Beekeeping/Chronic Paralysis Virus
Chronic bee paralysis virus Edit
Chronic bee paralysis virus (CBPV) is a common single-stranded RNA virus which may cause significant losses in honeybee colonies. It was first isolated in 1963 from diseased honeybees (Bailey et al., 1963; Olivier et al., 2008a, 2008b). CBPV has been directly detected by serological methods in dead adult bees from every continent (Ribière et al., 2010) except South America, where it has been detected by molecular techniques (Antúnez et al., 2005; Blanchard et al., 2007; Ribière et al., 2010). The prevalence of this infection did not appear to follow any seasonal pattern (Tentcheva et al., 2004).
This virus can persist through the years as a covert infection but may multiply to high levels in honeybees (Blanchard et al., 2007; Ribière et al., 2007; Olivier et al., 2008) and may cause an overt infection with significant losses in colonies (Allen and Ball, 1996; Olivier et al., 2008a, 2008b). Scarcity of food resources, severe winters or adverse weather conditions in summer may promote these outbreaks (Allen and Ball, 1996; Bailey et al., 1983; Olivier et al., 2008a, 2008b). In these overt infections CBPV was identified as a cause of a contagious disease of adult honeybees characterized by trembling, flightless and sometimes black individuals crawling at the hive entrance (Bailey et al., 1963; Allen and Ball, 1996; Chen et al., 2005; Ribière et al., 2007).
The CBPV overt infection is characterized by two different syndromes that can bees seen even in honeybees from the same colony (Bailey and Ball, 1991; Ribière et al., 2010). The most common one is characterized by abnormal trembling of the body and wings, bloated abdomens and partially-spread dislocated wings that causing an inability to flight. The bloated abdomen is caused by distension of the honey sac with fluid which accelerates the onset of dysentery. The affected honeybees die within a few days following the onset of symptoms (Ribière et al., 2007). The other syndrome is characterized by hairless, shiny and black appearing bees which makes them seem smaller than healthy bees, with a relatively broader abdomen. Because of their different appearance, the affected bees suffer nibbling attacks by healthy guard bees of their colony, which makes them, seem like robber bees. In a few days they become flightless, trembling, and soon die.
The CBPV paralysis appears to be due to the neurotopism of the virus, indeed the fifty percent of the many millions of CBPV particles which can be extracted from only one paralysed bee is concentrated in the head, which represents about one-tenth of the total body weight (Ball, 1999; Olivier et al., 2008a, 2008b). CBPV particles were observed in the neurons of the higher integration centres: the mushroom bodies and the central complex (Olivier et al., 2008a, 2008b). The mushroom bodies are involved in sensory processing, learning, memory storage and the control of motor patterns like walking (Menzel, 2001; Heisenberg, 2003; Olivier et al., 2008a, 2008b). The central complex is involved in higher locomotor control, orientation behaviour and regulation of arousal of the insect (Schildberger, 1983; Strauss, 2002; Wessnitzer and Webb, 2006; Olivier et al., 2008a, 2008b). CBPV particles have been seen in sections of brain tissue, hypopharyngeal and mandibular ganglia and in abdominal and thoracic ganglia (Giauffret et al., 1966; Olivier et al., 2008a, 2008b).
Laboratory experiments have proved that CBPV can be easily transmitted to bees by topical application to the surface of cuticle freshly denuded of its hairs (Ribière et al., 2007). Moreover, the crowded condition of the colonies promotes the spread of the virus by direct contact of healthy bees with paralysed individuals (Ribière et al., 2007). The systematic detection of CBPV particles in faeces of both naturally and experimentally infected bees with acclaimed symptoms proves an important source of environmental contamination in the colony (Ribière et al., 2007). Further studies will be necessary to clarify the resistance of the viral particles outside the host and its ability to infect healthy individuals confined in contaminated apiaries. The detection of CBPV in queens (Chen et al., 2005a, 2005b, 2006b; Ribière et al., 2010) and in all developmental stages of their offspring including eggs has been reported (Chen et al., 2006b;
Blanchard et al., 2007; Ribière et al., 2010), suggests the possibility of vertical transmission of this virus. CBPV infections have never been related to Varroa destructor infestations and the virus has not been reported in this parasite (Ribière et al., 2007).