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Beekeepers face a lot of challenges that range from predators, honey bee diseases, pests, parasites, and weather elements. It takes gut to raise a successful bee colony. Among the diseases that cripple honeybee colonies is the Israeli Acute Paralysis Virus (IAPV). This is one of the RNA viruses that pose a serious threat to the health and wellbeing of honey bee colonies. It causes some lethal and sub lethal infections. The IAPV falls in the dicistroviridae family.
Most viruses get into the honey bee system through ingestion. Once inside, they then pass through the gut epithelial cells. Proper hive hygiene, good nutrition, and regular hive maintenance can help prevent most of the viruses and diseases in bee colonies. The cultural, chemical, and mechanical solutions also help minimize and eliminate infections in case an hive has already been infested.
About the Israeli Acute Paralysis Virus
Israeli Acute Paralysis Virus (IAPV) as suggested by its name was first discovered in Israeli apiaries. This was in the year 2004. At the time, the virus had caused considerable deaths in honeybees resulting in heavy losses.
Laboratory tests confirmed the virus falls within Dicistroviridae family, meaning it is a close relative to KBV and ABPV. Asides the close genetic relationship, these viruses share some biological characteristics. For instance, the primary hosts life stage. They also exhibit a low yet widespread prevalence when asymptomatic. This is unlike the high virulence in experienced in experimental infections. Conversely, ABPV tends to differ in terms of genetic and serological characteristics when compared to the other two infections.
Honey bee colonies with IAPV infestation can persist without portraying any major symptoms. The virus adversely weakens the honey bee immunity and with the involvement of stress factors it results in mortality of the honey bees. Before the death of lethally infected adult bees, various signs begin to manifest. These include paralysis, shaking, lack of ability to fly, and darkening and loss of hair within the thorax and abdomen.
Various researchers have identified a close connection between virus infections and a greater risk of colony collapse during a season such as winter. It was pointed out that colonies with a number of viruses portray signs of Colony Collapse Disorder (CCD), suggesting that a combination or a group of viruses are the main culprits in this case that compromise the honeybee health.
Routes of Transmission
Israeli Acute Paralysis Viruses can easily be transmitted within and between honey bee colonies. This means it can infect one bee and move to another bee. It can also be transmitted to other insect species within the locality. The virus can be transferred from the drone to queen bee while mating, from the queen to the egg, from nurse bees to larvae when feeding, and from one worker bee to the other during trophallaxis.
The virus can also be transmitted through the environment, especially when the honey bees consume contaminated food, This could be contaminated honey reserves in the colony or flowers that are contaminated in the field.
Varroa mites mainly target the hemolymph of honey bees thus impairing their immune function. Interestingly, it has been noted that the female varroa mite raises more offspring on infected pupae, when compared to a healthy pupae. This therefore means, an invasion can worsen the situation where IAPV is concerned. The viral infection reduces the wound-healing ability in honey bees. Therefore the varroa mite offspring find it easier to obtain food from infected pupae. The cuts on the cuticle that have not healed pave way for the mites to burrow through and gorge on the pupae.
Another factor that can increase predisposition of honey bees to the Israeli acute paralysis virus is stress levels. These are ideally stress triggers that affect the immune system of the honey bees. For instance, an exposure to pesticides negatively affects the immune response in honey bees. These include chemicals such as organosilicones, neonicotinoids, and others.
Excessive use of chemical miticides for the treatment of varroa mites has also been found to reduce honey bee tolerance to viruses. Such naturally-derived chemicals should be used in moderation. Bees should also be supplied with high-quality diets, particularly pollen from different or diverse species of plants. This will boost the honey bee body defense mechanism against viral infections.
Symptoms of the Israeli Acute Paralysis Virus
As earlier mentioned, IAPV is closely related to ABPV and CBPV, thus share similar symptoms.
- Shivering in honey bees.
- The honey bees have dark and hairless abdomens and thoraxes. This can worsen and lead to paralysis and eventual death.
IAPV occurs predominantly in all honey bees life stages. It is has been identified to be closely linked with colony collapse disorder (CCD). Unfortunately, no direct relationship has been reported between the virus and CCD. IAPV can be extremely virulent especially in instances where cases of Varroa mites have been reported.
The symptoms of IAPV can be seen in adult honey bees portraying one or two sets of symptoms earlier mentioned. Type one include symptoms such as the trembling wings when moving. A group of honey bees that cannot fly, others crawl on the ground or some along plant stems, and as a cluster of bees. Other symptoms include a bloated abdomen, which results in dysentery. Such bees die within a couple of days after the symptoms are seen.
The early symptoms observed in infected honey bees during the first day include crippled or powerless front legs, and this greatly affected the bee mobility. During this stage, the adult bees move slowly and will not fly or buzz. Any slight disturbance such as gentle shaking of the honey bee colony will have no effect on the bees.
Laboratory tests have also been carried to find out more about IAPV. Various results came out. First off, the worker bees that received IAPV injection do not show symptoms. Additionally, this group of bees did not visit the food source (sugar water feeder) as frequently as one would expect under normal conditions. The infected worker bees showed a ‘quiet’ behavior and ignored the sugar water feeder. They even seem not to notice it.
The type two symptoms observed in honey bees infected with IAPV include the greasy, hairless, and blackened bees with inability to fly. A few days later, they become flightless, begin to tremble, and later die.
It is important to note that both types of syndromes may occur within the same colony. Instances of severely infection, especially with strongest colonies, will quickly lead to loss of adult worker bees, resulting in colony collapse. The remaining cluster of bees will be a few adult bees and a queen on a poorly guarded comb.
The symptoms of IAPV tend to be similar and thus confused with some other honey bee diseases. These include Nosema apis, chemical toxicity, tracheal mites, colony collapse disorder (CCD), and other infections.
Another notable sign of Israeli acute paralysis virus is the behavior of healthy worker bees. The normal healthy workers will in most cases isolate the sickened adult bees. This means the workers with symptoms like crippled or immobilized forelegs are separated from the rest of healthy honey bees. When this expelled group of workers with crippled/immobilized forelegs is isolated by the beekeeper, signs of the IAPV can clearly be seen.
The sick workers when kept alone within a new micro-colony and fed exhibit some signs such as: intense shaking of the abdomen and trembling of the body within 12 to 24 h. During this time, the sick bees cannot stand or walk. In a few days, that is, 2 to 3 days they will most likely die.
The Effects of the Israeli Acute Paralysis Virus on Honey Bee Colonies
Just like most dicistroviruses, an IAPV infection can be persistent without showing any severe symptoms in bee hives. Nevertheless, high titers of the virus infection individual pupae or adult bees can be virulent. The adversely affected bees are habitually characterized by the darkened thorax and abdomen, often accompanied by loss of hair. Further to these symptoms accompany weight loss, trembling, and paralysis. Paralysis is also a well-known sign of other dicistroviruses, such as Cricket paralysis virus.
IAPV disrupts the mitochondrial function, with the ultimate effect of disrupting all energy-related processes in the honey bee system. Another effect associated with IAPV is the effect on bee behavior through reduction to sucrose responsiveness. Tests that were carried out in the past involving 13 Proteomic analysis showed viral proteins at 12 and 36 hour from the time of viral injection.
In another test referred to as Gene ontology (GO) analysis, the results showed noteworthy 36 h enrichment of proteins responsible for translation functions. These include functions such as; mRNA binding and metabolic activities. This therefore implies the virus adversely disrupts regular cellular functions in honey bees that are infected. In addition, other crucial functions are down-regulated; expression of proteasomal proteins, and mRNA 3’-UTR binding proteins, and unfolded-protein-binding components.
According to other studies partial IAPV sequences were confirmed to be integrated within the honey bee genome. The northern and western blot translated and expressed the sequences. This implies the IAPV and the honey bee reciprocal exchange of the sequences pertains to the partial honey bee sequences that are found in an IAPV-associated RNA. Honey bees that were injected with IAPV during the study died of viral infection depending on positive and negative strand RNA presence.
Conversely, healthy honey bees did not have IAPV sequences imbedded within their genomes and survivors developed to healthy adult bees. This group of survivors carried the viral sequence, that is, within their structural protein. These evidences imply honey bees with partial IAPV sequences have some resistance to IAPV.
Additionally, recent studies indicate that incorporation of viral sequences within a host genome gives extra mechanism of antiviral immunity. This is achieved by enhancing the RNAi-mediated protection. The studies mentioned suggest this could be happening with regard to IAPV.
Transmission of the Israeli Acute Paralysis Virus
IAPV can be transmitted through various ways: vertically or horizontally in honey bees and honey bee colonies
Vertical transmission happens through a number of ways. First off, IAPV was detected in queen ovaries. Secondly, the virus has also been found in semen and spermathecae of honey bee drones. This finding of IAPV in sexual organs may imply the virus could be transferable through sexual intercourse in bees.
Horizontal transmission in this case refers to the transmission of the virus through food or vector-borne routes. It may be transmitted through food given the fact that various tests confirmed the presence of IAPV in honey bees’ digestive tracts. Positive results have also been found for IAPV in feces of queen bees. The food supplies have also shown some traces of the virus. Furthermore, IAPV is detectable in all honey bee developmental stages and bee colony castes.
The parasite is a vector of most honey bee infections and this includes the IAPV. It mainly targets the bee hemolymph and acts as a vector of IAPV. These mites not only transmit IAPV but also act as a host for IAPV. Various tests have confirmed the presence of IAPV negative strand in varroa mites. This suggest mite-ingested virus. The virus has been detected in the salivary glands of the varroa mite, further confirming the fact that Varroa is a vector IAPV. Interestingly, immune-related genes in bees seem to decline or weaken as a result of mite infestation. This means mite infestation paralysis bee immunity and ultimately aggravates virus infection and replication.
Diagnosing and Managing Israel Acute Paralysis Viral Infections
Certain viruses show clear symptoms that can suggest the presence of the virus. Diagnosis in this case becomes easier. Unfortunately, this might not work in case symptoms are not apparent. Therefore, identification of the infections within these colonies will only be possible through molecular approaches. These tests help confirm the presence of the virus and evaluation of its prevalence or levels of infection. One such test is the polymerase chain reaction (PCR).
The use of PCR is highly effective when it comes to direct diagnosis of honey bee viruses. Most of the viruses are difficult to diagnose but PCR helps overcome these difficulties. PCR helps identify positive cases of Israel acute paralysis virus (IAPV) in honey bee colonies. Various samples collected from various regions are subjected to reverse transcription-PCR. These comprise colonies that suffer from symptoms of depopulation, paralysis, dark coloring, or sudden collapse. The Sequence analysis show IAPV is nearly related to KBV.
Control and Treatment of the Israeli Acute Paralysis Virus
IAPV virus usually persists in a normal and healthy honey bee colony, just for it to explode in times of stress. Just like most viruses, IAPV is destructive when complemented by another stressor such as Varroa, nutritional deficiencies, Nosema, or pesticides. Consequently, an active and integrated management of the Varroa mites and these stressors will help manage viral infections.
Routine inspection of colonies is also recommended as a way of detecting early signs of the disease or infections. Check potential signs or symptoms. Be keen if colonies appear to be slow to build up. Check out any sporadic brood patterns which can indicate the brood has been removed.
In case you have a valid reasons to suspect there a disease or infection, take out some samples and let the experts conduct an RT-PCR.
An Integrated Pest Management Approach will help control the parasites that transmit viruses such as IAPV.
The use of honey bee stocks that have some resistance to varroa mite works. These include; the Russian stock, stocks with varroa hygiene, and stocks of bees that are ankle or leg biter or chewers. These stocks instinctively suppress viral populations.
Other cultural control measures against IAPV include:
- Viral infections are high in areas that have higher density of honey bee colonies. Reduce number of colonies within an apiary. Honey bee colonies should also be spaced apart and facing different directions.
- Do not move frames from suspected colonies to healthy ones.
- Hives tools and other equipment should be thoroughly cleaned after use and disinfected using alcohol.
- Bees should be fed on high quality food. Provide bees with high-quality diets. The local area should also provide good quality pollen and nectar for foraging bees. The Beescape.org tool helps beekeepers ascertain if the local area provides the best quality forage for the bees. If it happens the forage quality is confirmed to be low, and/or you realize the honey bees no longer collect nectar or pollen, you will have no option but provide supplemental feed. Nonetheless, with studies suggesting that bee-collected pollen is of much better for bee health than supplemental diets, it makes more sense to consider other options. This could mean moving the hives to a better location. You may also use a pollen trap to gather pollen within strong bee colonies and use it to feed other colonies.
1. Remove Old Combs
The removal of old combs will help eliminate viruses and other pathogens that accumulate as wax comb age. A general guide, about ⅓ of the frames should be removed from each colony every year. These old combs should be disposed.
2. Propolis Deposition
Propolis increases the production of immunity genes in bees and helps counter levels of viruses. The honey bees collect pollen by nature and use it as disinfectant in hive entrances. It is also used for sealing gaps and crevices on the beehive hence helping insulate the hive.
Bees can be encouraged to accumulate propolis by using hive components that have rough inner surfaces. Moreover, a cotton duck cloth when used as inner cover encourages the bees to collect and accumulate propolis.
Naturally-derived chemicals helps treat viral infections in honey bees. These should be used in moderation since an excessive use can kill the bees or render mites and other pathogens resistant to the chemicals.
Recommended chemical solutions for IAPV include:
1. Thymol Treatment
Various tests carried out involving the use of 0.16 ppm thymol showed a reduction in levels of Israel bee paralysis virus. The solution was applied on just emerged bees then returned to their colonies. Unfortunately, thymol does not give consistent results. Thus more studies are required.
2. Propolis Solution
Apply propolis solution to the interior of beehives to keep off IAPV and other viruses that affect honey bees.
3. Fungal Extracts
Extracts from two species, that is, Ganoderma resinaceum and Fomes fomentarius will lessen levels of Israel bee paralysis virus.
Healthy honey bee colonies can never be affected by most virus infections, unless chronic stresses emerge. For instance, high levels of varroa mites. These mites trigger major infections in honey bees and can result in high levels of IBPV, resulting in severe symptoms or colony death. Cultural and mechanical practices can help counter viruses and minimize levels of viruses in honey bee colonies. They are also effective in reducing varroa mite populations.
Proper understanding of bee-virus biology and its interactions, and the use of recommended remedies of the viral infections are helpful in improving bee colony wellbeing.IBPV is a widespread virus that affects the honey bee digestive system. The virus infects the mid gut epithelial cells, paving way for the virus and other infections. Once IBPV and these viruses find their way into the hemolymph, they invade other cells in the honey bee body.
A parasite, such as Varroa destructor is a vector for IAPV and other infections. It consumes bee hemolymph and inflicts openings that act as a highway for viruses to go in. These viruses rarely cause an infection if ingested orally, but will cause an infection when stressors such as mites provide way. The Varroa mite is the main culprit that spreads viruses in honey bees is and its control can help prevent most of these viruses.