Q fever is a worldwide disease with acute and chronic stages caused by the bacteria Coxiella burnetii. Cattle, sheep, and goats are the primary reservoirs although a variety of species may be infected. Organisms are excreted in milk, urine, and feces of infected animals. During birthing the organisms are shed in high numbers within the amniotic fluids and the placenta. The organism is extremely hardy and resistant to heat, drying, and many common disinfectants which enable the bacteria to survive for long periods in the environment.
Infection of humans usually occurs by inhalation of these organisms from air that contains airborne barnyard dust contaminated by dried placental material, birth fluids, and excreta of infected animals. Other modes of transmission to humans, including tick bites, ingestion of unpasteurized milk or dairy products, and human to human transmission, are rare. Humans are often very susceptible to the disease, and very few organisms may be required to cause infection.
The following is a list of symptoms commonly seen with acute Q fever. However, it is important to note that the combination of symptoms varies greatly from person to person.
- high fevers (up to 104-105°F)
- severe headache
- general malaise
- chills and/or sweats
- non-productive cough
- abdominal pain
- chest pain
Although most persons with acute Q fever infection recover, others may experience serious illness with complications that may include pneumonia, granulomatous hepatitis (inflammation of the liver), myocarditis (inflammation of the heart tissue) and central nervous system complications. Pregnant women who are infected may be at risk for pre-term delivery or miscarriage. The estimated case fatality rate (i.e. the proportion of persons who die as a result of their infection) is low, at < 2% of hospitalized patients. Treatment with the correct antibiotic may shorten the course of illness for acute Q fever.
The best protection against Q fever infection is vaccination of those at risk (abattoir workers, vets, agricultural workers). In Australia most vet students are vaccinated prior to commencing their studies, and abattoir workers are strongly encouraged to become vaccinated.
Domestic cats and dogs have also been unrecognised intermediate hosts, spreading Q fever to veterinary staff assisting at surgical procedures.
Although protection for at-risk workers can be provided by Q fever vaccination, no licensed vaccine is available in the United States; a vaccine for use in animals has also been developed, but is not available in the United States (http://www.cdc.gov/qfever/prevention/index.html).
An Australian company makes a Q fever vaccine (Q-VAX) composed of formalin-inactivated suspension of _Coxiella burnetii_ organisms, which had been grown in the yolk sacs of embryonated eggs (http://www.csl.com.au/docs/39/836/Q-Vax_PI_V4_TGA-Approved-17%20January%202014.pdf). In Australia, Q fever vaccination is recommended for those working in "at-risk" occupations such as abattoir workers, farmers, stockyard workers, shearers, animal transporters, and others exposed to cattle, camels, sheep, goats and kangaroos or their products (including products of conception), veterinarians, veterinary nurses, veterinary students, professional dog and cat breeders, agricultural college staff and students, wildlife and zoo workers (working with high-risk animals) and laboratory personnel handling veterinary specimens or working with the organism; workers at pig abattoirs do not require Q fever vaccination (http://www.immunise.health.gov.au/internet/immunise/publishing.nsf/Content/handbook10-4-15).
If the person has a positive history of previous infection with Q fever, vaccination is contraindicated; in others, serum antibody determination and skin tests must be done before vaccination to exclude those likely to have severe local or systemic hypersensitivity reactions to the vaccine resulting from previous unrecognized exposure to the organism (http://www.immunise.health.gov.au/internet/immunise/publishing.nsf/Content/handbook10-4-15). Q fever vaccine is not routinely recommended for children aged less than 15 years of age and pregnant or breastfeeding women because safety of the vaccine in these situations has not been established. Revaccination is not indicated due to the possibility of severe hypersensitivity reactions.