Amoeba Disease

Amoeba disease is caused by the single-celled parasite Malpighamoeba mellificae settling in the excretory tubules (Malpighian tubules) of adult bees. It has no characteristic field sign of its own; its picture closely resembles nosema and it is often found together with it. There is no authorised medicine for it; prevention, as with nosema, means clean comb, a dry hive and a strong colony.

What is it and how is it transmitted?

The parasite settles in the fine Malpighian tubules, which filter the bee's body fluid and pass waste into the gut. The tubules swell and stop working properly; the bee's lifespan is shortened. The disease affects adult bees, not the brood.

The parasite forms resistant cysts. The cysts are passed out in the faeces and survive for a long time in the comb and on hive surfaces. Young bees that clean soiled comb and come into contact with faecally contaminated water or feed take in the cysts by mouth. For this reason old, faecally stained combs and damp hives make it easier for the disease to persist.

How to recognise it

There is no way to recognise amoeba disease in the field. The signs that may be seen are not specific and also occur with nosema, viruses or poisoning:

• A colony that does not build up in spring and whose bee numbers dwindle,
• Bees crawling in front of the hive, unable to fly,
• Brown faecal stains on frames and on the landing board (often due to accompanying nosema),
• Increasing losses of older bees, especially in late winter and spring.

The disease usually peaks in spring and recedes on its own in early summer.

Relationship with nosema

The two agents are often found together in the same colony and aggravate each other's effects. The triggering conditions are also shared: humidity inside the hive, long periods without flying, unsuitable winter feed and stress. In practice they do not need to be dealt with separately; the measures to be taken are the same.

Definitive diagnosis

The diagnosis can only be made in the laboratory. Collect a sample of older (forager) bees from the entrance; ask the laboratory in advance about the number of bees and how to preserve them (freezing or alcohol). The laboratory opens the bee and examines the Malpighian tubules under the microscope; infected tubules look swollen and glassy, with cysts visible inside. A nosema examination should also be requested on the same sample.

What to do

There is no authorised medicine; do not try antibiotics or any other medicine on your own initiative. The approach is to correct the conditions that weaken the colony:

1. Renew the comb regularly. Take faecally stained and very dark combs out of circulation; old comb is the main source of cysts.
2. Keep the hive dry. Good ventilation, a hive tilted slightly forward, and an apiary site that gets the sun and is sheltered from the wind.
3. Pay attention to winter feed. Honeydew honey (such as pine honey) and poorly ripened feed strain the bee's gut during long winters and lead to faecal staining.
4. Provide clean water. Prevent the bees from taking water from dirty puddles.
5. Unite weak colonies, and make sure there is enough pollen in spring.
6. Disinfect stored combs. In some countries disinfecting stored combs with acetic acid fumes is recommended; it is a corrosive substance and is applied in the open air with protective equipment.

Significance

Amoeba disease on its own rarely causes serious losses. Its real significance is that it weakens the colony together with other stress factors such as nosema, varroa and poor wintering. So rather than asking "which parasite?", what matters is correcting the conditions that weaken the colony.