however recent estimates suggest that one larva killed by the sacbrood virus contains enough virus to kill over one million larvae.
More research needs to be conducted on the sacbrood virus since it is unknown how the virus is actually transmitted to the larvae in nature, why severe outbreaks occur only during the build-up season, or how the virus persists from year to year.
Symptoms of sacbrood are partially uncapped cells scattered about the frame or capped cells that remain sealed after others have emerged. Diseased individuals inside cells will have characteristically darkened heads which curl upward. The dead prepupa resembles a slipper inside the cell. Diseased prepupae fail to pupate and turn from pearl white to pale yellow to light brown and finally, dark brown. The skin is flaccid and the body watery. The dark brown individual becomes a wrinkled, brittle scale that is easily removed from the cells (unlike AFB).
Fig. 1
Chronic Bee Paralysis
(Hairless black syndrome)
Viruses are pieces of genetic material that parasitize a host cell, making the cell produce more viruses. No vaccines or medications are available for any of the honey bee viruses. Therefore, good sanitation practices are the key to prevention. Comb replacement and requeening are the best practical responses to a virus infection. Symptoms of chronic bee paralysis are limited to adults. Individuals exhibit an abnormal trembling motion of the wings and body. Bees appear incapable of flight and may be seen crawling up the stems of grass in front of the hive. The abdomens may be bloated and the wings partially spread or dislocated. Bees afflicted with the virus may appear shiny and greasy because of the lack of hair, which should not be confused with robbing bees. Also, adult bees are chewed by other bees and harassed by guard bees at the entrance to the hive (again may be confused with signs of robbing). Adult bees die within a few days of the onset of symptoms. The virus is spread from bee to bee by direct body contact. Food exchange does not appear to be an important mode of spread. Bees vary genetically in susceptibility; therefore requeening is a good practice if symptoms appear.
Fig. 2
Black Queen Cell Virus
Viruses are pieces of genetic material that parasitize a host cell, making the cell produce more viruses. No vaccines or medications are available for any of the honey bee viruses. Therefore, good sanitation practices are the key to prevention. Comb replacement and requeening are the best practical responses to a virus infection.
Symptoms of BQCV are limited to queen larvae. The immature dies and turns black after its cell is sealed. There may be an association between Black queen cell virus and Nosema disease. Treating colonies with Fumidil-B® to control Nosema may help keep this disease at bay.
Deformed Wing Virus
Viruses are pieces of genetic material that parasitize a host cell, making the cell produce more viruses. No vaccines or medications are available for any of the honey bee viruses; however, new RNA Silencing technology may soon provide a means to reverse virus symptoms in DWV and other bee viruses. Until then, good sanitation practices are the key to prevention. Comb replacement, requeening, and Integrated Management of Varroa mites are the best practical responses to a virus infection.
DWV appears to be associated with parasitic Varroa mites which are known to spread the virus or at least activate it. Bee pupae are susceptible to infection at the white-eyed stage. The virus multiplies slowly which permits the infected individual to survive to adulthood. The newly-emerged adult has misshapen wings (Fig. 2) and soon dies.
The best management against DWV is aimed at parasitic Varroa mites.
Fig. 3