There are quite a few pathogens that can be carried by red mites, although it is difficult to estimate to which extent they are truly transmitted to hens, other animals and/or humans. Some examples of bacteria that have been found in red mite and have the potential to cause disease in humans include Pasteurella multocida and Salmonella enteritidis. For both it has been demonstrated that in fact red mite play a role in the transmission. Also Lyme disease can be passed on via red mite. Other bacteria that were isolated from mites include Listeria monocytogenes, E. coli and Staphylococcus spp.
Apart from bacteria, mites can also transmit viruses, one that is definitely worth mentioning in that regard is avian influenza A virus. Other examples of viruses red mite can carry include Newcastle disease and fowl pox.