The transmission of bacterial zoonotic pathogens from animals to humans can occur in several ways: - via inhalation or ingestion, via the conjunctiva or via bites and other injuries inflicted by animals. The literature suggests that for transmission to occur from animal to humans a degree of proximity is required or, as in most cases, contact needs to occur, as it is believed aerosol transmission occurs only over very short distances.
One pathogen commonly transmitted to humans via bite is Pasteurella multocida, a bacterium known to cause numerous endemic and epizootic diseases in a wide range of domestic and wild animal species. P. multocida is part of the normal flora in the upper respiratory tract of many animal species from wild birds, domestic animals, marine mammals to chimpanzee, but is also both an opportunistic and a primary pathogen. The disease symptoms observed depend on the mode of transmission, on the host species and on the strain of P. multocida. Transmission to humans has been reported due to bites, scratches and licks from wild and domestic animals. Our research group has researched unusual intra- species transmissions of P. multocida and we have been involved in cases of zoonotic infections associated with close relatives of P. multocida – Lonepinella spp and Mannheimia glucosida.
The worrying point is that transmission of these pathogens does not have to be due to bites or injuries. Rather, contact with abrasions of skin via licking or contaminated environment is enough. This indicates that health and safety issues are an important aspect when handling animals, be they wild or domestic animals.
Importantly, transmission is not only in one direction and can also involve transmission of disease from humans to animals, reverse zoonosis. Of particular importance, due to the link to antimicrobial resistance, is reverse zoonosis associated with methicillin-resistant Staphylococcus aureus (MRSA). It has been shown that strains of MRSA can be transmitted from humans to animals and vice versa.