Merck Manual

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Professional Version

Aegyptianellosis in Poultry


Arnaud J. Van Wettere

, DVM, PhD, DACVP, College of Veterinary Medicine, Utah State University

Reviewed/Revised Feb 2020 | Modified Oct 2022

Aegyptianellosis is an acute, tickborne, febrile disease caused by Aegyptianella spp, a rickettsia in the family Anaplasmataceae. Infection of avian species, including chickens, turkeys, guineafowl, quail, pigeons, crows, waterfowl, ratites, falcons, passerines, and psittacines has been described. A pullorum is pathogenic in chickens. Ticks, especially Argas spp, transmit the organism; infection can also be reproduced by blood inoculation.

Organisms stain purple with Romanowsky stain and appear as single or multiple, round, “signet-ring” (0.3–4 mcm) or irregular oval bodies in RBCs often lateral to the nucleus. They must be differentiated from trophozoites of Plasmodium and gametocytes of Haemoproteus. Infections are most common in tropical and subtropical areas of Africa, Asia, and Europe; infection of wild turkeys in Texas has been reported.

In endemic areas, infection is mild or asymptomatic. Ruffled feathers, anorexia, droopiness, diarrhea, fever, and high mortality in younger birds can occur in introduced or otherwise susceptible birds. Anemia, which can lead to right-side heart failure and ascites, enlargement of the liver and spleen, enlarged discolored kidneys, and pinpoint serosal hemorrhages, can be seen. Infestation with larval argasid ticks and Borrelia infection ( see Avian Spirochetosis Avian Spirochetosis ) may accompany the disease.

Tetracyclines, especially doxycycline, effectively control the disease and possibly eliminate the organism from chronically infected birds. Tick control is an important adjunct to treatment.

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