What is chronic paralysis (black disease)?

It is a contagious disease of the honey bee caused by a virus known as CBPV, an abbreviation of its English name Chronic Bee Paralysis Virus. It induces neurological disorders and morphological changes (black, hairless bees) in the three castes of adult bees, most often preceding the death of infected individuals. Synonyms: black disease, forest disease, little blacks.

Where is this disease found?

This disease occurs worldwide.

What regulations apply to this disease?

No regulatory status in France.

How is it transmitted?

Bees contaminate each other through ingestion of contaminated material (food exchanged by trophallaxis and excreta) or by contact. Lesions of the cuticle, caused by friction during periods of confinement or by injuries (Varroa destructor, pollen traps), facilitate entry of the virus into the bee’s body. An infected queen can transmit the virus to her offspring.

The virus is often present at low levels in the hive and only multiplies in larger numbers when predisposing factors occur, leading to the appearance of the clinical form of the disease.

What conditions favor its occurrence?

• All factors that lead to confinement of bees in the hive: periods of bad weather, particularly in spring, lack of resources to collect, excessive colony density, long migratory movements.
• Overcrowding, which facilitates transmission between bees, especially when bees are confined.
• Collection of honeydew from conifers, which often predisposes to “forest disease.”
• Consumption of honeydew, whose high mineral content may make it potentially irritating to the digestive tract, facilitating viral entry into the organism.
• Cuticular lesions (pollen traps, stings by Varroa destructor).
• Race and strain. Some bee races such as Apis mellifera anatoliaca are more sensitive. Rigorous selection can improve resistance to this disease.
• Certain pesticides which, by altering the nervous and immune systems, may have a synergistic effect with CBPV and exacerbate mortality.

How can it be recognized?

This disease can present in two different forms, which may nevertheless occur concomitantly.

• Type I: Neurological disorders (crawling bees, trembling of wings and body, inability to fly) and mortality are observed. This form can cause high losses over several weeks or months, potentially leading to colony loss.
• Type II: The presence of black, hairless bees with a shiny, glossy appearance that seem smaller is observed; they are often repelled at the hive entrance by guard bees. These bees gradually lose their ability to fly, develop neurological symptoms, and eventually die. The duration of disease progression is variable but generally fairly long (several weeks to several months).

How can a suspicion be confirmed?

A sample of at least 20 symptomatic or freshly dead bees collected inside and outside the hive can be sent to an accredited laboratory, which will perform PCR analysis to detect the virus and measure viral load.

It is important to inquire prior to sending the sample with the departmental reference laboratory [see DD (CS)PP] about its competencies (holding accreditation for this test), shipping conditions, and the cost of the analysis, which is borne by the beekeeper.

Interpretation of the result, taking into account the viral load detected and the different symptoms observed, remains delicate, especially in cases of suspected intoxication, a context in which testing for various pathogens, including CBPV, will be systematically carried out.

What is the prognosis?

For affected colonies, the prognosis is generally rather severe (especially Type I), and in the absence of beekeeping measures, decline and death of these colonies is the rule. However, cases of spontaneous recovery may be observed (Type II).

How is it treated?

There is no medicinal treatment capable of acting against CBPV.
It is recommended to replace the queen with one originating from a less sensitive strain. The most severely affected colonies should be eliminated.

What prophylaxis?

• Act on predisposing factors.
• Maintain a balance between colony density and environmental resources; avoid excessively large gatherings.
• Avoid anything that causes abrasion of the cuticle (moderate use of pollen traps, appropriate treatment against varroosis).
• Do not overwinter colonies on honeydew.
• Favor the multiplication of less sensitive strains.

 

Source: FNOSAD – Fédération Nationale des Organisations Sanitaires Apicoles Départementales