A Preliminary Study on Public Health Implications of Avian Tuberculosis in Selected Districts of the Oromia Region, Ethiopia

A review of avian mycobacteriosis: An emerging bacterial disease of public health concern

Avian mycobacteriosis is a chronic debilitating disease of birds which poses a public health threat. In avian species, the disease is primarily caused by Mycobacterium avium subspecies avium. Nearly all bird species are susceptible to this infection, with older birds being more susceptible than younger ones. Ingestion of feed and water contaminated by the excreta of infected or chronic carrier birds is the main route of Mycobacterium infection and transmission; however, the respiratory route is also possible. Migratory wild or free-living birds play an important role in mycobacteriosis transmission, and affected birds show severe depletion, emaciation, anemia, diarrhea, and respiratory manifestations. The appearance of characteristic tuberculous nodules in the digestive system, especially in the intestine, liver, and spleen, is pathognomonic. Confirmation of Mycobacterium infection can be achieved through isolation on specifically selected media, direct smear for detection of characteristic acid-fast bacilli, and detection of the bacterium using molecular diagnostic methods. Serological and allergic tests can also be applied. Different species of Mycobacterium, especially M. avium, have public health significance and can be transmitted from birds to humans. Such zoonosis is especially dangerous in human immunocompromised patients. Authorities and governments have implemented strict and comprehensive eradication programs for avian mycobacteriosis. These biosecurity measures, including surveillance monitoring programs and antimicrobial susceptibility testing, are essential for the prevention and treatment of Mycobacterium infection in poultry production systems. This review was designed to focus on avian mycobacteriosis in birds and humans.

Epidemiology of Avian Tuberculosis in Selected Districts of Oromia Region, Ethiopia

Avian tuberculosis is a growing public health concern and a significant impediment to socioeconomic development, especially in developing countries, where the risk of infection is high. The disease is predominantly caused by Mycobacterium avium belonging to serotypes 1, 2, 3, and 6 (genotypes IS901 and IS1245) and Mycobacterium genavense. It mostly occurs in older birds and immunocompromised individuals due to the greater opportunity for infection with age and host immunity. A cross-sectional study anticipated to generate epidemiological information on avian tuberculosis was carried out from November 2016 to June 2017 at highland areas of Gerar Jarso, Ada’a (midland), and Boset (lowland) districts of Oromia region, Ethiopia. Two hundred seventy-three village chickens comprising local breeds, exotic breeds, and crossbreeds of both sexes were used in the study. Single intradermal avian tuberculin test, postmortem inspection of positive reactors, mycobacteriological culturing, and histopathological examination were used to assess information on the epidemiology of the disease. Subsequently, avian tuberculin test revealed an overall apparent prevalence of 11.4% (31/273) and a specific prevalence of 6.8% (6/88) in the highland, 13.4% (13/97) in the midland, and 13.6% (12/88) in the lowland study districts. Besides, it signified a higher odd of exposure in crossbreeds and females as compared to locals and males. In addition, greater odd of exposure was observed in chickens at mid- and low altitudes as compared to those at the highland. Moreover, 40.9% (9/22) of positive reactor chickens sacrificed for necropsy showed gross pathological lesions. Similarly, histopathological examination revealed a granuloma characterized by central necrosis and peripheral mononuclear lymphocytes. Nevertheless, only 0.02% (2/120) of the cultured tissues had shown colonial growth up to 12 weeks of incubation, and both were seen on sodium pyruvate-enriched Lowenstein–Jensen medium slants. Generally, the study revealed an overall increment of the apparent prevalence of avian tuberculosis with decreasing altitude. Besides, it signified a relative breed and sex variation in the risk of acquiring the disease, with crossbreeds and female chickens having higher odds of exposure.