There have been several publications that claim to have shown virus replication in varroa mites, and many that have challenged their conclusions. Hence, the debate, which is ongoing.
Grozinger and Flenniken (2019) state: "many bee-associated viruses are found and can replicate in Varroa destructor mites."
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The question is, what do we accept as evidence of viral replication? There are several indicators that have been suggested: negative strand RNA; non-structural proteins; high viral titres.
1) Negative-sense RNA-specific PCR indicated that VDV-1 replicates in the Varroa synganglion and all other tissues tested (Campbell).
2) The absence/scarce detection of non-structural proteins compared with high-abundance structural proteins suggest that the viruses did not replicate in the mite (Erban).
3) A virus titre in mites of (10 to the 10th) to (10 to the 12th) strongly correlated with viral replication, suggesting that such a high virus titre can only be achieved through replication in mites (Gisder).
Peter L Borst
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