The effect on American foulbrood of standard oxytetracycline hydrochloride treatments for the control of European foulbrood of honeybees (Apis mellifera)

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Abstract
Twenty honeybee colonies were treated with various oxytetracycline hydrochloride (OTC) preparations at the time of inoculation with Bacillus larvae spores or after American foulbrood (AFB) disease signs had developed.Treatment with 1 g OTC, at the time of inoculation delayed the development of AFB disease signs in four hives for periods between 2 months and 1 year. One colony so treated did not contract the disease.Colonies with a light AFB infection treated with 1 g of OTC recovered from the disease in 3-4 weeks, but AFB disease signs reappeared in three of five colonies the following season. Colonies with a well-established infection showed complete recovery from AFB disease signs after various OTC treatments. However, nearly all of these colonies developed AFB disease signs in the following season.B. larvae was cultured from adult bee samples from colonies that were AFB disease-free at the time of sampling but subsequently developed disease signs, and from colonies that were AFB disease-free at the time of sampling but did not subsequently develop disease signs.The results show that recommended treatments for European foulbrood (EFB) effectively mask AFB disease, making it likely that beekeepers treating EFB also suppress signs of AFB disease if it is present. As it is common practice in Australia to treat EFB prophylactically with OTC, an escalation of AFB in Australian hives is anticipated.