C. burnetii an obligate intracellular gram-negative bacterium is a very infective organism and highly resistant to harsh environmental conditions such as physical and chemical stresses
This bacterium is usually grown in two stages with two different morphological types namely the large-cell variant (LCV) and the small-cell variant (SCV).
Due to the resistant SCV morphotype, C. burnetii is stable in the environment and resistant to physicochemical stresses such as disinfectants, dehydration, irradiation or osmosis. Thus, the bacterium can survive for a long time in dairy and meat products as well as aborted fetuses, manure, wool, animal feed, equipment and clothes.
C. burnetii is the cause of Q fever, recognized in 1935 as an occupational disease of workers in abattoirs in Australia and as a tick-transmitted disease in the United States.
This bacterium naturally infects some animals, such as goats, sheep, and cattle. C. burnetii bacteria are found in the birth products (i.e., placenta, amniotic fluid), urine, feces, and milk of infected animals. Shedding of C. burnetii can persist for several months up to 1-2 year in vaginal mucus, feces, and milk, after initial infection. People can get infected by breathing in dust that has been contaminated by infected animal feces, urine, milk, and birth products.
Among food products of animal origin, the raw milk is considered as the most significant source of C. burnetii. C. burnetii is excreted in the milk of infected animals (cattle, sheep and goats) with clinical signs of infection or not for variable periods during lactation.
After the Second World War, a high prevalence of Q fever and serological conversion was observed among the population in Europe and North America, in regions where raw milk and raw milk products were commonly consumed.
Bacteria associated with raw milk - Coxiella burnetii
