The study of bee viruses is revealing many new things. I have heard
that if one controls mites, one controls viruses. This would appear to
be an oversimplification because of the many different viruses and the
various means of transmission.

> Virus transmission in honey bees appears to involve foodborne transmission, venereal transmission, vector-borne transmission, and mother-to-offspring transmission. Both vertical and horizontal transmission pathways are believed to be important survival strategies for honey viruses not only for their long-term persistence in bee population but also for their establishment in nature, leading to the following model for viral epidemiology.

> In horizontal transmission, viruses are transmitted among individuals of the same generation. Horizontal transmission can be further classified as direct or indirect. Horizontal transmission by a direct route includes airborne infection, food-borne infection, and venereal (sexual) infection, whereas transmission by an indirect route involves an intermediate biological host, like a mosquito vector, which acquires and transmits virus from one host to another. In vertical transmission, viruses are passed vertically from mother to offspring via egg, either on the surface of the egg (transovum transmission) or within the egg (transovarian transmission).

> When colonies are under non-competitive and healthy conditions, viruses maintain in bee colonies via vertical mechanism of transmission and exist in persistent or latent state without causing honey bees to show any overt signs of infections. Alternatively, when honey bees live under stressful conditions such as infestations of Varroa mite, co-infection of other pathogens, and a decline in food supply which can result in reduction of host growth rate, viruses appear to leave their latent state. High numbers of produced virions then become much more infectious via horizontal transmission mechanism, leading to the death of hosts and possible collapse of the whole bee colony.

Source

"Horizontal and vertical transmission of viruses in the honey bee,
Apis mellifera"
Yanping Chen, Jay Evans, Mark Feldlaufer
USDA-ARS, Bee Research Laboratory, Beltsville, MD 20705, USA

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