American Foulbrood: Symptoms and Treatment
American Foulbrood (AFB) is a bacterial disease that kills honeybee larvae and can wipe out a colony if left unchecked. It’s one of the most serious diseases in beekeeping, and spotting it early makes a real difference in what options you have. This guide covers what to look for and why the standard response is so strict.
Early Symptoms to Watch For
The first sign of AFB is usually scattered dead larvae in the brood pattern. Instead of a neat, solid patch of capped brood, you’ll see some cells capped normally and others sunken or with small holes in the cappings. The affected larvae turn brown or tan and eventually become a dark, sticky mass at the bottom of the cell.
Look for a foul smell—not the normal musty hive smell, but something distinctly rotten. Many beekeepers describe it as similar to rotting meat or glue. The smell gets stronger as the disease progresses. You might also notice the bees are slower to clean out dead larvae than usual, which is actually a sign the disease is overwhelming them.
Another clue is spotty brood patterns that don’t match the queen’s normal laying. A healthy queen lays in a tight, organized pattern. With AFB, you see empty cells mixed randomly among capped brood. The colony may also seem weaker than expected for the time of year, with fewer bees emerging and less food stores being built up.
Don’t confuse AFB with European Foulbrood (EFB), which is less serious. EFB typically kills younger larvae before they are capped, so you see dead larvae in open cells that are still white or light yellow. AFB most characteristically affects older larvae and prepupae after capping, which is why you see sunken or perforated cappings as the most telling sign.
The Ropey Test
The ropey test is the quickest field confirmation for AFB. Take a toothpick or small stick and poke it into a cell containing a dead larva from a suspicious-looking area. Slowly pull the toothpick straight up. If the larva strings out like a thin rope that stretches an inch or more before breaking, that’s a strong indicator of AFB. The breakdown of larval tissue by the bacteria creates a sticky consistency that doesn’t break cleanly.
This test isn’t foolproof—you might get a false positive with other issues—but it’s reliable enough to act on. If you get a positive ropey test, treat it as AFB until proven otherwise. Some beekeepers also send a sample to their local extension office or a bee lab for microscopic confirmation, which takes a week or two.
The ropey test is one of the few field tests that actually tells you something useful without lab equipment, and it should be your first step any time you see sunken cappings combined with a foul smell.
Why Most Regions Require Reporting
In many places, AFB is classified as a reportable disease, meaning you’re expected to notify your local agricultural department or state apiary inspector if you find it — but whether that’s a formal legal requirement, and what exactly it involves, varies by state and country, so don’t assume your area’s specific rule. Reporting is worth doing regardless: AFB spores can survive for decades in equipment, honey, and pollen, and notifying your inspector helps track and contain outbreaks before they spread further.
A single infected hive can spread spores to neighboring apiaries through robber bees (bees from other colonies that enter a weak hive to steal honey, picking up spores in the process), shared equipment, or even on your clothes and tools. If you move infected frames to another hive or sell contaminated equipment, you’re potentially infecting every beekeeper nearby.
Inspectors in many regions also have authority to quarantine equipment or apiaries, and requirements for destroying versus treating infected colonies vary by location. Check your state’s apiary program website or contact your county extension office to learn what’s actually required where you keep bees, rather than relying on a general guide for the specifics.
Why Treatment Usually Means Destroying the Hive
AFB has no reliable cure. Antibiotics like oxytetracycline (Terramycin) can slow the disease but don’t eliminate it—the spores survive and the disease returns. Some regions still permit antibiotic treatment under strict conditions, but most inspectors and experienced beekeepers recommend burning the hive.
The reason is simple: AFB spores are nearly indestructible. They survive extreme heat, cold, and starvation. A single spore can infect a new colony if it lands in their food or on their comb. If you try to save the bees by shaking them onto new frames, you’re moving spores with them. If you reuse the hive boxes or equipment, you’re guaranteeing reinfection.
Burning the infected hive—frames, brood, honey, woodenware, and all—is the only way to guarantee the spores don’t spread. It’s harsh, but it’s effective and protects your other colonies and your neighbors. Some beekeepers attempt to salvage metal parts such as queen excluders or entrance reducers, but many inspectors advise against reusing any equipment from an AFB hive. Always defer to your local apiary inspector on what, if anything, can be safely kept.
The financial loss is real and painful, especially for beginners. This is why prevention through clean equipment, regular inspections, and careful sourcing of bees and queens matters so much.