This is an important bacterial disease caused by Melissococcus plutonius, a non-spore forming, gram + cocci. M. plutonius (named after the Roman god, Pluto) attacks young larvae in open cells, before they are capped. The young larvae twist in their cells and when they die appear yellowish brown. The consistency of dead larvae can vary, even appear melted, but they are not "ropey". The organism is transmitted in the brood food fed to the young larvae by the nurse bees. M. plutonius then multiplies in the developing gut and causes death within 3-4 days of egg hatching. When the house bees clean out the dead larvae the bacteria can rapidly spread within the hive. Robbing and contaminated equipment can further the spread.
EFB occurs most commonly in the spring when brood is at its height but it can occur in summer and even extend into the fall. It can spread rapidly within infected colonies and it can also move slowly with minimal damage. Scattered brood with dead larvae in uncapped cells may indicate the infection. In some apiaries it remains as a covert infection leading to periodic outbreaks. With a good honey flow, strong colonies may spontaneously recover. Weaker colonies, whether nutritionally deficient or with PMS, may succumb. Any stress can be a contributing factor. Biosecurity is very important at all times of year to help prevent disease outbreaks.
There are antibody field test kits available for EFB with high specificity. A field confirmation allows more efficient detection and treatment. This is the only bacterial disease that we can treat with the antibiotic oxytetracycline. This may not be the solution however and highly infected colonies should be destroyed. Discuss the diagnosis and treatment options with your veterinarian.