Host Genotype and Tissue Type Determine DWV Infection Intensity

Abstract

Varroa mite-vectored viruses such as Deformed wing virus (DWV) are of great concern for honey bee health as they can cause disease in individuals and increase colony mortality. Two genotypes of DWV (A and B) are prevalent in the United States and may have differential virulence and pathogenicity. Honey bee genetic stocks bred to resist Varroa mites also exhibit differential infection responses to the Varroa mite-vectored viruses. The goal of this project was to determine if interactions between host genotype could influence the overall infection levels and dissemination of DWV within honey bees. To do this, we injected DWV isolated from symptomatic adult bees into mite-free, newly emerged adult bees from five genetic stocks with varying levels of resistance to Varroa mites. We measured DWV-A and DWV-B dissemination among tissues chosen based on relevance to general health outcomes for 10 days. Injury from sham injections did not increase DWV-A levels but did increase DWV-B infections. DWV injection increased both DWV-A and DWV-B levels over time with significant host stock interactions. While we did not observe any differences in viral dissemination among host stocks, we found differences in virus genotype dissemination to different body parts. DWV-A exhibited the highest initial levels in heads and legs while the highest initial levels of DWV-B were found in heads and abdomens. These interactions underscore the need to evaluate viral genotype and tissue specificity in conjunction with host genotype, particularly when the host has been selected for traits relative to virus-vector and virus resistance.

Honey Bee Genetic Stock Determines Deformed Wing Virus Symptom Severity but not Viral Load or Dissemination Following Pupal Exposure

“…All colonies were similarly maintained in three yards near the USDA laboratory (with Carniolan, Italian, and Saskatraz sharing one yard, while Pol-Line and Russian colonies were maintained in two separate yards). To allow for direct comparison, the same colonies were used in a complementary study following DWV levels over 10 days in newly emerged adult bees (Penn et al, 2021).…”

“…To determine potential interactions of bee stock and DWV, we exposed honey bee pupae, the life stage that is most commonly infested with mites (Ifantidis, 1983(Ifantidis, , 1984Donzé and Guerin, 1994), to Varroa mites or injected them with a sublethal dose (10 5 ) of DWV sourced from symptomatic (e.g., deformed wings) adult bees. Upon adult emergence, we determined DWV levels and dissemination throughout different tissue types [abdomen, head, hypopharyngeal gland, and a rear leg as in the study by Penn et al (2021)], the number of days until adult emergence, and DWV symptom presence and severity. The tissue types selected were chosen as legs have been used to indicate viral dissemination in other arthropods (Boncristiani et al, 2009;Diagne et al, 2015); the head has been an indicator of overt bee infections (Yue and Genersch, 2005;Möckel et al, 2011); hypopharyngeal glands may provide possible transmission by food trophallaxis (Chen Y. et al, 2006, Chen et al, 2006Möckel et al, 2011); and the abdomen as the site of mite feeding and our injection treatment groups.…”

Critical View on the Importance of Host Defense Strategies on Virus Distribution of Bee Viruses: What Can We Learn from SARS-CoV-2 Variants?

“…Sequence information on the viral genomes of most bee viruses has enabled research on the viral adaptation of bee viruses, which also gained a lot of attention lately. Here, most studies worked with the DWV-complex, a quasispecies for which three master variants are identified (DWV-A, DWV-B and DWV-C), based upon nucleotide identity and differences in effects on replication, virulence, and pathology [ 61 , 62 , 63 , 64 , 65 ]. Furthermore, despite mutations, recombination events between variants have also been identified [ 60 , 66 , 67 ] and are known to play a role in the generation of new variants with picorna-like viruses [ 68 ].…”

“…The underlying nature of this variant shift has not been fully clarified. Yet some studies point to the higher replication and reduced virulence costs of DWV-B infection, which may be due to different tissue tropism [ 64 , 73 , 78 , 79 ]. The virus may evolve to less severe and more contagious/transmissible variants, causing less harm to the host.…”

“…However, other studies find that DWV-B is more virulent compared to DWV-A [ 80 , 81 ]. The discrepancies between studies may be attributed to the complex host-genotype-virus interaction determining the virulence of a certain variant [ 64 ], or other confounding factors, such as differences in the presence of V. destructor between studies. Further research is needed to elucidate this.…”