Abstract
Although it had been reported that Israeli acute paralysis virus (IAPV) can cause systemic infection in honey bees, little is known about how it establishes this infection and results in the typical symptoms, paralysis and trembling. Here, we used our previously constructed IAPV infectious clone to investigate viral loads in different tissues of honey bees and further identify the relation between tissue tropism and paralytic symptoms. Our results showed that tracheae showed a greater concentration of viral abundance than other tissues. The abundance of viral protein in the tracheae was positively associated with viral titers, and was further confirmed by immunological and ultrastructural evidence. Furthermore, higher viral loads in tracheae induced remarkable down-regulation of succinate dehydrogenase and cytochrome c oxidase genes, and progressed to causing respiratory failure of honey bees, resulting in the appearance of typical symptoms, paralysis and body trembling. Our results showed that paralysis symptoms or trembling was actually to mitigate tachypnea induced by IAPV infection due to the impairment of honey bee tracheae, and revealed a direct causal link between paralysis symptoms and tissue tropism. These findings provide new insights into the understanding of the underlying mechanism of paralysis symptoms of honey bees after viral infection and have implications for viral disease prevention and specific therapeutics in practice.
Highlights
Honey bees provide pollination services for crops and wild plants in both natural and agricultural ecosystems [1]
We found that the trachea was the preferred tissue of Israeli acute paralysis virus (IAPV) infection and down-regulation of the expression of succinate dehydrogenase (SDH) and cytochrome c oxidase (COX) genes, leading to heavy breathing and progressing to paralysis and trembling
IAPV-infected bees start to die accompanied by body trembling at 36 h post-infection and paralytic bees are frequently observed at the same time
Summary
Honey bees provide pollination services for crops and wild plants in both natural and agricultural ecosystems [1]. Varroa destructor, an important ectoparasitic mite of honey bees, can vector several bee viruses, including deformed wing virus (DWV) and IAPV, and turn covert infection into overt infection, with typical signs ranging from discoloration, black abdomen, hairlessness and deformed wings to leg paralysis, body trembling and increased mortality [14,18]. For DWV and IAPV infection, clinical symptoms were not closely linked to the tissue tropism, indicating that overt infection might be associated with the most heavily damaged organs To address these gaps in the knowledge, we used an IAPV infectious clone to avoid the potential interference of other viruses to explore the exact tissue tropism [20], and identified the underlying cause of the typical paralysis signs of IAPV. These results showed that paralytic symptoms were not really paralysis but a way of mitigating the shortness of breath
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