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The honey bee is targeted by more than 18 viruses, along with various pests, parasites and predators. One of the viruses that has been isolated and described is the Chronic Bee Paralysis Virus (CBPV). As the name implies, it causes chronic paralysis in bees and is found worldwide.
The virus is common and detectable throughout the year. Nonetheless, it stays dormant in asymptomatic bees. An outbreak of severe disease symptoms tends to be erratic, and will appear mostly during spring and summer, when the honey bee colony is at its peak of production.
Susceptibility to Chronic Bee Paralysis Virus
The Chronic Bee Paralysis Virus affects mainly adult honey bees and results in a chronic paralysis (as suggested by its name). The infection can easily be transmitted to other bees within a colony. Once honey bees are infected with CBPV, symptoms can be seen within 5 days, and they die a few days later.
The Chronic Bee Paralysis Virus is linked to the collapse of honeybee colonies. It is of paramount importance that the beekeeper understands factors and diseases that affect honey bees, since bees play a vital role in ecological balance and resilience. Consequently, beekeepers will be able to respond accordingly to various viruses during the different seasons. They will also be able to develop measures against these infections, for as you know, prevention is better than cure.
The Chronic bee paralysis virus can infect adult honey bees and those in earlier developmental stages. However, tests done have proven the developing bees in most cases host significantly lesser viral loads, unlike the adult honey bee. Similar tests have also shown that queen bees will least likely be infected with CBPV unlike the worker bees.
Unfortunately, young queen bees that interact with infected worker bees will contract the virus and die eventually. That notwithstanding, developing bees mortality due to CPBV is extremely low and insignificant.
Symptoms of Chronic Bee Paralysis Virus
The symptoms of the Chronic bee paralysis virus can be seen within five days of infection. Some notable signs and symptoms of CBPV include:
- V or K-wings
- Wing color or wing size changes
- Presence of Varroa mites
- Behavioral changes
- Neurological changes
- Social or digestive symptoms.
Other CBPV disease signs include:
- Darkened bees
- Trembling or paralysis
Signs of intoxication in honey bees include phenotype changes such as crippled bees, paralysis, and high mortality.
Symptoms can be categorized in two distinct ways: Type I and Type II infection, with Type I being the most predominant.
The honey sac is filled with a fluid leading to bloated stomach in the infected honey bees. Weak trembling wings can be seen in infected bees. The bees crawl on the ground and form a cluster close to the entrance of the beehive since the weakened wings affect their ability to fly.
Some of the signs in this category include: loss of abdominal hair, with the bee appearing black or greasy at the abdominal area. Affected bees may still fly for 2 to 3 days from the time the symptoms begin to show, then lose their flying ability and eventually die.
The symptoms of an infection does not show completely even though the bee is already infected. You will not be able to notice any of the classic symptoms mentioned earlier. Consequently, infected honey bees transmit the virus within and beyond their own hive. This category of bees have a high level of CBPV in the brain.
Laboratory tests have shown the most affected parts of the paralyzed bees are the stomata and neuropile regions. Predominantly, CBPV affects higher neuronal regions like the optical and sensorial neuropile of the brain.
A CBPV outbreak leads to excessive loss of worker bees, that eventually results in colony collapse. The virus can wipe out both workers and young queens bees.
Diagnosing Chronic Bee Paralysis Virus – Clinical Examination of the Honey bee Colony and Observations of Living Bees
An extensive observation of all stages of the honey bee is essential. This means a comprehensive evaluation of all the bees within the colony: worker bees, the drones and the queen bee. All stages of the brood and the hive material should also be checked. Remember, honey bees are social insects that live as a super organism. The colony can only survive when each of the individual bees does their share of work.
The clinical examination of honey bee colonies and the hive materials should be carried out together with the beekeeper. This makes it possible for the experts to do a comprehensive analysis of the beekeeper´s operation while working on the bees. Some of the general aspects assessed at this time include the behavior of the colony, any odor and the strength of the colony. A healthy bee colony usually has a smell that is similar to wax. Any abnormal smell such as vinegar or any other will suggest possible infection or disease.
The colony size should also be checked during this time. A sure way of determining the colony size is by analyzing the intercomb space count. This is where you can see honey bees. All the bees in every colony should be checked for any abnormalities. Check out any body deformities, behavior, neurological, wing abnormalities, presence of mites, mite social or digestive symptoms and many others.
The frames are assessed when conducting the examination of the honey bees. This entails checking wax color and brightness, which should correspond to the age of the combs. The old wax is easy to notice since they tend to be much darker due to the number of times they have been during brood cycles. Contrarily, newly produced wax is lighter. Beehive frames can tell if the honey bees are sick. For instance, clean ones imply a healthy colony, whereas the presence of fecal spots suggests possible digestive disorders.
An evaluation of the pollen and honey stores is also crucial. The ease or difficulty of removing frames from the hive is a good indicator of various aspects. First off, it may mean the beekeeper has not been conducting routine checks. Secondly, it suggests heavy foraging for propolis by the honey bees.
Colony investigation entails an evaluation of the queen bee. Any abnormalities is identified in the queen bee and compared with those shown by the worker bees. In most cases, the queen may not portray similar symptoms as the other bees, even if it is the same virus load.
Some of phenotype changes in honeybees with possible causes:
- Shortened abdomens, hairless and darkened abdomens – CBPV
- Genetic or mechanical problems such crippled wings or legs antennae – Varroosis
- Deformed wings virus – intoxication or CBPV.
- Bloated abdomens and diarrhea – Nosemosis, CBPV, proboscis virus diseases, intoxication or Malpighamoeba mellificae.
Investigation of the Phenotype of Bees and Pathological Changes
This laboratory test involves the use of bee samples that will help when investigating the phenotype of the honey bees. The tests also entail an evaluation of pathological changes details. Living and symptomatic honey bees are the most useful for the tests with an exception of cases of increased mortality. In the latter, freshly dead bees will be collected near the beehive as samples. However, there might be a possibility of false-negative results during virus diagnostics due to the fact the RNA is unstable in such an environment.
The various diagnostic methods demand a specified bee number for each test, which should be considered before collecting any sample. As a general rule, the base reference value is normally 100 mL equated to about 330 honeybees or 31 g of honey bees. Once the sample is collected, it is euthanized by freezing for about 15 min, at −20 ◦C. The use of 96 percent ethanol and carbon dioxide also works. Even so, it is advisable to seek clarity from the responsible laboratory when it comes to size and condition of the honey bee samples.
Examination of Dead Bees
The examination of dead bees will also help identify their phenotype. The sampled honey bees are sorted and grouped based on size and symptoms.
Smaller honey bees with shortened abdomens may mean they are infected with a virus such as the Deformed Wing Virus. Those with hairless and darkened abdomens will most likely be infected with CBPV. There may also be other reasons for this, which could be genetics, mechanical or other reasons.
Breaking hairs or darkened abdomens may occur at times due to robbery and fighting. However, this will affect only a few individuals and not entire colonies. On the flipside, genetics, CBPV, and other conditions affect entire honey bee colonies. If several bees show signs of bloated abdomens, pressure, or a light-brown fluid coming out of the gut, these need to be sampled for further analysis. The laboratory tests will evaluate the gastro-intestinal tract of the affected bees.
Examination of Debris
Believe it or not, debris examination provides useful information such as; colony health, development or colony strength. Some of the materials that can help when testing include: wax scales, pollen, sugar, crystals, melicitose, diluted food drops, cell lids, drops of propolis, and cell components. These components are crucial indicators of colony strength.
In some tests, debris collected may contain Varroa mites or separated honey bee parts such as legs and wings. You might also find pollen and wax particles, or some traces of predator feces. If you find parts of honey bees, that is certainly an indication of wasps or mice invasion. The presence of feces will also give more details. For instance long feces indicate mice and small dark brown feces indicate the wax moth.
Debris examination also helps when checking out for Varroa infestation. It is easy to see the mite with the naked eye. Physical examination of the number of mites collected by a tray placed under the hive can help predict the level of infestation. It is also worth mentioning that the validity of the information collected from debris relies on prevailing weather conditions, the season and length of time the collecting tray remained under the beehive.
For laboratory testing, real-time PCR is used. This helps in the diagnosis of the Chronic Bee Paralysis Virus for all honey bee developmental stages: egg to adult. Tests done in the past showed the presence of the virus in all caste, that is worker, Queen, and Drone. A significantly higher virus load was found in guard bees than in foragers, drones and hive bees. In most cases, the only survivors of a CBPV outbreak are the queen and a few worker bees. What this means is that the bees have instinctively developed mechanisms for protecting the queen from CBPV and not for the rest of the honey bees.
Routes of Transmission of the Chronic Bee Paralysis Virus
There exist two routes through which CBPV can be introduced into a beehive. First off, is through contact among adult honey bees. The healthy honey bees that stay as a cluster with sick or infected bees directly contract the virus. Secondly, the virus can spread through particles in honey bee feces of the paralyzed bees, when ingested by the nest mates.
Crowding in honey bee colonies is common during spring and early summer, making it ideal for the two routes of transmission. During the various experiments done, honey bees contracted the virus when they were fed with sugar solution that had been mixed with the virus. The experimental infected bees showed disease symptoms within 5–6 days, just like one would expect with naturally infected honey bees. Contrastingly, honey bees require a higher number of virus particles to get infected when the virus is introduced through topical application or oral infection. However, injection tends to be more effective transmitter of the virus.
Monitoring the Varroa Infestation
The notorious varroa mite remains the key stressor of honey bees, and perhaps a global threat to honeybee colonies. Additionally, ants or Formica rufa and Camponotus vagus have been identified as CBPV potential secondary hosts, especially those within close proximity to the honey bee colonies. Nevertheless, it is yet to be proven if they play any role in terms of spreading the infection.
Proper control of varroa mites is recommended since it is a mechanical and biological carrier of many honey bee viruses that includes CBPV. Colonies that have a high mite load in most cases weaken and eventually collapse.
One way of monitoring varroa mite infestation involves collecting large samples of brood cells. These are passed through a sieve system that separates the mites from the brood. A second method is the natural mite fall, which refers to a method where a drawer is placed under the hive for 2 to 5 days. This is usually lined with a sticky paper that will trap the mites that fall naturally from the hive. All mites collected are counted, to determine the number of mites per day
Tests done in the past by researchers suggest that approximately 300 young adult bees correspond to 100 mL sampled from a frame containing uncapped brood. This number of bees is sufficient for use in other methods for determining mite populations. These include the flotation or powdered sugar methods.
The flotation method, honey bees mix and shaken in alcohol solution for about five minutes. These bees die and the mites can be removed and can be counted. The powdered sugar method involves the honey bees being dusted with icing sugar then shaken gently for about two minutes, two times. This dislodges the mites from the honey bee body. The sugar can then be sieved or dissolved in water. Once this is done, the mites are separated mites and counted.
Results suggest the following:
- If mite infestation rate is below 5% – honey bee colony is vaguely affected.
- If mite infestation is above 10% – immediate treatment is required.
Dysentery is one of the signs of infection in honey bee colonies. It is common in cases of infections such as CBPV, Malpighamoeba mellificae and Nosema species. Dysentery is also a symptom of stressed honey bees. Tests conducted have shown that 43% of 21 honeybee colonies examined that had fecal spots, proved to be Nosema-positive. Interestingly, Nosema can be present in honey bee colonies without causing any harm. Unfortunately, they can be an additional stressor that weakens the honeybees. In other instances, nosema species create pathways for infections and diseases due to the damage they inflict on the epithelial layer.
Nosema and Malpighamoeba mellificae can be tested in the laboratory using a microscope at 400x magnification. Samples collected include 20 freshly dead bees that are crashed and mixed with 5 mL aqua purificata. Water is then added to make 1mL per bee. This sample is then placed onto the microscope slide for examination.
The same process is employed when testing for Nosemosis. 20 honeybee abdomens are collected and placed in a mortar. It is then crushed and aqua purificata is added. This sample is then taken to the microscope for examination. Nosema spores can be seen as oval-shaped and approximately 4 to 7 µm and about length 2 to 4 µm in width. However, the two species of N. Apis and N. ceranae are not distinguishable through this method. PCR will be required for further differentiation.
Result interpretation can be done as follows: spores that can be seen per visual field should be counted and grouped these three categories:
- 20 spores or less per visual – slight infestation,
- 20 and 100 spores per visual – moderate infestation
- 100 plus spores – severe infestation.
Treatment for Chronic Bee Paralysis Virus
Unfortunately, there are no existing treatment options for the Chronic Bee Paralysis Virus. The infected honey bees will eventually die out. These dead bees should be removed from the beehive immediately so that virus spread is eliminated.
Struggling hives can also be supplemented with healthy bees from stronger colonies to avoid colony collapse for the heavily infested colonies.
Since the Chronic Bee Paralysis Virus has been confirmed to be more common during winter, it is wise to be well prepared for winter. Honey bees should be well fed prior to winter and sufficient food reserves such as honey left within the hive for their survival during the season. Remember healthy colonies have higher chances of surviving through winter.
Finally, varroa parasite management is the surest way to keep off major infections in honey bees and that includes CBPV infection. You can use naturally-derived chemicals once mites are detected. Early treatment is effective since mites can quickly develop some resistance. Recommended pesticides include Apistan, Apiguard, and Formic Acid. You can also remove mites from the hive by dusting the honey bees and hive floors with powdered sugar. This will suffocate the mites.
Honey bees that are normally infected with the Chronic Bee Paralysis Virus have millions of the viral particles with about half of infected bees head concentrated with virus. The ultimate effect of this is an impaired neurotropic activity due to a damaged nervous system. Once infected, the virus concentrates in two regions and replicates quickly. One of these areas is the center of the mushroom bodies, where memory motor control and learning is controlled. Secondly, the central body, that is the center of the brain that controls sensory processing. When impaired, it affects arousal, locomotion, bodily orientation, and behavior. The virus completely paralyses the honey bees’ brain.