EFFECT OF 1,3-1,6 Β-GLUCAN ON NATURAL AND EXPERIMENTAL DEFORMED WING VIRUS INFECTION IN NEWLY EMERGED HONEYBEES (APIS MELLIFERA LIGUSTICA) Atti del 71° Congresso SISVet:

The European honeybee (Apis mellifera ligustica L.) is the most managed pollinator species. Honeybees have recently suffered extensive losses mainly due to exposure to pesticides, malnutrition and pathogens, including bacteria, fungi, mites and viruses. Among honeybee’s pathogens, viruses play an important role in honeybee diseases (1). Deformed Wing Virus (DWV) is associated with honeybee colony losses. DWV can be transmitted vertically and persist in the bee colony as asymptomatic and symptomatic infections with clinical signs consisting of crumpled wings and a bloated abdomen. Symptomatic infections leading ultimately to the collapse of the colony are observed in apiaries infested by Varroa destructor which supports replication of DWV to high titers. During the first stage of the infection DWV is detected in the abdomen, at later stages presence of an actively replicating virus is also detectable in the head (2). The aim of this study was to investigate the effect of 1,3-1,6 β-glucan, a natural immune-modulator molecule, on honeybee response to both low-titer natural and high-titer experimental DWV infection. To date there are still few studies done to know the effect of ß-glucans on the immune response of honeybees. The investigation on their possible nutraceutical antiviral therapy may represent an innovative alternative to the use of synthetic chemical substances also for other diseases, with important benefits for the welfare of animals, humans and a positive impact on the environment. Two parallel experiments were performed; newly emerged honeybees, which were sampled from a Varroa-free apiary and harbored a low endogenous DWV viral titer where fed with 1,3-1,6 ß-glucan at a concentration of 0.5% and 2% respectively. Bees feed a 0.5% and 2% 1,3-1,6 ß-glucan diet were divided in three experimental cohorts and each of those was subjected to one of the following experimental treatments: no injection, injection into the haemocel of a high-copy number DWV suspension (experimental DWV infection) and PBS injection into the haemocel (physical injury). Control bees fed a ß-glucan-free diet were subjected to the same treatments. Twenty-five small cages with a maximum of 30 honeybees per cage were kept at 28°C for 13 days. Viral load was measured by qRT-PCR performed on RNA extracted from abdomen and head on honeybees. Insects were monitored daily and those found dead were collected to calculated the survival rate. Results indicated that administration of 0.5% ß-glucan to infected honeybees was associated with a significant reduction DWV viral load and with a significant increase of the survival rate suggesting that this natural immune modulator molecule might contribute to increase honeybee resistance to viral infection by restraining viral replication ultimately prolonging the honeybee lifespan.