In this article, we present two clinical cases of Chronic Bee Paralysis Virus (CBPV) from Spain. We extend our gratitude to Ana Mompó and Inma Segura (ADS APIVAL), as well as Fernando Calatayud and Enrique Simó (ADS APIADS), for providing these insightful cases. Before examining the specific cases, we will review the etiology, pathogenesis, transmission, and symptoms of CBPV.
Chronic bee paralysis virus or CBPV consists of two separate positive-stranded RNA molecules. Its classification is unclear, so it is not included in any genus or family, although it shares characteristics with the plant virus family Tombusviridae and Nodaviridae.1
A considerable increase in the incidence and viral load of chronic paralysis virus has been observed in Europe, Asia, and the United States.2
Natural transmission of the virus within the colony is believed to occur by close contact (rubbing) between infected and healthy bees, and by contact with the feces of diseased bees, the virus is capable of infecting honey bees at all stages of development. The possibility of transmission increases during adverse weather episodes in spring, when hives are overcrowded, very active and bees are unable to forage.3
Under these circumstances the most severe cases have occurred in recent years in our country, as an example it is worth remembering the intense and persistent rains in the spring of 2020 in the Mediterranean area and the numerous severe outbreaks of CBPV, as well as the cases that have occurred at the end of the spring of 2024 in areas of the interior of the Iberic Peninsula.
Bordin et al. (2022)4 have studied the incidence of various pathogens in northeastern Italy and with respect to CBPV they comment that the prevalence was very high in the springs of 2020 and 2021, 98.8% and 82.2% respectively, and state that the appearance of the clinical form of infection by this virus is related to episodes of overcrowding in the hive, especially during episodes of unexpected bad weather in spring and summer and/or by the consumption of honeydew. The relationship between this virosis and the consumption of honeydew by bees has been known for a long time and is therefore called “forest disease” in some European countries.
Characteristic symptoms may include:
All this ends up producing such a depopulation that the colonies become unviable, considerably increasing the mortality rate in the farm.
A differential diagnosis is the process of identifying a disease by distinguishing it from other conditions with similar symptoms.
As a differential diagnosis, the following affections should be considered:
In the first case, there is a symptomatology compatible with that produced by the chronic paralysis virus, being its recurrent presentation in a single apiary in a beekeeping farm of a professional beekeeper. The onset of symptoms is always on the same dates (February) and has been occurring annually since the beekeeper began to install hives in that location (2020).
In the case of the apiary in question, we believe that one of the main triggers may be due to the natural food collected by the bees in the area, since in the rest of the apiaries of the same beekeeper and managed in the same way, this does not happen.
The apiary is located in a Mediterranean-type mountain area, at an altitude of 770 m, with no nearby crops, which helps to rule out agro-environmental intoxication. As predominant flora we find: rockrose, heather, rosemary, thyme, pennyroyal, savory, cat’s tail (Acalypha hispida), dandelion, horehound, borage, kermes oak, mastic …, among others less abundant. At 130 m from the apiary there is a hydraulic structure, like an irrigation pond.
Very recent studies have established a direct relationship between the bee gut microbiota and the transmission and clinical manifestation of chronic paralysis virus. Bees have a gut community that is fairly well characterized.5 These bacteria, as in those of any vertebrate animal, favor the correct assimilation of food and play an important role in immunity against various diseases, mainly viral attacks.
CBPV utilizes the host immune system to decrease the population of probiotic core species and then increases the proliferation of opportunistic pathogens to facilitate viral infection.2
It appears that habitat plays an important role in shaping the gut microbiota of bees 6, this may help us to understand why despite all apiaries of this beekeeper being managed in the same way, recurrent infections in terms of chronic paralysis virus are recurrent in this one apiary.
It would be interesting for possible prevention to prepare the bees by means of food supplements that promote the multiplication of “good” bacteria in the intestine to see if this somehow influences a lower manifestation of the disease.
The administration of specific probiotics for the same purpose may also be of interest.
This is a particularly extreme case, but it illustrates very well the potentiating effect that the confinement of bees in bad weather produces in the transmission of the chronic paralysis virus inside the hive. During the spring of 2021, the rains in the area of Ribera del Xúquer (Valencia) were so intense in spring that they caused occasional flooding of some fields near water courses. In an apiary of about 20 hives located in one of these points, the field was flooded to a level of about 40-50 cm, so that the hives were partially flooded, despite being seated on metal supports. The hives were very crowded and with a lot of brood, some of them with a super. The bees, under these conditions, were forced to confine themselves in a volume reduced by the water, so that the contact and friction between the bees increased enormously. A few days after the end of the flooding, some dead bees began to appear in the bee box, as well as brood pupae killed by the effects of the water.
Later, many bees with tremors, paralysis and the shiny black cuticle typical of CBPV infection (“black robbers”) began to appear. The infection with this virus was so severe that after 2-3 weeks, near the entrance, there were thousands of dead bees accumulated and hundreds of bees with typical symptoms. At the end of the viral process, more than half of the hives suffered almost total depopulation, others suffered a severe loss that made them practically unviable and only the 4-5 hives that were less vigorous before the flooding managed to survive.
CBPV poses a significant threat to bee colonies, particularly under conditions of overcrowding and adverse weather. Understanding the role of habitat and gut microbiota in CBPV transmission can offer new preventive strategies. Further research into dietary supplements and probiotics may provide effective measures to mitigate the impact of this virus on bee populations.
REFERENCES
Copyright: National Bee Unit
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