Cause

European foulbrood is caused by the germ Streptococcus pluton. These lancet-shaped bacteria are usually present in large numbers in sick and recently dead larvae.

European foulbrood is found all over the world; in some areas it is considered far more serious than American foulbrood.

Effect

All castes of bees are susceptible to European foulbrood, although differences in susceptibility can be found in various stocks.

European foulbrood is most common in the late spring. This is a period when brood rearing is at its height, although the earliest brood is rarely affected.

Sometimes the onset of the disease is quite subtle and difficult to detect. It spreads slowly through the colony with little apparent damage. In severe cases, however, colonies are seriously weakened.

The disease usually subsides by midsummer, but it occasionally stays active through summer and fall. Sometimes the disease subsides in the summer and reappears in the fall. A good honey flow hastens recovery.

Symptoms

In European foulbrood the "pepperbox" pattern of capped and uncapped cells develops only when the disease attains serious proportions. Unlike American foulbrood, most of the larvae die before their cells are capped. However, you can sometimes observe discolored, sunken, or punctured cappings.

The most significant symptom of European foulbrood is the color change of the larvae. They change from normal glistening white to a faint yellow. Larvae also lose their plump appearance and appear undernourished.

Figure 5. Honey bee larvae killed by European foulbrood, as seen in the cells.

Most larvae die while in the coiled stage. (See fig. 5. ) When the larvae become brown their white tracheal system becomes visible. The diseased larvae sometimes appear to collapse from their upright state. In such cases larval remains appear twisted or melted to the bottom of the cell.

(A) Healthy larva at earliest age when the brood dies of European foulbrood.

(B) Scale formed by a dried-down larva. (C) One of several positions of sick larva prior to death. (D) and (E) Longitudinal views of scales from larvae that assumed a lengthwise position prior to death.

Recently dead larvae are rarely ropy. Scales can be removed easily from the cells and are rubbery rather than brittle as in American foulbrood.

The odor of European foulbrood varies. Typically, a sour odor is present from decayed larvae.

Spread

Spores are not formed by Streptococcus pluton but the organism often overwinters on combs. It gains entry into the larvae in contaminated brood food, multiplies rapidly within the gut of the larvae, and causes death about 4 days after egg hatch.

Not all infected larvae die from the disease. Sometimes larvae develop normally and void the germ, or regurgitate the bacteria onto the underside of the capping. These materials become sources of the disease.

Since the honey of infected colonies is contaminated the disease can be spread by robber bees or by the interchange of contaminated equipment among colonies and drifting bees.

Control

In some cases, European foulbrood can be eliminated by requeening colonies with a young queen. Requeening accomplishes two things: it gives the colony a more prolific queen, and it permits a time lag between brood cycles that allows the house bees to remove diseased larvae from their cells.

Treatment. -The antibiotic oxytetracycline has been used for the prevention and control of European foulbrood. However, consult with State apiary inspectors, extension apiculturists, or State entomologists before using this drug.