Diseases of Honey bee:
American Foulbrood disease:
It is the most destructive microbial disease and it affects bee brood. The disease is confined to the colonies of Apis mellifera. In areas, where there is ample sunlight and temperatures are relatively high throughout the year, the disease causes severe damage to bee colonies. The disease is spreadable and the pathogenic bacterium can remain dormant for more than 50 years. It is initiated by a spore-forming bacterium, which only affect bee brood. Adult bees remain safe from infection. The disease transfer quickly within the colonies.
At the initial stage, isolated capped cells can be seen on the comb. The caps of these dead brood cells are generally darker than the caps of healthy cells. These are sunken and often punctured. As it spreads within the colony, a scattered, irregular pattern of sealed and unsealed brood cells can be easily distinguished from the normal and compact pattern of healthy brood cells.
A search and destroy strategy is best to minimize damage to api¬aries. The procedure includes regular hive inspect¬ions. The population that is infected by foul¬brood is killed and hive materials are disinfected by burning. The bees are generally killed by poisonous gas such as the burning of sulphur powder. The plastic hives should be cleaned and brushed with 3 to 5 per cent sodium hydroxide.
Chemotherapeutic methods of control includes the application of antibiotics or sodium sulfathiazole, in various formulations. These are mixed with powdered sugar or sugar syrup and feed to bees. Antibiotics and sulphonamides prevent multiplication of the spores, though it does not kill the spores. There¬fore, multiplication may begin again. So the method must be repeated in much shorter intervals.
European foulbrood disease:
Apis mellifera and A. cerana colonies are subjected to European foulbrood disease. The damage by the disease is variable. European foulbrood disease is usually considered less virulent than American Foulbrood. Although greater losses have been recorded in some areas. The pathogenic bacterium is lanceolate in shape. It occurs singly, in chains or in clusters. The bacterium does not form spores.
The larvae killed by this disease are younger. Mostly, the diseased larvae die in the coiled stage, when they are four to five days old. The colour of the larva changes from shiny white to pale yellow and then to brown as it decays.
A sour odour can be perceived from the decayed larvae. Most of the affected larvae die before their cells are capped. The sick larvae appear slightly displaced in the cells.
The selection of control method depends on the strength of the infection. If the infection is weak, by adjusting the hive to a good foraging site can control the disease. A better result is accomplished if the individual combs are sprayed with a diluted honey solution. If the infestation is stronger, elimination of number of pathogens in the colony will give worthy result. Replacement of the queen with better egg-laying queen can strengthen the colony, thus increasing its resistance to the disease and continuing the ongoing brood cycle giving enough time to remove infected larvae from the hive. Sometimes chemotherapeutic measures such as application of antibiotics are recommended, however, their application, always risks the danger of residues.
In Asia, Japan, temperate America and Europe it has been reported to cause serious issues to bee-keepers. This disease is caused by the fungus. It affects the brood. It only forms spores during sexual repro¬duction. Infection by spores of the fungus is generally observed in larvae that is three to four days old. The spores are absorbed either via food or by the body surface.
Originally the dead larvae swell to the size of the cell and are covered with the whitish mycelia of the fungus. Later, the dead larvae harden, shrink and appear chalk-like. Its colour varies with the growth stage of the mycelia: first white, then grey and finally, when the fruiting bodies are formed, it turns black.
During the white stage, it continues to develop at the hive bottom. If these are not removed quickly, the spores may enter the brood cells through circulating air. During early stages of chalkbrood infection, adding young adult workers into the hive and hatching brood, combined with sugar-syrup feeding is considered beneficial. There is no known successful chemical control against chalkbrood. In most cases, commer¬cialized substances are sprayed, or fed with sugar water as described above.
Sac brood disease:
It is native to the Asian continents. This disease is caused by Morator aetotulas and is the most common viral disease of honey bees. In Asia, at least two major types have been recorded. Sac brood disease affects the common honeybee Apis mellifera and the Asian hive bee Apis cerana. The nurse bees are the vectors of the disease.
Larvae are infected via brood-food gland secretions of worker bees. Diseased larvae fail to pupate after four days. They remain stretched out on their backs within their cells. The larva anterior section changes colour. It changes its color from white to pale yellow and then finally to dark brown and black. Its skin becomes tough and internal organs become watery. Thus the infected larva has the appearance of a small, watery sac.
Field inspection to determine the pathogenic virus can carried out by observing symptoms. No any chemo¬therapeutic treatment is effective in preventing this disease. The recovery largely depends upon the hygiene behaviour of the bees.
The disease usually occurs when the colony is under stress, i.e., shortage of food, space issue, unfavourable climatic conditions (such as damp during the rainy or cold season), unhygienic hive interior, poor queen health, etc.
In severe cases, re queening the colony, removing infected brood combs and taking other management measures to restore colony strength by providing food and adding worker population usually gives better result.
Nosema disease (Nosemosis):
It is generally regarded as one of the most destructive diseases of adult bees, affecting workers, queens and drones alike. Affected worker bees are unable to fly and crawl at the hive entrance or may stand on top of the frames. The disease is caused by the protozoan, Nosema apis. The spores are absorbed with the food and thus infest the bees as these germinates in the mid-gut. After penetration into the gut wall the cells multiply and new spores infect new gut cells. The nutrition of the bees is impaired, particularly the protein metabolism
In severe cases, the abdomen of an infected worker becomes swollen and shiny in appearance. The most reliable method of detecting this disease involves laboratory procedures using a microscope. If the disease exists, large individual bacilliform spores with bright, fluorescent edges will be observed.
It can be controlled by keep¬ing colonies as strong and eliminating pos¬sible causes of stress. Colonies should receive adequate ventilation and protection from cold and humidity. The bees should have the possibility of foraging regularly in order to excrete. It will prevent spreading of the spores within the colony.
Bee¬keepers should always ensure that their colonies and queens come from disease-free stock. The only effective chemotherapeutic method for treating Nosema is to feed the colony with fumagillin (25 mg active ingredient per litre of sugar syrup). It is preferably applied during stress conditions, such as during a long winter or rainy season. The active ingredient is an antibiotic.