Q fever was first recognised in Australia during the 1930’s when workers at a Brisbane meat processor became ill with a fever. As the cause of the illness was unknown, the workers were diagnosed with ‘Query’ fever. This was eventually abbreviated to Q fever. With the possible exception of a few European countries and New Zealand, cases of Q fever have been reported worldwide and from every State and Territory in Australia.
Reservoir and Livestock Infection
The organism, Coxiella burnetii, that causes Q fever in humans can exist in a variety of domestic and wild animals without the animal displaying apparent signs of infection. An infected animal excretes large amounts of the organism in its urine, faeces and milk and, in high concentrations in the birth fluids, placenta, on the foetus and newly born and in the uterine discharges following the birth of young. Organisms in the placenta are particularly concentrated; one gram of placental tissue may contain one billion organisms.
The important feature of the organism is its ability to withstand harsh environmental conditions; resisting heating, drying and sunlight to survive for more than a year at 4ºC in a dried state. The organism dried on wool has been shown to remain infective for 7 to 9 months at 15ºC to 20ºC and for 12 to 16 months at 4ºC to 6ºC. Infected tick faeces has demonstrated its ability to remain infectious, in a dried state, for approximately 2 years.
The organism is highly contagious within domestic herds where infection is mostly maintained through inhalation of infected dusts and contaminated droplets liberated from the products of an infected animal. Within a few months of the organism being introduced to a herd, 80% of the stock may become infected. The infection almost invariably spreads to neighbouring stock, native and feral animals and sometimes domestic cats and dogs. Once a herd is infected, it normally remains infected.