Researchers Steven Carlson and Mark Rasmussen at the National Animal Disease Center (NADC) in Ames, IA have found that an antibiotic-resistant strain of Salmonella enterica DT104 is especially virulent when associated with naturally-occurring protozoa in the rumen of cattle.
This is the first reported suggestion of protozoa as reservoirs of disease in animals although the process has been observed in free-living protozoa and was discovered when associated with a deadly outbreak of Legionnaires’ disease in 1976. The Ames scientists also found a way to combat this virulent Salmonella strain by use of a cleansing process similar to deworming, called "defaunation," which rids the rumen of protozoa.
The research suggests that being inside the protozoa activates certain bacterial defense mechanisms that can later be used to cause infection. Some bacterial pathogens appear to resist destruction while inside the protozoa which may lead to the selection of a more virulent pathogen.
Source:
USDA, ARS Agricultural Research Magazine, February, 2006