Nosema Disease: Causes, Symptoms, and Prevention of Diarrhea

Learn the strategy to combat nosema disease, one of the most dangerous gastrointestinal diseases in bees, which can reduce honey yields by almost half.

Nosema disease, also known as “infectious diarrhea,” is an invasive disease of adult bees, queens, and drones caused by the single-celled parasite Nosema apis, which attacks the epithelium of the midgut. This disease generates enormous economic losses – it is estimated that with just 10% of bees in a colony infected, honey yields drop by 43%, translating to a loss of 15 to 25 kg of honey per colony per season.

1. Etiology and Pathogen Survival

Nosema apis spores exhibit extraordinary resistance to external factors, making their elimination from the apiary difficult.

• In honey and on combs: survive for about 1 year.
• In dead bees: from 4 months up to 6 years.
• In dry feces: up to 2 years.
• Critical parameters: Spores die at a temperature of 65°C after 10–15 minutes, and in steam (100°C) within 1–5 minutes. Sunlight destroys dry spores in 15–32 hours.

2. Why Does Infection Occur? (Predisposing Factors)

The mere presence of spores in the hive does not always mean disease. Nosema disease breaks out when the living conditions of the bee colony deteriorate. The main causes include:

• Low-quality winter feed: the presence of honeydew in stores (above 5% honeydew honey content drastically increases the risk) and contamination with pesticides.
• Poor ventilation and moisture: high humidity in the hive during winter stimulates parasite development.
• Premature brood: the appearance of brood in winter raises the temperature in the cluster to about 32°C, which is an ideal condition for spore germination.
• Autumn mistakes: feeding sugar too late or excessively in autumn weakens bees going into winter.

3. Recognizing Symptoms and Diagnosis

The disease manifests most strongly at the end of winter and in spring.

• External symptoms: Front walls of hives, side bars of frames, and combs soiled with feces. Bees exit the hive sluggishly, have enlarged (bloated) abdomens, trembling wings, and cannot take flight.
• Anatomical changes: Upon dissection of infected individuals, the midgut is whitish, lacking characteristic folding, and ruptures very easily.
• Laboratory diagnosis: For examination, send about 30–50 bees (live or fresh dead bees) from each suspected colony.

4. Treatment Methods and Medication Administration

Modern beekeeping relies on the use of specific antibiotics and supportive preparations.

A. Fumagillin (Fumidil B / DCH): The most effective agent, administered in spring or autumn (never during the honey flow).

1. Dosage in syrup: 20 mg of active substance per 1 liter of syrup or 1 vial (20g) per 25 liters of syrup.
2. Method of administration: The colony should receive a total of about 5 liters of medicated syrup in doses of 0.25–0.5 liters daily over a period of 3 weeks.
3. Dosage in candy (fondant): 1 vial per 2.5 kg of candy (or 4–8 g per 1 kg).

B. Alternative Preparations:

• Sulfadimethoxine: 1 g per 1 liter of syrup, administered 3–4 times every 4–5 days.
• Wormwood extract: Tincture in alcohol (young leaves soaked in vodka for 3 days) added to syrup.

5. Disinfection of Combs with Acetic Acid

Disinfection with acetic acid is a crucial step in eliminating nosema disease foci.

1. Preparation: Hive bodies are filled with combs intended for disinfection.
2. Sealing: All cracks and entrances are plugged (e.g., with clay or tape).
3. Application: A cloth soaked in 80% acetic acid is placed on top of the frames at a dose of 200 ml per one 12-frame hive body.
4. Exposure: Keep at a temperature of 16–18°C for 3 days (or 5–7 days at lower temperatures).
5. Airing: Combs must be aired until the odor completely disappears (approx. 20–48h) before giving them to the bees.

6. Prevention – Golden Rules

To avoid nosema disease, colonies must be provided with:

• Queen replacement: Queens older than 3 years are more susceptible to infections.
• Good stores: A minimum of 18–30 kg of carbohydrate food for winter.
• Protein: Ensuring at least 3200 cm² of bee bread in the nest before winter.
• Hygiene: Systematic replacement of old, dark combs where spores accumulate.