Evidence of Carriage of Antimicrobial Resistant Salmonella species of Public Health and Veterinary Significance in the Intestines of House Crows (Corvus splendens) in Tanzania

Background: The Indian house crow, Corvus splendens (Vieillot) was introduced in Zanzibar, Tanzania by the British and immigrants from India in 1897 to help clean the town. The crow is responsible for polluting the environment, water sources and human surroundings by their droppings and the rubbish they carry. This behavior has led to concern that, the crows may be responsible for the spread of certain pathogens including Salmonella and their persistence in the environment.Given the zoonotic potential of Salmonella, the main aim of this study was to investigate the occurrence of antimicrobial resistant Salmonella infections in Indian house crows and to determine if the isolates were similar to those associated with disease in livestock or humans.
Methods: Indian house crows were lured with meat and blood baits to land into the crow live-trap set at the Mabibo compound of the National Institute for Medical Research (NIMR) in Dar es Salaam city in Tanzania. A total of 100 house crows were captured, humanely sacrificed, and their small and large intestines were obtained by using aseptic techniques for microbiological investigations. Culture technique was employed to detect the presence of Salmonella in intestinal contents; and preliminary identification of the isolates was based on colonial characteristics on selective media and microscopic examination of smears following Gram staining. Confirmation of Salmonella species was done by biochemical tests. Antimicrobial susceptibility testing was done by using the disc diffusion method on Mueller Hinton agar.
Results and Discussion: Eight isolates were identified by standard microbiological techniques as Salmonella spp. (6 suggestive of Salmonella gallinarum and 2 suggestive of S. Typhi). All isolates were found to be susceptible to ciprofloxacin but resistant to amoxicillin. Lower levels of susceptibility were noted for chloramphenicol and ceftriaxone. Our results demonstrate the presence of antimicrobial resistant Salmonella spp. in the Indian house crows’ population and provide an indication of potential public and poultry health risks associated with these birds in the coastal area.
Conclusion: The occurrence of antibiotic resistant S. Typhi and S. gallinarum among Indian house crows has both veterinary and public health consequences as they may be transmitted to poultry and humans. This therefore provides further rationale for the public action on eradicating the house crows.