Prevalence and Transmission of Honeybee Viruses

Abstract

Transmission mechanisms of six honeybee viruses, including acute bee paralysis virus (ABPV), black queen cell virus (BQCV), chronic bee paralysis virus (CBPV), deformed wing virus (DWV), Kashmir bee virus (KBV), and sacbrood bee virus (SBV), in honey bee colonies were investigated by reverse transcription-PCR (RT-PCR) methods. The virus status of individual queens was evaluated by examining the presence of viruses in the queens' feces and tissues, including hemolymph, gut, ovaries, spermatheca, head, and eviscerated body. Except for head tissue, all five tissues as well as queen feces were found to be positive for virus infections. When queens in bee colonies were identified as positive for BQCV, DWV, CBPV, KBV, and SBV, the same viruses were detected in their offspring, including eggs, larvae, and adult workers. On the other hand, when queens were found positive for only two viruses, BQCV and DWV, only these two viruses were detected in their offspring. The presence of viruses in the tissue of ovaries and the detection of the same viruses in queens' eggs and young larvae suggest vertical transmission of viruses from queens to offspring. To our knowledge, this is the first evidence of vertical transmission of viruses in honeybee colonies.The honeybee, Apis mellifera L., plays a vital role in agriculture by assisting in the pollination of a wide variety of crops, with an annual added market value exceeding 15 billion dollars (13). However, the health and vigor of honeybee colonies are threatened by numerous parasites and pathogens, including viruses, bacteria, protozoa, and mites. Among pathogens attacking honeybees, viruses are probably the least understood because of the lack of information about the dynamics underlying viral disease outbreaks.A most crucial stage in the dynamics of virus infections is the mode of virus transmission. In general, transmission of viruses can occur through two pathways: horizontal and vertical transmission. In horizontal transmission, viruses are transmitted among individuals of the same generation, while vertical transmission occurs from adults to their offspring. Transmission can occur through multiple routes in social organisms. Over the past several years, horizontal transmission of honeybee viruses has been documented in bee colonies. experimentally demonstrated that the parasitic mite Varroa destructor obtained deformed wing virus (DWV) from infected bees and acted as a vector to transmit the virus to uninfected bees, which developed morphological deformities or died after mites fed on them for certain periods of time. Our recent study with Kashmir bee virus (KBV) established the role of V. destructor in virus transmission and provided evidence of miteto-brood transmission and mite-to-mite acquisition of viruses in bee colonies (5). Although these results demonstrated horizontal transmission of viruses, virus transmission in honeybees is still not completely understood. For instance, in our subsequent studies with DWV (4, 6), we detected virus in honeybee eggs and young lar...

Horizontal transmission of deformed wing virus: pathological consequences in adult bees (Apis mellifera) depend on the transmission route

“…This is in agreement with other studies, which either showed high viral titres in the abdomens of infected bees (Chen et al, 2006;Iqbal & Mueller, 2007;Yue & Genersch, 2005) or directly identified the digestive tract as one of the predominantly infected tissues (Fievet et al, 2006). Further experiments are needed to analyse the spread of the virus from the midgut to other tissues.There are studies showing qualitatively that DWV is present in the midgut content (Fievet et al, 2006) and in faeces (Chen et al, 2006), suggesting a faecal-oral route of transmission, but there is no quantitative data allowing the estimation of the absolute viral titre. The same is true for absolute DWV titres in different developmental stages of the bee.…”

“…There are studies showing qualitatively that DWV is present in the midgut content (Fievet et al, 2006) and in faeces (Chen et al, 2006), suggesting a faecal-oral route of transmission, but there is no quantitative data allowing the estimation of the absolute viral titre. The same is true for absolute DWV titres in different developmental stages of the bee.…”

“…Detection of DWV in the midgut content (Fievet et al, 2006) and bee faeces (Chen et al, 2006) suggests the additional possibility of a faecaloral route of transmission between adult bees. Oral transmission of DWV might also occur through trophallaxis or when DWV-infected pupae are cannibalized by nurse bees in order to remove these pupae as part of the social immune response.…”

Seasonal prevalence of pathogens and parasites in the savannah honeybee (Apis mellifera scutellata)

“…The health of honeybees has been one of the most important topics in apicultural research in recent years (Genersch, 2010). This is primarily due to the recent emergence of high honeybee colony losses in many parts of the world (Le Conte et al, 2010;Neumann and Carreck, 2010;Stokstad, 2007;vanEngelsdorp et al, 2008) and the vulnerability of honeybees to parasitic mites, fungi, viruses and bacteria (Bailey and Ball, 1991;Chen et al, 2006;Dietemann et al, 2012;Genersch, 2010;Genersch et al, 2010;Martin, 2001;Ribière et al, 2010;Sammataro et al, 2000). These pathogens and parasites can have harmful effects on honeybee health and the services they offer, which in turn can lead to severe economic losses (Genersch, 2010;Morse and Calderone, 2000;Shen et al, 2005).…”

Scientific note on PCR inhibitors in the compound eyes of honey bees, Apis mellifera

“…A study showed that the insect eye pigment could cause false-negative PCR results and the elimination of the PCR inhibitors was achieved by cutting out eyes prior to DNA isolation (Bextine et al 2004). Our earlier study showed that deformed wing virus (DWV), one of the most prevalent and common honey bee viruses, was not detected in the head of infected bees (Chen et al 2006). However, a later publication by Genersch (2005) showed the detection of DWV in the head of infected bees when an additional step of column purification was included in the regular method of RNA extraction.…”